Registration of UPR‐Mp‐34 and UPR‐Mp‐42 common bean germplasm with enhanced resistance to ashy stem blight

Common bean (Phaseolus vulgaris L.) breeding lines (BL) UPR‐Mp‐34 (Reg no. CV‐313, PI 701379) and UPR‐Mp‐42 (Reg no. CV‐314, PI 701380) were developed at the University of Puerto Rico. UPR‐Mp‐34 was derived from A 195/‘PC 50’//SEA 5, and UPR‐Mp‐42 was developed from BAT 477/NY6020‐4//PRA154 common bean populations. Both BL have intermediate levels of resistance (mean scores, 4–6) to two inoculations of the PRI21 Macrophomina phaseolina (Tassi) Goidanich isolate (the causal agent of ashy stem blight) compared with BAT 477, SEA 5, TARS‐MST1, and XAN 176, which mostly had susceptible scores (7–9) in the greenhouse and field evaluations. UPR‐Mp‐34 has an indeterminate growth habit Type III, has a cream seed (average weight, 26.5 g per 100 seeds), initiates flowering at 32 d after planting, and reaches harvesting maturity at 86 d. Mean seed yield was 730 and 340 kg ha−1 in Isabela and Lajas, respectively. UPR‐Mp‐42 possesses black seed (23.8 g per 100 seeds), has a determinate growth habit Type I, initiates flowering at 30 d, and matures at 76 d. Mean seed yield was 750 kg ha−1 in both locations. The intermediate levels of ashy stem blight resistance from both BL could be combined with other sources of resistance and introgressed into common bean cultivars from different market classes. Core Ideas Ashy stem blight causes yield losses over 60% in susceptible common bean genotypes. Genetic resistance is the most important method to manage the ashy stem blight disease. UPR‐Mp‐34 and UPR‐Mp‐42 breeding lines have intermediate resistance to ashy stem blight. Both breeding lines may be used to increase the levels of ashy stem blight resistance in common bean cultivars.