Agro-morphological characterization of mungbean (vigna radiata) entries and their use in cross-combinations for breeding purposes in Uganda.

Abstract

Mungbean (Vigna radiata (L.) Wilczek) is a species of the pan-tropical genus Vigna that is native to Asia; it is widely grown and used in Africa, Latin America and Asia for human and livestock consumption. Dry seeds, fresh green pods or leaves, which contain high protein, vitamins and minerals, are all utilized. Mungbean also adds appreciable amounts of nitrogen in soils when planted in rotation with cereals. However, a world average Mungbean yield of 384kg/ha is very low due to lack of sufficient genetic diversity in desirable traits for breeders to substantially improve the crop. As prerequisite for initiating a mungbean breeding program to improve yields and disease resistance, it was necessary to collect and characterize germplasm of diverse origins and genetic diversity, both local and exotic, for use in selecting genotypes that can broaden the genetic base of mungbean. The current study therefore collected and characterized agro-morphological variability in Ugandan and exotic mungbean germplasm; and determined the mode of inheritance of key traits and the potential of broadening mungbean genetic base using its relatives. Exotic mungbean from the World Vegetable Centre (AVRDC) as well as local mungbean lines assembled by the National Semi Arid Resources Research Institute (NaSARRI) were planted at Makerere University Agricultural Research Institute Kabanyolo (MUARIK) and NaSARRI for two seasons using an alpha lattice experimental design in three replications. Data was collected at appropriate stages using standard procedures on a total of 28 qualitative descriptors and 14 agro-morphological traits including; earliness, phonological traits and yield. There was substantial genetic variability within and between local and exotic mungbean lines indicating genetic diversity in the 14 quantitative and 28 qualitative agro-morphological descriptors within and among genotypes. However, a single link dendrogram drawn from data of 28 morphological markers showed a close genetic relationship among mungbean lines. Correlations between quantitative descriptors showed moderate association between seed size and seed yield (P<0.01), confirming how seed size is a critical trait for yield. Late maturing lines significantly (P<0.001) yielded higher than early maturing lines. Inheritance of earliness, yield and yield related traits was determined in the F2 progenies obtained from crosses of 4 large seeded exotic lines (female parents) and 2 adapted local lines. (male parents) that were planted and evaluated at MUARIK in an alpha lattice design replicated thrice. Results revealed a high Baker’s ratio ranging from 0.77 to 1 for primary braches, plant height, pods per plant, seed size and grain yield per plant indicating importance of GCA over SCA. The low Baker’s ratio of 0.44 and 0.26 for earliness measured as days to first flowering and days to 80% maturity respectively indicated prominence of SCA over GCA. Earliness had a low narrow sense coefficient of genetic determination (NS-CGD below 0.5) while rest of the traits were above 0.5. Broad sense coefficient of genetic determination (BS-CGD) was generally high for all traits ranging between 0.62 and 1. Results also revealed that there were some barriers to crossing mungbean with its relatives; blackgram and ricebean. There is substantial variability within the collected germplasm to start a viable mungbean breeding program that can develop disease resistant and high yielding lines. With the exception of earliness, the breeding strategy for traits considered in inheritance study should be early selection as there are non-significant non-additive gene effects. This significantly reduces the number of segregating lines to be tested in later generations thus saving resources. Interspecific hybridizations seem to have some barriers thus techniques such as embryo rescue should be employed to obtain viable F1 plants thereby introgressing lacking desirable traits in mungbean from ricebean and blackgram.