Assessing rhizosphere Trichoderma asperellum strains for root colonizing and antagonistic competencies against Fusarium wilt through molecular and biochemical responses in castor

Abstract

The study was aimed at identifying the effective strain(s) of Trichoderma asperellum to colonize castor roots, promote growth and limit pathogen infection. Two castor genotypes; DCS-107 and 48-1 varying for stress tolerance to Fusarium wilt were treated with four Trichoderma asperellum strains; 7316, N13, TV5 and TV2B16 to analyze root colonizing and antagonistic competencies. A significant decline in the colony-forming unit (CFU) counts was observed in Trichoderma-treated bulk and rhizosphere soil compared to controls indicating a high rhizosphere competence of the Trichoderma asperellum strains; 7316 followed by N13. These strains also showed high mycoparasitic propensity against Fusarium oxysporum through dual culture-confrontation and in-planta assays. Bio-priming with Trichoderma strains enhanced plant growth in the tolerant genotype, DCS-107 compared to the susceptible genotype, 48-1 suggesting differential responses of the host genotypes. An increase in shoot length by 46.2, 28.9 and 21.7% was observed upon treatment of DCS-107 genotype with the Trichoderma strains, 7316, N13 and TV5 respectively. Further, a quantitative polymerase chain reactions (qPCRs) of 13 stress and defence response genes revealed gene transcript reprogramming, causing a transient repression of the plant immune responses to enable root colonization. Further, biochemical analysis revealed higher antioxidant enzyme activity of catalase, superoxide dismutase and glutathione peroxidase and total phenol content in co-stressed conditions compared to the controls suggesting that Trichoderma confers protection against oxidative stress damage. Trichoderma strains, 7316, N13 and TV5, either individually or in combination could be utilized as potential biocontrol agents to enhance growth and confer resistance to wilt pathogen, Fusarium oxysporum ricini.