Management of Ascochyta blight of chickpea (Cicer areientinum l.) caused by Ascochyta rabiei l. using fungicides

Abstract

Chickpea (Cicer arientinum L.) is an important dry land legume whose full potential in Kenya has not been realized due to abiotic and biotic stresses. The objectives of this study were to evaluate the use of seed treatment and foliar sprays as disease management options against Ascochyta blight caused by Ascochyta rabiei in chickpea. The study was conducted in two sites; Egerton University Njoro and Agricultural Training Centre (ATC) Koibatek. One genotype Chania Desi (ICCV97105) was evaluated in three experiments. The first experiment was conducted both in vitro and in vivo. In the in vitro experiment, seeds from two categories (symptomatic and asymptomatic) were evaluated under a randomized complete block design (RCBD) using the agar plate method to determine germination and A. rabiei infection levels. In the in vivo experiment seeds within each category were left treated or untreated with either of the fungicides, Azoxystrobin 250g/L, Difenoconazole 250g/L, Azoxystrobin 250g/L+Difenoconazole 125g/L and Metalaxyl 40g/Kg+Mancozeb 640 g/Kg. The emergence of plants and the development of Ascochyta blight (AB) lesions on plants from the two batches were monitored in the greenhouse. The second experiment was to evaluate the efficacy of different fungicides in control of Ascochyta blight. A split-split plot design with four fungicide treatments and four spray regimes, one variety and three replications. The third experiment evaluated one variety and one fungicide only based on the result of the second experiment under a split-split plot design. Data on severity and incidence was collected and subjected to Analysis of Variance (ANOVA) at P≤0.05 and significant means at the F-test were separated using Fischer’s protected LSD test. Seed treatment with azoxystrobin+difenoconazole combination and azoxystrobin alone had the most significant effect in emergence under greenhouse and field conditions. Seed dressing with either of the fungicides used had a significant increase in seedling emergence as compared to non-dressed seeds. Decrease in incidence and severity of ascochyta arising from seed dressing effect was not significant. PDI reduced by 65.5%, 62.25%, 40.55% and 33% in Njoro and 52.8%, 49.63%, 51.41% and 22.64% in Koibatek following application of 6, 5, 4, and 3 foliar sprays respectively compared to control. Combining seed treatment with foliar sprays did not show any superiority over the use of foliar sprays alone at all stages of growth. Upto six foliar sprays with difenoconazole and five sprays with azoxystrobin may be required for control of ascochyta blight in susceptible lines under high disease pressure.