Male to female row ratio and fungicide application during panicle development to control sorghum ergot in the Mexican Highlands

Abstract

The effect of male to female row ratios and fungicide application at several panicle development stages to control sorghum ergot, under field conditions and natural infection was studied at Texcoco, State of Mexico. A pair of isogenic sorghum lines (A9/B9) was sown in May 3 and June 10, 2005; and in April 3, 2006. Two male to female row ratios (M:F = 2:4, 2:6) were used in 2005, and 2:8 and 2:12 in 2006. Propiconazole (Tilt®) was sprayed on the female rows at a rate of 250 g a.i. ha−1 from panicle emergence to the end of flowering, with one, two and three applications. Pollen viability was quantified in the B9-line. Seed yield per hectare, seed production per panicle, disease incidence and severity, number of sclerotia per panicle, seeds contaminated by honeydew per panicle, and seed germination were registered in the A9-line. Pollen viability varied from 76 to 89 % among sowing dates despite the fact that at microsporogenesis, mean minimum temperature was below 9.2 °C. Fungicide application accounted for 49 % of the observed variance. The greatest seed yield (2,358 kg ha−1) was obtained in 2006, which surpassed by 195 kg ha−1 the mean value of the dates sown in 2005. Disease incidence and severity were significantly greater in the 2006 trial than at both planting dates in 2005. In contrast, sowing dates showed small differences in seed production per panicle and seed germination. Fungicide treatment with three applications produced a better ergot control than treatments with one or two applications.