Biological and chemical control of fungal seedling diseases of cowpea

Abstract

Cowpea is a worldwide-distributed crop, and is important to the livelihood of poor people in developing countries. Cowpea is also susceptible to a wide range of pests and pathogens, which can cause damage to the crop at all stages. Seedling diseases caused by pathogens such as Rhizoctonia solani Fusarium solani and Pythium spp. affect cowpea and result in low yields especially in rural areas where there are few or no control measures against these pathogens. This research aimed at evaluating the efficacy of a biological control agent and fungicides against fungal seedling diseases of cowpea. The bacterium, Bacillus cereus1, and the fungicides, Apron®, Subdue® and Celest® were screened for the control of cowpea seedling diseases, after obtaining promising in vitro results on their effectivity against Rhizoctonia solani, Pythium ultimum and Fusarium solani. The experiment was conducted in a greenhouse using seedling trays with 128 cells, each filled with pasteurised growing medium (Braaks lawn dressing). Seedling trays were placed randomly on greenhouse tables with four replication per treatment, each replication consisting of 56 plants. Cowpea seeds (Cultivar-Pietersburg blue) were obtained from the Dry Bean Seeds Producers Organisation. The pasteurised growing medium was artificially inoculated with the three fungi. Two plugs of actively growing fungal mycelium of the three pathogens were inoculated in each cell of the polystyrene seedling trays. Trays were drenched with Bacillus cereus1 at 106 cells/ml (3 ml per tray cell) at planting and fungicides were applied on the 14th and 28th days at the recommended rate. The experiment was conducted at temperatures ranging from 22-25 oC. Plants were harvested on the 35th day after planting and percentage germination, diseased height of the plants and dry mass of roots and shoots were determined. Results indicated that the biological control agent (B. cereus1) was able to significantly reduce the damage done by the pathogens Rhizoctonia solani, Pythium ultimum and Fusarium solani in all trials. It was also confirmed that the application of the biological control agent during planting could reduce disease incidence. The biological control agent increased seed emergence rate and shoot length. All three fungicides significantly reduced the disease incidence caused by all pathogens. All fungicides treatments applied increased emergence rate and shoot length. Seedling diseases should be given too much attention, as they cause severe losses to many crops. There is a need for future research on the effectivity of B. cereus1 as relatively little work has been published on its antagonistic behaviour against seedling diseases. There are also few registered fungicides available for the control of these seedling diseases on cowpea, therefore research on these and other potential products is required as seedling diseases play a major role in reducing yield of many crops.