Antifungal potential of zinc against leaf spot disease in chili pepper caused by Alternaria alternata.

The fungal pathogen, Alternaria alternata is responsible for causing leaf spot disease in many plants, including chili pepper. Zinc (Zn) an essential micronutrient for plant growth, also increases resistance in plants against diseases, and also acts as an antifungal agent. Here, in vitro effects of ZnSO4 on the propagation of A. alternata were investigated, and also in vivo, the effect of foliar application of ZnSO4 was investigated in chili pepper plants under disease stress. In vitro, ZnSO4 inhibited fungal growth in a dose-dependent manner, with complete inhibition being observed at the concentration of 8.50 mM. Hyphae and conidial damage were observed along with abnormal activity of antioxidant enzymes, Fourier-transform infrared spectroscopy confirmed the major changes in the protein structure of the fungal biomass after Zn accumulation. In vivo, pathogen infection caused the highest leaf spot disease incidence, and cumulative disease index, which resulted in a significant reduction in the plant's growth (length and biomass), and physiochemical traits (photosynthetic pigment, activity of catalase, peroxidase, polyphenol oxidase, and phenylalanine ammonia lyase). The heat map and principal component analysis based on disease, growth and, physico-chemical variables generated useful information regarding the best treatment useful for disease management. Foliar Zn (0.036 mM) acted as a resistance inducer in chili pepper plants that improved activities of antioxidants (CAT and POX), and defense compounds (PPO and PAL), while managing 77% of disease. The study indicated foliar ZnSO4 as an effective and sustainable agriculture practice to manage Alternaria leaf spot disease in chili pepper plants.

Lupeol acetate as a potent antifungal compound against opportunistic human and phytopathogenic mold Macrophomina phaseolina.

Antifungal activity of Monotheca buxifolia methanolic extract and its various fractions were assessed against Macrophomina phaseolina, a soil-borne fungal pathogen of more than 500 vegetal species as well as rare and emerging opportunistic human pathogen. Different concentrations of methanolic extract (3.125 to 200 mg mL-1) inhibited fungal biomass by 39-45%. Isolated n-hexane, chloroform and ethyl acetate fractions suppressed fungal biomass by 32-52%, 29-50% and 29-35%, respectively. Triterpenes lupeol and lupeol acetate (1, 2) were isolated from n-hexane while betulin, ß-sitosterol, ß-amyrin, oleanolic acid (3-6) were isolated from chloroform fraction. Vanillic acid, protocatechuic acid, kaempferol and quercetin (7-10) were isolated from the ethyl acetate fraction and identified using various spectroscopic techniques namely mass spectroscopy and NMR. Antifungal activity of different concentrations (0.0312 to 2 mg mL-1) of the isolated compounds was evaluated and compared with the activity of a broad spectrum fungicide mancozeb. Different concentrations of mencozeb reduced fungal biomass by 83-85%. Among the isolated compounds lupeol acetate (2) was found the highest antifungal against M. phaseolina followed by betulin (3), vanillic acid (7), protocatechuic acid (8), ß-amyrin (5) and oleanolic acid (6) resulting in 79-81%, 77-79%, 74-79%, 67-72%, 68-71% and 68-71%, respectively. Rest of the compounds also showed considerable antifungal activity and reduced M. phaseolina biomass by 41-64%.