Vicia faba blight
Bacterial blight of broad beans, also known as the disease caused by Pseudomonas fabae, is a serious threat to legume crops. Initially, dark, short streaks or small spots appear at the top of the stems, slightly sunken in appearance. Under warm and humid conditions, these lesions can rapidly expand along the stem, reaching lengths of up to 15–20 cm or even covering two-thirds of the stem. The affected stems turn black, become soft and sticky, or shrink into a thin line. As the disease progresses, the upper leaves begin to wilt and eventually rot and die. In drier climates, the disease spreads more slowly, with irregularly shaped to elongated lesions forming on the stems. Most infected stems turn black, and the upper leaves wither, leaving only the blackened ends of the stems.
The pathogen responsible for this disease is Pseudomonas fabae, a Gram-negative, rod-shaped bacterium measuring between 1.1–2.8 µm in length and 0.8–1.1 µm in width. These bacteria are typically solitary or occur in pairs, lack spores, and possess 1–4 polar flagella. They thrive best at 35°C, with an upper limit of 37–38°C and a lower threshold of 4°C. At 52–53°C, they are killed within 10 minutes. Besides affecting broad beans, P. fabae can also infect kidney beans, peas, soybeans, and lupines.
The primary mode of transmission is through infected seeds, which introduce the pathogen into the plant through stomata or wounds. To manage the disease effectively, farmers should focus on using resistant varieties and establishing disease-free seed fields to prevent seed-borne infections. Early intervention is crucial—applying 72% streptomycin sulfate soluble powder or neophytin diluted at 4000 times, 50% potassium oxycarbonate copper wettable powder at 500 times, or 30% basic copper sulfate suspension at 400 times can help control the spread. Additionally, 77% copper oxychloride WP diluted at 500–600 times can be used. Spraying should be repeated every 7–10 days, with 2–3 applications recommended for optimal results.
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