diseases of chickpea, lentil, pigeon pea, and tepary bean in

Diseases of Chickpea, Lentil, Pigeon Pea, and Tepary Bean in Continental United States andPuerto RicoAuthor(s): Walter J. KaiserSource: Economic Botany, Vol. 35, No. 3 (Jul. - Sep., 1981), pp. 300-320Published by: Springer on behalf of New York Botanical Garden PressStable URL: http://www.jstor.org/stable/4254300Accessed: 31/03/2010 12:27

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Diseases of Chickpea, Lentil, Pigeon Pea, and Tepary Bean in Continental United

States and Puerto Rico1

WALTER J. KAISER2

The Leguminosae (pea or bean family) are composed of some 690 genera and 18,000 species (Purseglove, 1968). It is the second largest family of seed plants (following the Gramineae) (Aykroyd and Doughty, 1964). Within the Legumino- sae, there are 18-20 species that are cultivated widely for their edible seeds which are high in protein (17-25+%) (Aykroyd and Doughty, 1964). The seeds of legumes are second only to cereals as the most important source of food for humans and animals (National Academy of Sciences, 1979).

The term food legume generally is given to species of Leguminosae, the seeds, pods, and/or leaves of which are eaten by humans. The word pulse is used in some countries colonized by Great Britain, like India and Pakistan, to denote the dry, mature seeds which are consumed by humans.

A chronic protein deficiency exists in most developing countries of the world (Mayer, 1976). In these countries food legumes usually provide the main, and at times the only, source of protein and essential amino acids in the diets of poorer inhabitants for social, economic, or religious reasons. Legumes are an important complement to diets heavily dependent on high carbohydrate foods (cereals and root and tuber crops) (National Academy of Sciences, 1979).

In the United States and its territories, several food legumes are grown on a commercial scale. After soybean [Glycine max (L.) Merr.] and peanut (Arachis hypogaea L.) (which are also classified as oil crops), bean (Phaseolus vulgaris L.) is the most important food legume cultivated in the United States (USDA, 1979a). The seeds of some food legumes, like bean, pea (Pisum sativum L.), soybean, and lentil (Lens culinaris Medik.) are exported in large quantities and aid in correcting the nation's sizeable balance of trade deficits (USDA, 1979a).

In most developed countries of the world, with the exception of Japan, food legumes are consumed in small amounts, and, therefore, contribute minimally to satisfying daily protein requirements. Protein from animal sources satisfies most of that need, but this is a very inefficient method of producing protein (Mayer, 1976). With the recent dramatic rise in the cost of energy and nitrogenous fertil- izers, a search will be made to find cheaper, energy-saving methods of increasing food production. Food legumes will undoubtedly assume a more important role in providing a larger share of the protein requirements of the inhabitants of many developed countries, including the United States, particularly as the price of

1 Received 25 August 1980; accepted 28 December 1980. Presented at the Symposium on Legumes at the Twenty-first Annual Meeting of the Society for Economic Botany, Bloomington, Indiana, June 16-17, 1980; symposium organized by Dr. A. Douglas Kinghorn. Mention of a trade name or pro- prietary product does not constitute a guarantee or warranty of the product by the U.S.D.A. and does not imply its approval to the exclusion of other products that may also be suitable.

2 Research Plant Pathologist, Regional Plant Introduction Station, U.S.D.A., SEA, AR, 59 Johnson Hall, Washington State University, Pullman, WA 99164.

Economic Botany, 35(3), 1981, pp. 300-320 (O 1981, by the New York Botanical Garden, Bronx. NY 10458

1981] KAISER: LEGUME DISEASES 301

TABLE 1. LIST OF PATHOGENS AND THE DISEASES THEY CAUSE IN CHICKPEA, LENTIL,

PIGEON PEA, AND TEPARY BEAN IN CONTINENTAL U.S. AND PUERTO RICO.

Type of disease

Foliage Seed or Mosaic Stem Pod

seed- Yel- and/or and/or spot ling Root low- defor- Spot- petiole or

Crop Pathogen rota rot Wilt ing mation ting blight rot

Chickpea Fungi: (Cicer Fusarium lateritium arietinum) f. sp. ciceri + +

F. oxysporum f. sp. ciceri + +

F. solani f. sp. pisi + + Macrophomina phaseolina + + Pythium ultimum + + ?

Rhizoctonia solani + + ?

Verticillium albo-atrum + +

Virus or virus-like: Alfalfa mosaic + + ?

Bean yellow mosaic + + ?

Pea enation mosaic ? + +

Lentil Fungi: (Lens Alternaria alternata +

culinaris) Ascochyta pinodella + + Botrytis cinerea + + + ?

Cladosporium herbarum + Fusarium oxysporum f.

sp. lentis ? + F. roseum 'Avenaceum' + F. solani f. sp. pisi + + Pythium'ultimum + + Rhizoctonia solani + + Sclerotinia sclerotiorum ? ? + + + Verticillium albo-atrum + +

Virus or virus-like: Alfalfa mosaic + Bean yellow mosaic + Pea enation mosaic + Pea streak + ? +

Pigeon pea Fungi: (Cajanus Alternaria tenuissima + +

cajan) Botyrosphaeria

xanthocephala ? Cercospora cajani + C. instabilis + Colletotrichum cajani + + + + Creonectria

grammicospora ? Fusarium semitectum + Megalonectria

pseudotrichia ?

302 ECONOMIC BOTANY [VOL. 35

TABLE 1. CONTINUED.

Type of disease

Foliage Seed

or Mosaic Stem Pod seed- Yel- and/or and/or spot ling Root low defor- Spot- petiole or

Crop Pathogen rota rot Wilt ing mation ting blight rot

Phoma sp. + + + Phomopsis sp. + +

Physalospora sp. + Phytophthora parasitica + Pleonectria megalospora ? Rhizoctonia ferrugena + Sclerotium rolfsii + + + Uredo cajani + ? Uromyces dolicholi + ?

Virus or virus-like:

Rhynchosia mosaic + + Witches'-broom + +

Nematodes: Criconemoides sp. + Helicotylenchus dihystera + Hoplolaimus galeatus + Meloidogyne arenaria + M. javanica + Pratylenchus brachyurus + P. schribneri + Rotylenchulus reniformis + Trichodorus christiei + Tylenchorhynchus

claytoni +

Tepary bean Fungi: (Phaseolus Fusarium solani f. sp. acutifolius phaseoli + var. Sclerotinia sclerotiorum + + + + latifolius) Uromyces phaseoli

var. typica + ?

