​Antagonistic Activity of Panchagavya and Trichoderma spp. against Wilt Complex causing Pathogens of Chickpea (Cicer arietinum L.)

Background: Chickpea wilt complex caused by several soil-borne pathogens is the major yield-reducing malady worldwide. Biological control is one of the best, low-cost and ecologically sustainable method for managing plant diseases caused by soil-borne pathogens. Methods: In this present investigation Panchagavya and Trichoderma spp. were evaluated by following poisoned food technique and dual culture technique against wilt complex causing pathogens i.e. Fusarium oxysporum f. sp. ciceri, Fusarium solani and Macrophomina phaseolina. Result: Among the different isolates of Trichoderma spp. evaluated, Trichoderma viride (AAU isolate) was highly antagonistic to F. oxysporum f. sp. ciceri (52.78%) and F. solani (65.37%) whereas, Trichoderma asperellum (AAU isolate) was highly antagonistic to M. phaseolina (65.93%). Panchagavya at the highest concentration (50%) showed significantly higher efficacy (80.74, 66.62 and 49.67%) in inhibiting the mycelial growth of all three pathogens and at the lowest concentration it was moderately effective.

Phytostimulation and growth promotion activities of Trichoderma spp. on groundnut (Arachis hypogaea L.) crop

Groundnut (Arachis hypogaea L.) suffers from many soil borne pathogens that deteriorate the quality of the seeds and are responsible for high yield loss. Practically Trichoderma sp. is used for seed treatment, it minimizes the seed and soil borne pathogens and supports plant growth promotion activities. In the present study, five different isolates of Trichoderma spp. were isolated from groundnut (A. hypogaea ) rhizosphere soil. All the five isolates were confirmed by morphological methods and using molecular tools through Polymerase Chain Reaction (PCR) amplification of Internal Transcribed Spacer (ITS) region of Trichoderma sp. and DNA gets amplified in 650 bp to 700 bp. Trichoderma spp. were molecularly identified as T(SP)-20 (Trichoderma longibrachiatum), T(AR)-10 (T. asperellum), T(VT)-3 (T. hamatum), T(BI)-16 (T. longibrachiatum), T(TK)-23 (T. citrinoviride). Phytostimulation activities of all the six isolates viz., phosphate solubilization, Ammonia production, IAA production, and Siderophore production, were evaluated. Among the six isolates, T(SP)-20, T(AR)-10, and TNAU-TA showed higher phytostimulation activities. The growth promotion of Trichoderma spp. on groundnut was assessed through the roll towel method. The isolate T(SP)-20 (T. longibrachiatum) produced the highest germination percentage of 93.33 and vigor index of 2246.2. This work developed a new isolate of T. longibrachiatum (T(SP)-20) which is a native isolate having significant phytostimulation and growth promotion activities and it could be exploited for other soil borne disease managing successfully.

Exploration of Soil and Weather Factors on Mulberry Root Rot Incidence in the Western Zone of Tamil Nadu, India

Aims: To record the occurrence of mulberry root rot disease, epidemiology, interaction of weather and soil parameters with the soil-borne pathogens in Western zone of Tamil Nadu during 2019-2020. Study Design: Survey. Place and Duration of Study: Surveyed in Coimbatore, Tiruppur, Erode, Dharmapuri and Krishnagiri districts of Tamil Nadu. Laboratory experiments were carried out at Department of Sericulture & Department of Plant Pathology, Tamil Nadu Agricultural University (TNAU), Coimbatore between July 2019 and Jan 2021. Methodology: Per cent disease incidence of root rot was recorded in all surveyed gardens. To analyze the soil and weather parameters, the composite soil samples were subjected to textural analysis and weather data were collected from TNAU Agro Climate Research Centre. To predict soil temperature for all surveyed locations, the model regression equations were derived. The correlation analysis was done between per cent disease incidence, weather and soil parameters. Results: The highest disease incidence was recorded in Nallampalli block of Dharmapuri district (54 per cent) whereas the lowest in Udumalaipettai block of Tiruppur district (0.06 per cent). The infected mulberry root samples yielded complex of soil-borne pathogens including Macrophomina phaseolina, Lasiodiplodia theobromae, Fusarium sp., and pathogenicity was proved. The results revealed that root rot incidence was recorded in all types of cultivars, significantly in ruling variety V1 irrespective of its age, soil type, spacing, and irrigation method. Soil parameters like texture, temperature and moisture content were found to augment the disease. Per cent disease incidence had significantly positive correlation with the weather factors like air and soil temperature whereas negative correlation with relative humidity and rainfall. Conclusion: Synergism of abiotic stress factors hinders the mulberry plant health and increases its susceptibility to the soil-borne pathogens.

