Gas Exchange, Photosynthetic Pigment and Secondary Metabolites Concentration of Soy bean (Glycine max L.) Plants Grown in Western Kenya under Rhizobial Inoculation and Aluminium Application

Soy bean production continues to be very low, there is potential for increased production of the crop. Acidic soils negatively affect plant nutrition and productivity. Rhizobia inoculation has previously been shown to improve legume production. There is need to understand how inoculation of Bradyrhizobium japonicum increase N content for leaf activity and enable pod filling that increase yield under Al application. The objective of the study was to investigate gas exchange, photosynthetic pigment concentration and secondary metabolites response of GAZZELLE, NAMSOI and TGX soy bean genotypes grown in western Kenya to aluminium application and Rhizobium inoculation. The experiment was carried out at Maseno University under greenhouse conditions. Three replicates, three genotypes and eight treatments {water (control), 480µM Al, 750µM Al, 960µM Al, Control & inoculation, 480µM Al & inoculation, 750µM Al & inoculation and 960µM Al & inoculation} were used in RCBD. Gas exchange parameters were collected. Absorbance were read at 480, 645 and 645nm to determine chlorophyll a, b and carotenoids. Plant secondary metabolites were also determined. Tukey`s HSD tests at 5% was used to separate treatment means. Significant differences were observed when GAZZELLE was compared to NAMSOI and TGX at T1, T3, T5, T6 and T7. Therefore USDA-Rhizobia may have high potential to colonize roots of GAZZELE. Significant differences found for Ci, A and gi showed GAZZELLE and TGX to be photosynthesizing best under USDA-inoculation. Therefore they have potential production in acidic soils. Anthocyanin and phenolic compounds were found highly concentrated in GAZZELLE and NAMSOI, they then may have highly formed Al-complexes that limited Al stress. Inoculation ameliorated significantly the effects of Al to Chl a, Chl b and carotenoids. A reduction of Chl a was lowly in GAZZELLE indicating that it was less affected when Al was treated. These findings show that Bradyrhizobium japonicum inoculation alleviates Al effects and improve soy bean yield.