Screening for Heat-Resistant Pea Cultivars in Seed Development in Relation to Ovule, Pod, and Node Positions.

Elevated temperatures pose a threat to global crop production with current climate change. A better understanding of how heat stress impacts seed development will enable successful screening for heat-resistant cultivars to maintain agricultural food production. The objectives of this study were to screen for heat-resistant field pea (Pisum sativum) cultivars by ovule and seed retention, and to diagnose whether hierarchy exists in different ovule, pod, and node positions under heat stress. Sixteen cultivars were investigated for seed development in growth chambers with two temperature regimes (24/18°C and 35/18°C day/night temperatures for seven days) during reproductive development, as well as under field conditions. Measurements related to seed development were collected from the first four reproductive nodes. Results showed that seed development in pea was susceptible to heat stress damage, and heat stress accelerated flower bud abscission in younger nodes (Node 3 and 4),  and accelerated seed abortion in all different ovule positions within pods. Cultivars, ‘40-10’ and ‘Naparnyk’ were able to retain the most ovules and seeds, whereas ‘MFR043’ aborted seeds when exposed to heat stress. In over half the cultivars tested in the controlled environment, ovules at the pod’s medial and stylar-end positions were more likely to develop into seeds compared to ovules at the base, which was consistent with seven of the 16 cultivars tested under field conditions. For seven other cultivars in the field, ovules at the medial position reached maturity, whereas ovules at the basal end were less likely to develop into seeds. Seed to ovule ratio was positively correlated with seed number per pod, ovule number per pod, and pod length. In contrast, cultivars with large seed size had a lower seed to ovule ratio. In summary, cultivars were identified with greater pod, and ovule retention within a pod.