Bacteria:

Pseudomonas phaseolicola + + ? + Xanthomonas phaseolicola + + ? +

Virus or virus-like:

Alfalfa mosaic ? + Bean common mosaic + Bean golden mosaic + + Curly top + Pod mottle + Whitefly-transmitted

agents + +

a+, pathogen capable of producing disease in host; +, pathogen may or may not produce disease in host; ?, pathogenicity of microorganism in doubt.

19811 KAISER: LEGUME DISEASES 303

animal protein increases and people become more concerned about conserving their nation's scarce natural resources and dwindling energy supplies.

To anticipate some of the problems that may be encountered in expanding the area under cultivation of different food legumes, it will be necessary to investigate the different factors which may adversely affect production. Diseases frequently limit yields and reduce quality of edible legumes in the United States and elsewhere. The diseases of some of these crops, like bean (Silbernagel and Zaumeyer, 1973; Zaumeyer and Meiners, 1975), pea (Hagedorn, 1974, 1976) and soybean (Sinclair and Shurtleff, 1975) have been reviewed elsewhere. It is the purpose of this paper to discuss the diseases of 4 less common food legumes that are cultivated in the continental United States and Puerto Rico. These crops are chickpea (Cicer arietinum L.), lentil, pigeon pea [Cajanus cajan (L.) Huth], and tepary bean (Phaseolus acutifolius A. Gray). For easy reference, the pathogens affecting these 4 crops in the continental United States and Puerto Rico have been listed according to the type of disease(s) produced in each crop (Table 1).

CHICKPEA (CICER ARIETINUM L.)

Chickpea, also called garbanzo, gram, or Bengal gram, is an annual, self-pollinated food legume that is cultivated in many countries of the world, frequently under semiarid conditions (van der Maesen, 1972). In 1978, chickpeas were cultivated worldwide on 10,481,000 ha (26,202,500 acres) with over 90% grown in India (FAO, 1979). Chickpeas are grown commercially in the United States, primarily in the central coastal areas of California. In 1978, 5,200 ha (13,000 acres) were harvested in California (California, 1980). However, in the same year, im- ports of chickpea seeds into the United States exceeded $7,500,000 (USDA, 1979b). Currently, there is an interest in testing chickpea as an alternative crop in the dryland areas of other states, e.g., northern Idaho and eastern Washington (Anonymous, 1980; W. J. Kaiser, unpublished).

Diseases

Different diseases affect chickpea when they are grown under dryland as com- pared to irrigated conditions. In some countries, like India or Iran, diseases of this crop are an important factor contributing to low and erratic yields and quality (Kaiser and Danesh, 1971b; Nene et al., 1978; Sen Gupta, 1974). Much of our knowledge of chickpea diseases in the United States is from research carried out in California during the last 25-30 yr.

Cultivation of chickpeas in the southern coastal counties of California dates back to the founding of the Spanish missions over 175 yr ago (Smith et al., 1950). By the mid-1930s, chickpeas had become a commercial crop in this region with an annual production of some 2,500,000 lb (1,136,364 kg) (Smith et al., 1950). Of the several diseases reported to affect chickpeas in this region, Erwin and Snyder (1958) considered virus yellows and Fusarium wilt to be the most serious and widespread. Symptoms of both diseases in chickpea consisted of yellowing and wilting of the foliage and death of infected plants. Symptoms of different wilt-like disorders of chickpea are illustrated and described in a recent publication by Nene et al. (1978). At least 3 viruses were isolated from yellows-affected plants in California (Snyder et al., 1956). These were identified as bean yellow mosaic,


1S~~~~~~~~~~~~~~

Fig. 1-4. Fig. 1. Fusarium root rot (right) is a serious soilborne disease of chickpea worldwide. Roots of infected plants (right) are dark in color and rotted; healthy plants (left). Fig. 2. Lentil plants (light colored) in a field planting are dying due to root rot caused by a complex of soilborne pathogens, including Pythium ultimum and Rhizoctonia solani. Fig. 3. Infection of pigeon pea foliage by the rust pathogen may result in premature defoliation and reduced yields. Fig. 4. Stunted tepary bean plant (left) is infected with the NY 15 strain of bean common mosaic virus; healthy plant (right).


alfalfa mosaic, and pea enation mosaic viruses. Bean yellow mosaic virus was isolated most frequently from plants exhibiting symptoms of virus yellows. In- cidence of virus yellows varied from year to year but in some plantings as many as 50% of the plants were infected (Snyder et al., 1956). Yields of virus-infected chickpea are usually reduced by more than 50% (Kaiser and Danesh, 1971a) and mortality may be high, particularly when plants are infected early (Kaiser and Danesh, 1971a; Snyder et al., 1956).

The pathogen causing Fusarium wilt of chickpea in the south coastal areas of California was identified as Fusarium lateritium Nees emend. Snyder & Hans. f. sp. ciceri (Padwick) Erwin (Erwin, 1958a). The fungus produced typical wilt symptoms of the shoot and discoloration of the vascular elements. Erwin (1957, 1958b) also identified another soil-borne pathogen, Verticillium albo-atrum Reinke & Berth., as causing a chickpea wilt disease of minor importance in California. The isolates of V. albo-atrum from chickpea were microsclerotial types.

In recent years, the commercial chickpea-producing areas in California have shifted northward to the central coastal region of the state (Phillips, 1979; Wes- terlund et al., 1974). In a survey of 7 chickpea plantings in California's central coastal area between 1971 and 1972, Westerlund et al. (1974) identified the following fungi as causing root rot and wilt diseases of chickpea: Fusarium oxysporum Schlecht. f. sp. ciceri (Padwick) Matuo and Sato, F. solani (Mart.) Appel & Wr. f. sp. pisi (E. R. Jones) Snyder & Hans., Macrophomina phaseolina (Tassi) Goid., Pythium ultimum Trow., and Rhizoctonia solani Kuhn. Virus diseases are less a problem than in the south coastal areas (Westerlund et al., 1974).

