Some Physical Factors Affecting the Formation and/or Net Accumulation of Medicarpin in Infection Droplets on White Clover Leaflets

Abstract

A quantitative study was made of the effect of several physical factors in the environment on the formation and/or net accumulation of medicarpin in infection droplets on excised white clover leaflets following inoculation with Monilinia fructicola (Wint.) Honey. Incubation experiments (duration 40 h) showed that the optimum temperature for medicarpin formation was 25°C. Medicarpin was first detected at 6 h and rose to a maximum concentration in the infection droplet at 30 h following inoculation. Predisposition experiments showed that medicarpin concentrations were highest where plants had been grown under high temperature regimes (day/night 30/25 and 33/28°C). It was formed in significantly greater concentration where plants had been grown under long-day rather than short-day treatments. Level of light intensity was found to have no effect. Time of day of leaf detachment from a plant significantly affected the level of medicarpin formed.

*Part XI11 of 'Studies on Phytoalexins' (Part XU, PI. Physiol., Lancaster, 1972, 50, 660–6).