Organic management of Alternaria leaf spot of cotton

Introduction

Cotton is one of the most important fiber crops of India and plays a dominant role in the agricultural economy of India. It provides the basic raw material as cotton fibre to cotton textile industry. In India, cotton provides direct livelihood to 60 lakh farmers and about 4 -5 crore people are employed in cotton trade and its processing. Cotton is referred to as "king of Fibres" and is also popularly known as "white Gold". India is the largest cotton growing country in the world with an area of around 12.24 MH. Total production of cotton in India is 36.1 million bales of 170 kg and productivity is 501 kg ha-1.India's share in global cotton exports is around 22% (Anonymous, 2019) [1] . Cotton has major share in global agriculture economy; however, its production and yield are compromised due to various biotic, abiotic, and climatic factors. To meet the global need, innovative research has been carried out to enhance the cotton production. Starting from the conventional breeding strategies to the modern technologies, there is a long history of cotton research (Zaib et al., 2020) [14] . Alternaria leaf spot is generally associated with late-season development of cotton plants or senescing plant tissues. It is characterized by small, brown, circular lesions on the leaves that are surrounded by distinct purple margins. Similar symptoms can be observed on buds, flowers, and bolls in mature plants. As the disease progresses, the lesions expand and become dry and gray in the centre, exhibiting shot-hole symptoms on leaves. These spots may coalesce and occupy large leaf areas resulting in severe defoliation, affecting cotton yield and quality (Watkins, 1981) [13] .

Gwalior (M.P.). The details of materials used, experimental procedures followed and techniques adopted are given as under The experiment was conducted at Research field of B. M. College of Agriculture, Khandwa and In-vitro experiments were conducted in laboratory at Department of Plant Pathology, B. M. College of Agriculture, Khandwa under RVSKVV, Gwalior (M.P.). Isolates of Alternaria alternata were isolated from wilt infected plant collected from Khandwa district of M.P and they were cultured and used during the course of study. The following Organic amendments were used in In-vitro and In-vivo against Alternaria alternata in theTable-1. Peeled potatoes were cut into small pieces and boiled in 1/2 litre distilled water in a sauce pan for 10 min. In another pan agar powder was boiled in half litre of distilled water separately. Potato extract was filtered with the help of muslin cloth, then added to dissolve agar solution along with dextrose and heated for 5 minutes. The media was poured into flask of graduated marks of 250 ml or 500 ml. The PDA media was autoclaved by putting cotton plug on the rim of flask and covered with aluminium sheet paper at 121.6 °C for 15 minutes. Before pouring the media to petri plates, bactericide (Streptomycin) is added at the rate of 1.0 g/lit.

In-vitro evaluation of organic amendments against

Alternaria alternata

The bioassay studies were carried out by employing the Poisoned Food Technique as reported earlier. Three cow products and three botanicals viz., Cow dung, Cow urine, Milk whey, Azadiracta indica (leaf) extract, Garlic bulb extract and Calotropis gigantean (leaf) extract were incorporated aseptically in sterilized Potato Dextrose Agar medium in their original 20% concentrations. 20 ml of the Potato Dextrose Agar medium was poured in each of the sterilized petri plate. Then these petri-plates were inoculated with a 5 mm disc cut placed with a sterilized cork borer from an actively growing ten days old culture of Alternaria alternate.

The inoculated petri plates were incubated at 25±1 °C. Each treatment was replicated three times. Suitable control (without treatment) was also maintained. The radial growth of Alternaria alternata was recorded after seven and ten days. Sporulation from the pathogen was also be noted as (+) for positive sporulation and (-) for no sporulation. After recorded radial growth, we calculate the growth inhibition percentage with the following formula-

Where C = Growth of test fungus in control T = Growth of test fungus in treatment in mm

Observations: Percent Disease intensity (PDI), and Yield PDI will be taken from five plants of each place randomly of middle, lower and upper leaves of a plant. Five randomly selected plants in each plot and were tagged for taking observations for disease component. Percent disease intensity will be calculated as per 0 to 4 disease scale developed by Sheo Raj (1988) [10] table-2. All other cultural and pest management practices were imposed as recommended in package of practices. The first spray of each treatment was initiated as soon as the first symptom of leaf spot was seen in the field and repeated at an interval of 15 days. Five plants were selected randomly in each plot and observation on severity of the disease on the foliage (using 0-4 scale) was recorded under different treatments one day before each spray and 15 days after the final spray. The cotton yield in each treatment was recorded.

