Blight disease is caused by Alternaria solani belongs to the sub-division Deuteromycotina, class Hyphomycetes, family Dematiaceae. The genus is characterized by the formation of polymorphous conidia either singly or in short or longer chains and provided with cross, longitudinal as well as oblique septa and having longer or short beaks. The conidia are porospores produced from simple, dark, septate conidiophores in simple and borne singly. (1)
Among the different diseases caused by the genus Alternaria, blight disease is one of the most dominant one that causes average yield loss in the range of 32-57%(2).Symptoms of this disease include presence of irregular, often circular brown to dark brown colour leaf spots on the leaves with concentric lines inside the spots. Often the circular spots coalesce to form large patches resulting in the leaf blight. In several cases, small dark coloured spots are also formed on pods and tender twigs. (3).
For Alternaria blight management, early sowing (4) of properly stored clean certified seeds after deep ploughing along with clean cultivation, timely weeding and maintenance of optimum plant population , avoidance of irrigation at flowering and pod formation stages are some of the steps to be followed for an efficient management of the disease.Since a number of Alternaria species infect crops of economic importance, there is a strong need to effectively control for this pathogen. There are different methods which are there for needed for its control
The life cycle starts with the fungus over wintering in crop residues or wild members of the Solanaceae family. In the spring, conidia are produced. Multicellular conidia are splashed by water or by wind onto an uninfected plant. The conidia infect the plant by entering through small wounds, stomata, or direct penetration. Infections usually start on older leaves close to the ground. The fungus takes time to grow and eventually forms a lesion. From this lesion, more conidia are created and released. These conidia infect other plants or other parts of the same plant within the same growing season. Every part of the plant can be infected and form lesions. (5).
Alternaria solani infects stems, leaves and fruits of potato (S. tuberosum), tomato (Solanum lycopersicum L.), eggplant (S. melongena L.), bell pepper and hot pepper (Capsicum spp.), and other members of the Solanum family. Distinguishing symptoms of A. solani include leaf spot and defoliation, which are most pronounced in the lower canopy.
There are numerous fungicides on the market for controlling early blight. Some of the fungicides on the market are azoxystrobin, pyraclostrobin, chlorothalonil, copper products, hydrogen dioxide, mancozeb, potassium bicarbonate, and ziram. The most common and effective method for the control of early blight is through the application of foliar fungicides. Protectant fungicides recommended for late blight control (e.g. maneb, mancozeb, chlorothalonil, and triphenyl tin hydroxide) are also effective against early blight. (6)
On the other hand the pesticide treatment is not protected as chemicals pollute environment, effect health vulnerability in humans and when these harmful chemicals enter into the food chain become hazardous to all living entities (7). Botanical derivatives like phenols, tannins, and flavonoids are environmentally safe and may be used as an alternative to commercial fungicides for controlling pathogenic fungi (8).
Plants are rich in a wide variety of secondary metabolites such as tannin, terpenoids, alkaloids, flavonoids, phenols, steroids glycosides and volatile oils etc. These secondary metabolites posses antimicrobial property as well as play an important role in defense against attack by insects and herbivores (9) Investigation of antimicrobial properties of plants identifies them as but for developing a medicinal formulation from plants
The world is gradually turning to bioformulations which are known to be effective against a large repertoire of diseases and ailments. More importantly, they are not known to cause any notable derogatory effects and are readily available at affordable prices (10). However, add a note of caution stating that plant remedies are effective and without side-effects, provided they are selected properly and taken under proper medical supervision. Various organic substances such as cow dung, neem oil cake, mustard oil cake, coconut oil cake etc. are used by farmers as organic manure (11). Some workers also reported the significant antifungal properties of the organic substances (12). The present work proposes to develop a formulation by combining plant extracts with these traditionally used organic substances for control of early blight of tomato caused by Alternaria solani. This type of formulation will provide a cheap and environmentally safe herbal fungicide that can be further used as a commercial herbal bio-control agent. In the recent times, agricultural scenario is witnessing a trend towards organic farming. It is seen that agricultural products produced through organic farming, without using any inorganic fertilisers and pesticides, fetch high demand and price in the international market. Organic farming has its root in Nature and it makes use of only organic materials. Organic farming is not for a single crop but it envisages the entire farm. The main objective of organic farming includes mulching, crop rotation, cover cropping green manuring, animal waste, composting, bio-gas slurry, biofertilisers and organic recycling.
The world is gradually turning to bioformulations which are known to be effective against a large repertoire of diseases and ailments. More importantly, they are not known to cause any notable derogatory effects and are readily availabile at affordable prices. However, add a note of caution stating that plant remedies are effective and without side-effects, provided they are selected properly and taken under proper medical supervision. The active component, most often a secondary metabolite, varies in quality and quantity for a given plant species growing in different locations. The market value of such plants depends on their active content rather than merely their luxuriant growth. Reckon that close to 70,000 species of the plant kingdom have been used as herbal medicine at one time or other (13) discriminate use of fungicides may lead to toxic residues, development of fungicide resistance, environmental contaminations and carcinogenic, teratogenic and mutagenic effects in humans, animals and plants (14). In this context, biocontrol approaches may help to develop an eco-friendly control stratagey for management of serious plant diseases. Recent studies have shown the importance of biocontrol agents as possible non- phytotoxic systemaic and easily biodegradable alternative fungicides. (15).
Folk medicines of almost all civilizations of the world abound in herbal remedies. Majority of the traditional medicines used in healthcare are obtained from plants (16). In spite of several advancements in the field of synthetic drug chemistry and antibiotics, plants continue to be one of the major raw materials for drugs treating various ailments of humans. Clinical and pharmaceutical investigations have in fact elevated the status of medicinal plants by identifying the role of active principles present in them and elaborating on their mode of action in human and animal systems (17). Some workers noticed that the neem seed oil has more effective than the powder formulation in reducing egg-laying and adult emergence of the bruchid (18).The excessive misuse of a wide range of fungicides has led to it being harmful to the environment and increases the resistant pathogen populations (19). For this reason, alternative methods to control the disease had been studied with emphasis on biological control using fungi or bacteria to reduce fungicide application and decrease cost of production. Biological control has the potential to manage plant disease which occurred through different mechanisms such as antibiosis, competition, suppression, direct parasitism, induced resistance, hypovirulence and predation.
Hence, there would be no chance of residual toxicity of the oil on taste of the commodities. Similarly there are several reports which showed that herbal formulations or plant extracts do not leave any harmful residue (20), thus the chance of residual toxicity in case of extracts is also very less