Effect of Heat Stress and Its Timing on Reproductive Organs and Seed Set in Field Pea.

Pea (Pisum sativum L.) is a major legume crop grown in the semi-arid climate of western Canada, where heat stress affects pollination, seed set and yield. Flowering plants are highly sensitive to heat stress during the reproductive phase, which covers floral initiation to seed maturity. The objective was to diagnose effects of controlled heat stress exposure on specific development stages of floral buds, open flowers and early set pods.  High temperature (35/18^oC day/night temperatures, 16/8 hr photoperiod) exposure during early floral bud and pollen development (T1) was more detrimental to reproductive output compared to heat exposure started later when flowers at the second reproductive node were fully open (T2). The flower abortion rate was greater when plants were first exposed to heat stress and when young floral buds were visible at the first reproductive node (T1). Similarly, seed-set, pod development, and yield were more negatively affected when high temperature exposure started at T1 compared to T2. Due to the staggered timing of flower appearance and age on a nodal raceme and along the main stem, heat stress impacted young, barely visible floral buds in the developing apex the most compared with more advanced buds and open flowers. Further, combining synchrotron based phase contrast X-ray imaging (PCI) and Fourier transform mid-infrared (FTIR) spectroscopy revealed internal flower structures and biochemical composition associated with flower development in non-stressed pea.