Interactive Effects of High Temperature and Light Quality on Floral Bud Development in Cowpea

Abstract

Floral bud development of cowpea (Vigna unguiculata (L.) Walp.) is arrested by high night temperature and long days under natural sunlight, but not under all types of artificial lighting systems. The objective of this study was to determine whether floral bud development at high night temperature is influenced by the red/far red (R/FR) ratio during the day. Cowpea plants were grown in glasshouses with natural sunlight, and growth chambers having either metal halide-based (MH) or fluorescent-based (EL) lighting systems. Plants were subjected to R/FR ratios of 1.3, 1.6, or 1.9 with both lighting systems. Floral bud development was arrested by high night temperature under natural sunlight with R/FR ratio of 1.2, and under MH and FL lighting systems when the R/FR ratio was 1.3 or 1.6. High night temperature did not affect floral bud development of plants grown under MH or FL light with a R/FR ratio of 1.9 and the plants produced flowers, but pod set was inhibited at this temperature. Floral bud development and pod set of a heat-tolerant cowpea genotype were normal under high night temperature and not influenced by light quality or lighting system. Apparently, the degree to which high temperatures injure floral bud development depends on the R/FR ratio during the day, and values of 1.3 to 1.6 are required to elicit the same responses as those that occur in sunlight.