Wild relatives to improve heat tolerance of cultivated quinoa (Chenopodium quinoa Willd): pollen viability and seed number

Quinoa is well-known for high nutritional value and wide adaptability, but it is considered to be heat sensitive. To address that, two tetraploid wild relatives, C. berlandieri and C. hircinum - native to hot environments - were evaluated alongside cultivated quinoa under field conditions with changing planting dates. The C. berlandieri showed the best yield under extreme heat during the last planting (P3), followed by lowland quinoa, C. hircinum, and highland quinoa. The yield advantage of C. berlandieri was achieved by maintaining higher grain number/seed set. Pollen viability was positively correlated with seed set under heat stress in cultivated quinoa, indicating its limiting effects on seed set. Considerable variation was observed for pollen viability among five representative accessions after a five-day 38/33oC (day/night) treatment, with an 80% reduction observed in highland quinoa, whereas C. berlandieri had only a 30% reduction. The most heat-sensitive period for pollen viability was 8 to 10 days before flowering, corresponding to early pollen mother cell stage and it was conserved among different species. Lastly, in vitro pollen germination also demonstrated heat tolerance of C. berlandieri. This research suggests that wild relatives, particularly C. berlandieri, could be crossed with cultivated quinoa to introduce reproductive heat tolerance.