In vitro evaluation of fungicides and chemicals against Fusarium fujikuroi associated with stem rot disease of dragon fruit in Kerala

A survey was conducted in the dragon fruit growing regions of Kottayam and Thiruvananthapuram district of Kerala, which revealed the prevalence of basal stem rot disease caused by Fusarium fujikuroi . In the Palode region of Thiruvananthapuram, stem rot disease was common in dragon fruit plantations. Infected plants showed characteristic symptoms, like brownish-red coloured lesions with water-soaked margins and rotting of stem near the soil line. The pathogenic isolates were subjected to cultural, morphological, and molecular characterisation. The pathogen produced a cottony white, raised mycelium on PDA medium, accompanied by moderate to profuse sporulation and pigmentation ranging from light yellow to dark red. The microconidia were round to oval in shape, while the macroconidia were sickle-shaped with blunt ends. It was confirmed through ITS primer and gene-specific primers like TEF1-α. In in vitro studies, among the biocontrol agents tested, Bacillus amyloliquefaciens and Trichoderma asperellum were the most effective in inhibiting fungal growth, fungicides like difenoconazole and a combination of trifloxystrobin and tebuconazole completely inhibited the pathogen. Additionally, chemicals like calcium chloride and potassium phosphonate were found to be highly effective in suppressing F. fujikuroi . These results hold great promise for guiding the efficient management of stem rot in dragon fruit in Kerala, India.