Fusarium solani f. sp. pisi (Fig. 1) is an important root rot pathogen of chickpea in California, as it was shown earlier to be in Washington (Kraft, 1969). Wester- lund et al. (1974) isolated F. solani f. sp. pisi from 47% of wilted chickpea plants, but F. oxysporum f. sp. ciceri from only 6%. Also, they failed to isolate F. lateritium f. sp. ciceri from diseased chickpeas and they were unable to prove the pathogenicity of several of Erwin's original isolates of this fungus to chickpea. However, Erwin's original isolates that were tested by Westerlund et al. (1974) may have lost their pathogenicity to chickpea after being kept in culture for over 15 yr. Both Fusarium wilt and root rot were severe in fields previously cropped to chickpea, but they were not found in fields planted to chickpea for the first time (Westerlund et al., 1974).

Pythium ultimum and Rhizoctonia solani caused pre- and post-emergence damping-off and necrosis and death of small chickpea roots in California (Smith et al., 1950; Westerlund et al., 1974). Both pathogens were isolated most frequently from diseased plants on land with no previous history of chickpea production. Pythium ultimum is also the cause of a serious pre-emergence damping- off disease of white-seeded chickpeas in the Palouse region of eastern Washington (Kaiser and Hannan, 1981). Emergence of nontreated chickpea seeds was reduced by 60-80% or more by P. ultimum in Palouse soils with no previous history of chickpea cultivation.

Macrophomina phaseolina may induce a wilting disease of chickpea plants grown under dryland conditions, but only where plants receive less than adequate water (Westerlund et al., 1974). This pathogen generally is not a problem in the field when adequate soil moisture is maintained.


Erwin (1958a) found 4 chickpea lines that had high levels of resistance to F. lateritium f. sp. ciceri. These lines need to be tested for their resistance to Fu- sarium wilt caused by F. oxysporum f. sp. ciceri. In 1978, Phillips (1979) screened 279 lines from the International Crops Research Institute for the Semi-Arid Trop- ics (ICRISAT), Hyderabad, India. Thirty-four accessions remained free of wilt symptoms.

The prevalence of Fusarium diseases only in fields previously cropped to chickpea suggests the importance of crop rotation (Westerlund et al., 1974). Both F. solani f. sp. pisi (Westerlund et al., 1974) and F. oxysporum f. sp. ciceri (Haware et al., 1978) are carried on the seed which is one method by which Fusarium wilt and root rot can be introduced into new areas. Haware et al. (1978) showed that the wilt Fusarium was eradicated from seed by treatment with a mixture of Benomyl (methyl- 1-[butylcarbamoyl]-2-benzimidazolecarbamate) and Thiram (bis-[dimethylthiocarbamoyl]disulfide).

Ascochyta blight [Ascochyta rabiei (Pass.) Lab.] is a potentially devastating seedborne disease of chickpea which until recently was not reported from the Western Hemisphere. In 1974, Ascochyta blight caused extensive damage to experimental chickpea plantings at Saskatoon, Canada (Morrall and McKenzie, 1974). Wet, cool weather favors disease development. Apparently, the pathogen was introduced into Canada on imported chickpea seed. Since A. rabiei is readily seedborne, care should be exercised when chickpea seeds are imported into the United States for research or commercial purposes. Additional research is required to determine whether A. rabiei can be eradicated from chickpea seed by thermotherapy and/or chemical means. Preliminary results indicated that treatment of Ascochyta-infected chickpea seed with certain chemical compounds, especially the benzimidazoles, greatly increased emergence and reduced disease incidence and severity in seedlings (Kaiser et al., 1973).

LENTIL (LENS CULINARIS MEDIK.)

The cultivated lentil is a self-pollinated, cool-season annual that is of Old World origin and one of the first food crops to be cultivated by man (Zohary, 1976). In the United States, lentils are grown commercially in the Palouse region of eastern Washington and northern Idaho in rotation with wheat (Triticum aestivum L.) and dry-edible peas. Lentils were first planted in the Palouse in 1916 (Youngman, 1968), and have since become an important cash crop. In 1978, lentils were harvested from 52,400 ha (131,000 acres) (Idaho, 1979; Washington, 1978). Much of the lentil crop produced in the Palouse is exported. The value of lentil exports in 1978 exceeded $15,000,000 (USDA, 1979b).

Diseases

Considering the importance of lentil as an alternate cash crop in the Pacific Northwest, little information has been published on its diseases in the United States. The first published report of fungus diseases affecting lentils in the Pacific Northwest was by Wilson and Brandsberg in 1965. They made numerous isola- tions from diseased, field-grown lentil seedlings over a 2-yr period and found several soilborne fungi to be incitants of root (Fig. 2) and stem diseases of lentil in the Palouse region. Fungi pathogenic in their greenhouse and field inoculation

19811 KAISER: LEGUME DISEASES 307

studies included Ascochyta pinodella L. K. Jones, Botrytis cinerea Pers. ex Fr., Fusarium oxysporum (possibly F. oxysporum f. sp. lentis Vasudeva & Sriniva- san), Fusarium roseum (Lk.) Snyd. & Hans. 'Gibbosum,' Rhizoctonia sp., Scle- rotinia sclerotiorum (Lib.) d By., and Verticillium albo-atrum. In the Palouse region, Rhizoctonia solani has been isolated from discolored roots of diseased lentils and isolates of the fungus were pathogenic to germinating seeds and roots of inoculated lentils (W. J. Kaiser, unpublished data). With high moisture conditions, S. sclerotiorum can cause severe damage to the lentil crop in this region (Amer. Dry Pea & Lentil Assoc., 1980).

Fusarium wilt caused by F. oxysporum f. sp. lentis is one of the most important diseases of lentil in some lentil-producing countries, such as India (Sen Gupta, 1974). Wilson and Brandsberg (1965) isolated cultures of F. oxysporum from diseased Palouse lentils that were similar in cultural and morphological characteristics and in pathogenicity to a known isolate of F. oxysporum f. sp. lentis. Their pathogenic isolates of F. oxysporum caused a root rot and vascular wilt of inoculated lentils.

