Studies on Alternaria blight disease caused by Alternaria solani on brinjal

Introduction

Brinjal (Solanum melongena L.), also known as eggplant, is a premier vegetable crop in India, valued for its year-round availability and high nutritional content. India is the secondlargest producer of brinjal globally (FAO, 2023); yet its average productivity is often compromised by various biotic stresses, with fungal diseases being a major limiting factor. Among these, Alternaria blight, caused by the fungus Alternaria solani, is one of the most destructive diseases (Pandey and Vishwakarma, 1998) [8] . It affects the crop at all growth stages, from the nursery to harvest. The disease is characterized by small, brown spots with concentric rings on the leaves, known as the "target board" appearance. Severe infection leads to premature defoliation and a reduction in photosynthetic activity, which ultimately impacts yield (Dutta et al., 2015) [2] . Furthermore, the pathogen causes fruit rot, characterized by dark, leathery lesions that make the produce unmarketable, leading to significant economic losses for farmers. In Rajasthan, particularly in the Southern humid plain zone like Udaipur, climatic conditions often favor the rapid development of Alternaria species. Continuous monitoring of the disease is essential because environmental changes and local farming practices directly influence its severity. A roving survey is a fundamental tool for identifying disease hotspots and understanding the current status of the pathogen in specific agricultural clusters. This study was undertaken during the 2024-25 season to assess the incidence and severity of Alternaria leaf blight and fruit rot in three major locations: Dabok, Menar, and Kaladwas. The data generated from this survey provides a critical baseline for developing region-specific integrated disease management (IDM) strategies and helping farmers mitigate losses in the Udaipur region.

Survey Sites and Sampling

A roving survey was conducted in three major brinjalgrowing localities of the Udaipur district: Dabok, Menar, and Kaladwas. In each locality, five fields were randomly selected to ensure a representative assessment of the disease status in the region. In each field, ten plants were selected at random for detailed observation of leaf blight and fruit rot.

Assessment of Disease Incidence: Disease incidence was calculated by counting the number of infected plants and fruits out of the total plants and fruits observed. The following formula was used (Mayee and Datar, 1986) [6]: Disease Incidence (%) = 𝑁𝑜.𝑜𝑓 𝑖𝑛𝑓𝑒𝑐𝑡𝑒𝑑 𝑢𝑛𝑖𝑡𝑠 Total no.of units observed × 100

Assessment of Disease Severity (PDI)

To determine the Percent Disease Index (PDI), the severity of leaf blight was recorded based on a visual 0-4 numerical rating scale (Mayee and Datar, 1986) [6] . The per cent disease severity will be calculated according to McKinney (1923)

Assessment of Fruit Rot

Fruit rot incidence was assessed by observing the symptoms such as dark, sunken lesions on the fruits. The percentage of infected fruits per plant was recorded using the incidence formula mentioned in section 2.2

Results and Discussion Field Survey Observations

The survey data revealed a significant variation in disease prevalence across the three localities of Udaipur. The environment in Southern Rajasthan during the cropping season proved conducive for A. solani.

Leaf Blight Incidence and Severity

Among the surveyed localities, Kaladwas emerged as the most affected area, recording the highest leaf blight incidence of 44.32% and a PDI of 16.95%. This was followed by Dabok, which showed an incidence of 31.22% and a PDI of 11.18%. The lowest disease pressure was recorded in Menar (21.55% incidence and 7.53% PDI). The overall mean leaf blight incidence for the surveyed region was 32.36%, with a mean PDI of 11.89%.The higher severity in Kaladwas could be attributed to higher humidity, continuous cropping of solanaceous crops, and the use of susceptible local varieties. These results align with the findings of Abhishek et al. (2024) [1] , who reported similar disease patterns in Southern Rajasthan. Further supporting this study, Raina et al. (2018) [9] observed that the variation in Alternaria blight severity across different locations is primarily governed by the micro-climatic conditions and the amount of primary inoculum present in the soil. Similarly, the high incidence of fruit rot recorded in our study (up to 27.07%) is in close agreement with the findings of Jakatimath (2016) [5] , who reported that fruit infection is a direct consequence of severe foliar blight, as conidia are easily dispersed to the fruits. Furthermore, Sharma et al. (2023) [10] highlighted that intensive cultivation of brinjal without proper crop rotation leads to a significant build-up of Alternaria solani, supporting our observations in the Kaladwas region. The strong correlation between leaf blight and fruit rot incidence indicates that early foliar protection is essential to prevent subsequent fruit damage.

Fruit Rot Incidence

The fruit rot incidence followed a similar pattern as foliar infection. Kaladwas recorded the maximum fruit rot (27.07%), followed by Dabok (17.02%) and Menar (11.72%). The mean fruit rot incidence was 18.60%. The study confirms a positive correlation between leaf blight severity and subsequent fruit rot development.

Conclusion

The roving survey clearly demonstrates that Alternaria blight (leaf blight and fruit rot) is widely prevalent in Udaipur, Rajasthan. The high PDI and fruit rot incidence in areas like Kaladwas indicate a serious threat to the livelihood of brinjal growers. This data provides a crucial baseline for the development of integrated disease management (IDM) strategies, emphasizing the need for timely fungicidal applications and resistant varieties.

References

1. Abhishek A, Jain AK, Meena RS. Survey and surveillance of major diseases of brinjal in Southern Rajasthan. Journal of Plant Disease Sciences. 2024;19(1):45-50.
2. Dutta S, Kuiri S, Das S. Status of Alternaria blight of brinjal in West Bengal and its management. International Journal of Vegetable Science. 2015;21(4):375-381.
3. Food and Agriculture Organization of the United Nations. World vegetable production statistics. Rome: FAO; 2023. Available from: FAOSTAT
4. Gopalan C, Rama Sastri BV, Balasubramanian SC. Nutritive value of Indian foods. Hyderabad: National Institute of Nutrition, ICAR; 2007.
5. Jakatimath S. Studies on fruit rot of brinjal caused by Alternaria solani [master's thesis]. Dharwad (Karnataka): University of Agricultural Sciences; 2016.
6. Mayee CD, Datar VV. Phytopathometry. Technical Bulletin-1. Parbhani: Marathwada Agricultural University; 1986. p. 95.
7. McKinney HH. Influence of soil temperature and moisture on infection of wheat plant by Helminthosporium sativum. Journal of Agricultural Research. 1923;26:195-218.
8. Pandey KK, Vishwakarma SN. Survey of diseases of brinjal in Eastern Uttar Pradesh. Indian Phytopathology. 1998;51(3):286-288.
9. Raina A, Khan MA, Bhat NA. Status and distribution of Alternaria leaf blight of brinjal in Kashmir valley. Journal of Pharmacognosy and Phytochemistry. 2018;7(5):2341-2345.
10. Sharma R, Gupta S, Patel M. Impact of continuous cropping on Alternaria blight incidence in Solanaceous crops. Indian Journal of Agricultural Sciences. 2023;93(2):112-118.