Genetic diversity of indigenous Bradyrhizobium nodulating promiscuous soybean [Glycine max (L) Merr.] varieties in Kenya: Impact of phosphorus and lime fertilization in two contrasting sites

Abstract

While soybean is an exotic crop introduced in Kenya early last century, promiscuous (TGx) varieties which nodulate with indigenous rhizobia have only recently been introduced. Since farmers in Kenya generally cannot afford or access fertilizer or inoculants, the identification of effective indigenous Bradyrhizobium strains which nodulate promiscuous soybean could be useful in the development of inoculant strains. Genetic diversity and phylogeny of indigenous Bradyrhizobium strains nodulating seven introduced promiscuous soybean varieties grown in two different sites in Kenya was assayed using the Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) of the 16S-23S rDNA intergenic spacer region and 16S rRNA gene sequencing. PCR-RFLP analysis directly applied on 289 nodules using Msp I distinguished 18 intergenic spacer groups (IGS) I-XVIII. Predominant IGS groups were I, III, II, IV and VI which constituted 43.9%, 24.6%, 8.3% 7.6% and 6.9% respectively of all the analyzed nodules from the two sites while IGS group VII, IX, X, XI, XII, XIV, XVI, XVII, XVIII each constituted 1% or less. The IGS groups were specific to sites and treatments but not varieties. Phylogenetic analysis of the 16S rRNA gene sequences showed that all indigenous strains belong to the genus Bradyrhizobium. Bradyrhizobium elkanii, Bradyrhizobium spp and Bradyrhizobium japonicum related strains were the most predominant and accounted for 37.9%, 34.5%, and 20.7% respectively while B. yuanmigense related accounted for 6.9% of all strains identified in the two combined sites. The diversity identified in

Cowpea (Vigna unguiculata L. Walp) hosts several widespread bradyrhizobial root nodule symbionts across contrasting agro-ecological production areas in Kenya

“…Previous studies on bradyrhizobia from Africa relied mostly on DNA-based discrimination methods, such as PCR-RFLP fingerprinting, 16S rRNA gene and ribosomal IGS single-marker or MLSA sequencing ( Krasova-Wade et al, 2003 ; Wasike et al, 2009 ; Pule-Meulenberg et al, 2010 ; Mathu et al, 2012 ). Also other studies on legume-nodulating Bradyrhizobia from other parts of the world are, nowadays, relying on MLSA ( Ormeño-Orrillo et al, 2006 ; Rivas et al, 2009 ; Delamuta et al, 2013 ; Delamuta et al, 2015 ).…”

Variability of soybean response to rhizobia inoculant, Vermicompost, and a legume-specific fertilizer blend in Siaya County of Kenya

“…Sympal is a legume-specific fertilizer blend (N: P 2 O 5 : K 2 O 0: 23:15 + 10CaO + 4S + 1MgO + 0.1Zn) and was applied at a rate equivalent to 30 kg P ha -1 and thoroughly mixed with the soil for the inoculated treatments (i.e.,≈300 kg Sympal ha -1 ). Soybean variety (TGx1740-2F) was selected due to its better nodulation with a range of rhizobia than local varieties in different parts of Kenya [43]. Seeds were surface-sterilized by soaking in 3.5% NaClO solution for 2 min and rinsed thoroughly 5 times with sterile distilled water.…”

Microsymbiont diversity and phylogeny of native bradyrhizobia associated with soybean (Glycine max L. Merr.) nodulation in South African soils

“…The B. japonicum and B. elkanii species have been found in various climatic regions across the world, while B. liaoningense , B. yuanmingense and Bradyrhizobium canariense have not yet been surveyed worldwide. The alkaline soils of temperate to subtropical climates of South and South-east Asia are home to B. liaoningense [2] , [6] , [22] , [33] , while the warm tropical climates of India, Kenya and Nepal favour B. yuanmingense [6] , [46] , [64] . The acid-tolerant B. canariense was found in North-east China [69] .…”