Although Botrytis cinerea was isolated infrequently from diseased lentil seedlings, Wilson and Brandsberg (1965) considered it to be a potentially important pathogen of lentil in the Pacific Northwest. Recent studies have demonstrated that B. cinerea is transmitted in a low percentage of seed of field-grown Palouse lentils (W. J. Kaiser, unpublished data).

Foliar diseases of lentil are usually of minor importance in the Palouse. Fungi associated with foliar diseases include Alternaria tenuis Nees. [=A. alternata (Fries) Keisslers], Cladosporium herbarum Pers. ex Fr., and Stemphylium bot- ryosum Wallr. (Wilson and Brandsberg, 1965). In Canada, Alternaria sp. and Cladosporium sp. also were associated with leaf blight diseases of lentil (Mc- Kenzie and Morrall, 1975).

Lentils are a cool season crop with an indeterminate growth habit. High temperatures adversely affect growth and flowering of lentils and may predispose plants to disease. For instance, in greenhouse studies, Lin and Cook (1977) demonstrated that F. solani f. sp. pisi, normally a root rot pathogen of pea (Pisum sativum), caused a black root rot of lentil at high (25-30 C), but not at low (<20 C) soil temperatures. In nature, F. solani f. sp. pisi would normally not be a pathogen of lentil because average soil temperatures found in the Palouse during the lentil growing season are below 25 C.

Pythium ultimum is an important seed-rotting, damping-off, and/or root rot pathogen of several food crops in the Pacific Northwest, including peas and wheat, that are grown in rotation with lentil (Kraft and Burke, 1971; Cook et al., 1980). This pathogen has been isolated from discolored roots of lentil seedlings and flowering plants exhibiting symptoms of stunting and chlorosis in Iran and Washington state (Kaiser and Homer, 1980; W. J. Kaiser, unpublished data). Several isolates of P. ultimum from different food crops grown in the Palouse region were pathogenic to lentils in greenhouse inoculation tests (W. J. Kaiser, unpublished data). In the absence of obvious root rot symptoms, Lin and Cook (1977) found lentil inoculated with P. ultimum to be smaller in size and to have fewer branches than noninoculated plants.

New or modified cultural practices, like minimum tillage cultivation to control erosion, may affect the importance and severity of previously minor or uniden-


tified diseases of a crop. An example of this phenomenon with lentils was demonstrated recently by Lin and Cook (1977). They showed how a previously un- diagnosed root rot disease of lentil caused by Fusarium roseum 'Avenaceum' increased in importance when nontilled lentils were direct-seeded into undis- turbed (zero tillage), dead bluegrass sod in eastern Washington.

The lentil crop in the Pacific Northwest is free from the ravages of a few important and destructive diseases. Notable among these is Ascochyta blight (Ascochyta sp., possibly A. lentis Bond. & Vassil.), a seedborne disease that attacks the leaves, stems, pods, and seeds of lentil. Ascochyta blight was reported recently in Canada (Slinkard and Drew, 1980), where it is considered to be a potentially important disease of lentil (R. A. A. Morrall, personal communication). Every effort should be made to exclude this and other potentially devastating diseases from lentil-growing areas of the United States.

In Iran, lentils are naturally infected by alfalfa mosaic (AMV), bean yellow mosaic (BYMV), cucumber mosaic, and pea leaf roll viruses (Kaiser, 1973), while in Italy, they are a natural host of pea enation mosaic virus (PEMV) (Vovlas and Rana, 1972). Information is meager on the distribution, incidence, and importance of virus diseases of lentil in the United States. In the Palouse area, several viruses have been isolated from diseased lentils, including AMV, BYMV-type isolates, PEMV, and pea streak virus (R. 0. Hampton, personal communication). Inci- dence of virus infection appears to vary greatly from year to year and may be related to migrations of aphid vectors and the proximity of virus-infected alternate hosts to lentil plantings. Virus diseases of lentil is an area that merits additional research.

Pea seedborne mosaic virus (PSbMV) may be a potential threat to the lentil crop in the Pacific Northwest (Hampton and Muehlbauer, 1977). However, primary or secondary infection of lentil by PSbMV has not yet been observed in the field. PSbMV is easily transmitted from peas, a natural host of the virus, to lentils by artificial means and is then seed-transmitted in lentil at frequencies of 32-44% (Hampton and Muehlbauer, 1977). Four lentil lines in the USDA plant introduction (PI) collection were found to be immune to PSbMV (Haddad et al., 1978).

PIGEON PEA [CAJANUS CAJAN (L.) HUTH.]

The pigeon pea is a woody, short-lived perennial shrub that is cultivated widely in the tropics and subtropics, often as an annual. It is a drought-tolerant crop frequently grown in semiarid regions on poor soils (De, 1974; Purseglove, 1968; Royes, 1976). Pigeon peas, also called arhar, red gram, Congo pea, and gandul, are cultivated on some 3,000,000 ha (7,500,000 acres) worldwide, with over 90% of the production in India (Rachie and Roberts, 1974). In the American tropics, the pigeon pea is an important food crop where the seeds are consumed as green (immature) or dry (mature) peas. In some countries, it is also used as forage for animals or as a green manure or cover crop (Purseglove, 1968; Morton, 1976).

The Commonwealth of Puerto Rico is the only location in the United States where pigeon peas are presently grown as a commercial crop. Pigeon pea is the most important food legume cultivated in Puerto Rico, where an important can- ning industry has developed around this crop. During 1975-1976, pigeon peas were harvested from approximately 6,000 ha (15,000 acres) (Conjunto Techno- l6gico, 1977). However, due to an increased demand for fresh, canned, and frozen


pigeon peas, over 870,000 kg were imported into Puerto Rico and the continental United States during 1978-1979 (USDA, 1979c).

Diseases

A number of diseases of varying severity affect the roots, stems, petioles, leaves, pods, and seeds of the pigeon pea in tropical and subtropical areas of the United States, including Florida, Hawaii, Puerto Rico, and Texas (Barnes, 1973; Nene, 1978; Spence, 1975; USDA, 1960). The diseases are caused primarily by fungi, although a few disorders of unknown etiology with virus- or mycoplasmalike symptoms have been observed in Puerto Rico (Maramorosch et al., 1974a,b; Bird et al., 1975; Vakili and Maramorosch, 1974).

