In vitro efficacy of fungicides against fungal pathogens associated with boll rot of cotton

Introduction

Cotton (Gossypium sp.) is cultivated in tropical and subtropical regions and plays a crucial role in global agricultural economies by providing fibre, edible oil, livestock feed and industrial raw materials. In recent years, global cotton production has remained relatively stable, with approximately 26 million tonnes of lint produced worldwide during the 2025-26 season, indicating continued dominance of cotton as a major natural fibre crop in the international textile sector (ICAC, 2026) [1] . India continues to occupy a prominent position as the second-largest cotton producer globally, with an estimated production of about 23.2 million 480-lb bales in 2024-25 and 23.5 million bales projected for 2025-26, cultivated across approximately 11.2 million hectares (USDA-FAS, 2025-26) [2] . Indian cotton production is spread across a wide array of agro-ecological zones, ranging from irrigated, high-input farming systems to low-input, rainfall-dependent regions. Nearly sixty per cent of the country's cotton growing area is rainfed, which means that fluctuations in monsoon patterns, prolonged dry spells and uneven rainfall distribution directly influence crop growth and boll retention (Venugopalan et al., 2019) [3] . The boll development phase in particular is highly sensitive to environmental stress and any disruption during this stage affects fibre formation and ultimately determines economic yield. Cotton is exposed to several diseases during its lifecycle, including Fusarium wilt, Verticillium wilt, Alternaria leaf spot, bacterial blight, grey mildew and cotton leaf curl disease (Hillocks, 1992; Ali et al., 2019) [5,4] . While foliar diseases generally reduce photosynthetic efficiency and overall plant vigour, diseases affecting the reproductive structures, especially bolls, pose a much greater economic threat. Among these, boll rot is one of the most destructive problems faced by cotton growers. Unlike many diseases caused by a single pathogen, boll rot constitutes a complex involving multiple fungal and bacterial organisms that invade the boll tissue under favourable environmental conditions (Mani et al., 2017) [6] . The boll rot complex includes pathogens such as Fusarium, Aspergillus, Rhizopus, Penicillium and Xanthomonas species (Kumar et al., 2016) [7] . These organisms typically enter the boll through natural openings or injuries caused by insects, rain induced cracks or mechanical abrasions. In many cases, the role of insect pests especially the pink bollworm is critical, as larval feeding creates ideal entry points for infection (Gopalakrishnan et al., 2020) [8] . Under such circumstances, boll rot can cause severe yield losses, with certain reports documenting reductions ranging from 15% to more than 50% (Patel et al., 2015) [9] . Although research on specific pathogens related to boll rot is available, comprehensive work on the entire disease complex its epidemiology, environmental triggers, varietal responses and integrated management is still limited (Meena et al., 2018; Thombre et al., 2021) [10,11] . This gap was particularly evident in major cotton-growing regions such as Maharashtra, where climatic variability, prolonged humidity and pest interactions often intensify the disease. Farmers frequently resort to indiscriminate chemical applications without clear information on causal organisms or effective control strategies, leading to inconsistent results and higher production costs. With this background, the present study was undertaken to evaluate the comparative in vitro efficacy of seven commonly used fungicides, representing different chemical groups and modes of action, against the four fungal pathogens Aspergillus niger, Fusarium sp., Rhizopus sp. and Alternaria sp. associated with boll rot of cotton in this region, with the objective of identifying the most promising candidate(s) for field level validation.

Materials and Methods

Experimental site

The present investigation was carried out during Kharif, 2025-26 in the laboratory of the Department of Plant Pathology, Government College of Agriculture, Dhule, Maharashtra.

Collection of disease samples

The rotted cotton bolls were collected from different cotton growing areas of Dhule, Nandurbar and Jalgaon district for isolation of pathogens.

