SALINITY EFFECTS ON ROOT-GROWTH AND SENESCENCE IN TOMATO AND THE CONSEQUENCES FOR SEVERITY OF PHYTOPHTHORA ROOT-ROT INFECTION

Roots respond first to edaphic stresses, vet little is known about roo t response to stress in mature, soil-grown plants. We investigated the effects of salinity and phytophthora root rot on root growth and sene scence in tomato (Lycopersicon esculentum Mill.). Using minirhizotron- and rhizotron-based methodologies, we quantified intraspecific differ ences in root-system response to salinity and inoculation. Genotype su sceptibility to salt-induced disease was related to root vulnerability to salt. 'UC82B' was vulnerable to infection by Phytophthora parasiti ca when subjected to salt stress and produced thinner roots and almost -equal-to 50% higher root-senescence rates compared to the phytophthor a root rot-resistant 'CX8303'. Root growth at the peripheral regions o f the 'CX8303' root system was inhibited by salinity, but otherwise ro ot dynamics were not affected by salinity or inoculation. Overall, roo ts from the central root system and roots from the periphery responded differently to salt stress. Monitoring the diameters of new initiated roots indicated the vulnerability of a stressed root system to diseas e and early senescence.