Much of the pioneering research on pigeon pea diseases in the Western Hemi- sphere was done by researchers located at the Mayagiiez and Rlo Piedras experiment stations in Puerto Rico, beginning in the early 1900s. A majority of the early studies dealt with diseases caused by fungi, particularly those inciting diseases of the foliage, stems, and pods.

Over 60 yr ago, Stevenson (1917) reported on the etiology and occurrence of several diseases of pigeon pea in Puerto Rico. These were leaf spots caused by Cercospora cajani P. Henn. [=Mycovellosiella cajani (P. Henn.) Rangel & Trotter], Uromyces dolicholi Arth. and an unknown stem canker disease, possibly of fungal etiology.

Two rust diseases have been reported to infect pigeon pea in the United States (Commonwealth Mycological Institute, 1968; Nene, 1978; Spence, 1975; Tucker, 1927a; USDA, 1960). These rusts were identified as Uredo cajani Syd. and Uro- myces dolicholi. Some confusion exists concerning the proper identification of these 2 fungi on pigeon pea foliage. Differentiation is possible only when the telial spore stage is found and this has yet to be observed in U. cajani (Commonwealth Mycological Institute, 1968). Rust is a potentially important disease of pigeon pea in the Caribbean (Fig. 3). In Jamaica and Trinidad, Spence (1975) observed that severe rust infection resulted in the shedding of infected leaves and may be responsible for significant yield reductions. Many of the dwarf pigeon pea varieties developed by the University of the West Indies are highly susceptible to rust infection. Pigeon pea varieties recommended for cultivation in Puerto Rico are tolerant to rust (Conjunto Technologico, 1977). Different strains of U. cajani may exist in the Caribbean area (Spence, 1975).

Two Cercospora species, C. cajani and C. instabilis Rangel, cause leaf spot diseases of pigeon pea in Puerto Rico (Nene, 1978; Stevenson, 1917, 1918; Tuck- er, 1927a; USDA, 1960). Infection may result in premature shedding of leaves. The Cercospora lesions on pigeon pea leaves are similar to those caused by Colletotrichum cajani. Cercospora leaf spots are common diseases of pigeon pea in Puerto Rico and are generally of minor importance (Tucker, 1927a).

Anthracnose caused by Colletotrichum cajani is an important foliar disease of pigeon pea that was first described in Brazil in 1916 (Rangel, 1916). In 1925, C. cajani caused a destructive disease of the leaves, pods, and seeds of pigeon pea in Puerto Rico (Tucker, 1927a,b). The disease was most severe during periods of heavy rainfall. Infection by C. cajani frequently resulted in spotting, necrosis, deformation, and/or shedding of pigeon pea pods and leaves, and shriveling and reduction in size of infected seeds (Tucker, 1927a,b). Symptoms of C. cajani on


young pigeon pea leaves and pods were similar to those frequently observed on beans (Phaseolus vulgaris) infected with anthracnose caused by C. lindemuthian- um (Sacc. & Magn.) Briosi & Cav. However, the bean anthracnose pathogen does not infect pigeon pea nor vice versa.

Periodically, stem and crown canker diseases of pigeon peas have occurred in epidemic proportions in Puerto Rico. A Phoma sp. was reported by Alvarez Garcia (1960) and Lopez Rosa (1969) to cause a serious stem canker disease of pigeon pea in commercial plantings on the island. The pathogen, which is transmitted in a low percentage of seeds (Lopez Rosa, 1969) affects both seedlings and older plants, sometimes resulting in death of infected plants (Aponte Aponte, 1963). Pycnidia of the pathogen developed in lesions on stems, branches, and pods (Alvarez Garcia, 1960). Phoma isolates appeared to vary greatly in their pathogenicity to pigeon pea. A few were highly virulent to Kaki pigeon pea, but the majority were avirulent (Lopez Rosa, 1969). Lopez Rosa (1969) observed the perfect stage of Phoma on agar media, and found it to be a heterothallic ascomycete. Ascospore cultures formed pycnidia in 4-5 days. No mention was made regarding the identity of the perfect stage nor whether it was pathogenic to pigeon pea. Earlier, Leach and Wright (1930) had reported that a collar rot and stem canker disease of pigeon pea in Trinidad was caused by Physalospora sp., an ascomycete, which had 2 pycnidial stages belonging to Phoma and Macrophoma.

Phytophthora parasitica Dastur is a potentially important pathogen of pigeon pea in Puerto Rico (Kaiser and Melendez, 1978; Abrams et al., 1978). Necrotic, depressed cankers developed on stems, branches, and petioles of naturally infected and artificially inoculated plants. Cankers up to 6 cm in length frequently girdled stems, causing branches above infection sites to wilt and die. Several food crops grown in rotation with pigeon pea in Puerto Rico were also hosts of P. parasitica, notably eggplant and tomato (Kaiser and Melendez, 1978). Pigeon pea isolates of the pathogen were more virulent to pigeon pea than those from eggplant and tomato. Wounding of pigeon pea tissues favored infection. In India, other Phytophthora spp. have been identified as the cause of a stem blight disease of pigeon pea (Amin et al., 1978; Kannaiyan et al., 1980; Pal et al., 1970; Williams et al., 1975).

Stevenson (1917, 1918) isolated several fungi from the dead wood and bark of pigeon pea plants in Puerto Rico. He believed that some of these fungi were involved in the death and rotting of stems of mature plants, particularly Mega- lonectria pseudotrichia (Schw.) Speg., Creonectria grammicospora (Ferd. & Winge) Seaver (=Nectria grammicospora Ferd. & Winge), and Pleonectria megalospora Speg. [=Thyronectria megalospora (Speg.) Seaver & Chardon] (Ste- venson, 1917, 1918). However, pathogenicity of these fungi to pigeon pea was not tested. Tucker (1927a) reported that perithecia of Botryosphaeria xanthocephala (Syd. & Butl.) Th. & Syd. were found in the bark of diseased pigeon pea plants in Puerto Rico. Although B. xanthocephala was associated with a serious canker disease, Tucker (1927a) did not demonstrate its pathogenicity to pigeon pea.

