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.