Efficiency of Reductive Soil Disinfestation Affected by Soil Water Content and Organic Amendment Rate

Reductive Soil Disinfestation (RSD) is a good method which can restore degraded greenhouse soil and effectively inactivate soil-borne pathogens. However, the approach needs to be optimized in order to facilitate its practical application in various regions. In the present work, we investigated the effect of soil water content (60% water holding capacity (WHC), 100% WHC and continuous flooding) and maize straw application rates (0, 5, 10, and 20 g kg−1 soil) on the improvement of soil properties and suppression of soil-borne pathogens (Fusarium oxysporum, Pythium and Phytophthora). The results showed that increasing the soil water content and maize straw application rate accelerated the removal of excess sulfate and nitrate in the soil and elevated the soil pH. Elevating the water content and maize straw application rate also produced much more organic acids, which could strongly inhibit soil-borne pathogens. Soil properties were improved significantly after RSD treatment with a maize straw amendment rate of more than 5 g kg−1, regardless of the water content. However, RSD treatments with 60% WHC could not effectively inactivate soil-borne pathogens and even stimulated their growth by increasing the maize application rate. RSD treatments of both 100% WHC and continuous flooding could inactivate soil-borne pathogens and increase the pathogens mortality indicated by cultural cells relatively effectively. The inhibited pathogens were significantly increased with the increasing maize application rate from 5 g kg−1 to 10 g kg−1, but were not further increased from 10 g kg−1 to 20 g kg−1. A further increased mortality of F. oxysporum, indicated by gene copies, was also observed when the soil water content and maize straw application rate were increased. Therefore, RSD treatment with 60% WHC could improve soil properties significantly, whereas irrigation with 100% WHC or continuous flooding was a necessity for effective soil-borne pathogens suppression. Holding 100% WHC and applicating maize straw at 10 g kg−1 soil were optimum conditions for RSD field operation to restore degraded greenhouse soil.

Trichoderma harzianum-Mediated ZnO Nanoparticles: A Green Tool for Controlling Soil-Borne Pathogens in Cotton

ZnO-based nanomaterials have high antifungal effects, such as inhibition of growth and reproduction of some pathogenic fungi, such as Fusarium sp., Rhizoctonia solani and Macrophomina phaseolina. Therefore, we report the extracellular synthesis of ZnONPs using a potential fungal antagonist (Trichoderma harzianum). ZnONPs were then characterized for their size, shape, charge and composition by visual analysis, UV–visible spectrometry, X-ray diffraction (XRD), Zeta potential, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The TEM test confirmed that the size of the produced ZnONPs was 8–23 nm. The green synthesized ZnONPs were characterized by Fourier transform infrared spectroscopy (FTIR) studies to reveal the functional group attributed to the formation of ZnONPs. For the first time, trichogenic ZnONPs were shown to have fungicidal action against three soil–cotton pathogenic fungi in the laboratory and greenhouse. An antifungal examination was used to evaluate the bioactivity of the mycogenic ZnONPs in addition to two chemical fungicides (Moncut and Maxim XL) against three soil-borne pathogens, including Fusarium sp., Rhizoctonia solani and Macrophomina phaseolina. The findings of this study show a novel fungicidal activity in in vitro assay for complete inhibition of fungal growth of tested plant pathogenic fungi, as well as a considerable reduction in cotton seedling disease symptoms under greenhouse conditions. The formulation of a trichogenic ZnONPs form was found to increase its antifungal effect significantly. Finally, the utilization of biocontrol agents, such as T. harzianum, could be a safe strategy for the synthesis of a medium-scale of ZnONPs and employ it for fungal disease control in cotton.

