Metodo para obtener alta severidad de la roya del frijol en areas con humedad relativa baja

A total of 18 bean var. with different degrees of rust resistance in the field were subjected to 4 treatments, to obtain high severity of Uromyces phaseoli under low RH. Treatments were (1) greenhouse inoculation, with optimum temp. and RH for disease development, (2) field inoculation in infection beds, with daily irrigation on the leaves and plastic mulch to create a humid chamber, (3) same as (2) but with no humid chamber, and (4) field inoculation in infection beds, without both irrigation and humid chamber. Av. day/night temp. (degrees C) and RH (percentage) for treatments (1), (2), (3), and (4) were 24.7/21.5 and 78.7/91.8, 28.0/21.0 and 74.8/98.6, 25.8 and 85, and 28.0/25.8 and 53.1/73.7, resp. In treatment (1), the fungus incubation and dormancy period in the var. evaluated ranged between 6 and 10 days, and between 7 and 12 days, resp. Ranges in treatments (2) and (3) were similar. In treatment (4), the lack of daily irrigation resulted in an extension of the incubation and dormancy period, significantly reducing disease, due to the low uredospore germination resulting from unfavorable environmental conditions. Disease severity was greater in the greenhouse than in the field. However, in field conditions, irrigation provided the necessary RH for U. phaseoli to develop. In low RH areas, high rust severity can be obtained in bean var. or lines evaluated for resistance to the pathogen. (CIAT)