Tucker (1927a) reported Rhizoctonia ferrugena Matz. to cause a pre- and post- emergence damping-off disease of pigeon pea seedlings in Puerto Rico and that the disease was most destructive during wet weather. He found the host range of R. ferrugena was extensive and includes several vegetable crops that were


grown in rotation with pigeon pea. Parmeter and Whitney (1970) observed that an isolate of R. ferrugena obtained from the Centraalbureau voor Schimmelcul- tures, The Netherlands, had clamp connections and formed sclerotia similar to those of Sclerotium rolfsii Sacc. It is possible that Tucker may have been dealing with a fungus resembling S. rolfsii. Sclerotium rolfsii was isolated from dead and dying pigeon pea seedlings from Isabela, Puerto Rico, and the fungus proved to be pathogenic to seedlings of this crop in greenhouse inoculation studies (W. J. Kaiser and P. L. Melendez, unpublished data).

Recently in Puerto Rico, the role of internally seedborne fungi on germination and emergence of seeds in the field was revealed (Ellis and Paschal, 1977, 1979; Ellis et al., 1977, 1978). During 1976, emergence of seed in several commercial plantings was low (28-45%) and it appeared that the high incidence of internally seedborne fungi was a primary factor contributing to poor seed germination, thus limiting commercial production of pigeon pea in Puerto Rico (Ellis and Paschal, 1979). Fungi frequently isolated from poor quality pigeon pea seed (as measured by seed germination and seedling emergence) were Alternaria tenuissima (Fr.) Wilts., Fusarium semitectum Berk. & Rav., Lasiodiplodia theobromae Pat., Phomopsis sp., Aspergillus sp., Cladosporium sp., and Penicillium sp. There was a negative correlation between the occurrence of A. tenuissima, F. semitectum, L. theobromae and Phomopsis sp. and in vitro germination and field emergence of pigeon pea seed (Ellis et al., 1977). Pigeon pea seed quality also was correlated with the site of production in Puerto Rico. The quality of seed produced at Isabela, Puerto Rico, a high-rainfall area, was poor in comparison with seed produced at Fortuna, Puerto Rico, an arid, low-rainfall area (Ellis et al., 1978). Delaying the harvest of seed past maturity frequently resulted in a significant increase in the incidence of Phomopsis sp., A. tenuissima, F. semitectum, and L. theobromae. Treatment of pigeon pea seed from Isabela, Puerto Rico, with Captan (N-trichloromethylthio-4-cyclohexene- 1,2-dicarboximide) and Thiram (protectant fungicides) or Benomyl (systemic fungicide) significantly increased germination and field emergence over nontreated seeds. Likewise, foliar appli- cations of Benomyl several times during the growing season significantly reduced subsequent infection of seed by several internally seedborne fungi that played a major role in reducing seed quality.

Recent investigations with internally seedborne fungi have emphasized the important role that these microorganisms play in reducing quality of seed of pigeon pea and other food legumes produced in Puerto Rico (Ellis et al., 1977). Addi- tionally, they point out the need of selecting suitable sites in Puerto Rico, like the south coastal area, for the production of high quality seed for use in estab- lishing new plantings (Ellis et al., 1978; Conjunto Technologico, 1977).

A few virus- and mycoplasma-like diseases of uncertain etiology affect pigeon pea in Puerto Rico and other islands in the Caribbean (Bird and Sanchez, 1971; Bird et al., 1975; Maramorosch et al., 1974a,b). Since the late 1950s, Bird and his colleagues (1971, 1975) in Puerto Rico have studied various 'rugaceous' diseases that affect different food crops and weed species in the Caribbean. These rugaceous diseases are transmitted by whiteflies (Bemisia tabaci Genn.). One of these diseases, Rhynchosia mosaic, infects pigeon pea naturally in Puerto Rico, producing a yellow mosaic symptom (Bird et al., 1975). The primary reservoir of the yellow mosaic pathogen is Rhynchosia minima DC., a wild legume. Several high-


yielding pigeon pea lines developed in Puerto Rico have resistance to yellow mosaic (Bird et al., 1975).

A witches'-broom disease of pigeon pea has been reported from several countries, including Puerto Rico, Dominican Republic, and Haiti (Hirumi et al., 1973; Maramorosch et al., 1974a,b; Nene, 1978; Vakili and Maramorosch, 1974). Symp- toms of witches'-broom frequently consisted of a dwarfing of leaves and a pro- liferation of shoots at the nodes. Electron micrographs of pigeon pea tissues from witches'-broom-infected plants revealed the presence of mycoplasma-like organ- isms and rhabdovirus-like particles (bullet-shaped) in phloem cells (Hirumi et al., 1973; Maramorosch et al., 1974a,b). The vector of the disease is unknown. There was a high incidence of witches'-broom in Haiti. This disease is a potential threat to pigeon pea cultivation in Puerto Rico (Vakili and Maramorosch, 1974).

In the Caribbean, surveys of agricultural soils have shown that various plant parasitic nematodes are associated with the roots of pigeon pea (Ayala, 1962a,b; Singh, 1975). High population densities of different ecto- and endoparasitic nematode species around pigeon pea roots result in damage to the roots which contribute to poor growth and reduced seed yields from diseased plants. As early as 1911, pigeon peas were reported to be a natural host of rootknot nematodes [Heterodera radicicola (Greef) Muller (=Meloidogyne spp.)] in the United States (Bessey, 1911). In Puerto Rico, pigeon pea roots are attacked by Meloidogyne javanica (Treub.) Chitwood, Rotylenchulus spp. (including R. reniformis Linford & Oliveira), Criconemoides sp., Helicotylenchus sp., and Hoplolaimus sp. (Ay- ala, 1962a,b). Rotylenchulus reniformis appears to be the most important nematode pathogen of the roots of pigeon pea and several other food crops in Puerto Rico (Ayala, 1962a; Ayala and Ramirez, 1964; Steiner, 1960). In Hawaii during the 1930s, several legumes, including pigeon pea, were tested as potential rotation and trap crops for pineapple on land that was heavily infested with rootknot nematodes. Pigeon peas proved to be one of the most rootknot-resistant legumes tested (Godfrey, 1928).

