Key message The Common Bean Angular Leaf Spot Resistance Gene Phg - 2 was fine-mapped to a 409-Kbp region, and molecular markers for breeders were developed and validated in field experiments. Abstract Common bean ( Phaseolus vulgaris L.) is an important food legume in Latin America, Asia and Africa. It is an important source of protein, carbohydrates and micro-minerals, particularly for smallholder farmers. Common bean productivity is affected by angular leaf spot (ALS) disease caused by the pathogenic fungus Pseudocercospora griseola , resulting in significant yield losses, particularly in low-input smallholder farming systems in the tropics. The ALS resistance gene Phg - 2, which was found in several highly resistant common bean genotypes, was investigated in crosses between Mesoamerican pre-breeding lines and elite Andean breeding lines. Next-generation sequencing (NGS) data sets were used to design new SNP-based molecular markers. The Phg - 2 locus was confirmed to be the major locus providing ALS resistance in these crosses. The locus was fine-mapped to a 409-Kbp region on chromosome 8. Two clusters of highly related LRR genes were identified in this region, which are the best candidate genes for Phg - 2 . Molecular markers were identified that are closely linked to the Phg - 2 resistance gene and also highly specific to the donor germplasm. Marker-assisted selection (MAS) was used to introgress the Phg - 2 resistance locus into Andean breeding germplasm using MAB lines. The usefulness of molecular markers in MAS was confirmed in several field evaluations in complex breeding crosses, under inoculation with different ALS pathotypes. This project demonstrates that NGS data are a powerful tool for the characterization of genetic loci and can be applied in the development of breeding tools. Electronic supplementary material The online version of this article (10.1007/s00122-019-03334-z) contains supplementary material, which is available to authorized users.
Tepary bean (Phaseolus acutifolius A. Gray) is a drought and high ambient temperature tolerant crop native to the Sonoran Desert, the hottest and driest region in the United States and Mexico. Although tepary bean is an orphan crop with little current commercial production, there was a brief period of larger scale production in the early 1900s in California. Tepary bean has great potential as a novel crop in a warmer world climate and can be introduced as an alternative pulse crop in hot and/or dry regions worldwide. TARS-Tep 23 (Reg. no. GP-309, PI 698457) is an improved tepary bean germplasm with wide-ranging adaptation to tropical and temperate regions experiencing high temperature and drought stress conditions, with broad resistance to bean rust and with resistance to common bacterial blight.It has a flat, mottled black seed type with good seed size, a Type III plant habit, and a short crop cycle of 55-61 d in the environments tested. This germplasm was developed cooperatively by the USDA-ARS, Zamorano University, the University of California-Davis, and the University of Nebraska. The use of this improved germplasm by farmers in production zones affected by abiotic and biotic stresses, or by breeding programs, can potentially increase seed yields of this climate-resilient crop.Abbreviations: BGYMV, Bean golden yellow mosaic virus.
The production of the common bean ( Phaseolus vulgaris L.), one of the most important sources of protein and minerals and one of the most consumed grain legumes globally, is highly affected by heat and drought constraints. In contrast, the tepary bean ( Phaseolus acutifolius A. Gray), a common bean‐related species, is adapted to hot and dry climates. Hybridization to introduce complex traits from the tepary bean into the common bean has been challenging, as embryo rescue is required. In this study, we report three novel interspecific lines that were obtained by crossing lines from prior common bean × tepary bean hybridization with Phaseolus parvifolius Freytag in order to increase the male gametic diversity to facilitate interspecific crosses. These interspecific lines enhanced the crossability of the common bean and tepary bean species while avoiding the embryo rescue process. Crossing these three interspecific lines with tepary beans resulted in 12‐fold more hybrid plants than crossing traditional common beans with tepary beans. Whole‐genome sequencing analysis of these three interspecific lines shows large introgressions of genomic regions corresponding to P. parvifolius on chromosomes that presumably contribute to reproductive barriers between both species. The development of these lines opens up the possibility of increasing the introgression of desirable tepary bean traits into the common bean to address constraints driven by climate change.
Tepary bean (Phaseolus acutifolius A. Gray) is an underutilized drought tolerant annual legume, originating from the Sonoran Desert, that may be a beneficial forage/hay for beef cattle in the Southern Great Plains of the US (SGP). The SGP has erratic rainfall and periods of intermittent drought exacerbated by high summer temperatures. In 2020 and 2021, a split-plot design was used to evaluate 13 genotypes of tepary bean and a forage soybean (control) at El Reno, OK, USA to compare production of plant biomass and forage nutritive value parameters under seven harvest regimes. Genotypes were used as the main plot and cutting management as the sub-plot. Biomass production of all tepary bean genotypes equaled that of soybean (p > 0.05), while several genotypes had superior forage nutritive value traits (p ≤ 0.05). Overall, a 15-cm cutting height and 30-day harvest interval produced the best overall product (average dry biomass of 5.8 Mg ha−1 with average relative feed values (RFV) of 165). Although all harvest regimes reduced total seasonal biomass, forage nutritive value increased. However, the tradeoff between forage production and nutritive value may be unacceptable to most producers. Further agronomic and breeding research is needed to encourage producers to grow tepary bean as a forage/hay in the SGP.
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