Bipolaris oryzae associated agent at the leaf spot disease in Cocos nucifera hybrid “Brazilian Green Dwarf”

Background/objective. In Tecoman, Colima, Mexico, a leaf spot (LS) disease was detected with an incidence of 92.0% in Cocos nucifera hybrid Brazilian Green Dwarf (BGD). The objective was to characterize morphologically, molecularly and biochemically the fungus associated with LS in BGD coconut palm and evaluate its susceptibility to commercial biological fungicides. Materials and methods. The isolate was characterized morphologically and molecularly. Their growth, sporulation and laccase production were evaluated using different culture media. The in vitro mycelial inhibition and mean lethal doses (LD50) of commercial biological fungicides based on antagonistic fungi (Trichoderma harzianum and T. viride), bacteria (Bacillus subtilis and B. amyloliquefaciens) and actinobacteria (Streptomyces lydicus and S. jofer) were determined. Results. Bipolaris oryzae was the associated agent of LS, it produces 25.54 and 22.17 U mg of protein-1 of laccase activity in the Sivakumar and wheat bran (WB) media. The WB medium allowed the greatest sporulation. Trichoderma harzianum inhibited B. oryzae at 100% in the four evaluated doses. B. subtilis and B. amyloliquefaciens inhibited B. oryzae at 100% at the highest tested doses (20 mL L-1). Conclusion. Bipolaris oryzae is the associated agent of LS, it produced the highest laccase activity in Sivakumar and WB culture media. The highest sporulation and daily growth rate were in WB. T. harzianum stood out over T. viride by inhibiting B. oryzae growth by 100%. B. subtilis, S. lydicus and B. amyloliquefaciens were more effective against B. oryzae in vitro compared to S. jofer.