To evaluate the role of phaseolinone, a phytotoxin produced byMacrophomina phaseolina, in disease initiation, three nontoxigenic avirulent mutants of the fungus were generated by UV-mutagenesis. Two of them were able to initiate infection in germinatingPhaseolus mungo seeds only in the presence of phaseolinone. The minimum dose of phaseolinone required for infection in 30% seedlings was 2.5 (Μg/ml. A human pathogen,Aspergillus fumigatus was also able to infect germinating seeds of P.mungo in the presence of 5 (Μg/ml concentration of phaseolinone. Phaseolinone seemed to facilitate infection byA. fumigatus, which is not normally phytopathogenic, by reducing the immunity of germinating seedlings in a nonspecific way. Levamisole, a non-specific immunopotentiator gave protection against infection induced byA. fumigatus at an optimum dose of 50 (gmg/ml. Sodium malonate prevented the effects of levamisole.
Volume 45, 2020
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