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Kumar KA and Andrews DJ, 1993. Genetics of qualita-tive traits in pearl millet: a review. Crop Sci 33:1-20.Mengesha MH and Appa Rao S, 1989. Some newly iden-tified genetic tra its in pearl millet. Perspect Cytol Genet6:825-831.Neuffer MG, Jones L, and Zuber MS, 1968. The mutan tsof maize. M adison, Wisconsin: Crop Science Society ofAmerica.Received August 4, 1994Accepted January 24, 1995Corresponding Editor: Prem P. Jauhar

Inheritance and Allelic Studyof Brown Midrib Trait inPearl MilletS. C. GuptaIn pearl millet [Pennisetum glaucum (L.) R.Br.], two brown midrib lines are reported.One line (Pbmr) was developed at PurdueUniversity through chemical mutagenesis,and the other l ine SDML 89107 developedby SADC/ICRISAT through selection froma germplasm accession from Zimbabwe.Allelism crosses am ong these two lines re-vealed that their brown midrib genes areallelic to each other. In another study, F,,F2, and test crosses derived from 10crosses between six normal midrib par-ents and two brown midrib lines werestudied. The results revealed that thebrown midrib trait in most of the crosseswas controlled by one major recessivegene in the nuclear gen ome of pearl millet.It appears that there are modifying and/orepistatic gene(s) that affect the expressionof the brown midrib trait. The gene symbolbm tbm , is proposed for the major genepresent in SDML 89107 and Pbmr. Thebrown midrib trait in pearl millet is relative-ly simply inherited, and 20%-30% plantswith brown midribs can be expected in F2populations segregating for this character.The lignin content of a plant limits its useas a forage and its forage digestibility byruminants. Genetic control of the lignifi-cation process offers the most directmethod of reducing lignin content and in-creasing dry matter digestibility. Brownmidrib mutations are seen as one way tofavorably modify lignin quality and quan-tity (Cherney 1990; Cherney et al. 1991).Brown midrib mutants in maize (Zeamays L.) were identified as early as 1924(Jorgensen 1931). He described these linesas having brown pigmentation in the leafmidrib, stem tassel, cob, and roots. Fournonallelic brown midrib genes have beenidentified in maize (Kuc and Nelson 1964)

and are designated bm , to bm 4, bm, beingthe first gene described by Jorgensen(1931). Inbreds and F2 populations carry-ing these genes were evaluated for fibercomposition by Muller et al. (1971) andLechtenberg et al. (1972). They found thebm 3 gene to be the most effective in re-ducing lignin percentage. Barnes et al.(1971) and Lechtenberg et al. (1972)showed that the bm 3 mutant had the high-est in vitro dry matter digestibility.Porter et al. (1978) treated seeds fromtwo grain sorghum [Sorghum bicolor (L.)Moench.] lines, 954114 (short) and 954104(tall), with diethyl sulfate to induce mu-tations. Nineteen independently occurringbrown midrib mutants were identified insegregating M3 head rows and designatedbmr-1 through bmr-19. Allelism testsamong 12 of these brown midrib mutantsof sorghum gave inconsistent results, butindicated that more than one gene locusis involved in the brown midrib trait (Bit-tinger et al. 1981).

Three low-lignin, brown midrib sorghummutants, designated bmr-6, bmr-12, andbmr-18, were each backcrossed to normalgrain and grassy type sorghums (Fritz etal. 1981). In both genetic b ackgroun ds, thebrown midrib mutants showed lower lig-nin percentages and higher digestibilitythan normal genotypes.In 1989, four sorghum accessions withbrown midrib plants were identified in Ma-lawi germplasm growing at Makoka Re-search Station, Malawi (Gupta 1990). Thebrown midrib gene(s) in four naturally oc-

currin g brown midrib linesIS 23787, IS23789, IS 21549, and IS 23765were allelicto each other and to bmr-6 (Gupta 1995).The brown midrib gene(s) in all these fivelines were nonallelic to bmr-12 and bmr-18, whereas bmr-12 and bmr-18 were alle-lic (Gupta 1995), confirming the report byBittinger et al. (1981).In pearl millet, two brown midrib lineshave been reported. One line, Pbmr, wasdeveloped at Purdue University by treat-ing two inbreds derived from Tift 23D2B,/2 X PI 185642 through chemical mutagen-esis (Cherney et al. 1988). The other line,

