Five long-day pigeonpea [Cajanus cajan (L.) Millsp.] genotypes were evaluated for field resistance to rust (Uredo cajani) with seven planting dates per year during 1992,1993 and 1994 at the Isabela Substation of the University of Puerto Rico, Mayagüez Campus. Rust was a frequent problem over the three-year testing period but less serious when pigeonpea was planted in February. Planting date had a significant effect on the intensity of rust and the field reaction. For all genotypes, the effect

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... years was the same for disease reaction and different for infection intensity. Long-day genotypes showed levels of intermediate resistance to moderate susceptibility. The average rust infection of early maturing I-8-2, with largest pustule sizes (rated as moderately susceptible) was significantly greater (P < 0.05) than that of late-maturing II-56 (intermediate). The remaining late maturing I- 13, I-58-3 and early genotype 1-58-1 also had intermediate resistance to rust, but pustule sizes were greater than those observed on II-56. It Is evident that distinct host variation existed among long-day pigeonpea genotypes for level of susceptibility or relative resistance to U. cajani.