Insights of gummy stem blight disease in Karnataka

Introduction

Watermelon [Citrullus lanatus (Thumb)] is one of the important Cucurbitaceous crops belonging to the family Cucurbitaceae grown in different parts of the world. The crop originated from Southern Africa and has been cultivated since ancient times (Wein, 1997) [21] . In India, watermelon is cultivated in an area of 101 thousand hectares with a production of 24.80 lakh tons The major watermelon-growing states of India are Punjab, Haryana, Karnataka, Assam, Madhya Pradesh Andhra Pradesh, Haryana, Maharashtra, Telangana, West Bengal, Odisha, Himachal Pradesh, Uttar Pradesh and Tamil Nadu (Anonymous, 2017) [2] . Cultivation of watermelon and other species of the family Cucurbitaceae is severely affected by several fungal diseases. Among the diseases, gummy stem blight caused by Didymella bryoniae is an emerging and devastating disease in the cultivation of watermelon. This pathogen is assumed to be present in most parts of the world where hot and humid weather is prevailing. The maximum incidence of the disease was found in Central and South America, the Caribbean, Asia, Africa, Europe and Oceania (CABI, 2015) [6] . In Tunisia, the first report of GSB was on grafted watermelon (Boughalleb et al., 2007) [5] . In Turkey, D. bryoniae was first reported in cucumber (C. sativus) plants in the greenhouses across various districts of the Elazıg province by Mutlu et al. (2015) [16] with a prevalence rate and disease severity of 10.79 percent and 20.02 percent, respectively. Stagonosporopsis cucurbitacearum (Fr.) Aveskamp, Gruyter & Verkley, has been suggested as the anamorph of this pathogen (Aveskamp et al., 2010) [3] . The disease caused complete wilting of plants with an estimated yield loss of up to 100 percent (Bala and Hosein, 1986) [4] in Trinidad. Sudisha et al. (2004) [20] first reported gummy stem blight on muskmelon in India, with 41.00 percent disease incidence. The first report of gummy stem blight by S. cucurbitacearum on watermelon in India was reported by Mahapatra et al., 2020 [14] . Gummy stem blight is one of the most common foliar diseases on watermelon, muskmelon, honeydew and other melons in the southeastern United States caused by Didymella bryoniae anamorph (Phoma cucurbitacearum). The pathogen can affect the host at any stage of growth in its development and affects all parts. Gummy stem blight appears in three distinct phases: leaf spots, crown cankers and fruit rots. The common name "blight" indicates the disease often affects the entire plant. However, gummy stem blight starts as distinct dark spots. Symptoms generally consist of circular dark tan lesions that leads to, water-soaked leaves, stem cankers and gummy brown ooze that exudes from cankers, giving it the name gummy stem blight.

Gummy stem blight reduces yields of edible cucurbits by devastating the vines, leaves and rotting the fruits in the later stages. Gummy stem blight is caused by three species of the fungus Stagonosporopsis citrulli is by far, the most common species on watermelon and melons in the southeastern United States. The second, less common species is Stagonosporopsis caricae. The third species, Stagonosporopsis cucurbitacearum, is more common in the northeastern and mid-Western United States than in the Southeast. Gummy stem blight is one of the main reasons for the yield loss of watermelon cultivation in India. Most of the varieties of watermelon are susceptible to gummy stem blight. Therefore, it is necessary to identify the pathogen, disease severity, pattern and survey has to be conducted. In this present study a survey of gummy stem blight disease on watermelon on major watermelon districts of Karnataka has carried-out.

Materials and Methods

Field survey and collection of samples

In 2022-2023, a roving field survey was conducted in a few watermelon-growing regions of Karnataka. The districts of Karnataka were covered were Chamarajanagaraa, Chikkaballapura, Koppal, Kolar, Tumkuru and Yadgiri.

During the survey, the information on different aspects such as date of survey, farmer's name, village, taluk, district, soil type, age of the crop, name of the cultivar, previous crop, plant protection measures followed, other pest and diseases noticed, symptoms, Global Positioning System (GPS) coordinates, disease incidence was recorded. Using the McKinney formula (1923) [15] , the percent disease index (PDI) was computed using data on the disease scores of individual seedlings.

Sum of all numerical rating PDI = × 100 Number of observations × Maximum disease rating scale During the field survey, fields were selected randomly and inspected for percent disease index, a (0-9) disease scale was used. Plants were diagnosed based on typical symptoms like lesions on the stem, petiole, necrotic spots on the leaves, gummy ooze on fruits and finally rotting of stem and death of plants. The collar regions, leaves and fruits of infected plants were assessed for lesions, necrotic spots and gummy ooze. Samples were collected, labelled and further work was carried out in the laboratory.

