Recurrent selection for quantitative resistance to soil-borne diseases in beans in the Mixteca region, Mexico

Abstract

Most of the bean breeding for disease resistance has been done considering it as a qualitative trait. This work reports on bean breeding for resistance as a quantitative trait. Recurrent mass selection was used in order to simultaneously increase the polygenically inherited resistance to all locally important bean pathogens but with emphasis on bean common mosaic virus (BCMV) and bacterial blight (BB) in the Mixteca Region, Mexico. Qualitative resistances against soil-borne diseases, induced mainly by facultative pathogens, possessing little parasitic specialization, are unlikely to occur, and although breeding against these kinds of diseases was not originally planned, it turned out to be part of collateral field screening. The accumulation of quantitative resistance against soil-borne diseases in advanced lines of this program is described and includes two field experiments, a cycle for seed augmentation in large plots and two greenhouse experiments. The majority of lines of the advanced breeding cycles produced consistently higher yields and higher survival rates, when compared with the original parents and commercial varieties. However, the regional land races still have higher survival rates but they have lower yields. Soil-borne diseases were present during all breeding cycles carried out under field conditions in the Mixteca Region. This work indicates that breeding for quantitative resistance involves all locally important pathogens. It is then feasible to accumulate high levels of quantitative resistance, in a relatively short time, even to these intermittently severe, soil-borne diseases that are otherwise so difficult to manage.