Management of Alternaria species diseases on Cleome gynandra in Zimbabwe

Abstract

Background: Angular leaf spot and blight, caused by fungi of the genus Alternaria, known as most destructive diseases affecting Cleome gynandra, a potential Indigenous African vegetable, being promoted in Zimbabwe. Information on its disease management is scanty.
Aim: To isolate, evaluate and propose potential management options against the diseases caused by Alternaria alternata and Alternaria senecionicola, obtained and identified from Marondera University of Agricultural Sciences and Technology, Agro Industrial Park (MUAST AIP) and Premier areas of Zimbabwe.
Setting: Efficacy of fungicides, in a CRD (6*2 factorial experiment), Biological Control Agents (3*2 factorial experiment) and organic agent (2*2 factorial experiment), was evaluated against these species on C. gynandra, with three replications.
Methods: Fifteen cm plants under greenhouse conditions at MUAST AIP were inoculated and monitored. Data on incidence and severity were collected every week for 3 weeks.
Results: A. alternata and A. senecionicola Area Under Disease Progress (AUDPs) and disease incidence were effectively suppressed by all test fungicides (p = 0.02) on days 7–14 and AUDPCs on days 14–21 and had no interactions (p = 0.07). There was interaction between Alternaria species and fungicides for % disease incidence for day 7 (p = 0.009), day 14 (p = 0.04) and day 21 (p = 0.04). Biological control using Trichoderma harzianum (T77) and Saccharomyces cerevisiae was effective in reducing disease severity and incidence. There were no interactions on AUDPCs days 7–14 (p = 0.6), but noted on days 14–21 (p = 0.02). The cattle bile was effective, and it was noted without interactive effects on AUDPCs days 7–14 (p = 0.2) and days 14–21 (p = 0.4). % disease incidences lack interactive effects on day 7 (p = 0.3), and noted on day 14 (p = 0.001). There was no interaction on day 21 (p = 0.08).
Conclusion: Two Alternaria species can be managed by fungicides, BCAs and organic agents.
Contribution: Diseases were controlled.