Evaluation of Faba bean Cultivars, Fungicides and Bio-control Agents for the Management of Chocolate Spot (Botrytis fabae Sard.) Disease in Kellem Wollega, Western Oromiya, Ethiopia

Abstract

Faba bean (Vicia faba L.) is an important legume crop in the daily diet, good source of food nutrients, cash to the farmers and also foreign currency in Ethiopia. The chocolate spot disease caused by Botrytis fabae Sard is one of the most devastating soil-borne diseases and also the main constraints contributing to the low productivity of faba bean resulting in yield losses of up to 68% in Ethiopia. Therefore, an experiment was conducted at Haro Sabu Agricultural Research Center, Kellem Wollega, Western Oromiya, Ethiopia during the main cropping season of 2016, to evaluate three faba bean cultivars (Gora (EK01024-1-2), NC-58 and one local) combination with three fungicides (Mancozeb 80% WP, Folpan 80% WDG, and Mancolaxyl 72 WP (Mancozeb 64% + Metalayxl 8%) and two bio agents (Trichoderma harzianum and T. viride) under field conditions for the management of chocolate spot disease and also to assess the yield losses. A total of eighteen treatments were arranged in a randomized complete block design with three replications for the field experiment and non- spray fungicides and non-inoculated bio-agents treatments were used as control. There was a significant difference in the chocolate spot disease incidence, severity, and infected pods per plant, infected seeds and Area under Disease Progressive Curve (AUDPC) among treatments. Chocolate spot incidence, severity, infected pods per plant and AUDPC were highest in the control plots of NC-58 and Local cultivars when compared to the fungicides and bio agents treated seed plots. On the final date of disease assessment, among the cultivars, Gora cultivar was recorded the lowest disease incidence (42.33%) and the severity (18.63%), whereas the highest disease incidence of 100 and 90% and severity of 72.16 and 64.96 % were recorded on the NC-58 and Local cultivars on control plots, respectively. The highest reduction on disease severity (71.69%) was recorded on three times sprayed plots of Gora cultivar treated plots. Faba bean cultivars showed significant differences in their grain yields and hundred seeds weight but the fungicides sprayed plots were recorded significantly different from bio-agents treated and control plots. The highest grain yield of 3496 and 3340 kg /ha were also recorded from plots sprayed with Mancozeb 80% WP and Folpan 80 WDG on local cultivar. Relative yield losses of 2.57-53.17% on NC-58 cultivar, 4.46-40.96% on Local cultivar and 5.92-33.65% on Gora cultivar were recorded. The highest relative yield losses occurred on unsprayed (control) plots of NC-58 cultivar (53.17%) followed by Local (40.96%) and Gora cultivars (33.65%), respectively. The PDI, PDS and AUDPC were negatively correlated with PP, grain yield and HSW and positively correlated with each other. Mancozeb 80% WP fungicide applied on three cultivars exhibited maximum partial cost net benefit from all plots that means the highest (56135.00 ETB ha^-1) was recorded on cultivar Gora followed by on Local (52415.00 ETB ha^-1) and on NC-58 cultivar (45285.00 ETB ha^-1). Also the highest cost net benefit was recorded on Folpan 80 WDG fungicide treated plots on Gora (50637.00 ETB ha^-1) cultivar followed by Local (47692.00 ETB ha^-1), respectively. The results of the present study revealed that the novel possibility of using Mancozeb foliar spray with three times and T. harzianum seed treatments which were found to be an effective in decreasing chocolate spot disease symptoms on faba bean cultivars in Kellem Wollega, Western Oromiya and increased yield. This study could be provided some evidences on the response of faba bean cultivars, effect of bio-control agents and efficacies of fungicides and its application frequencies for the disease development and substantial increase on yield. Further, the effective and feasible integrated management options need to be developed on faba bean chocolate spot disease in the country.

Keywords: Faba bean, Chocolate spot disease, Cultivars, Fungicides, Bio-control agents, Yield and Yield loss, Cost benefit.