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Negative effects of enhanced UV-B radiation have been demonstrated in plants, but impacts under realistic field conditions remain uncertain. Adverse impacts to major crops, such as rice (Oryza sativa L.), that are grown in areas with currently high ambient levels of UV-B, could have consequences for food security. To address the response of rice to UV-B, we conducted an intensive and extensive series of field experiments from 1992 to 1995 documenting the effects of supplemental UV-B (simulating approximately 20% ozone depletion for the Philippines), using irrigated rice cultivars under tropical conditions. This multiseason study indicated that supplemental UV-B had no significant effects on rice grain yield (including the yield components spikelet filling percentage, and 1000-grain weight) or growth parameters (plant height or panicles per square meter). The absence of UV-B effects was consistent across seasonal environment (four dry and three wet seasons), cultivar, and type of exposure system. Thus, rice yields are not likely to be affected by increases in UV-B under realistic field conditions.

The protective effect of a synthetic terpenoid analog of abscisic acid (ABA), coded LAB 173711, on transplant shock in rice was investigated under field conditions. Rice seedlings (Fujisaka 5 and IR 20) were taken from a seed bed and their roots were immersed in aqueous solutions of the growth regulators for 24 h. Afterwards they were drought-stressed for 3 or 6 h by exposing them to direct sunlight before they were transplanted to the field. A pretreatment with either LAB 173711 alone or in combination with the growth retardant tetcyclacis reduced the loss of water during the exposure to sunlight, increased the percentage of survival of the seedlings in the field, and increased the percentage of grain filling of the plants which had survived. The combined application of growth regulators was most effective and may be useful for minimizing transplant shock in rice and other crops.

Plants exhibited differential response for ratoon growth and development under different temperature regimes before and after main crop harvest. Low temperature (23°/20 °C) before cutting induced ratooning whereas similar temperature after cutting delayed and reduced ratoon tillering. Ratoon grain yield and its attributes were significantly affected under various temperature regimes. Ratoon grain yield under low temperature regime before cutting did not differ from that of the control. Ratoon growth duration was maximum under low temperature regime after cutting. High temperature (37°/27 °C) after main crop cutting resulted in high spikelet sterility in the ratoon crop.