GENOTYPIC VARIATION OF BAMBARA GROUNDNUT (Vigna subterranea L. Verdc) FOR TOLERANCE TO LOW PHOSPHORUS IN ACIDIC SOILS

Abstract

Low available phosphorus (P) in acidic soils limits productivity and growth of Bambara groundnuts.The objectives of this study were to (1) evaluate the growth and yield performance of Bambara genotypes under varying levels of lime and P, (2) determine the efficiency and genotypic variation of bambara groundnut for P accumulation (PA) and (3) investigate traits underlying differential phosphorus use efficiency in bambara genotypes. Twelve genotypes were evaluated at 2 sites in Siaya (0.2510N, 34.2540E) and Busia (0.2500N, 34.2530E) counties in Randomized Complete Block Design in split-split plot arrangements during long and short rain seasons in 2018. Treatments comprised 2 lime levels (0, 4 tonnesha-1), 2 P levels (0, 35 kgha-1) with genotype as whole plot, lime as sub-plots, and phosphate as sub-sub plots. Genotypes were further screened in pot culture applied with 0 or 160 μM Potassium orthophosphate (KH2PO4). Effects due to genotypes, lime and P, and season × site interaction were significant (P ≤ 0.05) for plant height, number of nodules and number of lateral roots. Significant effects due to season were observed for the number of nodules per plant while site significantly affected number of nodules and lateral roots. Genotypes exhibited variation for plant biomass, seed and biological yield due to lime, P, site, seasons and interaction effect of genotype × lime and genotype × site BAM011, BAM010 and BAM002 had increased number of lateral roots and had high seed yields in the two seasons and sites under low and adequate P in limed and un-limed soils.BAM002, BAM010 and BAM012 were responsive to both P and lime application. Genetic variation in PA and P-use efficiency among the genotypes was observed in this study. Phosphorus accumulation (PA) in biomass, seed and biological yields differed due to genotype, P level and genotype × P level interaction. BAM011, BAM010 and BAM002 had high values of seed yields, phosphorus harvest index, phosphorus physiological efficiency index and PA at low P showing that they are efficient in P use. Cultivars were categorized into in-efficient, medium and efficient as per the total index score. Principal component analysis categorized genotypes BAM011, BAM010 and BAM002together at the contrastinglevels of P.Tap root length (TRL), branching number (BN), branching diameter (BD)root volume (RV), rootand shoot biomassdiffered among the genotypes and were highly correlated to each other indicating that these traits are useful for P acquisition and P utilization efficiency. BAM001, BAM002, BAM010 and BAM011 exhibited high values of TRL, BN, BD, RV and root and shoot biomasses at varying levels of P Bambara groundnut contains genetic variation for tolerance to low P and respond well to applied P in acidic soils.Root traits including TRL, BN, BD and RV are among the mechanisms that underlie differential accumulation of P and phosphorus use efficiency in bambara genotypes.High performing responsive and P-efficient cultivars should be multiplied and distributed to farmers for cultivation in low P soil.