Studies on variability and different factors affecting pathogenicity of Alternaria species causing early blight of tomato and its integrated disease management

Abstract

Roving survey (rabi 2019-20 and 2020-21) conducted at Madhya Pradesh revealed that the disease incidence was highest (58.63%) in Sagar district followed by Jabalpur (41.72%) and Damoh (29.90%). Twenty isolates of Alternaria species exhibited notable cultural variability viz., mycelial colour, growth pattern, centrecolour, surface, margins and zonation of colony and morphological variability viz., mycelial width, conidial size, septation and beak length. Based on the level of similarity, they have been sub divided into different clusters. Pathogenic variability through detached leaf assay method and spray inoculation methods revealed significant differences in virulence among twenty Alternaria isolates out of which Alt 3 was found most virulent. With the increase in disease intensity (DI%) due to pathogen, total chlorophyll and carotenoids content reduced while proteins and phenols increased in host plant. Total leaf area, stomatal density of inoculated host plants was also comparatively less than un inoculated control. Furthermore, Molecular identification of the most virulent test pathogens revealed isolate Alt 3 as A. solani (ON 416546), Alt 2 as A. tenuissima (ON 416543) and Alt 1 (OM 996084), Alt 4 (ON 416545), Alt 5 (ON 416544) as A. alternata based on the nucleotide homology. Among biocontrol agents, T. viridewas the most efficient against the test pathogen by significantly inhibiting mycelial growth.Among fungicides, propiconazole (0.1%) and Azoxystrobin+ Difenoconazole (at 0.15) were highly effective against pathogen. However, T.viride was found highly compatible with Azoxystrobin and Propineb. While least compatible with Hexaconazole and Propiconazole. Among nanoparticles, AgNP at150 ppm performed best in reducing disease severity (in pot culture experiment) as compared to control. Jeevamrit+ neem leaves extract combination (at15%), micronutrients (ZnSo4 and FeSo4) and biopolymer (at150 ppm) showed higher efficacy in retarding growth of pathogen. All the tested micronutrients, nanoparticles and chitosan were found highly compatible with T. viride. Integrated disease management (IDM) strategies conducted during rabi 2020-21 and 2021-22 for the management of early blight resulted in the higher fruit yield and lower disease incidence. Lower disease incidence (PDI-7.20%), with less (AUDPC-239.8) disease progress rate was noticed in treatment combination comprises of soil application with T. viride + P. flourescens + seedling treatment with Azoxystrobin along-with foliar spray of Azoxystrobin + Difenoconazole (T6A plot) followed by T6B plot (soil application with T. viride + P. fluorescens + seedling treatment with Azoxystrobin followed by foliar spray of Jeevamrutha + Azadirachtin (at1.5%) with fruit yield (292.00 q/Ha) and PDI (12.16%), AUDPC (404.5) respectively, compared to other treatment plots. Similar results were obtained at farmers field during validation of the experiment. Hence, these findings underscore the importance of studying disease distribution pattern at different geographical locations at current climate change scenario, morpho-cultural, pathogenic and molecular variability among the associated pathogens with different chemicals used for managing the crop diseases and their judicious use in integrated management practices for combating early blight and ensuring sustainable tomato production in Madhya Pradesh. newline