Screening of mustard germplasms against Alternaria blight (Alternaria brassicae & A. brassicicola) in the Terai zone of West Bengal

Introduction

Mustard [Brasica juncea (L.) Czern & Coss] belonging to the family Brassicaceae (syn Cruciferae) is one of the major rabi oilseed crop in India (Verma et al., 2025) [23] . It occupies first position in oilseed crops after groundnuts and contributes 33.24% of the total oilseed production (Anonymous, 2024) [5] . India is one of the leading countries with respect to production, consumption and import in vegetable oils The crop accounted for 25 percent total area and 1/3 of total oil production. India ranked third after Canada and China in area and production (Shekhawat et al., 2012; Saharan et al., 2016) [18,16] . In India area, production and productivity of mustard were 6.21 million hectares, 7.32 million tonnes and 1180kg/ha, respectively (Anonymous, 2014) [3] while those for the oilseeds in the country were 262.06 lakh hectares, 32.10 million tonnes, and 1225 kg/ha, respectively during 2016-17 (Anonymous, 2017-18) [4] . Rapeseed-mustard occupied an area of 9.18 million hectares with a production of 13.26 million tonnes and a mean productivity of 1444 kg/ha in the year 2023-24 (ICAR-DRMR, 2024). The estimated area, production and productivity of the crop in India during 2021-2022 were 9.168 million ha, 11.75 MT and 1178 kgha -1 , respectively (Ministry of Agriculture and Farmers Welfare, GoI (2022) [15] . The Area, production and productivity of mustard in India during 2021-22 was 9.168 million ha, 11.75 MT and 1178 kg/ha, respectively (Ministry of Agriculture and Farmers Welfare, GoI, 2022) [15] . The crop contributes nearly 30% of the total oilseed acreage and over 33% of the total oilseed production in the country. Rapeseed-Mustard crops in India are grown in diverse climatic conditions ranging from north-eastern/north-western hills to down south. The major mustard growing states in India are Uttar Pradesh, Punjab, Rajasthan, Madhya Pradesh, Bihar, Orissa, West Bengal and Assam.

Alternaria brassicae and A. brassicola causing Alternaria blight of mustard resulted yield losses (15%-71%) and reduction in oil content (14.6%-36%), respectively (Meena et al., 2016) [13] . More than 30 diseases have been reported on Brassica in India among which Alternaria blight caused by Alternaria brassicae (Berk.) Sacc. is one of the most common and destructive diseases of mustard inflicting up to 30-40% yield loss. The estimated yield loss due to Alternaria blight in India ranged from 10-70% (Kumar, 1997) [11] . Yield losses due to this Alternaria blight under favourable environmental condition ranges from 10 to 70% (Singh et al., 2020) [21,22] . The yield losses were reported to the tune of 17-34% (Yadav and Gupta, 2011) [24] . The diseases are found regularly in moderate to severe form. The susceptibility of crop plants including Indian mustard to various biotic, abiotic stresses, nutritional quality and low genetic diversity are the major limiting factors for its improvement (Srivastava et al., 2023) [19] Management of diseases of mustard depends largely on chemical fungicides. These chemical fungicides are effective against the diseases of mustard but their excessive use caused environmental pollution, new resistant strain development of pathogen, and human health hazard. The indiscriminate use of agrochemicals including chemical fertilizers and pesticides resulted environmental pollution (Hermosa et al., 2012) [7] . The environmental hazard caused by the chemicals changed human attitude towards the utilization of chemicals including fertilizers and pesticides for farming (Meena et al., 2015) [12] .

Materials and Methods

The experiment was conducted during Rabi 2020-21 and Rabi-2021-22 at Instructional Farm of Uttar Banga Krishi Vishwavidyalaya (UBKV), Pundibari, Cooch Behar. The experiment was laid out in Randomised Block Design (RBD) using the seventy-one (71) germplasms (treatments) with three replication including control check (B-9) collected from the Department of Genetics & Plant Breeding, UBKV. Seeds of each genotype were sown in the plot of size measuring 2 m x 2m and maintained spacing of 30 cm. (row to row) X 15 cm. (plant to plant) following scientific package and practices. Visual estimation of these two diseases on all the 71germplasm including check (B-9) was performed using10 randomly selected and tagged plants from each germplasm for occurrence of disease symptoms and recording disease severity data at 7-days interval during the vegetative as well as true leaf stage, i.e., 45 days after sowing (DAS) under natural field conditions. 0-9 disease rating scale for calculating severity of Alternaria blight was used as stated in Table 1. (0-9 scale of AICRP on Rapeseed & Mustard, 2011) [2] . The percent Disease Index (PDI) was calculated using the following formula.

Percent Disease Index (PDI) = Sum of total numerical rating/Total no. of observation X 100/Max. grade

Results and Discussions

During rabi 2019-20 and rabi 2020-21, screening of 71 germplasm of mustard including check (B-9) was carried out against Alternaria leaf blight. Two years mean data of PDI of Alternaria blight of mustard was pooled to get pooled mean data. The pooled mean data exhibited that out of the 72 germplasm, none of the germplasms found immune (I) or highly resistant (HR) (Table 2; Table 3). Same results were found with study conducted by Yadav et al. (2014) [24] exhibited no immune or highly resistant response among the all 31 germplasms against the disease. In present study, out of seventy one (71) , ten ( against the disease (Table 2; Table 3). The result is in accordance with previous findings in mustard (Ali et al., 2016) [1] . The symptom of the disease first found on the lower leaves during November December and reached at its peak towards the upper leaves. The reaction of different germplasms of mustard against the disease varied significantly. The severity of the disease is extremely influenced by the environmental factors. Out of the 71, ten (10) germplasms found resistant to the disease which agreed the findings of Chakrabarty et al. (2018) [6] , Singh et al. (2018) [20] , Singh et al. (2020) [21,22] and Muhammad et al. (2022) [14] . Host resistance is most important aspect of integrated disease management. It was found that resistance of plant against the disease is mediated by several factors including leaf enzymes such as polyphenol oxidase, peroxidase, and catalase involved in phenolic pathway; high content of sugar in leaf, and presence of wax material on the leaf surface preventing germination of conidia and germ tube as wax act as hydrophobic coating against adhesion of water-borne inoculum (Meena et al. 2016) [13] . Therefore, it is very important to give emphasis on these parameters in order to get resistant genotype of mustard against Alternaria blight. Hence, it is necessary to have donor parents with high degree of resistance against Alternaria blight and white rust.

Future Scope

To achieve the goal, it is necessary to conduct controlled laboratory tests on large number of mustard genotypes for the disease. It is also necessary to confirm resistance in glasshouse under controlled artificial inoculation and employ disease resistant gene-linked molecular markers followed by testing under field conditions because often disease escaped and plant exhibited resistant reactions. In order to supress resistance in the disease resistance host, pathogen require more virulent genes. Therefore, more resistance gene of the host will prevent the evolution of new races of the pathogen.

References

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