Marker-Assisted Gene Pyramiding for Powdery Mildew Resistance in Thai Mungbean Variety SUT1 by Backcross Breeding

In Thailand, all Thai-certified varieties of mungbean [Vigna radiata (L.) R. Wilczek] preferentially grown by farmers are susceptible to powdery mildew (PM) disease. Marker-assisted gene pyramiding (MAGP) for improving resistant varieties is a sustainable strategy to overcome its outbreak in mungbean fields. In this study, two PM resistance genes from donor parent A2 were pyramided into the Thai-certified variety, namely Suranaree University of Technology 1 (SUT1) using marker-assisted backcrossing (MABC). Three polymorphic marker loci linked to PM resistance genes and three marker sets with 72 polymorphic loci were subsequently used for foreground and background selection, respectively. As a consequence, three pyramided BC₄ lines B1, B2, and D5, carrying all foreground marker loci in homozygosity, were obtained. Their recurrent parent genome (RPG) recovery was 100.0%, 100.0%, and 98.8% for background marker Sets A, B, and C, respectively. In field conditions, it was found that a low level of PM severity was exhibited in the pyramided BC line D5, which also had most of the agronomic traits similar or superior to SUT1. Moreover, the yield performance of this line was higher than SUT1, by up to 8.3–12.2%, during PM outbreaks or in the absence of disease. Thus, this pyramided BC line can be further used to develop a new resistant variety for farmers in the future.