Introduction

Groundnut (Arachis hypogea L.) also known as peanut, earth nut, wonder nut, monkey nut, goobers, is an annual leguminous plant. It is called as king of oil seed. Today groundnut is widely distributed and is cultivated in more than eighty countries in tropical and sub-tropical regions of the world [9]. It belongs to the family of Fabaceae, subfamily Papilionaceae and contains a valuable source of all nutrients. India is the second largest producer of groundnut after China. China ranks first in groundnut production with 17.57 million tonnes, followed by India 6.73 million tonnes.  In India, groundnut was sown in an area of 6014.95 thousand hectares with a production of 10244.08 thousand tonnes and a productivity of 0.1703 tonnes ha^-1. In Telangana State, during the year 2020-21, groundnut was cultivated in an area of 127.0 thousand hectares with a production of 290.26 thousand tonnes and a productivity of 0.2286 tonnes ha^-1 [2].  In Telangana state, the major groundnut growing regions in the state are Khammam, Wanaparthy, Mahabubnagar, Gadwal, Mahabubabad, Vikarabad, Suryapet, and Nalgonda. In India among the soilborne fungal diseases of groundnut, stem rot is caused by Sclerotium. rolfsii is a potential threat to production and is of considerable economic significance for groundnut grown under irrigated conditions. Stem rot is an important disease, causing significant yield losses in several groundnut growing countries [5]. The pathogen attacks the host plant at all stages when conditions are favorable [6]. S. rolfsii the incitant of groundnut stem rot is a soil inhabitant, polyphagous, facultative parasite. The pathogen has a wide host range of over 500 plant species in 100 families, throughout the world [4]. This fungus survives in the soil for many years by producing sclerotial bodies and causing the disease either in the form of stem rot or foot rot or root rot or collar rot in addition to leaf blight on several of its hosts [8]. The symptoms of stem rot produced by S. rolfsii on groundnut plants under field conditions were characterized by the formation of a deep brown lesion on the stem region of the plant just near the ground followed by yellowing of groundnut leaves and than by loss of vigor and premature death. The fungus infects the stem preferentially by forming a whitish mycelial mat, but it can also infect any part of the plant including leaf, pod, and root. The infected plant showed poor root growth and rotting of the stem region. Death of the plant occurred more rapidly under dry conditions during which necrosis instead of browning appeared. On young pods light brown lesions were noticed mycelium and sclerotia developed on even inside the pods. Kernels were infected in the advanced stage of plant growth, such kernels were small and shriveled in size [11].

In order to increase self-sufficiency in groundnut production, the area is being increased to yield good productivity and the disease is being reduced by taking up plant protection measures. Since, in Telangana there is no systematic study taken on stem rot disease and their control measures. The survey would ultimately help indicate the areas with high disease incidence which can be managed timely to avoid any disease epidemic.

Material and methods

A comprehensive roving survey was conducted from October to December 2022. The collection of isolates was taken up in the groundnut growing areas of erstwhile Khammam district of Telangana. The collection was done during the months of October to December 2022. A total of 15 isolates were collected randomly from the groundnut cultivars grown in the groundnut growing areas. The external signs and symptoms such as the presence of white mycelial growth, sclerotia, lesion on the stem, wilting, drying or dead plants were used to determine the incidence of the stem rot disease in the fields surveyed. Five plots measuring 1 m x 1 m were selected such that one plot was in the center of the field and the rest were randomly placed on the four corners leaving 1 m from the border. A total number of plants and a number of stem rot infected plants were counted in each plot and per cent disease incidence was calculated by the following formula:

Per cent Disease Incidence (PDI) = Number of plants infected by a particular disease ×100

                                                                     Total number of plants observed

STATISTICAL ANALYSIS

 The statistical analysis was done by using the collected data on the per cent disease incidence. Scoring was given based on common variables and characters. Principal Component Analysis of recorded survey data was done using SPSS software [3]. Survey data of erstwhile Khammam district was clustered into the accurate selection of the most varied individuals based on Hierarchial analysis by using unweighted pair group method arithmetic mean (UPGMA) analysis of NTSYS –PC Software [10].

Fig.1. QGIS Map showing groundnut stem rot disease incidence observed from major groundnut growing areas of erstwhile Khammam district during a roving survey conducted in the year 2022 – 2023.

Fig. 2a. Infected stems showing whitish mycelial growth, brown lesions

Fig. 2. Symptoms of groundnut stem rot disease observed under field conditions during the roving survey conducted in the year 2022-2023.

