Zbl. Bakt. II. Abt, 136 (1981),45-48

[Mycology Laboratory, Botany Dept., Faculty of Science, Assiut University, Assiut, Egypt]

Pathogenicity of Ten Seed-borne Fungi of Peanut Seeds

S. I. ABDEL-HAFEZ, F. T. HISSY, and S. K. M. HASSAN

Summary

Peanut seeds conditioned to 15 %, 20 %, and 25 % moisture content were inoculated sepa­rately with each of ten common seed-borne fungi. Aspergillus floou«, A. jumigatus, A. niger, A. ter­reus, and Rhizopus stolonifer were the most serious ones and induced complete mortality after4 weeks at 25 %and after 8 weeks at 15 %and 20 %. A. chevalieri was of moderate pathogenicity.Drechslera spicifera, after 12 weeks, was non-injurious at 15 % and caused a slight loss of germin­ability at 20 %, but became very serious at 25 %. In general, the increase of the moisture contentof the seed increased the rate of fungus invasion and mortality of seed embryo.

Zusammenfassung

Erdnul3samen mit einem Feuchtigkeitsgehalt von 15, 20 und 25 % wurden mit je 10 krank­heitserregenden Pilzarten beimpft. Aspergillus flavu«, A. jumigatus, A. niger, A. terreue undRhizopus stolonifer verursachten den groJ3ten Schaden und fUhrten bei 25 % Feuchtigkeitsgehaltnaeh 4 Wochen und bei 15 % und 20 % nach 8 Wochen zum volligen Absterben des Keimlings.A. cheoalieri war mal3ig krankheitserregend. Drechelera spicijera bewirkte bei 15 % Feuchtigkeitnach 12 Wochen keinen und bei 20 % nur einen geringen Verlust der Keimfahigkeit, verursachtejedoch bei 25 % schwere Sehadigungen. Die Zunahme des Feuchtigkeitsgehaltes der Samen fUhrteim allgemeinen zu einer Erhohung der Befalls- und der Absterberate der Keimlinge.

Artificial infection of surface-disinfected cereal seeds has been used by CHRISTEN­SEN and his collaborators to study the effect of common seed-borne fungi, alone orin combination, on the germinability and other qualities of seeds and to determinethe moisture requirements of every fungus. CHRISTENSEN and KAUFMANN (1965)found that the lower limit of moisture content required for the invasion of starchygrains was as follows: A. restrictus 13.2-13.5 %; A. amstelodami, A. chevalieri, andA.ruber 15-15.2%; A.flavus17.5-18%; and A.candidus and A.ochraceus15 to15.2 %. FIELDS and KING (1962) studied the pathogenicity of Aspergillus flavus,A. ruber, A. candidus, and A. restrictus on pea seeds, stored under 10-30°C and75-92 % r.h, for 2-8 months and found that A. flavus was the most pathogenicspecies. In Egypt, MOUBASHER et al. (1972) observed that A. niger, Penicilliumcitrinum, and P. variabile caused severe deterioration of wheat, corn, and sorghumgrains when the seeds were adjusted to 15 % moisture content and incubated at30°C for 8 weeks.

The aim of the present investigation was to test the pathogenicity of ten commonpeanut seed-borne fungi to assess how much each of them could participate in thedeterioration of peanut seeds on storage.

Material and Methods

Artificial infection of peanut seeds

Peanut seeds were first surface-sterilized by shaking in 2 % sodium hypochloride solution for2 minutes, rinsed in three changes of sterile distilled water. Thereafter, they were placed in asterile flask, containing a suspension of spores of a single fungus in an amount of sterile distilled

46 S. 1. ABDEr,-HAFEZ et al.

water, sufficient to raise the moisture content of the seed to 15 %, 20 % .or 25 % by the methoddescribed by LUTEY and CHRISTENSEN (1963) and employed by MOUBASHER et al. (1972). Theinfested seeds were stored for 12 weeks at 30 DC, during which the population of the fungus wasperiodically counted and the germinability of the seed was determined. Ten fungi which are corn-mon on peanut seeds were used.

Results and Discussion

The results in Table 1 show that all tested fungi were injurious to peanut seeds,and in all cases the least injury was recorded at 15 % moisture content and thehighest at 25 %. The counts of each fungus also increased markedly with the rise ofthe moisture content.

Table 1. Percentage germination of surface-sterilized peanut seeds, conditioned to 15 %,20%, and25% moisture contents inoculated with ten fungi separately and incubated for 12 weeks at 28 DC.Counts of fungi per g dry seed

Organism Incubation Percentage germination Fungus countperio.]

15 ~!;) 20% 25% 15% 20% 25%(weeks)

Asperqillus chevaiieri II 100 100 100 2fiO 320 340(Mangin) Thorn and 1 100 92 92 300 400 600Church 2 SS SO 74 400 600 850

4 liS 44 20 1600 7 (3) 12 (3)S 24 0 0 8 (3) 15 (3) 21 (3)

12 0 0 0 25 (3)

Ai flaous Link II 100 100 100 420 400 4901 91i 92 92 500 510 6002 SS fi4 4S 7 (4) 8 (4) 9 (4)4 40 12 0 1 (5) 3 (5) 7 (5)S 0 0 0 9 (!\) 4 (7) 5 (7)

A. [umiqatue Fres. II 1110 100 100 440 420 4551 9fi 92 92 800 1200 15002 SS 80 eo 2 (4) 4 (4) 5 (4)4 44 12 0 9 (5) 3 (6) 5 (6)S 0 0 0 1 (7) 6 (7) 8 (7)

A. niger v. Tiegh. II 100 100 100 385 390 3801 \Hi 92 92 4 (3) 5 (3) 5 (3)2 SS 72 (is 9 (4) 2 (5) 4 (5)4 5H 20 0 2 (6) 6 (6) 3 (7)S 0 0 0 2 (8) 5 (S) 9 (8)

