Severity of root rot on tomato plants caused by Phytophthora nicotianae under nutrient- and light-stress conditions

Abiotic stress induced by three concentrations of nutrients in solution, and biotic stress caused by three inoculum densities of Phytophthora nicotianae, were imposed on tomato plants grown hydroponically under natural light in the glasshouse. The pathogen causes stem and root rot, thereby inducing water deficiency symptoms. The progress of the disease, as measured serologically by DAC-ELISA, was markedly accelerated by enhanced concentrations of nutrients. Significant differences in proline content of infected and noninfected plants were observed at a nutrient concentration equivalent to 5.0 dS m (1). Higher nutrient concentrations increased further proline concentration in leaves. Inoculation of tomatoes under two light regimes in a phytotron produced significantly more affected roots with increasing inoculum density, but disease was not affected by different light treatments. However, higher light intensity accelerated the appearance of symptoms and produced higher proline contents in tomato leaves. It is suggested that the proline content of tomato leaves is a suitable marker for stress induced by both abiotic and biotic factors.