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

Quinoa (Chenopodium quinoa) is well-known for high nutritional value and wide adaptability, but it is considered to be heat sensitive. To address this issue, accessions from two tetraploid wild relatives, C. berlandieri and C. hircinum, both native to hot environments, were evaluated alongside lowland and highland ecotypes of cultivated quinoa under field conditions with differing planting dates. Chenopodium berlandieri showed the best yield under the extreme heat experienced during the last planting, 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. Considerable variation was observed for pollen viability among representative accessions of each species/ecotypes after a 38/33 °C day/night treatment for 5 d, ranging from an 80% reduction observed in highland quinoa to a 30% reduction in C. berlandieri. The most heat-sensitive period for pollen viability was 8-10 d before flowering, corresponding to the early pollen mother cell stage and it was conserved among the different species. In vitro pollen germination tests also demonstrated the heat tolerance of C. berlandieri. Taken together, our results suggest that wild relatives, particularly C. berlandieri, could be crossed with cultivated quinoa to introduce reproductive heat tolerance.