Partial characterization of toxins associated with stem end rot of mango caused by Lasiodiplodia theobromae

In this study, the toxicity of liquid culture media from different isolates of Lasiodiplodia theobromae was characterized and some properties of the toxic metabolites were distinguished. In this work toxin producing ability of L. theobromae was revealed by studying the physical parameters viz., osmotic potential, toxin concentration, pH, temperature and biological parameter like host specificity and wilting index. The obtained results showed that the optimal toxin-production conditions for L. theobromae in potato dextrose broth under pH 6.0, at 25-35°C for 7 days. The liquid culture from all isolates were toxic to mango plants and induced the rapid wilting. The toxin obtained from the liquid culture has thermal, acid base stability and a broad range of toxicity to main host and non-host plants. Moreover, the direct bioassay for two components of the liquid filtrates precipitated by ethanol showed that the active ingredient of the toxin is a kind of non protein substance, which was further endorsed by the papain hydrolysis analysis. Our results confirmed the chemical nature of toxic compound elucidating the favorable environmental conditions for toxin production of L. theobromae and proved potential role of toxic metabolites in the mechanism of disease development.