PHYSIOLOGICAL AND DEVELOPMENTAL ASPECTS OF INCREASED PLANT-GROWTH IN SOLARIZED SOILS

Soil solarisation enhances plant growth even in the absence of known major pathogens. This phenomenon is known as increased growth response (IGR). Corn, cucumber, sorghum, tobacco and tomato plants under controlled conditions revealed distinct IGR in solarised soil as compared to control non-treated soil. IGR was recorded in shoots of tomato (Lycopersicon esculentum Mill. cv. Rehovot 13) seedlings, 15 days after transplanting and in roots only two weeks later. Detailed studies on the third true tomato leaf showed significantly higher levels of chlorophyll and protein contents in plants from solarised soil as compared to those from the control. In addition, the degradation of these compounds, decrease of net photosynthesis at near-saturation light intensity and of photochemical yield with ageing were delayed in plants growing in solarised soil as compared to the control. The ratio of variable to maximal chlorophyll fluorescence was independent of soil treatment and was comparable to normal levels measured in other plants. Therefore, no apparent environmental stress seems to be involved in either of the soil-plant systems. It is concluded that the initial IGR in solarised soil is independent of improved root growth. Delayed leaf senescence appeared to be a plant response contributing to IGR.