Resistance to leaf spot disease in peanut

Full text: Leaf spot disease causes defoliation of peanut plants during pod development thereby reducing yield. To induce mutations for resistance to the disease, dormant seeds of peanut were irradiated with 10-40 kR gamma rays with pre- and post-irradiation treatments to minimize radiation damage. Spores of the causal fungi, Cercospora arachidicola Hori and Cercosporidium personatum (B and C) Deigh., were cultured under asceptic conditions in PDA medium with 2-3 drops of 10% table salt solution to enhance development of spores. The first two leaves of M2 seedlings were hand-inoculated two or three times in the field at one week intervals. Out of a total of 2,453 M2 seedlings inoculated thrice, 9 plants showed complete resistance based on degree of infection. However, after recurrent selection, only 3 M5 lines gave complete resistance, the rest exhibiting only intermediate resistance. The disease resistant lines yielded almost twice as much as several commercial varieties due to extensive leaf defoliation in the latter. One of the mutant lines is being crossed with some popular susceptible varieties. Inheritance studies showed that leaf spot resistance is governed by two recessive mutant genes acting complementary. The F2 ratio was close to 15:1. The mutant lines are presently evaluated through the Bureau of Plant Industry before seeds are distributed to peanut growers. (author)