A. terreus ThOll1 0 100 100 100 335 340 3651 100 100 96 1400 1500 16002 80 72 60 12 (3) 2 (4) 6 (4)4 se Hi 0 11 (4) 6 (5) 8 (5)S 0 0 0 2 (6) 3 (7) 6 (7)

Penicillium funicu- 0 100 100 100 200 210 215I08um Thorn 1 96 92 92 2 (3) 3 (3) 3500

2 SS 76 56 18 (3) 3 (4) 8 (4)4 72 36 16 9 (4) 4 (5) 7 (5)8 4 0 0 3 (6) 9 (Ii) 2 (7)

12 0 0 0 8 (7)

Pathogenicity of Ten Seed-borne Fungi 47

Table 1. (Cont..)

Organism Incubation Percentage germination Fungus countperiod

1.'5% 20% 25% 15% 20% 25%(weeks)

P. notatum West!. 0 100 100 100 215 210 2451 100 100 IHI 1800 2 (3) 4 (3)2 S8 72 60 2 (4) 4 (4) 7 (4)4 fiO 20 12 26 (4) 6 (5) 8 (5)S 0 0 0 9 (6) 1 (7) 3 (7)

Fusarium oxusporum. 0 100 100 100 150 165 lfiOSchlecht. 1 100 92 92 200 275 300

2 S4 (18 64 5 (3) 88 (3) 9 (3)4 1i4 40 24 4 (4) 7 (4) 9 (4)S S 0 0 8 (4) 14 (4) 3 (5)

12 0 0 0 2 (5)

Rhizopus stolonifer 0 100 100 100 210 215 230(Ehrenberg et Pries) 1 100 9() 92 860 940 1 (3)Lind 2 SS 68 .'52 1 (4) 2 (4) 3 (4)

4 1)4 16 0 8 (4) 3 (5) 6 (.'5)S 0 0 0 3 (6) 5 (6) 8 (6)

Drechslera spicifera 0 100 100 100 315 335 320(Bain.) von Arx, 1 100 100 96 338 35fJ 378

2 SS 86 (iO 395 42fJ 4554 S(I 82 40 484 422 9 (3)S 7S 71 0 412 414 14 (3)

12 74 li9 0 440 420

Control 0 IOI) 10O 1001 100 100 1002 92 88 S.'54 \lO S4 70S S2 7S 71

12 74 7S 6li

Figures in parentheses roproserrt the number of "()"s to be added to the right of the original figures;2 (3) = 2000.

However, the tested fungi showed variable degrees of pathogenicity. Aspergillusflavus, A. fumigatus, A. niger, A. terreus, Penicillium notatum, and Rbiurpue stolo­nifer displayed the highest activity and all induced complete mortality after 8 weeksat the 3 levels of moisture content. These fungi, except P. notatum, caused completemortality of seeds conditioned to 25 %after 4 weeks.

A. cheoalieri was of relatively moderate activity. After 8 weeks it induced completemortality of the seeds conditioned to 20 %and 25 %, but at 15 %, 24 %of the seedscould survive. At the latter moisture content complete mortality was exerted after12 weeks.

Drechslera epicijera was completely non-injurious at 15 %and caused a slight lossin percentage germinability at 20 % after 12 weeks. At 25 %it became very seriousand exerted complete mortality after 8 weeks, like all other fungi. Its count showedthat it could grow and increase its population very slightly at 15 % and 20 %, butat 25 % it sharply increased, especially after 4 and 8 weeks. The results of this spe­cies present a good evidence that the pathogenicity of any fungus depends upon

48 S.1. ABDEL·HAFEZ et al., Pathogenicity of Ten Seed-borne Fungi

its ability to grow and increase its population at the expense of the seed embryo.After 8 and 12 weeks its counts at 15 % and 20 % moisture content increased veryslightly over the initial count. But at 25 % its population sharply increased, startingfrom the fourth week when it became very harmful. This organism can be oonsidereda typical field fungus in the light of CHRISTENSEN and KAUFMANN'S (1965) classi­fication of seed-borne fungi, which need 24-25 %moisture content to invade starchygrains.

Fusarium oxysporum behaved as a storage fungus, since it could invade peanutseeds at 15 %. Fusarium is included by CHRISTENSEN and KAUFMANN (1965) amongfield fungi which require high moisture content for their invasion. This observationrecalls the question raised by MOUBASHER et al, (1972), i.e., where can be drawn thelimit between storage and field fungi?

Acknowledgement

The authors are very grateful to Prof. A. H. MOUBASHER, Dean of the Faculty of Science andHead of Botany Department, for reading the manuscript and for valuable discussions.

References

CHRISTENSEN, C. M., and KAUFMANN, H. H.: Deterioration of stored (wheat) grains by fungi.Ann. Rev. Phytopathology 3 (1965), 69.

FIELDS, R. W., and KING, T. H.: Influence of storage fungi on deterioration of stored pea seeds.Phytopathology 52(1962),336.

LUTEY, R. W., and CHRISTENSEN, C. M.: Influence of moisture content, temperature and lengthof storage upon survival of fungi in barley kernels. Phytopathology 53 (1963),713.

MOUBASHER, A. H., ELNAGHY, M. A., and ABDEL-HAFEZ, S. 1.: Studies on the fungus flora ofthree grains in Egypt. Mycopathologia, Haag 47 (3) (1972), 261.

Authors' address:

Dr. S. 1. ABDEL-HAFEZ, Dr. F. T. HISSY, and Dr. S. K. M. HASSAN,Mycology Laboratory, BotanyDept., Faculty of Science, Assiut University, Assiut, Egypt.