Influencia de el tipo de pustula de roya (Uromyces phaseoli (Reben) Wint.) sobre el rendimiento de cultivares de frijol (Phaseolus vulgaris L.)

Yield losses due to Uromyces phaseoli were determined in 9 bean var. selected for pustule size: BAT 93, BAT 308, and EMP 81 (type 3 pustules; more than 300 millinicrons in diameter, approx.); Jamapa, ExRico 23, and BAT 883 (type 5 pustules; more than 500 millimicrons in diameter, surrounded by a chlorotic halo), and BAT 41, BAT 527, and BAT 153 (type 3, 4, or 5 pustules). The expt. was conducted at CIAT with the following treatments: (1) naturally inoculated plots, (2) artificially inoculated plots, and (3) plots periodically protected with fungicide. Day/night av. temp. and RH during the exptl. period were 28/26 degrees C and 75/99 percent, resp., optimum conditions for rust development in beans. Var. with type 3 pustules (BAT 93, BAT 308, and EMP 81) showed the lowest areas under the curve in disease progress. Var. with type 5 pustules (Jamapa, ExRico 23, and BAT 883) showed the largest areas and var. with type 3, 4, or 5 pustules (BAT 41, BAT 527, and BAT 153) showed areas with intermediate value. In the fungicide-protected treatments, disease was not controlled in ExRico and BAT 883 (highly susceptible var.). With natural infection, small-pustuled var. yielded an av. of 334 kg/ha more than large-pustuled var. (1.5 times more). Disease control with fungicide allowed an increase of 770 kg/ha in the av. yield of large-pustuled var., equivalent to 3.4 times more than the increase in the av. yield potential of the small-pustuled var. This significant increase suggests that current yields can be increased more economically, adding resistance genes. (CIAT)