Genetic analysis of downy mildew in pearlmillet
R. Kumar* and P. Sagar
Department of Genetics and Plant Breeding
CCS Haryana Agricultural University,
Hisar-125 004 (Haryana), India
*(e-mail : rameshkrgr@gmail.com)
(Received : 18 December, 2012, Accepted : 25 January, 2013)
SUMMARY
The genetics of downy mildew was studied in 144 hybrids developed by crossing six A- and their six B-lines with 12 R-lines of pearl millet in a line x tester mating design. The six A- lines 81A1 and 8A1 (A1), Pb 313A (A2), Pb 402A (A3), 81A4 and 81A5 and their corresponding B- lines represented five different systems of male sterility and were very diverse. The 24 parents and the 144 hybrids were grown separately in contiguous blocks in 2R × 2.5 m × 0.45 m in randomized block design with two replications in six environments under natural condition viz., early sown non-cut crop (E1, E4), ratoon crop (E2, E5) and late sown non-ratooned (E3, E6) at Research Farm, CCSHAU, Hisar and two environments in sick plot (SP1, SP2) Department of Plant Pathology, CCS HAU, Hisar. The downy mildew incidence was recorded on all plants in the plot under natural and sick plot after 30 days (stage I) and 60 days (stage II) of sowing. The data on downy mildew incidence (%) were subjected to angular transformation for analysis of variance. The analysis of variance was conducted by developing statistical model involving all genotypes–lines (A-, B-), testers (R-lines), A- x R- and B- x R-hybrids, environments and all possible interactions. The combining ability analysis was carried out following line x tester model. The genotypes, parents, lines (A-, B-), testers (R-lines), A- x R- and B- x R-hybrids differed significantly at both the stages but A- vs. B- lines and A- x R- vs. B- x R-hybrids contrasts did not differ significantly showing no role of cytoplasm in downy mildew vulnerability. The significant differences among lines, testers and lines x testers (hybrids) indicated parental and hybrids variation for general combining ability (gca) and specific combining ability (sca) variances and effects, respectively, under natural as well as sick plot at both the stages. The fixed effect mean square variances due to general combining ability (gca) and specific combining ability (sca) revealed that magnitude of sca variances exceeded at 30 DAS and that of gca variances excelled sca variances at 60 DAS indicating that final selection should be carried out at latter stage. The lines Pb. 402A3 and Pb. 402B3 with negative gca effects combined significantly better for downy mildew resistance at both the stages. The other lines combined poor to average with most of the non significant gca effects.
Key words : Genetic resistance, downy mildew, pearlmillet, environment