In greenhouse studies, pigeon peas were shown to be a good host for several ecto- and endoparasitic nematode species when planted in soils from cotton, peanut, and soybean fields in Alabama (Ingram and Rodriquez-Kabana, 1977; Rodriquez-Kabana and Ingram, 1978). These included Helicotylenchus dihystera (Cobb) Sher, Hoplolaimus galeatus (Cobb) Thorne, Meloidogyne arenaria Chit., Pratylenchus brachyurus (Godfrey) Filipjev and Schuurmans Steckhoven, P. schribneri Steiner, Trichodorus christiei Allen, and Tylenchorhynchus claytoni Steiner.

TEPARY BEAN (PHASEOLUS ACUTIFOLIUS A. GRAY)

The tepary bean is a drought-tolerant annual that originated in the New World, probably in the southwestern United States and northwestern Mexico (Evans, 1976; Nabhan and Felger, 1978; National Academy of Sciences, 1979; Purseglove, 1968). From archeological remains, it appears that the tepary bean was a domesticated crop in Mexico over 5,000 yr ago. Teparies are still found growing in the wild at elevations up to 1,650 m as far south as Guatemala and as far north as central Arizona (Nabhan and Felger, 1978). Cultivated lines of P. acutifolius are classified as var. latifolius Freeman. Tepary beans are adapted to hot, arid environments and will usually produce a crop in 60-90 days under these harsh


conditions where other Phaseolus species, like bean (P. vulgaris) would fail. They will not tolerate frost or waterlogged soils. Hendry (1918) reported that tepary seeds germinated rapidly in soils with low moisture content, but rotted quickly in cold, moist soils. Teparies had become an important field crop in the arid Southwest by 1918 where in California alone they were cultivated on some 6,800 ha (17,000 acres) (Hendry, 1919), but their importance declined rapidly thereafter, due to a combination of factors, including small seed size, flavor and odor when cooked, changing land-use trends, and cultural preferences (Hendry, 1918; Nabhan and Felger, 1978; National Academy of Sciences, 1979). Today tepary beans are cultivated for their edible dry seeds on a limited scale by commercial and subsistence farmers in southwestern North America (Nabhan, 1979; Nabhan and Felger, 1978).

Teparies are a potentially important high-protein food legume suited to cultivation in the arid and semiarid regions of the world. It may be possible to transfer some of the tepary bean's desirable characteristics, such as tolerance to drought and heat, to other Phaseolus species by interspecific hybridization (National Academy of Sciences, 1979; Waines, 1978).

Diseases

Very little information is available on the diseases affecting wild or domesticated tepary beans under natural conditions in the arid regions of southwestern North America. In one of the earliest reports on cultivation of this crop in the United States, Freeman (1912, 1913) mentions that tepary beans differed from beans in being more resistant to heat, drought, and insect pests. However, no mention was made of diseases. Subsequently, several reports have appeared in the literature on the susceptibility or resistance of tepary bean accessions to different diseases. A majority of these reports are based on infection of teparies by various pathogens in field or greenhouse trials, but not under natural conditions in farmers' fields. A recent report by the National Academy of Sciences (1979) on tropical legumes states that while some tepary bean accessions are highly resistant to the bean common blight bacterium [Xanthomonas phaseoli (E. F. Sm.) Dows.], they are only mildly resistant to most other diseases and pests. Our knowledge of the diseases affecting tepary beans in nature is fragmentary and incomplete.

Tepary beans are reported to be infected either experimentally or naturally by several viruses. In 1922, Nelson (1932) observed natural spread of a seedborne bean virus, presumably bean common mosaic virus (BCMV) from virus-infected beans to different Phaseolus species, including tepary bean, in field trials at East Lansing, Michigan. Several tepary bean accessions were shown to be susceptible to natural and artificial infection in Puerto Rico and Iran, respectively, by 2 or more strains of BCMV (Kaiser and Mossahebi, 1974; W. J. Kaiser, unpublished data). The virus was also transmitted in 20-25% of the seed harvested from the Puerto Rican BCMV-infected tepary bean plants (W. J. Kaiser, unpublished data).

Provvidenti and Cobb (1975) reported seed transmission of BCMV ranging from 7-22% in 4 P. acutifolius PI (USDA plant inventory) accesssions. All inoculated plants of 15 P. acutifolius accessions were susceptible in greenhouse inoculation studies to 3 isolates of BCMV from P. vulgaris (Provvidenti and Cobb, 1975).


Narrowing, mottling, deformation, and twisting of the leaflets and stunting were symptoms frequently observed in tepary bean plants infected with BCMV (Kaiser and Mossahebi, 1974; Provvidenti and Cobb, 1975) (Fig. 4).

In addition to BCMV, teparies were experimentally infected by other viruses, notably alfalfa mosaic (Zaumeyer and Thomas, 1957), bean yellow mosaic (Zau- meyer and Thomas, 1957), curly top (USDA, 1960), pod mottle virus (Zaumeyer and Thomas, 1957), and at least 4 whitefly-transmitted (Bemisia tabaci) mosaic diseases of Phaseolus lunatus L., Jacquemontia tamnifolia Griseb., Merremia quinquefolia Hall., and Rhynchosia minima (Bird et al., 1975; G'amez, 1971). The mosaic disease of P. lunatus, also called bean golden mosaic or bean golden yellow mosaic, is an important disease of bean and lima bean in several countries of the Caribbean and Central and South America (Bird et al., 1975; Costa, 1975; Gamez, 1971). Granillo et al. (1975) reported the high incidence of a whitefly- borne disease of P. acutifolius in variety trials in the coastal area of El Salvador. The disease was believed to be due to bean golden yellow mosaic.

The roots of tepary bean are susceptible to Fusarium solani f. sp. phaseoli (Burkh.) Snyd. & Hans., a soilborne fungus that causes a serious root rot disease of bean worldwide (USDA, 1960; Zaumeyer and Thomas, 1957). Fusarium root rot could become an important disease of P. acutifolius if they are planted on land with a history of bean root rot. This Fusarium disease is frequently more serious on beans that are growing under water stress (Silbernagel and Zaumeyer, 1973) as may occur when beans and tepary beans are grown under dryland conditions in arid and semiarid regions of the world. Tepary beans are susceptible to white mold (Sclerotinia sclerotiorum) in California (J. G. Waines, personal communication). Teparies will likely prove to be hosts to other soilborne fungi and nematodes that are pathogens of bean, notably Pythium spp., Rhizoctonia solani, Thielaviopsis basicola (Berk. & Br.) Ferr., Sclerotium rolfsii, and Me- loidogyne spp. (USDA, 1960; Silbernagel and Zaumeyer, 1973; Zaumeyer and Thomas, 1957).

