Reaction of different maize varieties against Curvularia leaf spot disease caused by Curvularia lunata

Introduction

Maize (Zea mays L.) commonly known as corn, is a globally significant cereal crop belonging to the family Poaceae (Gramineae), characterized by a diploid chromosome number of 2n = 20. In India, maize has covered about 12.09 million ha area with the annual production 43.41 MT and productivity of 3590 kg/ha in Kharif, 2024-25. Madhya Pradesh is the largest producer of maize with 6.64 million tonnes production followed by other major maize producing states i.e. Karnataka (6.19 million tonnes), Bihar (5.47 million tonnes), Maharashtra (4.75 million tonnes), Telangana (3.39 million tonnes), West Bengal (2.84 million tonnes), Rajasthan (2.68 million tonnes), Tamil Nadu (2.66 million tonnes), Andhra Pradesh (2.15 million tonnes) and Uttar Pradesh (1.96 million tonnes) (Anonymous, 2024-25a) [1,3] . In Rajasthan, maize grown over an area 949.38 thousand ha and production 2344.47 thousand tonnes with productivity 2469 kg/ha. The major maize growing division in Rajasthan are Udaipur, Banswara, Chittorgarh, Bhilwara, Rajsamand, Jhalawar, Bundi, Kota and Sirohi divisions (Anonymous, 2024-25b) [1,3] . Productivity of maize in India remains low due to both abiotic (drought, cold/frost, low N input, waterlogging) and biotic stress. In which biotic factors is the prevalence of several diseases caused by fungi, bacteria and viruses. Curvularia lunata as a pathogen causing leaf spot of maize was first identified in China by Wakker Boedijn in 1970 (Wang et al., 2022) [10] . Maize is affected by as many as 112 diseases globally, while in India, approximately 35 diseases have been reported. Among these, foliar diseases are major concern and Curvularia leaf spot (CLS) of maize has become increasingly severe across all state of India in recent years, largely due to changing climatic conditions. In last few years, Curvularia leaf spot disease of maize become a major disease in Rajasthan. The estimated yield loss in maize due to Curvularia leaf is 22.29 percent (Garhwal et al. (2022) [6] The pathogen causing Curvularia leaf spot exhibited common symptoms on maize include small, tan-colored lesions measuring about 0.5-2.0 mm long with brown margins that may be surrounded by a yellowish halo. Lesions can be scattered across the leaf or in dense groups and can join together into larger necrotic areas in early stage and then expand to round, oval, spindle shaped (Kumari et al., 2022) [8] Curvularia lunata is soil and seed borne necrotrophic fungus. It is characterized by production of brown geniculate conidiophores with smooth oval type of clavate, septate and curved conidia in host tissue and culture media (Aroca et al., 2018) [4] . Therefore, the identification and screening of resistant maize varieties is a crucial step in any integrated disease management program. Varietal screening involves the evaluation of different genotypes under artificial inoculation conditions to determine their relative resistance or susceptibility to Curvularia leaf spot disease. This process helps plant breeders and pathologists to identify promising lines that can be used directly in cultivation or as donors in breeding programs. Moreover, the knowledge gained from screening can assist in understanding the genetic basis of resistance, facilitating the development of improved cultivars through conventional and molecular breeding approaches. This ensures that newly released varieties retain effective resistance in the field. It also contributes to a sustainable crop protection strategy that minimizes dependence on fungicides and supports eco-friendly agriculture.

Materials and Methods

The experiments were conducted in the Instructional farm of Agronomy, Rajasthan College of Agriculture, Udaipur. Forty maize varieties were screened during Kharif season 2023 and 2024 under field condition for their relative resistance and susceptibility against Curvularia leaf spot pathogen caused by Curvularia lunata under inoculated condition. Seed of each varieties were sown in "paired plot technique" having 3 m length of rows by maintaining row to row and plant to plant distance as 60 and 20 cm respectively, with three replications in RBD design. For inoculation the virulent resident local isolate of C. lunata (CLSRCA) was multiplied on autoclaved sorghum grains. All test entries were spray inoculated with spore suspension of 1×10 6 conidia ml -1 on 25-days-old maize plants with the help of hand held sprayer to the run off level. High humidity (>90 percent) was maintained throughout the disease development period by frequent sprinkler irrigations. Observations for disease severity (disease rating) was recorded two times at 30 and 60 days after inoculations on a 1-9 disease rating scale (Anonymous, 2017) [2] . Based on the percent disease index, the different varieties of maize were categorized into various reaction grades to determine their relative degree of resistance reaction to the disease as mention in Table-1. Percent disease index was calculated using following formula (Wheeler, 1969) [12] .

Percent disease index =

Sum of all individual disease ratings Total No. of plant assessed × Maximum rating × 100

Table 1: Disease rating scale (1-9) for assessing resistance reaction against Curvularia leaf spot of maize, (Anon., 2017) [2] . Very heavy infection, lesions abundant scattered on all most all leaves, plant prematurely dried and killed (> 80%).

Score Percent infection

Results and Discussion

Host plant resistance is an ultimate tool to keep away the diseases. A simple and low cost method to know the source of resistance in varieties is screening under artificial epiphytotic field conditions. The evaluation of 40 different varieties for percent disease index (PDI) revealed significant variation across the two years, 2023 and 2024. Among the tested varieties of maize exhibited considerable variation in their response to percent disease index. [9] who also categorized both varieties as susceptible. The consistency between the present study and earlier reports indicates the stable susceptibility behavior of these genotypes across different environments and experimental conditions. Choudhary et al. (2011) [5] evaluated 35 maize inbred lines against C. lunata and identified five lines viz., EI 460, EI 585, EI 582, EI 586-1 and LM 10 as resistant, six as moderately resistant, 14 as susceptible and remaining ten lines as highly susceptible. Hooda et al. (2012) [7] screened two hundred maize entries of different maturity groups and specialty types for their response to Curvularia leaf spot and found that only 77 entries were resistant. Some of these resistant lines also exhibited multiple-disease resistance, whereas the remaining entries showed reactions ranging from susceptible to highly susceptible to other maize pathogens. Similarly, Wang et al. (2014) [11] evaluated 152 maize inbred lines for their response to Curvularia leaf spot and reported that 97.4% of the lines were either susceptible or highly susceptible. Among these, 85 lines were highly susceptible and 63 were susceptible, while only four lines (Shen 137, Qi 318, 77, and Nan 60-1) showed a moderately resistant reaction.

Conclusion

Based on percent disease index, maize varieties were categorized into the four classes during the observation of Kharif season 2023 and 2024. Forty varieties of maize were screened under artificial inoculation field conditions. Four maize varieties (DMRH 1410, DHM 121, LMH 616 and DKC 7074) was found to be resistant, seventeen varieties to be moderately resistant, eleven varieties to be moderately susceptible, and rest eight found susceptible to the disease.

Acknowledgement

AcknowledgementThe authors are highly grateful to the Dean, Rajasthan College of Agriculture, Udaipur, Head, Department of Plant Pathology for providing necessary facilities.

References

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