Background: Collar rot of groundnut (Arachis hypogaea L.) caused by Aspergillus niger is a significant constraint in groundnut cultivation and responsible for huge economic losses in India including Rajasthan. Methods: By surveying of eight major groundnut growing districts of Rajasthan, India, one representative Aspergillus niger isolate from each district was established (ANBK-01= Bikaner, ANCH-02= Churu, ANDA-03= Dausa, ANJP-04= Jaipur, ANJL-05= Jalore, ANJD-06= Jodhpur, ANNG-07= Nagaur and ANSK-08= Sikar) for studying variability in the pathogen as well as to know the response of groundnut varieties to the highly virulent isolate. The colony and spore characteristics were observed for cultural and morphological variability. For resistance response to the disease, ten varieties (M-13, RG-633-9, RG-382, Girnar-2, RG-604, RG-578, Gajraj 10, RG-510, RG-632-1 and RG-644) were evaluated in the field for two consecutive years against a highly virulent Aspergillus niger (ANJP-04) isolate. Result: Our investigations cleared that all the isolates were showed cultural and morphological variability such as shape, colour and size of colony and size of conidia, conidiophores and columella. Isolate (ANJP-04) collected from Khejroli village of Chomu tehsil in Jaipur district showed maximum mycelial growth, conidia diameter, length and diameter of conidiophores and length and diameter of columella, early sporulation and found most virulent as it produced higher disease incidence (54.43%). Ten released varieties of groundnut in the field conditions, revealed that none of the variety was found completely free from the disease whereas RG-644, M-13 and RG-510 were found resistant while RG-604, Girnar-2, Gajraj-10 and RG-632-1 were found moderately resistant and rest were found susceptible to highly susceptible to the disease. Conclusively, it can be finalized that famers may cultivate these resistant varieties in areas where collar rot is a severe constraint. The conclusion of this study can also be utilized to screen varieties/genotypes of groundnut against highly virulent isolate for sustainability of breeding material to the disease effectively.

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Collar rot disease caused by Aspergillus niger van Teighem is an important seed and soil borne disease of groundnut (Arachis hypogaea L.) which deteriorates kernel quality and reduces yield. The experiments were conducted during kharif 2019 and 2020 at SKN College of Agriculture, Jobner, Jaipur, Rajasthan. To see the interactive effect of seed treatment and drenching, fungicides and bio-agents were applied through seeds [carbendazim (0.1%), carboxin+ thiram (0.25%), hexaconazole (0.2%), carbendazim + mancozeb (0.25%), Trichoderma harzianum (0.6%) and Trichoderma viride (0.6%)] and through drenching [carbendazim (0.1%), carboxin + thiram (0.25%) and carbendazim + mancozeb (0.25%)] at 20 days after sowing (DAS). The effect of six mineral nutrients i.e. Cu (5 kg/ha), K (30 kg/ha), S (25 kg/ha), B (10 kg/ha), Fe (5 kg/ha) and Zn (5 kg/ha) was also evaluated through soil application against the disease. The lowest disease incidence (4.62%) and highest pod yield (25.86 q/ha) were recorded by treating the seeds with hexaconazole (@0.2%) and drenching with carbendazim + mancozeb (@0.25%) at 20 DAS and next best was seed treatment with hexaconazole (0.2%) and drenching with carbendazim (0.1%). Among six mineral nutrients, copper (@5 kg/ha) was most significant in reducing the disease incidence (46.05%) and in increasing pod yield (24.81%) followed by potassium. Conclusively, seed treatment with hexaconazole (@0.2%) and drenching with carbendazim + mancozeb (@0.25%) at 20 days after sowing results in significantly higher disease control with increased pod yield.

Background: Groundnut (Arachis hypogaea L.) is an important legume crop of tropical and sub-tropical areas of the world. This crop suffers from several diseases like early leaf spot, late leaf spot, rust, groundnut bud necrosis, peanut clump and collar rot etc. But collar rot caused by Aspergillus niger van Teighem is one of the most important seed and soil borne diseases causing huge economic (40-50 per cent) loss in India and abroad. Methods: A roving survey was conducted to assess the incidence of collar rot in eight major groundnut growing districts of western Rajasthan i.e. Bikaner, Jodhpur, Churu, Jalore, Jaipur, Sikar, Nagaur and Dausa during Kharif 2018. A field experiment was carried out for two consecutive years (2019 and 2020) to manage the disease through altering micro-climate under canopy with six levels of seed rates (80, 85, 90, 95, 100 and 105 kg/ha). Result: Our investigations cleared that this disease is prevalent in all the 200 fields surveyed in eight districts of Rajasthan with 22.99 per cent overall disease incidence which varied from 17.84 to 32.38 per cent with monetary losses. Maximum disease incidence was recorded in Jaipur (28.85%) district while it was lowest in Nagaur district (20.15%). Higher disease reduction (12.97%) with increased pod yield (27.65%) was observed with higher seed rate of 105 kg/ha as compared to standard recommended seed rate (80 kg/ha) as this pathogen is favoured by higher temperature and low soil moisture, dense canopy provides shade that increases humidity under the cropped area and lowers temperature. As a result of this, plant mortality can be compensated by increasing plant population through seed rate, as it modifies the microclimate and generate an environment which is less favourable for developing collar rot disease of groundnut.