Three of the diseases reported to affect the foliage of teparies are bean rust [Uromyces phaseoli (Pers.) Wint. var. typica Arth.] (USDA, 1960; Zaumeyer and Thomas, 1957), bean common blight (X. phaseoli) (Zaumeyer and Thomas, 1957), and bean halo blight [Pseudomonas phaseolicola (Burkh.) Dows.] (M. L. Schus- ter, personal communication). The latter 2 bacterial pathogens are seedborne in bean and probably would be transmitted in seed of susceptible tepary bean lines. Spread and disease development of both bacterial diseases are favored by rain and humid weather conditions.

The leaves and pods of many P. acutifolius accessions are highly tolerant to most isolates of X. phaseoli (Schuster, 1955; Schuster et al., 1973). Honma (1956) succeeded in making an interspecific cross between P. vulgaris and P. acutifolius by employing embryo culture techniques. He obtained 4 F1 plants which appeared similar to the P. vulgaris parent. Progeny from these 4 F1 plants varied greatly in their reaction to X. phaseoli (Honma, 1956). Field and greenhouse screening of the progeny from this interspecific cross eventually resulted in the release of the variety Great Northern (GN) Nebraska #1, Sel. 27, which exhibited a high level of tolerance to X. phaseoli isolates from the United States (Coyne and Schuster, 1974; M. L. Schuster, personal communication). Recently, GN Ne-


braska #1, Sel. 27 was shown to be slightly susceptible to isolates of X. phaseoli from Uganda and Colombia (Schuster et al., 1973). This variety is also tolerant to P. phaseolicola races 1 and 2 (Coyne and Schuster, 1974). Since it was released in the mid-1960s, GN Nebraska #1, Sel. 27 has been used as a source of resistance to common bacterial blight and halo blight by bean breeders in many countries (M. L. Schuster, personal communication).

In Puerto Rico, Vakili (1976) screened 151 P. acutifolius lines (many of which were PI accessions) for resistance to several diseases, including bacterial blight, bean common mosaic virus, root rot, and rust. He selected several lines that had moderate to high resistance to one or more of these diseases. Seed of the multiple- disease resistant selections were being increased for release to interested researchers.

STRATEGIES FOR CONTROLLING DISEASES OF FOOD LEGUMES

Various methods are used to control diseases affecting edible legumes in the United States and its territories. These include the use of chemicals, resistant varieties, and cultural practices.

Economic and environmental considerations probably will lead to a significant reduction in the application of pesticides to control foliar and soilborne diseases of many crops like the food legumes. However, application of fungicides to seed should continue to be an important method of controlling damping-off and other seedling diseases.

Cultural practices continue to be used extensively to control soilborne diseases caused by fungi and nematodes that attack the roots of edible legumes. Crop rotation is one method commonly used to control soilborne diseases that have a narrow host range, e.g., the Fusarium wilt or root rot diseases of chickpea. Other cultural methods, like eradication of overwintering and/or alternative hosts of certain pathogens or removal of crop residues may be required to achieve a satisfactory level of control of certain diseases.

Host plant resistance offers the most promising and potentially important method of controlling diseases of many food crops. Disease resistance has proved useful in controlling many diseases of edible legumes (National Academy of Sci- ences, 1972, 1979), but much more remains to be done in development of multiple disease- and pest-resistant cultivars of these food crops. It is possible that more emphasis will be given to host plant resistance as costs of other control measures that depend heavily on the use of fossil fuel energy and other scarce resources rise. This method of control requires that researchers have access to a large, variable source of germ plasm of different food legumes to use in their breeding programs. Plant germ plasm collections of numerous food crops have been maintained at various locations in the United States for many years. These germ plasm collections are an integral part of the National Plant Germplasm System (NPGS). The NPGS is a coordinated effort among federal, state, and private organizations in the United States to collect, introduce, maintain, evaluate, catalog, and dis- tribute all types of plant germ plasm (USDA, 1977).

Most or all plant germ plasm available to researchers from germ plasm centers in the United States have PI (USDA plant inventory) accession numbers assigned to them. The germ plasm collections for the 4 legume crops reviewed in this paper


are located at 2 of the 4 state-federal regional plant introduction stations in the United States:

Pullman, Washington: chickpea, lentil, tepary bean Experiment, Georgia: pigeon pea Significant strides have been made in the last 30 yr in controlling a number of

important diseases of food legumes and other crops. However, much remains to be done in preventing crop losses due to diseases and pests, particularly in the developing countries where chronic food shortages are a common occurrence and could worsen as the populations of these countries increase. New approaches of disease control must conserve resources and energy and promote a clean envi- ronment. The research challenges are great and the opportunities for success are promising.

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Plant Classification. Lyman Benson. 2nd ed. 901 pp. illus. D. C. Heath and Company, Lexington, Massachusetts, 1979. $22.95.

The first edition of Plant Classification is outstanding. Benson has now come out with an updated and completely revised book that bears little resemblance to the original edition except for the splendid and profuse black-and-white line drawings most of which are new. Depending upon the previous training of the student, this volume could be used as a comprehensive text for a one-semester course or for a less concentrated two-semester course in plant taxonomy and classification.

As an authority on Ranunlculus and Cactaceae in particular, Benson has numerous examples of the former in the section on keying in which he uses examples of keys from 13 different books covering practically all areas of the United States. He compares the various ways by which the different authors key a plant to a species of Ranunculus in all except one, Long and Lakela's Flora of Tropical Florida. Ranunculus does not occur in the area, and a species of Citrus is the example used in this instance.

I particularly like Benson's discussion of the major systems of classification from Theo- phrastus to Cronquist. Coverage of families and orders of dicotyledons and of morphology and economic plants of the groups is especially good. There is a minimum of factual error in this magnificent volume. My main regret is that the publisher's proof readers let so many printer's errors through.

This attractive and splendidly bound and printed book should be owned by all botanists regardless of their specialization.

EDWARD T. BROWNE, JR., MEMPHIS STATE UNIVERSITY, MEMPHIS, TN 38152

diseases of chickpea, lentil, pigeon pea, and tepary bean in

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