SDML 89107, was developed by SADC/ICRISAT through selection from a germ-plasm access ion from Zimbabwe (Gupta etal. 1993).Cherney et al. (1988) reported thatbrown midrib pearl millet was phenotypi-cally similar to brown midrib mutants insorghum. The lignin concentration inbrown midrib pearl millet was 40 g/kg,compared to 50 g/kg, its normal counter-part. The brown midrib genotyp e's in vitro

dry matter digestibility (IVDMD) was 726g/kg, compared to the normal genotype659 g/kg.At 50% flowering, the whole-plantIVDMD of SDML 89107 was 10.7% higher(690 g/kg versus 623 g/kg) than that of itsnormal counterpart, whereas its stemIVDMD was 16.2% higher (Gupta et al.1993).The number of loci and the allelic rela-tionships of genes controlling the brownmidrib trait in these two pearl milletbrown midrib mutants are of interest toplant breeders. The purpose of this studywas to (a) study the inheritance of thebrown midrib trait in pearl millet and (b)evaluate the allelic relationship of thenewly identified, naturally occurring,brown midrib line with the previously de-scribed chemically induced brown midribmutant.

Materials and MethodsInheritanceThe material consisted of two brown mid-rib pearl millet lines: Pbmr, developed atPurdue University through induced muta-tion (Cherney et al. 1988), and SDML89107, developed by SADC/ICRISATthrough selection (Gupta et al. 1993). Fouradvanced grain varietiesSDMV 89005,SDMV 89007, ICMV 82132, and ICMV87901were used as normal midrib par-ents.

These six entries were sown at Muzara-bani, Zimbabwe on 14 April 1990 to pro-duce F, crosses (including reciprocals) be-tween brown midrib and normal midribparents. The F, seeds and the brown mid-rib parents were sown at Aisleby, Zimba-bwe on 18 October 1990 to classify theirmidrib color. The brown midrib parentsand the F, seeds for eight crosses wherebrown midrib lines were used as femaleswere sown in a greenhouse at Matopos,Zimbabwe on 22 June 1992. F2's were pro-duced, and test crosses were made usingbrown midrib lines as female parents. Inaddition to the above crosses, the F, seedsfor two crossesPbmr X Purdue normal(Pnormal), and SDML 89107 X SDMV89107 (normal counterpart of SDML89107)were produced at Muzarabani inthe material sown on 26 May 1991. Thebrown midrib parents and F, seeds ofthese two crosses were sown in a green-house at Matopos on 2 April 1992 to pro-duce F2's and test crosses (using brownmidrib lines as female parents). The resul-tant 10 F2 popu lations and 10 test cro sses(Table 1) were sown at Bulawayo, Zimba-

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Table 1. Segregation in Fz populations, derived from crosses between brown midrib and normalmidrib lines, for midrib color in pearl milletF2 popula t ion( b r own X no r m a l )Pbmr X SDMV 89005Pbm r x SDMV 89007Pbmr X ICMV 82132Pbm r X ICMV 87901Pbmr x PNormalSDML 89107 x SDMV 89005SDML 89107 X SDMV 89007SDML 89107 X ICMV 82132SDML 89107 X ICMV 87901SDML 89107 x SDMV 89107

Num be rNormal60079128 339 538 845 250926 056 3240

of plantsBrown158231871531091181125221 371

x' va lue a t3:1

6.98**3.13 ns0.44 ns2.49 ns2.50 ns5.62*

16.06**11.56**2.48 ns0.78 ns

13:32.18 ns9.96**5.51*30.24**3.30 ns1.42 ns0.21 ns0.89 ns38.54**3.40 ns

' Significance at P = .05. Significance at P = .01.

ns = nonsignif icant .

bwe on 16 January 1993 to classify theplants for midrib color.Allelism StudyTwo brown midrib lines (Pbmr and SDML89107) were sown at Muzarabani on 26May 1991 to produce reciprocal crosses.The F, seeds of these two crosses weresown in the greenhouse at Matopos on 2April 1992 to classify their midrib colorand to produce F2 seeds. The resultant F2population was sown at Bulawayo on 1 Oc-tober 1992.Classification of Plants for MidribColorThe classification for normal midrib andbrown midrib plants was done at the sev-enth leaf stage (the brown midrib colorappears at sixth leaf stage and becomesclear at the seventh leaf stage). All thebrown midrib plants were identified andtagged.Statistical AnalysisThe x2 test was used to test the data forgoodness of fit (Steel and Torrie 1980).