Fig.3. Pure cultures of different isolates of S. rolfsii collected during survey conducted in erstwhile Khammam district during 2022-2023

RESULTS AND DISCUSSION:

Survey on the incidence of stem rot groundnut growing areas of erstwhile Khammam District

            A roving survey was conducted during October to December 2022 in major groundnut growing areas of erstwhile Khammam district viz., Khammam and Bhadradri kothagudem areas of Telangana to know the occurrence of groundnut stem rot disease caused by S. rolfsii. A total of fifteen fields were covered in eleven villages of Khammam and Bhadradri kothagudem areas during the survey. The information on latitude, longitude, variety/ hybrid, soil type, previous crop, type of irrigation and per cent Disease Incidence in these areas were collected. Based on the number of plants infected and a total number of plants, per cent Disease Incidence was calculated and the details are given in Table.1

Khammam: nine villages from five mandals of Khammam area viz., Dhammapeta Sathupalli, Kusumanchi, Thirmulayapalem and Chintakani respectively. Dhammapet village of Dhammapeta, Bethupally village of sathupalli was surveyed in the month of November -2022. Groundnut crop was grown in both sandy soils and red soils in these villages. In these villages they followed mostly sprinklers for irrigating groundnut fields. TAG24 is the major hybrid grown in these villages. A total of three isolates were obtained, one isolate (SR1) from Dhammapet village, where the least per cent disease incidence was observed (7.01) and two isolates (SR6, SR5) from Bethupally with per cent disease incidence of (23.53 and17.01, respectively).

Seven villages from three mandals viz., Keshavapuram and Agraharam villages of Kusumanchi mandal, Beerolu and Medidapalli villages of Thirmulayapalem mandal, Thimminenipalem, Chinna mandava, Thirlapuram villages of Chintakani mandal, were surveyed during December -2022. Groundnut crop was grown in both sandy soils and red soils in these villages. In these villages both sprinkler and flooding type of irrigation.  K6 is the major hybrid grown in these villages. Disease samples were collected during the vegetative stage, flowering stage and pod formation stages of the crop. The highest per cent disease incidence was observed in Thimminenipalem village (52.00), followed by Chinna mandava village (46.00) and Thirlapuram(32.34) of chintakani mandal, Medidapalli village(44.1) and Beerolu(36.00) of Thirmulayapalem, Keshvapuram village(45.00) and Agraharam village(42.02) of Kusumanchi mandal.

Bhadradri kothagudem: two villages from Aswaraopet mandal viz., Naramvarigudem and Achuthapuramof Bhadradri kothagudem area, were surveyed during the month of November -2022. Groundnut crop was grown in red soil in these villages. The survey was done during pod formation stage of the crop. TAG24 is the major hybrid grown in these villages. Sprinkler type of irrigation was observed in these villages. Per cent disease incidence in Achuthapuram village (33.00), Naramvarigudem village (28.00) of Aswaraopet mandal was observed. Similar findings reported by [7] that the stem rot incidence ranged from 7.4 to 10 per cent in major groundnut growing areas of Andhra Pradesh and Telangana. shivakumar et al. (2016) conducted a survey to assess the occurrence of stem rot in major growing areas of Tamil Nadu. The survey’s findings showed that the incidence of stem rot ranged from 7.88 to 32.02 %. The Cuddalore district’s Adhivaraganallur village recorded the highest incidence at 32.33 %. [1] reported that stem rot incidence ranged between 6.0 to 22.7 per cent in regions of Kadapa and Chittoor districts of Andhra Pradesh.

Comparison of per cent Disease Incidence of 15 different isolates of Sclerotium rolfsii  pathogen collected from different groundnut growing areas of erstwhile Khammam district

Fig.4. Graph representing the comparison of per cent Disease Incidence of 15 different isolates of S. rolfsii pathogen collected from different groundnut growing areas of erstwhile Khammam district.

Table.1 Details of survey on incidence of Sclerotium rolfsii in groundnut growing areas of erstwhile Khammam District  Among the 15 isolates, the highest per cent disease incidence was recorded in SR12 (52.00), SR 13 (46.00), SR7 (45.00), SR11 (44.10), SR8 (42.02), SR15, (41.00), SR9 (36.00), SR3 (33.00), SR14 (32.34), SR4 (32.30), SR2 (28.00), SR10 (28.00), SR6 (23.53), SR5 (17.01) and  SR1 (7.10) in the decreasing order of per cent disease incidence, respectively.

Principal Component Analysis of Sclerotium rolfsii population of different survey variables

The data collected during the survey was scored based on common variables and characters. Further, Principal Component Analysis of recorded survey data was done using SPSS software and the results are shown in Table 2.

Table.2. Principal Component Analysis of Sclerotium rolfsii population of different  survey variables

Fig.5 Screen plot for survey data of erstwhile Khammam district by using Principal Component Analysis.

According to Principal Component Analysis, Eigen value≥ 1 i.e., mandal and Village components was considered for the existence of variability among 15 different isolates of S. rolfsii pathogen. The results from the Principal Component Analysis of recorded survey data was shown in the form of Eigen values, which shows that the highest Eigen value recorded at mandal level indicating greater variability with regard to geographical location.

Dendrogram of 15 isolates of Sclerotium rolfsii generated by unweighted pair group method arithmetic mean (UPGMA) analysis of survey data of erstwhile Khammam district.

