Survey and distribution of rhizome rot disease of ginger (Zingiber officinale rosc.) in Shivamogga district, Karnataka, India

Introduction

India, known as the 'land of spices', has occupied a prominent position in the global spice trade since time immemorial (Thomas and Sanil, 2019) [11] . Ginger (Zingiber officinale Rosc.), popularly known as the "golden spice of India", is an important horticultural crop belonging to the family Zingiberaceae. In India, Karnataka is an important ginger-growing state, particularly in Hassan, Madikeri, Chikkamagaluru and Shivamogga districts. The area under ginger cultivation in India was 1,94,243 ha with a production of 23,33,000 tonnes during 2023-24, which changed to 1,93,258 ha and 22,46,292 tonnes during 2024-25. In Karnataka, the area and production increased from 21,344 ha and 2,32,839 tonnes in 2023-24 to 22,704 ha and 2,39,792 tonnes in 2024-25 (Spices Board of India, 2024, 2025) [9,10] . Despite its economic importance, ginger production is constrained by several biotic and abiotic stresses, among which rhizome rot diseases are particularly destructive. Major pathogens associated with the disease complex include Pythium aphanidermatum, Ralstonia solanacearum, Athelia rolfsii and Fusarium proliferatum (Mahesha et al., 2020) [5] . Rhizome rot has been reported from almost all ginger-growing states of India and may cause yield losses exceeding 50 per cent under favourable conditions (Joshi and Sharma, 1980) [3] . The disease complex includes soft rot, wet rot, bacterial wilt and Sclerotium rot, with their occurrence influenced by environmental and crop production conditions (Raghu, 2011) [6] . Shivamogga is an important ginger-growing district of Karnataka, where variations in soil type, crop growth stage, irrigation and other field conditions may influence rhizome rot development. However, information on the current incidence and distribution of the disease across ginger-growing locations of the district is limited. Therefore, the present study was undertaken to assess the incidence and distribution of ginger rhizome rot across different taluks and villages of Shivamogga district and to document the associated field conditions.

Materials and Methods

A random roving survey was conducted in the ginger growing areas of Shivamogga district viz., Sagara, Shivamogga, Soraba, Hosanagara and Shikaripura taluks for the incidence of ginger rhizome rot during 2025-26. During the survey, ginger plants showing the typical symptoms of rhizome rot were collected in polythene covers from the field. The collected samples were brought to the laboratory and utilized for further studies. Disease incidence (DI) was calculated by using the following formula given by Wheeler (1969) [12] .

Per cent Disease Incidence (PDI) = (Number of plants infected / Total number of plants observed) × 100

Results

A survey revealed that the disease incidence ranged from 10.10 to 11.90 per cent, with an overall district mean incidence of 11.02 per cent (Table 1). Among the surveyed taluks, the highest mean disease incidence was recorded in Sagara (11.50%), followed by Hosanagara (11.48%), Soraba (10.93%), Shivamogga (10.80%) and Shikaripura (10.50%). In Soraba taluk, disease incidence ranged from 10.40 per cent at Chikkasavi to 11.50 per cent at Hirekasavi, with a taluk mean of 10.93 per cent. In Sagara taluk, the incidence ranged from 11.10 to 11.90 per cent, with the highest incidence recorded at Iruvakki (11.90%) and a taluk mean of 11.50 per cent. In Shivamogga taluk, disease incidence varied from 10.30 per cent at Kumsi to 11.20 per cent at Tuppur and Sominakoppa, with a taluk mean of 10.80 per cent. In Hosanagara taluk, the incidence ranged from 11.20 per cent at Seegekoppa to 11.80 per cent at Maruthipura, with a taluk mean of 11.48 per cent. In Shikaripura taluk, disease incidence ranged from 10.10 per cent at Kyathinkoppa to 11.00 per cent at Beeranakere, with a taluk mean of 10.50 per cent. Overall, the highest village-level incidence was recorded at Iruvakki (11.90%), whereas the lowest was recorded at Kyathinkoppa (10.10%) (Table 1). The distribution of ginger rhizome rot incidence in relation to soil type is presented in Table 2. Among the surveyed fields, red loam soils accounted for the highest number of field observations (10), followed by red sandy loam (9 observations) and sandy clay loam (2 observations). The disease incidence in red loam soils ranged from 10.30 to 11.90 per cent, whereas in red sandy loam soils it ranged from 10.10 to 11.80 per cent. In sandy clay loam soils, the incidence ranged from 10.70 to 11.40 per cent. Thus, disease incidence was recorded across all three soil types included in the survey, with overlapping incidence ranges among the soil categories (Table 2).

Discussion:

The survey revealed that ginger rhizome rot occurred at all surveyed locations in Shivamogga district, with incidence ranging from 10.1 to 11.9 per cent and a district mean of 11.02 per cent, indicating its widespread establishment in the ginger-growing areas. Sagara recorded the highest taluk mean incidence (11.50%), while Shikaripura recorded the lowest (10.50%); Iruvakki and Kyathinkoppa recorded the highest (11.90%) and lowest (10.10%) village-level incidence, respectively. The incidence recorded in the present study was comparatively lower than earlier reports from Karnataka and other gingergrowing regions, where incidence reached 37-60 per cent (Ekka et al., 2009 [1] ; Raghu, 2011 [6] ; Mahesha et al., 2020 [5] ; Kumar et al., 2022 [4] ). The lower incidence of rhizome rot recorded in the present survey may be attributed partly to intensive fungicidal management of foliar diseases, which could have exerted an incidental suppressive effect on susceptible components of the rhizome-rot complex. Earlier studies have reported that fungicides such as carbendazim + mancozeb and metalaxyl + mancozeb are effective in reducing rhizome rot, particularly that caused by Pythium spp. (Singh, 2011) [8] . Consequently, repeated application of fungicides for the management of leaf blast and leaf spot diseases may have provided additional protection against soil-and rhizomeassociated fungal pathogens. However, the relatively low incidence observed may also reflect limitations in fieldbased symptom assessment. Rhizome rot commonly produces above-ground symptoms such as yellowing, wilting and drying of leaves, which can closely resemble or overlap with symptoms of severe foliar diseases. This symptom overlap is particularly important because ginger rhizome rot is a disease complex involving several soil-and rhizome-associated pathogens, and visible foliar symptoms may not always accurately indicate the infection status of the underground rhizome. Thus, severe leaf-blast or leaf-spot symptoms may have obscured early or mild rhizome-rot symptoms during field observations, potentially resulting in an underestimation of disease incidence. Therefore, the comparatively lower rhizome-rot incidence recorded in the present survey may represent a combination of actual disease suppression associated with fungicidal management and possible underestimation arising from the overlapping expression of foliar and rhizome-rot symptoms. The relationship between soil type and disease incidence was also examined, with red loam soils accounting for the largest number of field observations, followed by red sandy loam and sandy clay loam soils. Disease incidence ranged from 10.30 to 11.90 per cent in red loam, 10.10 to 11.80 per cent in red sandy loam and 10.70 to 11.40 per cent in sandy clay loam soils, the ranges overlapping considerably among the three soil types. Poorly drained, moisture-retentive soils tend to favour the soil-borne pathogens associated with the rhizome rot complex as reported by Singh (2011) [8] .

Acknowledgement

AcknowledgmentsThe work has been undertaken as part of the of M.Sc. research programme in Keladi Shivappa Nayaka University of Agricultural and Horticultural Sciences, College of Agriculture, Navile, Shivamogga, I'm thankful to My seniors, Friends and advisory committee for their support during M.Sc. degree programme..

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