2.3

Isolation of pathogens

The diseased portion of the rotted cotton boll was washed thoroughly in tap water to remove dirt and then blot dried. For isolation of the pathogens, the diseased portion of the cotton boll was cut into small pieces of 2 to 3 mm size with sterilized blade in such a way that half portion of healthy tissue must be present with it. These small pieces were surface sterilized in 0.1% mercuric chloride solution (HgCl 2 ) for 30 seconds followed by washing in three successive changes of distilled water to remove the traces of mercuric chloride and then dried on clean blotting paper. Three to four such pieces were aseptically transferred to Petri plates containing potato dextrose agar medium. The plates were incubated at 27 ± 2 °C for seven days and examined at regular intervals to see the growth of fungus surrounding the pieces. Soon after the fungal growth was noticed, well isolated fungal colony free from contamination was sub-cultured and transferred to agar slants by hyphal tip method. The pure culture obtained was maintained for further studies.

Purification of the isolated organisms

Purification of the fungal species was done by transferring small bit of hypha to PDA slants in aseptic condition.

In vitro evaluation of fungicides (poisoned food technique)

The efficacy of different fungicides for controlling the pathogen responsible for boll rot of cotton was determined by poison food technique on solid media. The medium was distributed as 100 ml in each 250 ml Erlenmeyer flasks and sterilized in autoclave at 15 lbs pressure for 15 minutes. The measured quantity of various fungicides was added in the flask after sufficient cooling so as to get the required final concentration with suitable control. A series of concentration were prepared. The fungicides were thoroughly mixed by stirring the flasks. The medium was then poured into Petri plates with three replications for each treatment. Seven days old culture grown on potato dextrose agar medium was used as inoculum. The plates were inoculated with 5 mm of each fungal disc removing with a sterilized cork borer and was transferred aseptically at the centre of the petri plates containing PDA medium with measured quantities of fungicides. Plates with PDA medium without fungicide served as control. These petriplates were then incubated at 27+1℃ for 7 days. Observations on colony diameter and sporulation of the test pathogens were recorded. The per cent inhibition of mycelial growth of inoculated pathogens were worked out by using a following formula.

I =

C-T C

Where, I = Percent inhibition on fungal growth. C = Growth in mm on the 7 th day after inoculation in control. T = Growth in mm on the 7 th day after inoculation in treatment.

Statistical analysis

Data on colony diameter and per cent inhibition were statistically analysed following Panse et al. (1978) [12] ; standard error (S.Em ±) and critical difference (C.D. at 1%) were computed for each pathogen.

Results and Discussion

The effectiveness of seven fungicides, namely Copper oxychloride 50% WP (0.25%), Tebuconazole 25.9% EC (0.05%), Carbendazim 50% WP (0.1%), Propiconazole 25% EC (0.1%), Propineb 70% WP (0.1%), Pyraclostrobin 20% WG (0.25%) and Azoxystrobin 11% + Tebuconazole 18.3% SC (0.01%), was assessed under in vitro conditions against four fungal pathogens, Aspergillus niger, Fusarium sp., Rhizopus sp. and Alternaria sp., using the poisoned food technique to determine their ability to suppress the growth of boll rotting fungi. The findings are summarized in the [13] they reported that fludioxonil and tebuconazole significantly reduced Rhizopus rot incidence. They concluded that postharvest fungicide application is effective when combined with proper handling. Arun Kumar (2008) [14] reported that among nine fungicides evaluated under in vitro conditions, propiconazole and hexaconazole at all tested concentrations (0.1%, 0.2% and 0.3%) completely inhibited the mycelial growth of A. alternata infecting cotton. Perane et al. (2015) [15] observed 88.75% inhibition of mycelial growth of A. macrospora with propiconazole 25% EC.

In vitro efficacy of fungicides against boll rotting fungi of cotton

Conclusion

The present study demonstrates that among seven fungicides evaluated by the poisoned food technique against the four pathogens of boll rot complex of cotton (Aspergillus niger, Fusarium sp., Rhizopus sp. and Alternaria sp.), Propiconazole 25% EC (0.1%) provided the most complete and consistent broad-spectrum inhibition, followed by Azoxystrobin 11% + Tebuconazole 18.3% SC and Tebuconazole 25.9% EC. However, Carbendazim 50% WP and Propineb 70% WP, while effective against specific pathogens, failed to control the full complex adequately. Propiconazole 25% EC is therefore recommended as the most suitable fungicide for chemical management of boll rot in the North cotton belt of Maharashtra.

References

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