 The data collected during the survey data in erstwhile Khammam district was clustered into the accurate selection of the most varied individuals based on Hierarchial analysis by using unweighted pair group method arithmetic mean (UPGMA) analysis of NTSYS –PC Software and a dendrogram was prepared and the phylogenic classification revealed existence of diverse isolates within the same species. Scores derived from the survey profile showed 77.7% similarity within the isolates of S.rolfsii. Based on UPGMA clustering, 195isolates were grouped into 6 clusters.

Fig.6. Dendrogram of 15 isolates of S.rolfsii generated by unweighted pair group method arithmetic mean (UPGMA) analysis of survey data of erstwhile Khammam district.

Among the 6 clusters, cluster-1 consist of 1 isolate i.e., SR1 collected from Dhammapet village of Dhammapeta mandal, Khammam area, having 7.01 per cent disease incidence.

 Cluster-2 consists of three isolates collected from two villages viz., Naramvarigudem, Achuthapuram of Aswaroapet mandal, Bhadradri Kothagudem area comprises of isolate SR2, SR3 and SR4 which in turn categorized into two subgroups. Frist subgroup consist of isolate SR2 collected from Naramvarigudem village having per cent disease incidence of 28.00 and the second sub-group constitutes two isolates SR3 and SR4 from Achuthapuram village having per cent disease incidence of 33.00 and 32.30 respectively.

Cluster -3 consists of SR5 and SR6 isolates collected from Bethupally village of Sathupalli mandal, Khammam area having per cent disease incidence of 17.01 and 23.53 respectively. Cluster-4 consists of SR9 and SR10 collected from Beerolu village of Thirumalayapalem mandal, Khammam area having per cent disease incidence of  36.00 and 28.00 respectively. Cluster-5 constitute three isolates which were further categorized into two subgroups. Isolate SR7 and SR8 were collected from Keshavapuram and Agraharam villages of Kusumanchi mandal having per cent disease incidence of 45.00 and 42.02 respectively. SR11 was collected from Medidapally village of Thirumalayapalem mandal which reported a per cent disease incidence of 44.10.

            Cluster-6 consists of 4 isolates which were further categorized into 3 subgroups. The first sub-group constitutes SR12 and SR13 collected from Thimminenipalem village of Chintakani mandal of Khammam area having per cent disease incidence of 52.00 and 46.00 respectively. The second sub-group consists of isolate SR14 collected from Chinna mandava village of Chintakani having per cent disease incidence of 32.34. The third sub-group constitutes of isolate SR15 collected from Thirlapuram of Chintakani mandal having  a per cent disease incidence of 41.00.

CONCLUSION:

            The present findings from the survey conducted and collection of 15 isolates done during the months of October- December 2022 in the groundnut growing areas of erstwhile Khammam district viz., Khammam and Bhadradri kothagudem of Telangana grown in this areas respectively to record the disease incidence of stem rot in groundnut revealed the variations in per cent disease incidence in major groundnut growing areas of erstwhile Khammam district. Of all the locations, The highest per cent disease incidence was recorded in Thimminenipalem village of  Chintakani mandal of Khammam district (52.0) and the lowest per cent disease incidence was observed in dhammapet village of dhammapeta mandal (7.1%). The results also shown that among the 15 isolates collected from the groundnut cultivars grown in the mentioned groundnut growing areas shown variations in the per cent disease incidence in the decreasing order of isolate SR12 (52.00), followed by isolates SR 13 (46.00), SR7 (45.00), SR11 (44.10), SR8 (42.02), SR15, (41.00), SR9 (36.00), SR3 (33.00), SR14 (32.34), SR4 (32.30), SR2 (28.00), SR10 (28.00), SR6 (23.53), SR5 (17.01) and  SR1 (7.10) respectively. The data generated will help in the identification and application of suitable control methods based on the per cent disease incidence recorded in different cultivars and different locations.

Acknowledgement

I sincerely thank the Department of Pathology, College of Agriculture, Rajendranagar, Hyderabad, Telangana, India, Krishi Vigyan Kendra, Wyra, Khammam, Telangana, India, Department of Biotechnology, College of Agriculture, Rajendranagar, Hyderabad, Telangana, India, Central instrumentation Cell, College of Agriculture, Rajendranagar, Hyderabad, Telangana, India for their constant help in my research work. I felt elated to express my bountiful thanks to those who directly or indirectly helped me in the successful completion of the work The authors are incredibly thankful to the editor and assistant editor for finding interest in the present study. Furthermore, we also thank the anonymous reviewers for their constructive ideas to strengthen the current research work are appreciated as well.

Conflict of interest

The authors declare that they have no conflict of interest

Ethical approval

This article does not contain any studies with human participants or animals performed by any of the authors.

Funding

The author (s) received financial support from the institutional research grant of Professor Jayashankar Telangana state agricultural University and the Government of Telangana for financial help and for providing research facilities which can’t be forgettable.

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