EFFECT OF STAGE OF DEVELOPMENT OF THE COWPEA RUST FUNGUS ON THE RELEASE OF A CULTIVAR-SPECIFIC ELICITOR OF NECROSIS

Aqueous exudates from differentiated or undifferentiated basidiospore germlings, as well as differentiated or undifferentiated urediospore germlings, of race 1 of the cowpea rust fungus were tested for their ability to elicit cell necrosis when injected into cowpea leaves. Only exudates from differentiated basidiospore germlings consistently exhibited high clicitation activity with the same cultivar-specificity as the fungus. Intercellular washing fluids from monokaryon-infected, but not from dikaryon-infected, leaves exhibited similar activity and cultivar-specificity to exudates from differentiated basidiospore-derived germlings. The results suggest that the production of the cultivar-specific elicitor of necrosis by the monokaryon is triggered by the formation of infection structures, and that this elicitor is produced in planta. The dikaryon either does not produce this elicitor or elicitor production is restricted to the haustorium. © 1992.