Post-Flowering Photoperiod Effects on Reproductive Development and Agronomic Traits of Long-Day and Short-Day Crops

Pre-flowering photoperiod effects on floral initiation, flowering time and yield components of various crops have been well studied, but the post-flowering photoperiod effects on major field crops are not clearly understood. A controlled environment study was carried out using six long-day (LD) crops, flax, sugar beet, broad bean, triticale, wheat, and rapeseed, and seven short-day (SD) crops including Adzuki bean, potato, rice, peanut, mungbean, cotton and corn with a major objective of evaluating the post-flowering photoperiod effects on their reproductive development and yield components. There were significant inter- and intra-specific differences in their response to post-flowering photoperiod treatments. The effects of short days on LD crops were similar to LD effects on SD crops. The post-flowering duration was prolonged by short photoperiod in LD crops and long photoperiod in SD crops. There was, however, significant genotypic variation within a species for such effects. The post-flowering LD treatment caused abscission of flowers and pods and the resumption of vegetative growth in Adzuki bean. The post-flowering LD treatment also delayed the shoot senescence of one of the two potato varieties and decreased the number of tubers per plant in both varieties. The LD treatment delayed maturation of rice and mungbean, and decreased seed yield and 100-seed weight of peanut, although the shoot senescence of peanut was not apparently affected. Rapeseed, wheat, cotton and corn genotypes in this study did not show any sensitivity to post-flowering photoperiod. In triticale (an LD crop) exposure to short photoperiod post-flowering increased the number of spikes per plant perhaps due to a greater assimilate accumulation over a longer duration. The results from the current study as well as those from our previous experiments suggest that post-flowering photoperiod responses do exist in diverse field crops, and that there are strong genotypic differences in sensitivity and magnitude of response to post-flowering photoperiod. Photoperiod after flowering substantially regulates the source/sink relationship, and promotes partitioning and accumulation of assimilates to storage organs of crops when it favours the reproductive development of crops.