Resistance to bean golden mosaic virus in bean genotypes

Bean lines MD 806, MD 807, MD 820, MD 829, MD 808, and MD 821, all with high levels of resistance to bean golden mosaic virus (BGMV), were selected under field conditions. On a 1 to 9 scale (1 = symptomless plant; 9 = severe symptoms), the mean disease severity of the MD lines ranged from 1.7 to 3.9 for mosaic symptom (foliar yellowing) and from 1.7 to 2.2 for malformation. In contrast, disease severity in the susceptible cultivars Carioca, Carnaval, and Iapar 20 ranged from 4.1 to 8.7 for mosaic and from 4.0 to 7.3 for malformation. Symptoms on the selected lines were expressed later than on susceptible controls. The MD lines yielded 1.2- to 5.9-fold the yield of the cultivars Carioca and Iapar 20. Under greenhouse conditions, reactions of the bean genotypes to BGMV were similar to those observed in the field. MD 806 and MD 807 were obtained from early crosses involving genotypes that reacted to BGMV infection with mild mosaic (Aete 1/38 and TMD-1) and mild malformation (Porrillo Sintetico and Turrialba 1). Parents of the lines MD 820 and MD 829 were Phaseolus coccineus (of unknown reaction to BGMV) and Carioca. Line MD 648 (DOR-selected line) was the ancestral parent of lines MD 808 and MD 821, which had the highest levels of resistance or tolerance to BGMV. Severity of all BGMV symptoms showed gradual reductions from the earliest parents to their later selected progenies. Responses of the parent genotypes and progenies to BGMV infection suggest a combination of resistance characters in the selected MD lines. MD 806, MD 820, and MD 821 were released in the state of Parana under the names Iapar 57, Iapar 72, and Iapar 65, respectively.