Role of Benzoic Acid and Lettucenin A in the Defense Response of Lettuce against Soil-Borne Pathogens

Soil-borne pathogens can severely limit plant productivity. Induced defense responses are plant strategies to counteract pathogen-related damage and yield loss. In this study, we hypothesized that benzoic acid and lettucenin A are involved as defense compounds against Rhizoctonia solani and Olpidium virulentus in lettuce. To address this hypothesis, we conducted growth chamber experiments using hydroponics, peat culture substrate and soil culture in pots and minirhizotrons. Benzoic acid was identified as root exudate released from lettuce plants upon pathogen infection, with pre-accumulation of benzoic acid esters in the root tissue. The amounts were sufficient to inhibit hyphal growth of R. solani in vitro (30%), to mitigate growth retardation (51%) and damage of fine roots (130%) in lettuce plants caused by R. solani, but were not able to overcome plant growth suppression induced by Olpidium infection. Additionally, lettucenin A was identified as major phytoalexin, with local accumulation in affected plant tissues upon infection with pathogens or chemical elicitation (CuSO4) and detected in trace amounts in root exudates. The results suggest a two-stage defense mechanism with pathogen-induced benzoic acid exudation initially located in the rhizosphere followed by accumulation of lettucenin A locally restricted to affected root and leaf tissues.

The resistance of peanut to soil-borne pathogens improved by rhizosphere probiotics under calcium treatment

Background Peanut (Arachis hypogaea L.) is an important oil and economic crop. Calcium modulates plants in response to abiotic stresses and improves plant resistance to pathogens. Enrichment of beneficial microorganisms in the rhizosphere is associated with plant disease resistance and soil development. The purpose of this study was to analyze the differences in peanut rhizosphere microbial community structure between the calcium treatment and the control during two growth stages and to explain why calcium application could improve the resistance of peanuts to soil-borne pathogens. Results The 16S rDNA amplicon sequencing of rhizosphere microbiome showed that calcium application significantly enriched Serratia marcescens and other three dominant strains at the seedling stage. At the pod filling stage, ten dominant stains such as Sphingomonas changbaiensis and Novosphingobium panipatense were enriched by calcium. Serratia marcescens aseptic fermentation filtrate was mixed with PDA medium and inoculated with the main soil-borne pathogens in the seedling stage, which could inhibit the growth of Fusarium solani and Aspergillus flavus. The aseptic fermentation filtrate of Novosphingobium panipatense was mixed with PDA medium and inoculated with the main soil-borne pathogens in the pod filling stage, which could inhibit the growth of Sclerotium rolfsii and Leptosphaerulina arachidicola. Conclusions Calcium application increases the resistance of peanuts to soil-borne pathogens by enriching them with specific dominant bacteria.

An In Vitro Study of The Spore Densities Effect of Trichoderma spp. as Biocontrol Agent for Fusarium Wilt in Cayenne Pepper (Capsicum sp.)

Root disease controlling has been a challenge in increasing plant productivity. The soil-borne pathogens become the main concern which mostly infects the root surface. One of the most common soil-borne pathogens is Fusarium oxysporum (Fo). Cayenne pepper (Capsicum sp.) is one of the most abundant commodities and contributes significantly to the economy. This plant is also susceptible to Fusarium wilt infection. The use of endophytic fungi as biocontrol agents is an alternative against soil-borne pathogens, one of which is Trichoderma spp. fungi. This study aims to determine the effectiveness of various spore densities of Trichoderma spp. against the pathogen Fo. The research was conducted through an in vitro study by antagonistic testing between spore suspensions of Trichoderma spp. (103, 105, and 107 spores/mL) with Fo. The results showed the density of 107 spores/mL gave the highest percentage of inhibition (54.59%) compared to spore density of 103 (35.27%) and 105 spores/mL (44.44%). The spore density of 107 spores/mL gave a significant difference in response to the density of other spores according to the BNT test at a significance level of 5% and was able to inhibit the growth of Fo more than 50%. The results of this study are expected to be a reference for the formulation of Trichoderma spp. which is ideal for controlling Fo pathogens in the fields.