CHARACTERIZATION OF RHIZOBIUM ISOLATES AS BIOCONTROL AGENTS AGAINST FUSARIUM SOLANI AND MACROPHOMINA PHASEOLINA

Abstract

This study recovered 15 Rhizobium and Bradyrhizobium isolates from nodules of different legume plants (Faba bean, Pea, Soybean, and Clover) grown in nine Egyptian governorates representing the delta region (Menoufia, Gharbia, Suez, Qalubia, Cairo, Sharkia, Behirah, Kafr El-sheikh, and Ismailia). The infectivity test proceeded with all isolates retaining and infecting their hosts, demonstrating that they are Rhizobium cultures. Molecular identification based on 16S rRNA gene sequencing revealed that the isolates belonged to two species of Rhizobium, namely Rhizobium leguminosarum (RL1, RL2, RL3, RL4, RL5, RL6, RL7, RL8, RL9, RL10, RL11, RL12, and RL13) and Bradyrhizobium japonicum (BJ1 and BJ2). Moreover, PCR based on specific primers was employed to detect nifH gene in the genomes of tested isolates. Most of the isolates exhibited sensitivity toward antibiotics, and were able to produce HCN. The isolates of RL4, RL6, RL9, and RL10 were positive for chitinase activity and exhibited clear zones ranging from weak to sturdy. The antagonism evaluation of Rhizobium isolates against Fusarium solani and Macrophomina phaseolina ensued under in vitro conditions. The isolates RL6 and RL9 of R. leguminosarum were the most effective, suppressing more than 50% growth of M. phaseolina. Similarly, the isolates RL4, RL6, RL9, and RL10 revealed the most effective and inhibited more than 50% growth of F. solani. Interestingly, the isolates RL6 and RL9, which exhibited high levels of suppression against M. phaseolina, also displayed high levels of suppression against F. solani.