The hypothesis that blotchy ripening (BR) of greenhouse tomatoes (Lycopersicon esculentum Mill.) was associated with a cumulative effect of alternating periods of bright sunshine and cloudy weather was tested in controlled environment chambers. Temperatures were programed to give diurnal changes between 11.7 C/26.7 C night/day representing sunny days, and 11.7 C/21.2 C night/day for cloudy days. The two levels of light were (1) 18,299 lx for sunny days, and (2) 16,656 lx for cloudy days. These two factors were combined in four regimes to represent (1) sunny-day temperature and light; (2) sunny-day temperature and alternate weeks of sunny-day and cloudy-day light; (3) alternate weeks of sunny-day and cloudy-day temperature and sunny-day light; and (4) alternate weeks of sunny-day temperature and light, and cloudy-day temperature and light. Four series of plants showed a common trend. Consistent sunny-day temperature and alternating weeks of sunny or cloudy-day light produced the highest incidence of BR. Alternating weeks of temperature levels with consistent sunny-day light produced less BR but not significantly so. When sunny-day temperature and light were alternated weekly with cloudy day conditions, there was a reduced percentage of BR and less severe symptoms. This regime suggests a compensatory effect when temperature is varied directly with changes in light intensity. The regime for consistent sunny-day temperature and light gave the lowest BR incidence with mild symptoms.
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