No abstract

In the present study, we investigated the role of Trichoderma virens (TriV_JSB100) spores or cell-free culture filtrate in the regulation of growth and activation of the defence responses of tomato (Solanum lycopersicum) plants against Fusarium oxysporum f. sp. lycopersici by the development of a biocontrol-plant-pathogen interaction system. Two-week-old tomato seedlings primed with TriV_JSB100 spores cultured on barley grains (BGS) or with cell-free culture filtrate (CF) were inoculated with Fusarium pathogen under glasshouse conditions; this resulted in significantly lower disease incidence in tomato Oogata-Fukuju plants treated with BGS than in those treated with CF. To dissect the pathways associated with this response, jasmonic acid (JA) and salicylic acid (SA) signalling in BGS- and CF-induced resistance was evaluated using JA- and SA-impaired tomato lines. We observed that JA-deficient mutant def1 plants were susceptible to Fusarium pathogen when they were treated with BGS. However, wild-type (WT) BGS-treated tomato plants showed a higher JA level and significantly lower disease incidence. SA-deficient mutant NahG plants treated with CF were also found to be susceptible to Fusarium pathogen and displayed low SA levels, whereas WT CF-treated tomato plants exhibited moderately lower disease levels and substantially higher SA levels. Expression of the JA-responsive defensin gene PDF1 was induced in WT tomato plants treated with BGS, whereas the SA-inducible pathogenesis-related protein 1 acidic (PR1a) gene was up-regulated in WT tomato plants treated with CF. These results suggest that TriV_JSB100 BGS and CF differentially induce JA and SA signalling cascades for the elicitation of Fusarium oxysporum resistance in tomato.

Plant immunization for resistance against a wide variety of phytopathogens is an effective strategy for plant disease management. Seventy-nine plant growth-promoting fungi (PGPFs) were isolated from rhizosphere soil of India. Among them, nine revealed saprophytic ability, root colonization, phosphate solubilization, IAA production, and plant growth promotion. Seed priming with four PGPFs exhibited early seedling emergence and enhanced vigour of a tomato cultivar susceptible to the bacterial wilt pathogen compared to untreated controls. Under greenhouse conditions, TriH_JSB27 and PenC_JSB41 treatments remarkably enhanced the vegetative and reproductive growth parameters. Maximum NPK uptake was noticed in TriH_JSB27-treated plants. A significant disease reduction of 57.3% against Ralstonia solanacearum was observed in tomato plants pretreated with TriH_JSB27. Furthermore, induction of defence-related enzymes and genes was observed in plants pretreated with PGPFs or inoculated with pathogen. The maximum phenylalanine ammonia lyase (PAL) activity (111U) was observed at 24h in seedlings treated with TriH_JSB27 and this activity was slightly reduced (99U) after pathogen inoculation. Activities of peroxidase (POX, 54U) and β-1,3-glucanase (GLU, 15U) were significantly higher in control plants inoculated with pathogen after 24h and remained constant at all time points. A similar trend in gene induction for PAL was evident in PGPFs-treated tomato seedlings with or without pathogen inoculation, whereas POX and GLU were upregulated in control plus pathogen-inoculated tomato seedlings. These results determine that the susceptible tomato cultivar is triggered after perception of potent PGPFs to synthesize PAL, POX, and GLU, which activate defence resistance against bacterial wilt disease, thereby contributing to plant health improvement.