Selection of groundnut lines for rust and leaf spot tolerance

Rust and leaf spot are the most destructive foliar diseases in groundnut-producing-area all over the word, including Indonesia. Yield loss up to 50 percent was common in susceptible lines. Fungicidal control has proved to be effectively control the diseases, however, it is costly and not readily available at farm level. Under these circumstances, planting tolerant variety is the best choice. A hundred groundnut lines, including four check varieties, were evaluated at Muneng Experimental Farm-East Java, during the dry season of 1999. Evaluation was conducted using two contrasting environments, i.e. optimum environment and disease-stress environment. No fungicide spray in the disease-stress environment, and in the optimum environment the plants were sprayed three times (30, 45 and 60 days after planting) using chlorothalonil. Susceptible check (Macan) and resistant check (Anoa) were planted in every 10 tested-row lines. Each line was planted in single row of 5 m long, 40 cm x 10 cm planting distance, 1 plant/hill. Each unit experiment was arranged in randomized completely block design, replicated three times. Data collected on yield and yield components, rust and leaf spot diseases intensity. Stress tolerance index was used as the selection criteria. Pod yield phenotypic variability among the tested lines was relatively low (27.7 percent), however, the yield average was high (360 g/2 m or equivalent to 1.8 t/ha). Rust disease intensity was higher compared to that in leaf spot. Rust disease intensity was as high as 100 percent at 80 days after planting observation. Three time applications of chlorothalonil decreased rust disease intensity of about 10-20 percent, leaf spot disease intensity of about 10 percent, and saved pod yield by 52 percent for the average. Stress tolerance index was in the range of 0.3-1.39 and the STI of the check varieties was 0.45-0.86. There were 17 lines with STI higher than the check varieties, which means that those 17-lines were more tolerant and possessed higher potential yield compared to the check varieties. Pod yield average of those 17 lines was 377.7 g/2 m in unsprayed and 575.3 g/2 m in sprayed plots. The disease intensities were 5.5-9 in unsprayed, and 4.5-6.5 in sprayed plots. Those lines were merit to be further evaluated