Dynamics of Free Pisatin Elicitor Accumulation in Infection‐droplets of Monilinia fructicola on Pea Endocarp*

Abstract

AbstractRapid elicitor accumulation in the infection‐droplet of the pea‐M. fructicola interaction began between 2 and 3 h after inoculation. Rapid accumulation of pisatin began between 2 and 3 h, however, low levels (0.06–0.1 μg/ml) were detected in the infection‐droplet as early as 1–2 h following inoculation with the fungus. The pisatin concentration reached levels inhibitory to the fungus between 6 and 12 h (ca. 1–5 μg/ml) and the ED50 value of 10 μg pisatin/ml for mycelial growth of M. fructicola was attained after 14 h.Elicitor activity in infection‐droplets after 4 and 18 h was a function of inoculum concentration and pisatin accumulation in diffusate after 40 h was a function of elicitor concentration (linear doseresponse curve). However, when elicitor was applied at zero time, the rate of pisatin accumulation over the first 12 h was indistinguishable from that which occurred when M. fructicola conidia were applied to the endocarp and elicitor accumulated with time. The initial rate of pisatin accumulation therefore appears to be dependent on the pea pod and independent of any time delays associated with conidial germination and elicitor accumulation. However, the final pisatin concentration which accumulated in the infection‐droplet was dependent on the, dose' of elicitor irrespective of the nature and timing of the elicitor treatment.The presence of elicitor activity was demonstrated in the interaction in space and time where and when these molecules could function as elicitors of pisatin in vivo.