The disease scale given by Gusmini et al., 2002 [8] was used for the scoring.

Isolation, purification and maintenance of the pathogen Tissue isolation method

A standard tissue isolation approach was used for the isolation of Stagnosporopsis cucurbitacearum from diseased plant samples having typical symptoms of lesions, necrotic spots and gummy ooze. The samples were sliced into bits of 0.5 to 1.0 cm. The tissue bits were initially surface sterilized with one percent sodium hypochlorite (NaOCl) for one minute and washed with sterile distilled water successively 3 times (30 seconds each time). The pieces were then dried with sterile tissue paper before being put on casted PDA media sterile Petri plate. The plates were then incubated at 26±1 °C until the growth started. The standard hyphal tip method was used to purify the cultures. The purified culture was then maintained on potato dextrose agar slants and refrigerated at 4 °C for later use.

Results and Discussion

A roving survey was carried out in the major watermelon growing districts of Karnataka during 2022-23 to assess the percent disease index in different locations Fig. Field view of watermelon fields visited during survey are depicted in (Plate 1). The percent disease index noticed in 1. Water-soaked necrotic spots on leaves 2. Lesions on stems and petiole 3. Gummy ooze on fruits 4. Death of the plant all the locations surveyed ranged from 28.88 to 46.66 percent and the data is presented in Table 1. Among the surveyed districts maximum mean percent disease index was observed in Chikkaballapura district (46.66) whereas, the least percent disease index was recorded in Tumkuru district (28.88). Among the eight taluks surveyed, the maximum percent disease index was noticed in Chinthamani taluk (46.66) of Chikkaballapura district followed by Yadgiri taluk (42.21) of Yadgiri district. Among the villages surveyed, the percent disease index was found highest in Devapalli village (62.22) of Chinthamani taluk of Chikkaballapura district followed by Homma village of Chamarajanagara taluk of Chamarajanagara district while, it was found lowest in Mantya village (28.88 percent) of Tumkuru taluk of Tumkuru district. In many countries, especially those where watermelon is cultivated on a large scale for commercial purposes, one of the main obstacles to the successful production of the crop is the gummy stem blight caused by S. cucurbitacearum. India is among the countries in the world where the disease is most prevalent. The gummy stem blight pathogen has a severe effect on watermelon and the disease's incidence is rising more quickly every day. Gummy stem blight has been detected in all watermelon-growing states in India, with varying degrees of severity. Global cucurbit production is impacted by GSB, which has a major effect on both profit and food security.

Fruit quality and yield can both be decreased by GSB (Keinath, 2000) [10] . GSB accounts for 17 percent to 43 percent of losses (Keinath, 2001; Keinath & Duthie, 1998) [11, 9] . The present results are similar to the results of Jabouri and Hussaini (2020) [23] who conducted survey in the fields of Salah Al-Din, Kut, Diwaniya and Sulaimaniyah provinces of Iraq in 2019. Maximum disease infection of 84 percent was reported in the Diwaniya province and the lowest disease infection of 52 percent was observed in the Salahaddin province. Maximum infection of 89 percent was recorded in the Sumer area of Diwaniya province and the lowest in Ishaqi area of Salahaddin province. In the present study, the percent disease index varied from district to district and higher incidence was observed in Chikkaballapura and Yadgiri districts. This might be due to the type of cropping pattern that farmers have been practicing, environmental conditions prevailing and hence, the buildup of the pathogen inoculum and even due to monocropping of susceptible hybrids Melody and Max that aggravates the disease occurrence. Seed-borne nature of the pathogen also makes it difficult for early detection of the disease. Apart from this, a lack of knowledge regarding the prophylactic management practices also made it difficult to manage the disease and even due to the use of local planting materials which are neither certified nor completely ensured that are from disease-free fields. [7,19,12] .

Collection and isolation of the pathogen

Isolates of the GSB pathogen were collected and isolated by tissue isolation method as in material and methods. [13,22,17,18] .

Conclusion

GSB-affected watermelon plants produced typical symptoms of necrotic spots on leaves and water-soaked lesions on stems and petioles. In severe cases, gummy ooze was seen on the collar region and rotting of fruits was seen.

The causal organism of the GSB is Stganosporopsis cucurbitacearum and it is a potential threat to watermelon production in Karnataka. The survey for gummy stem blight disease in major watermelon growing districts helps to pin down the real status of the disease.

