Читать книгу Dry Beans and Pulses Production, Processing, and Nutrition - Группа авторов - Страница 44

Breeding for improved tolerance to drought, heat, and low soil fertility have been the focus of breeding programs targeting abiotic stress tolerance. However, with increasing flooding and wet soil problems in the Upper Midwest during the spring and early summer months adversely affecting bean plantings and stands, an effort was made to search for genetic tolerance to flooding. Genotypes with improved tolerance to flooding were found in both Meso American (MA) and Andean (A) backgrounds (Soltani et al. 2018).

Two of the most flooding‐tolerant Andean beans were PR9920‐171 and one of its parents Indeterminate Jamaica Red (IJR) landrace, and the tolerance, in part, was attributable to physical seed dormancy conditioned by a pectin acetylesterase 8 candidate gene (Soltani et al. 2021). Interestingly, IJR is also a major source of heat tolerance that was used to develop heat‐tolerant kidney beans (Porch et al. 2010). Due to increasing heat‐ and drought‐related stresses resulting from climate change, there has been renewed emphasis in breeding for abiotic stress tolerance using wild germplasm resources (Porch et al. 2013). To screen for abiotic stress tolerance in bean, yield response in field trials with reduced inputs are used. Similarly, yield for the same set of breeding lines are grown under optimum inputs. Yield under stress and nonstress is then combined in a geometric mean analysis to identify the best performing lines across both sets of conditions. The bean breeders in Prosser, WA, have used a purgatory plot since 1960 to impose multiple stresses (drought, low soil fertility, compacted soils, high incidence of root rot, and short rotations) in the screening of breeding lines for abiotic stress tolerance using yield as the selection criteria. Only lines that yield well in the purgatory plot and in the yield trials with optimum inputs are advanced in the breeding program. Other breeders use similar stress plots to screen breeding materials for tolerance to low soil nitrogen or phosphorus levels and for drought tolerance by limiting water to simulate intermittent or terminal drought conditions. Tolerance to most abiotic stresses is quantitatively inherited and as a result is difficult to breed for (Miklas et al. 2006), with few exceptions. Resistance to zinc deficiency is conditioned by a single dominant gene (Singh and Westermann 2002). Some QTL, with major effect, have been identified for drought tolerance (Trapp et al. 2015), but have not been exploited by breeders. Associated traits besides yield have been sought to facilitate breeding for abiotic stress tolerance. Average green normalized difference vegetation index (GNDVI) and canopy temperature from multispectral images captured by drones have been examined for differentiating bean lines for response to stress under low N and drought (Zhou et al. 2017; Sankaran et al. 2018). Pod harvest index (PHI) reflecting biomass partitioned to seed as a proportion of total pod biomass has shown strong correlations with yield under drought stress (Polania et al. 2016). Seedling root architecture also showed significant association with yield in some stress environments (Strock et al. 2019). Whether any of these associated traits will supplant yield for selection for abiotic stress tolerance in breeding programs remains to be determined.