Vol. 9, Issue 4, Part D (2025)

The development of new biocontrol products against plant diseases requires screening of high numbers of candidate antagonists in vitro conditions using culture media that reflect the nutritional habitat of the pathogens, followed by efficacy testing in bioassays and under field conditions (Köhl et al., 2011) [17]. One of the biggest reasons for biocontrol failure is the lack of appropriate screening procedures (as they ignore the influence of biotic and abiotic factors in the rhizosphere) to select those microorganisms which are most suitable for disease control in diverse soil environments (Merriman and Russell 1990; Folman et al. 2003) [20, 21]. Screening of antagonists in vitro performed on agar media eliminates the influence of biotic and abiotic factors of diverse soil environments, resulting in failure of identified bio-agent. We performed the screening for antagonist in soil, and developed a technique to trace and resolve interactions in natural habitat. Comparable results were, obtained in Bi-and Tripartite (Trichoderma-Plant-Pathogen) interactions. Technique selects potential bio-agent screened in diverse soil environment, also justifies the importance of introduced bio-control agent in “microbiome-based biocontrol strategies”
In the present investigation the experimental setup consisted of Sclerotium rolfsii conducive soil developed in plastic trays (11 +2 trays). These Sclerotium rolfsii conducive soil was inoculated each with Trichoderma spp. isolates (T-4, T-5, T-81b, G2, M109, M117, M118, M126, M128, M136, M165) grown on tamarind seed powder was mixed thoroughly (20 gms inoculum). Trays were left undisturbed for 1 week.
It was observed that when developed Sclerotium rolfsii conducive soil, were inoculated each with Trichoderma spp. isolates (T-4, T-5, T-81b, G2, M109, M117, M118, M126, M128, M136, M165) colonization with typical initiating green sporulation (typical of Trichodrma spp.) all over the soil. It was expected that the growth of S rolfsii was suppressed by the introduced Trichoderma spp isolates. 
Trichoderma-mediated disease suppression is affected by a combination of mycoparasitism, antibiosis, induced defence response and competitive exclusion (Sharma et al., 2017) [35]. Trichoderma spp. are fast colonizers of the spermosphere (seed zone) and rhizosphere (root zone), which helps exclude invading pathogens when the biocontrol fungi are applied to seeds or roots. In direct antibiosis, secondary metabolites or secreted enzymes from Trichoderma inhibit pathogen growth or germination (Howell, 2003; Viterbo et al., 2001). The metabolites could also contribute to competition, mycoparasitism and IDR (Zeilinger et al., 2016a). T. harzianum expresses distinct b-1,3-and b-1,6-glucanases during co-culture with host fungi and upon growth in media containing fungal cell walls (Cohen-Kupiec et al., 1999; De la Cruz et al., 1995; Montero et al., 2005; Monteiro and Ulhoa, 2006; Gajera, 2012; Troian et al., 2014) [36, 37, 38, 39, 40, 41]. Similarly, Trichoderma asperellum reacted to fungal plant pathogens, expressing chitinases and b-1, 3-glucanases (Guigon-Lopez et al., 2015) [42]. T. atroviride (strain T11) is effective against Verticillium dahliae (Glomerellales). Proteolysis was a prominent process inferred from the transcriptome, with 10 proteases among the 143 up-regulated genes (Moran-Diez et al., 2019) [43].
This experimental setup established in trays helped us to drive the component of tripartite interaction. Plants are best to living expression systems to analyse the suppressive ability of the different introduced Trichoderma spp isolates following tripartite interaction. We therefore analyzed the establishment of rice seedlings (the third component of tripartite interaction) in the reclaimed Sclerotium rolfsii conducive soil by the blending of different Trichoderma spp. isolates.