Reaction of new long-day pigeonpea genotypes to rust (Uredo cajani)

Five long-day pigeonpea [Cajanus cajan (L.) Millsp.] genotypes were evaluat ed for field resistance to rust (Uredo cajani) with seven planting dates pe r year during 1992, 1993 and 1994 at the Isabela Substation of the Universi ty of Puerto Rico, Mayaguez Campus. Rust was a frequent problem over the th ree-year testing period but less serious when pigeonpea was planted in Febr uary. Planting date had a significant effect on the intensity of rust and t he field reaction. For all genotypes, the effect of years was the same for disease reaction and different for infection intensity. Long-day genotypes showed levels of intermediate resistance to moderate susceptibility. The av erage rust infection of early maturing I-8-2, with largest pustule sizes (r ated as moderately susceptible) was significantly greater (P < 0.05) than t hat of tate-maturing II-56 (intermediate). The remaining late maturing I-13 , I-58-3 and early genotype I-58-1 also had intermediate resistance to rust , but pustule sizes were greater than those observed on II-56. It is eviden t that distinct host Variation existed among long-day pigeonpea genotypes f or level of susceptibility or relative resistance to U. cajani.