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Bacillus amyloliquefaciens strains in the management of Cercospora leafspot of lettuce in Trinidad

Duraisamy Saravanakumar: University of the West Indies

<div>Lettuce (<em>Lactuca sativa</em>) is a vegetable crop that is favoured and highly demanded in many cultures around the world and mostly consumed fresh. It is a short crop, meaning, most varieties are harvested within 4-5 weeks after transplant. According to the United States Department of Agriculture (2016), the value of utilized lettuce in 2016 amounted to near $2 billion in the United States alone, falling second to tomatoes. Within recent times, there has been a growing concern over the use of pesticides and the impact they have on human health and the environment. In Trinidad, the fungal leafspot of lettuce caused by <em>Cercospora</em> <em>lactucae-sativae</em> is a growing concern as the disease severely affects the quality and reduces yield of the crop forcing farmers to resort to the only known remedy of chemical treatment. This research explored the potential of growth and biocontrol efficacy of indigenous <em>Bacillus</em> strains isolated from rhizosphere soils against leafspot disease. Preliminary research has showed the antagonistic potential of <em>Bacillus</em> <em>amyloliquefaciens</em> to inhibit the fungal pathogen by up to 74% <em>in-vitro</em> and boost the seedling growth (leaf area) by about 300%. The PCR analysis of antibiotic lipopeptides genes <em>viz</em>., Iturin, Bacillomycin, Bacilysin, Fengycin, Surfactin and Zwittermycin in those <em>B. amyloliquefaciens</em> strains were positive. <em>Bacillus</em> species which did not show positive for any of the lipopetides resulted in little or no inhibition, indicating that the antibiotic genes contributed significantly to inhibitory properties of the <em>B. amyloliquefaciens</em>. Further testing of the antagonistic <em>B. amyloliquefaciens</em> strains under protected and field settings is required to understand the biocontrol efficacy against leaf spot disease in lettuce.</div>

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