Formation of tomatine in tomato plants infected with Streptomyces species and treated with herbicides, correlated with reduction of Pseudomonas solanacearum and Fusarium oxysporum f. sp. lycopersici.

Pretreatment of tomato seeds with pendimethalin or metribuzin and inoculation of seedlings with the antagonistic Streptomyces corchorusii or/and Streptomyces mutabilis were tested for the formation of tomatine in roots and stems of tomato, infested with Pseudomonas solancearum or/and Fusarium oxysporum f. sp. lycopersici. All treatments induced the formation of variable quantities of tomatine, compared with untreated control. The variation was proportional to: the pathogen, Fusarium was more stimulating than Pseudomonas; the antagonistic organism, S. corchorusii being more eliciting than S. mutabilis; the herbicide and its concentration, pendimethalin at 2 x 10(-3) M being the most eliciting of tomatine; and according to the soil, plants grown in non-sterilized soil accumulated more tomatine than did these grown in sterilized soil. In all treatments, stems had more tomatine than roots and non-sterilized soil was better than sterilized soil. The antagonistic streptomycetes induced accumulation of tomatine more than did the herbicides. The highest amounts of tomatine were detected in plants pretreated with pendimethalin at 2 x 10(-3) M, grown in non-sterilized soil, infested with F. oxysporum, and inoculated with S. corchorusii and S. mutabilis. The effect of the extracted tomatine on the growth of Fusarium and Pseudomonas was examined in vitro. The crude extract of tomatine from all treatments reduced growth and sporulation of F. oxysporum and growth of P. solanacearum in defined media. The reduction varied according to the treatment and was proportional to the quantities of extracted tomatine, the highest amounts being the most effective. The mechanism of phytoalexins in controlling tomato wilt pathogens was also discussed.