Results and Discussion

Alternaria leaf spot of cotton is the major disease caused due to invade of Alternaria alternata. It is disastrous and reduces maximum yield in major cotton growing areas of Madhya Pradesh, Maharashtra and some other states. To ascertain the problems, in-vitro and in-vivo evaluation of cow products and botanicals against pathogens has been carried out for the research purposes in present investigation "Organic management strategy for Alternaria leaf spot of cotton ".

Symptomology

The symptoms of Alternaria leaf spot of cotton was observed on different plant parts. The symptoms first appear on the upper surface of leaves in the form of dot shape, light brown to blackish in colour, circular or irregular lesions, which later on turns dark brown due to the appearance of spore masses. These spots enlarged and coalesced forming large sized spots. In the centre of such spots, light brown dot surrounded by the number of dark alternating concentric rings also appeared in some cases. Affected leaves become dry, cracking and fall off. Veins of leaves also affected. The disease also causes cankers on the stem. The findingd of Watkins (1981) [13] is inagriment with the present findings hand he discribed the phenotypic symptoms of Alternaria leaf spot on different Species of cotton were evaluated. Small, dull to dark brown, circular or irregular shaped spots appear on leaf varying in diameter from 0.5 to 10 mm. They often develop concentric rings and represent a target board like appearance which is better defined on the upper surface. When mature they have dry, grey centres which may crack and even drop. The spots may coalesce and occupy large area of the leaf

Isolation of pathogen

The investigation was carried out and observations were made for appearance of the Alternaria leaf spot of cotton. Symptoms on cotton plants from the trail field, collect infected leaves in polythene bags, carried to the laboratory and isolation on Potato Dextrose Agar (PDA) medium. The pathogen was isolated from infected leaves of diseased plants were taken and cut into 3 to 5 mm long pieces with some healthy portion. Infected parts sterilized with 0.1% mercuric chloride for 25 to 30 second and then washed with autoclaved distilled water for three times then aseptically plated. Isolation done in sterilized Petri plates under Laminar-Air-flow cabinet and these plates incubated in BOD incubator at 25±2 °C. 7 days after incubation, when the well-developed mycelia growth of the pathogen was seen on the PDA medium, it was aseptically transferred onto another PDA media plate.

In vitro evaluation of cow products and botanicals against Alternaria alternata

To evaluate different cow products and botanicals against pathogen (Alternaria alternata), an experiment conducted at 10%, 20% and 25% concentrations in which three cow products (Cow dung, Cow urine and Milk whey) and three botanicals (Azadiracta indica (leaf) extract, Garlic bulb extract and Calotropis gigantean (leaf) extract) respectively are used. The effect of cow products and botanicals against pathogen is analyzed by Poison food technique. The effect of various cow products and botanicals on the Colony diameter, colour, type of colony, inhibition of mycelium and Spore germination of the pathogen was observed. All these findings are in agreement with the findings of Panchal and Patil (2009) [5] reported that garlic clove extract (10%) was proved to be best in inhibiting mycelia growth and sporulation of Alternaria alternata incident of fruit rot of tomato followed by turmeric and neem leaf extract on the contrary in present investigation Neem was recorded mean inhibition of (56.66). To circumvent pollution hazards due to injudicious use of agrochemicals and also to avoid development of resistance in pathogenic fungi against commonly used fungicides, use of plant extracts for the management of plant disease increased in recent years and proved to be very effective against plant diseases. Hassanein et al., (2010) [2] also reported that Inhibition effect of Azadirachta indica was tested Alternaria, their inhibitory effect studied at various concentrations (5, 10 and 20%). Neem extract inhibited mycelial growth of fungi and the degree of suppression proportionally increased with increasing concentration of extracts. Maximum percent inhibition was of 20% aqueous Neem leaf extract that decreased the incidence of disease from 53.2 to 42.5% after period of 2 weeks and 100 to 79.2% after period of 4 weeks.

