Influence of preinoculation light intensity on development and interactions of Botrytis cinerea and Clonostachys rosea in tomato leaves

Tomato plants produced in pots in a greenhouse were kept in low intensities of photosynthetically active radiation (400-700 nm at means of 384, 308, 135, and 14 mumol.m(-2).s(-1)) during 16-h photoperiods for 0, 5, 10, or 15 days. Immediately after treatment, leaflets of the fourth and fifth leaves were detached and inoculated with Botrytis cinerea Pers.:Fr. (10(6) conidia/mL), the biocontrol agent Clonostachys rosea (Link:Fr.) Schroers, Samuels, Siefert and W. Gams (10(7) conidia/mL), or both fungi (same final concentrations). Germination of each fungus was estimated after leaflets were incubated at high humidity for 24 h, and sporulation was measured after further incubation on paraquat-chloramphenicol agar medium. When B. cinerea was inoculated alone, germination incidence, germ tube length, and percent leaf area with conidiophores of the pathogen each generally increased as preinoculation light intensity was decreased and number of days in reduced light intensity was increased. Similar response patterns were found for C. rosea when inoculated alone, except that germination, high on untreated leaves, was affected by duration but not intensity of light treatment. On coinoculated leaves, germination and germ tube length of B. cinerea increased with duration of low-intensity light treatments, but no conidiophores were produced. Germination and germ tube length of C. rosea were each higher when the agent was coinoculated than when inoculated alone, but conidiophore production was similar. Germination, germ tube length, and conidiophore production of B. cinerea, inoculated alone, correlated with electrolyte leakage from the leaves (r = 0.78, 0.67, and 0.82, respectively). Respective values for C. rosea were r = 0.65, 0.68, and 0.67. Collectively, the data indicate that low-intensity light predisposed the leaves to development of B. cinerea and C. rosea on the phylloplane, and to sporulation of the two fungi, after leaves were killed on paraquat-chloramphenicol agar, but did not affect ability of C. rosea to control spore production of B. cinerea. A hypothesis that increased nutrient leakage from leaf cells mediated effects of low-intensity light was supported by the correlations of electrolyte leakage with development of B. cinerea and C. rosea.