Wild relatives to improve heat tolerance of cultivated quinoa (Chenopodium quinoa Willd.)

Quinoa (Chenopodium quinoa Willd., 2n = 4x = 36, AABB genome) is well-known for its high nutritional value and adaptability to marginal environments, but it is still mainly cultivated in relatively cool areas due to sensitivity to extended periods of high temperatures, particularly during the reproductive stages. The two AABB tetraploid wild relatives of cultivated quinoa, C. berlandieri and C. hircinum, can be found growing in hot lowland environments of North and South America, respectively, and may serve as a source of heat tolerance for introgression into cultivated quinoa. In our work, wild C. berlandieri showed the best yield performance under field heat conditions in late planting, followed by lowland quinoa, C. hircinum, and highland quinoa. The yield advantage of C. berlandieri at high temperatures was achieved by plants being able to maintain grain number at high temperatures better than the other genotypes. Further comparison between seed setting and pollen viability found positive trends between them under heat stress in cultivated quinoa, indicating limiting effects of pollen viability on grain setting. Therefore, we examined the effects of heat on pollen development and viability. Five representative accessions (C. berlandieri, C. hircinum Argentina, C. hircinum Chile, C. quinoa lowland, C. quinoa highland) were studied in detail with an environmentally-controlled heat treatment (five days at 38/33oC, day/night). Detrimental effects of heat on pollen viability in C. quinoa were observed, with an 80% reduction in the highland ecotype, whereas wild C. berlandieri had only a 30% reduction. The most heat-sensitive period, with respect to pollen viability, was 8 to 10 days before flowering, which we found corresponded to the early pollen mother cell stage of development. The period of highest sensitivity of pollen to heat was conserved among different Chenopodium species. At the end, in vitro heat treatments on pollen germination also demonstrated a comprehensive advantage of C. berlandieri over other accessions. This research suggests that wild relatives of quinoa, in particular C. berlandieri, could be crossed with cultivated quinoa to introduce reproductive heat tolerance.