Colony colour and type of colony

On the basis of colony colour, Alternaria alternate pathogen treated with different cow products and botanicals against Alternaria leaf spot of cotton was observed Greyish black colony colour in all treatments except cow urine and milk whey which shows Greyish colony colour after inoculation under in vitro condition. The present results of investigations are in accordance with the findings of Srinivasan (1994) [11] who discribed that A. alternata produces initially white colored mycelium, later at maturity it becomes dark colored in culture plates.

Conidiophores and conidia are golden brown. Conidiophore is simple, straight or curved, 1-3 septate, 50x3-6 μ with one to several apical scars. Conidia often in long branched chains, ovoid, obclavate, obpyriform, rarely ellipsoidal, with or without a short, conical or cylindrical apical beak not exceeding one third the length of conidium, smooth walled or warted, singly constricted at 3-8 transverse septa, with one or two longitudinal septa at the lower part, 18-63x7-18 μ .

To evaluate Inhibition of mycelium cow products and botanicals against Alternaria alternata under In-vitro condition. Food poison technique was used after 7 days of inoculation and their observed growth inhibition of mycelium per cent is shown below-The data of table 04 shows that all treatments were found slightly better over control. Two botanicals and one cow product found effective out of three cow product and three botanicals. Maximum Inhibition of mycelium was observed in Azadiracta indica (leaf) extract is 42.24% followed by Garlic bulb extract (39.77%) and Cow urine (37.37%) while minimum Inhibition of mycelium in Cow dung (25.86%) followed by Milk whey (28.61%) and Calotropis gigantean (leaf) extract 50% WP (33.35%). The findings of present investigations are similar to Turkusay and Onogur (1998) [12] reported that spore germination of A. alternata was inhibited by Hedera helix Lowc. extracts followed by Datura stramonium L. extracts. Ficus caricaL. and Avena sativa L. extract also affected colony development. Karade and Sawant (1999) [4] tested different plant extracts on solid and liquid media against A. alternata and reported that Allium sativum L. was found to be more effective. The bishkatali (Polygonum hydropiper L.), garlic (A. sativum L.), ginger (Zingiber officinale Rosc) and neem (Azadirachta indica A. Juss) extracts were effective against A. alternata (Rahman et al., 1999) [7] . Ranjan et al. (1999) [8] reported that out of five plant extracts tested against Alternaria alternata in vitro, Aegle marmelosleaf extract (5000 μg/ml) showed minimum colony diameter and maximum growth inhibition of A. alternata in comparison with the control. All the plant extracts were less effective at lower concentrations, there was a positive correlation between concentration and growth inhibition percentage.

The bulb extracts of A. sativum and leaf extracts of Ocimumba silicum L. at two per cent were most effective in suppressing radial growth and biomass production of A. alternata (Rashmi and Yadav, 1999) [9] . [3] who confirmed and determined antifungal activity of cow urine at various concentrations viz., 5, 10 and 15% against pathogen that were purified from infected plants of both Fenugreek, Okra. Among all, cow urine @ 15% was found most effective. When their inhibitory effects were evaluated, highest inhibition was examined against F. oxysporum (78.57%) @15% of cow urine followed by R. solani (78.37%) and S. rolfsii (73.84%). Present findings are also related to findings of Patni et al., (2005) [6] who reported that six medicinal plants were evaluated for inhibitory effect against A. brassicae causing blight in mustard. Among all, Calotropis, Eucalyptus and Polyalthia extracts, had shown significant effect in reducing the growth of the pathogen.

Conclusion

In the In vitro condition, Alternaria alternate was observed Greyish black colony colour and circular type colony growth while three cow products and three botanicals were tested and Azadiracta indica (leaf) extract and Garlic bulb extract found more effective than other treatments. In the In vivo condition, least Disease severity and maximum disease reduction was found in Azadiracta indica (leaf) extract and minimum reduction in cow dung than other cow products and botanicals was recorded.\

References

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