Testing of Commercial Inoculants to Enhance P Uptake and Grain Yield of Promiscuous Soybean in Kenya

The aim of this study was to assess the potential of commercial mycorrhizal inoculants and a rhizobial inoculant to improve soybean yield in Kenya. A promiscuous soybean variety was grown in a greenhouse pot study with two representative soils amended with either water-soluble mineral P or rock P to assess product performance. The performance of selected mycorrhizal inoculants combined with a rhizobial inoculant (Legumefix) was then assessed with farmer groups in three agroecological zones using a small-plot, randomized complete block design to assess soybean root colonization by mycorrhiza, nodulation, and plant biomass production in comparison to rhizobial inoculant alone or with water-soluble mineral P. Greenhouse results showed highly significant root colonization by commercial mycorrhizal inoculant alone (p < 0.001) and in interaction with soil type (p < 0.0001) and P source (p < 0.0001). However, no significant effect was shown in plant P uptake, biomass production, or leaf chlorophyll index. In field conditions, the effects of mycorrhizal and rhizobial inoculants in combination or alone were highly context-specific and may induce either a significant increase or decrease in root mycorrhizal colonization and nodule formation. Mycorrhizal and rhizobial inoculants in combination or alone had limited effect on plant P uptake, biomass production, leaf chlorophyll index, and grain yield. Though some mycorrhizal inoculants induced significant root colonization by mycorrhizal inoculants, this did not lead to higher soybean yield, even in soils with limited P content. Our results are further evidence that inoculant type, soil type, and P source are critical factors to evaluate commercial inoculants on a context-specific basis. However, our results highlight the need for the identification of additional targeting criteria, as inoculant type, soil type, and P source alone were not enough to be predictive of the response. Without the identification of predictive criteria for improved targeting, the economic use of such inoculants will remain elusive.

First Attempt to Identify and Map QTLs Associated with Promiscuous Nodulation in Soybean

ABSTRACTTo inform possibility of conducting marker assisted breeding of promiscuous soybean varieties, this study used 92 F2 lines from biparental cross to identify QTLs associated with promiscuous nodulation in soybean. GBS; genotyping by sequencing platform was used to generate SNPs through the pipeline 2 in TASSEL 5.0, Bowtie2 version 2.2.8 for tag alignment, Beagle version 4.1 to impute missing SNPs and R-QTL package in R for QTL identification. Four nodulation traits were assessedviznumber of nodules (NN), percent of effective nodules (NE), fresh weight and dry weight of nodules (NFW and NDW). Two QTLs were identified on chromosomes 10 and 13. Both QTLs were associated with NN, only QTL13 was associated NE and only QTL10 was associated with nodule ‘weights. It was observed that NN, NFW and NDW shared QTL10 and NN and NE share QTL13 allowing hypothetize on the existence of pleiotropic genes in those those two regions. Over dominance effect was observed for QTL10 and non additive effect for QTL13. The paper recommend investigations be pursued to validate those QTLs and set foundation for marker assisted selection of promiscuous soybean varieties. Also these findings could serve as starting point for gene cloning to better understand nodulation trait in soybean.

Symbiotic Effectiveness of Rhizobia Strains Isolated from Nigerian Savanna

Laboratory and screenhouse experiment were conducted to assess the symbiotic effectiveness (SE) of rhizobia isolated from southern Guinea savanna, northern Guinea savanna and Sudan savanna of Nigeria and response of promiscuous soybean varieties, TGx1448-2E, TGx1835-10E and TGx1955-10E to inoculation with ten indigenous rhizobia isolates. The soybean varieties were grown on sterilized sand at the screenhouse of the Department of Soil Science and Land Management, Federal University of Technology Minna and watered using Sandsman’s nutrient solution. The treatments were un-inoculated control, mineral nitrogen (urea) and ten rhizobia isolates arranged on a Completely Randomized Design (CRD) and replicated three times. The rhizobia isolates were Sg4, Sg6-3, Gw5, Gw3-2, Bg3, Bg1-4, Sk2-3, Am2, Am6-3 and Kr5-5 isolated from Sabon-gida, Gwada, Birnin-gwari, Shika, Amawa and Karaye sites of Nigerian savanna. The results obtained were subjected to Analysis of Variance using statistical analysis system (SAS 2008) computer software. The treatments mean was separated using Least Significant Different (LSD) at 5% probability. Nodulation and biomass yield of the varieties were assessed at six weeks after planting. Nodules were only produced in inoculated plants, SE was calculated. The result obtained showed that nodule dry weight, SE and shoot dry weight were significantly affected by the interaction between inoculation and promiscuous soybean varieties. Generally, inoculated plants gave higher shoot biomass gain than the un-inoculated control but lower than those treated with urea. The difference between those inoculated and those treated with urea was associated to environmental specificities and higher temperature during the period of the experiment. The SE was highest in northern Guinea savanna isolate reaching 67% and lowest in southern Guinea savanna isolate Sg6-3 recorded 53%. The result showed an SE of less than 100% in all the isolates which implies that the indigenous rhizobia isolates were not superior to the mineral nitrogen.