THE EFFECT OF ASSIMILATE DEMAND ON PHYTOPHTHORA INFECTION AND DISEASE DEVELOPMENT IN NFC-GROWN TOMATO PLANTS

Experiments were conducted on young, non-fruiting plants and on mature plants with 16 trusses of flowers and fruit. Treatments which increased the supply of assimilate to the root viz. removal of developing fruit, or supplementary illumination, lead to an increase in root infection from zoospore inoculum, and an increase in lesion size. Conversely the reduction of root assimilate induced by the competitive fruit sink in fruiting plants, or by partial defoliation or shading led to decreased infection.

Defruited plants under reduced assimilate demand all remained symptomless. Plants with a high fruit load, however, suffered severe wilting, chlorosis and necrosis leading to death 70 days after inoculation. The failure of disease to develop in plants which had had fruit removed was attributed to their capacity to initiate new roots from the available photosynthate. The results highlight the plants requirement for a minimal net healthy functional root system regardless of the presence of a root pathogen.

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