Results and DiscussionInheritanceIn 10 crosses involving two brown midriblines and six elite normal midrib lines, allthe F, plants had normal midribs. This in-dicates that the brown midrib trait inpearl millet is controlled by recessive al-lele(s).The segregation data for midrib color inF2 populations and test crosses are pre-sented in Tables 1 and 2. In three F2 pop-ulations, involving Pbmr and three normalmidrib lines (PNormal, ICMV 82132, andICMV 87901), midrib color segregation fita 3:1 (normal/brown) ratio. The segrega-tion in test cross data for midrib color inthese crosses fit a 1:1 ratio. These datasuggest that the brown midrib trait is con-trolled by a single recessive gene in thesecrosses.In one cross between Pbmr and SDMV89007, the segregation data in the F2 pop-ulation for midrib color fit a 3:1 (normal/brown) ratio. However, this is not sup-ported by test cross data for this cross asthe x2 value at the expected ratio, i.e., 1:1,

Table 2 . Segre gat ion in tes t crosse s , der ive d by cross ing brown midrib l ine wi th F, cros ses betw eenbrown midrib and normal midrib l ines , for midrib co lor in pearl mi l l e tTest c ross( b r own X no r m a l )Pbmr X (Pbmr X SDMV 89005)Pbmr x (P bmr x SDMV 89007)Pbm r X (Pbm r X ICMV 82132)Pbm r x (Pb mr x ICMV 87901)Pbmr X (Pbmr X PNormal)SDML 89107 X (SDML 89107 X SDMV 89005)SDML 89107 X (SDML 89107 X SDMV 89007)SDML 89107 X (SDML 89107 X ICMV 82132)SDML 89107 X (SDML 89107 X ICMV 87901)SDML 89107 X (SDML 89107 X SDMV 89107)

Number olNormal

4324 3581385922 31116724445

plantsBrown

32129571355011789699661

X2 va lue a t1:1

1.61 ns34.94**0.01 ns0.03 ns0.74 ns33.05**2.42 ns0.03 ns64.42**2.42 ns

3:112.48*18.58*37.01*87.04*25.32*16.06*40.56*48.04**1.90 ns59.89**

1 Significance at P = .05.' Significance at P = .01.

ns = nonsignificant.

was significant. In another F2 population,Pbmr X SDMV 89005, the x2 value at theexpe cted ratio of 13:3 was no t significant,indicating a good fit of the observed seg-regation to this ratio. This was supportedby segregation in test cross data wherethe midrib color segregation fit a 1:1 (nor-mal/brown) ratio.In F2 populations, involving SDML 89107and the norma l m idrib line SDMV 89107,

midrib color segregation fit a 3:1 (norm al/brown) ratio. This indicates that thebrown midrib trait is controlled by a sin-gle recessive gene in this cross. This issupported by segregation in test crossdata involving this cross in a 1:1 ratio.In another F2 population, SDML 89107 xICMV 87901, th e x 2 value at 3:1 (normal/brown) ratio is not significant, indicatingthat this trait is controlled by a singlegene. However, this is not supported bytest cross data for this cross as the x 2 val-ue at the expected ratio, i.e., 1:1, was sig-nificant.In the remaining three crosses, involv-ing brown midrib line SDML 89107, a two-gene epistasis model fit better than anyother ratio. The F2 populations involvingbrown midrib line SDML 89107 and threenormal midrib lines, the x2 values at theexpected ratio 13:3 are not significant, in-dicating a good fit of the observed segre-gations to this ratio. The segregation intest cross data of two crosses fit a 1:1 ra-tio, and for the third cross (SDML 89107x SDMV 89005), the x2 values at both 1:1and 3:1 (normal/brown) ratios are signifi-cant, indicating a poor fit of the observedsegregations to either of these ratios.It appears that the brown midrib trait inpearl millet, in most of the crosses involv-ing brown midrib lines, is controlled byone major gene. In a few crosses, this traitis controlled by two genes. Alternatively,modifying genes are present, which affectthe expression of the trait.

Allelic RelationshipsThe F, plants (194) in a cross betweenPbmr and SDML 89107, including a recip-rocal cross, had uniformly brown midribs.All the 312 F2 plants derived from thiscross also had brown midribs. This indi-cates that the gene(s) controlling this traitin these two brown midrib lines are allelic.The gene symbol bm,bm, is proposed forthis gene in both brown midrib lines SDML89107 and Pbmr.From the Sorghum and Millet Improvement Program ofSouthern African Development Community (SADC)/ln-ternational Crops Research Institute for the Semi-AridTropics (ICRISAT), P.O. Box 776, Bulawayo, Zimbabwe.

3 0 2 The Journal of Heredity 1995:86(4)

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