Evaluation of beneficial fungal root endophytes against fusarium rot in small cardamom

Abstract

The study entitled “Evaluation of beneficial fungal root endophytes against Fusarium rot in small cardamom” was conducted at College of Agriculture, Vellayani and Cardamom Research Station, Pampadumpara during 2020-21 to evaluate the colonisation and interaction of two beneficial fungi, Piriformospora indica and Glomus fasciculatum, in cardamom and their potential to manage Fusarium rot disease of cardamom and elucidation of the role of gibberellic acid in the endophytic fungimediated disease tolerance. Fusarium infection in small cardamom is characterised by root rotting, eye shaped lesion on pseudostem and panicle rot. Fusarium oxysporum Schledt was isolated from the infected roots of the farmer’s field of Pampadumpara in Idukki district. Koch’s postulate was proved by inoculation of the pseudostem of one year plants using pinprick method where the isolate produced the typical eye shaped lesion within two weeks. A pot culture experiment was conducted at CRS, Pampadumpara to assess the interactive effect of the fungal root endophytes P. indica and G. fasciculatum on the vegetative growth of small cardamom seedlings and suckers using four treatments and five replications. Both individual and combinatorial effects of the endophytes on the vegetative characters like plants height, number of leaves, leaf length, leaf width, root parameters, biomass etc. were evaluated. Successful root colonization was observed in P. indica and G. fasciculatum treated roots at six and seven days after their inoculation respectively. This is the first report of colonization of P. indica in small cardamom. The study revealed that the endophytes inoculated plants were superior to control plants in which maximum shoot growth was shown by the dually colonized plants followed by the P. indica-colonized which was then followed by G. fasciculatum colonised plants. The root parameters were higher for P. indica-colonized plants compared to the combined or G. fasciculatum colonized plants in cardamom seedlings whereas dually colonized plants had better root growth in cardamom suckers. P and K analysis of the whole plant clearly indicated the enhanced nutrient uptake to root, shoot and leaf in the endophytes-colonized plants. The IAA analysis of root samples also revealed a higher IAA content in the endophytes colonized seedlings compared to the control seedlings with P. indica colonized plants recording the maximum value of 83.80 µg g-1 in seedlings and 94.30 µg g-1 in suckers; and least value being observed in control plants recording 44.80 µg g-1 in seedlings and 94.30 µg g-1 in suckers. This study stipulate a scope of better establishment of cardamom in field especially in the case of seedlings during transplantation due to well established root system. There was also a reduction in nursery period by two months in the P. indica and G. fasciculatum dually colonized seedlings compared to the non-colonized seedlings. In vitro evaluation of P. indica against F. oxysporum and in vivo evaluation of both the bioagents against F. oxysporum in small cardamom was carried out to appraise the effect of bioagents in the management of Fusarium rot disease of cardamom. In in vitro evaluation, dual culture assay of P. indica with F. oxysporum was performed in PDA in which a percent inhibition of 64.4 (%), antagonism index of 20.53 and an obscure lysis zone was observed. There wasn’t any presence of inhibition zone, antibiosis, coiling, overgrowth, sporulation etc. In in vivo evaluation, a pot culture experiment was laid out at CRS, Pampadumpara with seven treatments and three replications including a bio agent check of 2% Pseudomonas fluorescens and chemical check of 2 % carbendazim as basal drench. The study revealed that the beneficial interaction with bioagent successively decreased the disease severity and lesion size, among which P. indica treated plants showed the best result having the least disease severity of 38.07 (%) and 31.48 (%) in seedlings and suckers respectively. The disease severity of the control plants were the highest, recording 86.62 (%) and 76.77 (%) in seedlings and suckers respectively. Combinatorial and P. fluorescens treatments were the other treatments showing promising results in disease management. Total Gibberellic acid was estimated from leaf samples of challenge inoculated experimental plants to elucidate the role of GA in endophyte mediated disease tolerance and the authors couldn’t interpret any role of GA in disease development. Moreover, the GA content was higher in P. indica colonised recording 18.60 µg g-1 and 10.65 in µg g-1 in seedlings and suckers respectively; and dually colonised plants recording 18.00 µg g-1 and 9.71 µg g-1 in seedlings and suckers respectively. Thus, the present study proclaims a very pronounced plant growth promotion in cardamom seedlings and suckers by the beneficial fungal root endophytes viz., P. indica and G. fasciculatum just before transplanting to the field and therein advocating better development and establishment in the field condition. Furthermore, the results also indicates an effective management of the destructive Fusarium rot disease in small cardamom using endophyte colonization especially in P. indica colonized and dually colonized plants.