Dry Beans and Pulses Production, Processing, and Nutrition. Группа авторов

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СКАЧАТЬ 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.

Breeding for direct harvest systems

      Advances in plant breeding drive agronomic change. This has been observed with the green revolution in parts of Asia (Peng et al. 2010), mechanization of processing tomato, and pickle cucumber harvesting in the US. In the absence of these genetic changes, agronomic or management changes would not have been possible. In dry beans, the traditional harvest method across the country was to undercut and pull bean plants at maturity, windrow these plants into larger rows, and thresh plants when dry using a pickup reel on the combine, all in separate operations. These traditional operations are costly in terms of time, equipment, fuel, and labor that prevent growers from expanding bean acreage.

With the development of taller, more upright varieties that resist lodging (Kelly 2000; Soltani et al. 2016), growers started to explore the possibility of direct harvesting beans similar to soybeans. Without that change in improved plant architecture, growers would not have had that opportunity. In Michigan, over 80% of beans planted are direct harvested (Figure 2.6) in a shorter time-period with minimum wear to the combine (no root/soil entering the machine), resulting in a cleaner product to sell to the elevator. The same growers can plant 25–30% more acres to beans compared to traditional harvest methods, freeing up additional tractors for other farm operations. The change in plant architecture has positively impacted all MA bean classes but has had little effect on the shorter-statured bush type kidney and cranberry beans.

Symbiotic nitrogen fixation (SNF)

Genetic variability exists for enhanced SNF (Kamfwa et al. 2015; Oladzad et al. 2020). However, under conventional systems, modest amounts of nitrogen (50kg N/ha) are applied to most breeding nurseries. SNF capacity of beans is diminished in the presence of N fertilizers preventing easy selection of improved lines (Reinprecht et al. 2020). By selecting under low N-inputs or soils, breeders could enhance SNF. Any gain in SNF would be advantageous for conventional growers, who could reduce the nitrogen being applied to the crops. This would be particularly favorable for growers in the Great Lakes watershed or numerous other regions that have significant drainage basins where issues of both surface and ground water contamination are serious. This would also help organic production, as organic system producers cannot apply N‐fertilizer and have to rely on crop rotations, animal manures, or compost to meet the nutritional needs of the crop, and it has been found that nitrogen is a limitation in organic bean production (Heilig et al. 2017b). Since beans are also an important crop of small, low‐income producers in developing countries, improved N‐fixation would be a most beneficial trait for these resource poor farmers (Graham et al. 2003).

Fig. 2.6. Direct combining navy beans in Michigan.

      The use of marker‐assisted breeding for SNF related traits is one way to circumvent the need to select under low N conditions. Multiple studies have been undertaken to identify QTL that enhance SNF. One study was undertaken in a black bean population that was a cross between a commercial variety Zorro and a Mexican landrace, long reported to have high SNP capacity (Chaverra and Graham 1992; Heilig et al. 2017a). GWAS studies on Andean and Middle American diversity panels both identified multiple SNF related QTL (Kamfwa et al. 2015; Oladzad et al. 2020). These studies offer potential candidates for marker‐assisted breeding.

Processing quality

      In the US, canned bean products represent a major segment of the dry bean market. As a ready‐to‐eat food, canned beans offer a convenient alternative to home preparation of dry beans, which require long cooking times. The value of canned bean products in the US in 2020 was $2.5 billion. This is 13% of the canned food market value and 82% of US dry bean dollars is associated with canned products (Nielsen Consumer LLC). For a dry bean variety to be commercially successful it must meet industry standards for processing quality and bean breeders have incorporated canning quality as a trait for improvement. A comparison of canning quality characteristics in five historically important navy bean varieties released from 1915 to 2008 revealed no difference in visual appearance of the canned beans, underscoring the importance of this trait (Butler and Cichy 2011).

Canning quality of breeding lines is assessed with a small scale protocol that approximates industrial canning on limited sample sizes. Typically, breeding lines are evaluated for canning quality beginning in the F₆ generation and a 250 g seed sample is needed. The protocol was developed by Hosfield and Uebersax (1980) for US canning industry standards and has been modified for beans in tomato sauce (van der Merwe et al. 2006) and to suit the requirements of the Canadian Agricultural Standards Act (Balasubramanian et al. 2000). These evaluations ensure that canning quality standards are met and further improved upon. Canning quality is evaluated as an aggregate of individual components, including seed coat splitting and appearance as related to bean texture. Color retention СКАЧАТЬ