References

1. Al-Jubouri F, Hussain HZ. The first recording of gummy stem blight disease caused by Didymella bryoniae (Stagonosporopsis cucurbitacearum) on watermelon crop in Iraq. Annals of Tropical Medicine and Public Health. 2020;23:231-619.
2. Anonymous. Crop wise area and production of horticultural crops in India; 2017. Available: https://www.nhb.gov.in.
3. Aveskamp MM, De Gruyter J, Woudenberg JHC, Verkley GJM, Crous PW. Highlights of the Didymellaceae: a polyphasic approach to characterize Phoma and related Pleosporalean genera. Studies in Mycology. 2010;65:1-60.
4. Bala G, Hosein F. Studies on gummy stem blight disease of cucurbits in Trinidad. Journal of Tropical Agriculture. 1986;63:195-197.
5. Boughalleb N, El Mahjoub M, Abad-Campos P, PerezSierra A, Garcia-Jimenez J, Armengol J. First report of gummy stem blight caused by Didymella bryoniae on grafted watermelon in Tunisia. Plant Disease. 2007;91:468.
6. CABI. Didymella bryoniae (gummy stem blight of cucurbit) Datasheet (Full) Report. Crop Protection Compendium; 2015. Available: https://www.cabi.org/cpc/ [Accessed on 14.04.23].
7. Chiu WF, Walker JC. Physiology and pathogenicity of the cucurbit black-rot fungus. Journal of Agricultural Research. 1949;78:589-615.
8. Gusmini G, Wehner TC, Holmes GJ. Disease assessment scales for seedling screening and detached leaf assay for gummy stem blight in watermelon. Phytopathology. 2002;85(3):364-369.
9. Keinath AP, Duthie JA. Yield and quality reductions in watermelon due to anthracnose, gummy stem blight, and black rot. Recent Research Developments in Plant Pathology. 1998;77-90.
10. Keinath AP. Effect of protectant fungicide application schedules on gummy stem blight epidemics and marketable yield of watermelon. Plant Disease. 2000;84(3):254-260.
11. Keinath AP. Effect of fungicide applications scheduled to control gummy stem blight on yield and quality of watermelon fruit. Plant Disease. 2001;85(1):53-58.
12. Keinath AP. Diagnostic guide for gummy stem blight and black rot on cucurbits. Plant Disease. 2013;14:35.
13. Li YG, Song XL, Wang XQ, Zhang H, Tian S, Ji P. First report of fruit rot of watermelon caused by Fusarium equiseti in China. Plant Disease. 2018;102(9):1852.
14. Mahapatra S, Rao ES, Sandeep Kumar GM, Sriram S. Stagonosporopsis cucurbitacearum the causal agent of gummy stem blight of watermelon in India. Australasian Plant Disease Notes. 2020;15(1):1-3.
15. McKinney HH. Influence of soil temperature and moisture on infection of wheat seedlings by Helminthosporium sativum. USDA Publications. 1923;195-218.
16. Mutlu G, Kirbag S, Ostuner T. Determination of fungal diseases in greenhouse cucumber in Elazig Province. Bitki Koruma Bulteni. 2015;55:341-360.
17. Rahman MZ, Ahmad K, Siddiqui Y, Saad N, Hun TG, Mohd Hata E, et al. First Report of Fusarium equiseti Causing Fruit Rot Disease of Watermelon in Malaysia. Plant Disease. 2022;106(1):326.
18. Santos CPS, Negreiros AMP, Barros AP, Michereff SJ. First Report of Lasiodiplodia brasiliensis Causing Root Rot on Watermelon in Brazil. Plant Disease. 2022;125:10-63.
19. Santos GRD, Ferreira MSV, Pessoa-Filho MACDP, Ferreira ME, Café-Filho AC. Host specificity and genetic diversity of Didymella bryoniae from Cucurbitaceae in Brazil. Journal of Phytopathology. 2009;157(5):265-273.
20. Sudisha J, Vasanth Kumar T, Niranjana SR, Shekar Shetty H. First report of gummy stem blight caused by Didymella bryoniae on muskmelon (Cucumis melo) in India. Plant Pathology. 2004;53(4):533-543.
21. Wein HC. The cucurbits: cucumber, melon, squash, and pumpkin-the physiology of vegetable crops. CAB International. 1997;Chapter 9.
22. Zhao Q, Wu J, Zhang L, Xu L, Yan C, Gong Z. Identification and characterization of Cucurbita gummy stem blight fungi in Northeast China. Journal of Phytopathology. 2018;166(5):305-313.
23. Al-Obeidi HKM, Al-Jabouri AMJ, Othman AK, AlHussaini ZAH. Effect of benzyl adenine (BA) on in vitro multiplication of Citrus troyer citrange and Carrizo citrange rootstocks. Scientific Journal of the Atomic Energy Organization. 2001;3(1):63-73.