Can indigenous rhizobial strains, in their own environment, outperform elite exogenous strains as soybean inoculants? The Mozambican case study

Abstract

Indigenous rhizobial strains frequently outcompete inoculant strains impeding inoculation responses on soybean. Although indigenous rhizobial strains with outstanding symbiotic effectiveness have been reported, studies that investigate whether, on their own environment, indigenous rhizobial strains can outperform exogenous strains as soybean inoculants are rare. The objective of this study was to compare the performance of the five promising indigenous strains against that of three exogenous elite reference strains under field conditions with promiscuous and non-promiscuous varieties in different agro-climatic regions of Mozambique, in the 2017/2018 and 2018/2019 cropping seasons. The experiments were conducted at five locations in Manica (1), Nampula (1), Tete (2) and Zambézia (1) provinces, which represent the major soybean production region in the coutry. Five indigenous rhizobial strains, B. elkanii Moz 4, Moz 19 and Moz 22, B. japonicum Moz 27, Moz 61, were tested along with three exotic rhizobial strains, B. japonicum SEMIA 5079, and B. diazoefficiens SEMIA 5080 and USDA 110. And two controls, non-inoculated and non-N-fertilized control, and non-inoculated and N-fertilized control with 200 kg of N ha−1 as urea applied 50% at sowing and 50% at R2. The 2017/2018 crop season was characterized by prolonged drought spell throughout the study area. In the second second cropping season the experimental areas were hit by cyclones Ida and or Kenneth. These factor might have limited soybean nodulation, growth and yield. Moreover, the drought spells most probably had negative affect on the precision of the experiment masking the differences between the treatments. Therefore, the hypothesis that under their own environment indigenous rhizobial strains have better performance than exotic elite strains could not be satisfactorily tested.