Survey and epidemiological status of alternaria blight of clusterbean in northern Madhya Pradesh

Introduction

Clusterbean [Cyamopsis tetragonoloba (L.) Taub.], commonly known as guar, is an important drought-tolerant leguminous crop cultivated extensively in India. It is valued for its industrial gum, vegetable pods, fodder, green manure, and soil-enriching properties. India is the leading producer and exporter of guar gum in the world. Madhya Pradesh is emerging as an important clusterbean-growing state due to favorable agro-climatic conditions. Despite its economic importance, clusterbean cultivation is adversely affected by several fungal, bacterial, and viral diseases. Among these, Alternaria blight caused by Alternaria cyamopsidis is one of the destructive foliar diseases responsible for considerable reduction in yield and quality. The disease affects leaves, stems, petioles, and pods, resulting in premature defoliation and weakening of plants.

The disease initially appears as small, circular to irregular brown necrotic spots on leaves, which later enlarge and coalesce under favorable environmental conditions. Severe infection causes extensive blighting and drying of foliage. Warm temperature and high humidity favor disease development and spread. Knowledge regarding disease prevalence and distribution is essential for designing effective management practices. Therefore, the present investigation was conducted to assess the incidence and severity of Alternaria blight of clusterbean in major clusterbean-growing districts of Northern Madhya Pradesh during Kharif 2021 and 2022.

Materials and Methods

Survey area

A systematic roving survey was conducted during Kharif seasons of 2021 and 2022 in major clusterbean-growing districts of Northern Madhya Pradesh, namely Gwalior, Morena, and Shivpuri. Different villages and blocks representing major clusterbean cultivation areas were selected for disease assessment.

Method of survey

The survey was conducted at flowering to pod development stages of the crop. In each village, five fields were selected randomly for disease assessment. Observations were recorded on disease incidence and severity.

Disease assessment

Disease intensity was recorded based on visual symptoms observed on aerial plant parts including leaves, stems, petioles, and pods. Percent disease intensity was calculated using standard disease rating procedures. Percent Disease Intensity (PDI) = [Sum of all numerical disease ratings / (Total number of observations × Maximum disease grade)] × 100.

Statistical analysis

The mean disease intensity for districts, blocks, and villages was calculated for both years. Comparative analysis was carried out to determine variations in disease severity across locations and years.

Results

The survey conducted during Kharif 2021 and 2022 revealed that Alternaria blight disease was prevalent in all surveyed districts of Northern Madhya Pradesh. Disease intensity varied considerably among districts, blocks, and villages. Among the surveyed districts, Gwalior recorded the highest disease intensity during both years, followed by Morena, whereas Shivpuri exhibited the lowest disease intensity. The variation in disease severity may be attributed to differences in environmental conditions, crop management practices, varietal susceptibility, and inoculum availability. The results further indicated that disease intensity increased during 2022 compared with 2021. During 2021, mean disease intensity was 17.96%, whereas during 2022 it increased to 19.86%.

District-wise disease intensity

Gwalior recorded the highest incidence of Alternaria blight during both years. The Dabra block of Gwalior district consistently showed maximum disease intensity, and Lohgarh village recorded the highest disease severity. Morena district recorded moderate disease intensity during both years. Disease symptoms were commonly observed in surveyed fields, although severity remained lower than in Gwalior district. Shivpuri district recorded the lowest disease intensity among all surveyed districts. Within Shivpuri district, Karera block showed minimum disease intensity during both years, and Narahi village exhibited the lowest disease severity among all surveyed villages.

Comparison between Kharif 2021 and 2022

The present investigation demonstrated a noticeable increase in disease intensity during Kharif 2022 over Kharif 2021. The average disease intensity increased from 17.96% during 2021 to 19.86% during 2022. This increase in disease severity may be attributed to prevailing climatic conditions such as higher relative humidity, intermittent rainfall, and moderate temperatures that favored pathogen growth and infection.

Discussion

The findings of the present study are in close agreement with earlier reports. Sasode et al. reported maximum Alternaria leaf blight intensity (19.90%) in Gwalior district and stated that the disease significantly affects clusterbean productivity. [4] Tomar conducted a survey in clusterbean-growing regions of Gwalior and Morena districts and reported disease intensity ranging from 8.80 to 28.10%, with symptoms observed on all aerial plant parts. [5] Rangaswami and Rao first reported severe incidence of Alternaria blight on clusterbean during 1953. Subsequently, the disease was also reported from Pakistan and South Africa by Hussaini and Singh and Westhuizen et al., respectively. [1,3,6] Prasad et al. carried out a survey on Alternaria blight of pigeonpea in Eastern Uttar Pradesh and adjoining districts of Bihar during Rabi seasons 2009-10 and 2010-11. They observed maximum disease severity in different districts across the two seasons, indicating the influence of agro-climatic conditions on disease severity. [2] The consistency of the present findings with earlier investigations confirms that Alternaria blight is an economically important disease in pulse and legume crops under favorable environmental conditions.

References

1. Hussaini SS, Singh RA. Occurrence of Alternaria blight of clusterbean. Indian Phytopathology. 1989;42:275-278.
2. Prasad K, Singh RK, Singh AK. Survey and assessment of Alternaria blight of pigeonpea in Eastern Uttar Pradesh and Bihar. Journal of Food Legumes. 2013;26(1-2):87-90.
3. Rangaswami G, Rao AV. Studies on Alternaria blight disease of clusterbean. Madras Agricultural Journal. 1957;44:123-126.
4. Sasode DS, Sharma M, Tomar A. Survey of Alternaria leaf blight of clusterbean in Northern Madhya Pradesh. Journal of Plant Disease Sciences. 2022;17(2):145-149.
5. Tomar A. Studies on Alternaria blight of clusterbean in Gwalior and Morena districts of Madhya Pradesh [MSc thesis]. Gwalior: Rajmata Vijayaraje Scindia Krishi Vishwavidyalaya; 2000.
6. Westhuizen GCA, Human DJ, Venter SL. Alternaria disease of guar in South Africa. Plant Disease Reporter. 1987;71:430-432.