Resistance to early blight in the tomato was assessed by examining various parameters of the progress of the disease. Artificial inoculation and the scoring technique were standardized. Test plants were inoculated with 125 cfu/ ml of a 12-day-old culture of a pathogenic isolate of Alternaria solani. Screening under artificial conditions was more informative than that under natural epidemic conditions. Tomato cultivars CLN-2071-C, CLN-2070-A, BSS-174, and DTH-7 with resistance expressed as slow blighting against four pathogenic isolates of A. solani, were selected for cultivation in disease-prone areas. Disease intensity increased with the age of plants under the same inoculum load. The area under the disease progress curve (AUDPC) was positively correlated with the percentage disease index and negatively with resistance. Calculation of the apparent infection rate (r) was more informative for natural epidemics than for artificial conditions. The sequential apparent infection rate between observation periods was better correlated with disease progress than was the total apparent infection rate between the first and last observations. A double sigmoidal disease progress curve during the same cropping season was characteristic of some varieties when fungal infection took place during the vegetative phase of crop growth.

Early blight (Alternaria solani) is an important disease causing severe damage in tomato. The eleven isolates of A. solani designated as So, Dh, Sh, Va-5, Ka, Ma, Hy, Ba-1, My, Va-3 and Mi were collected from different agroclimatic conditions and these isolates were characterized for cultural, morphological, pathogenic and molecular variations. The pigmentation varied from yellow, brown, black, brownish to greenish black in isolates of A. solani on potato dextrose agar medium. In general, radial growth of all isolates ranged between 14.9 mm and 32.2 mm on PDA and 24.3 mm to 53.7 mm on three selective media i.e., ASM, V-8 juice agar and V-8 juice agar (synthetic) on the fourth day. The fastest radial growth was recorded in the So isolate and slowest in the Ka isolate on PDA, while isolates Dh, Ba-1 and Va-3 were recorded to be faster in growth on ASM, V-8 juice agar and V-8 juice agar (synthetic) medium. The thickness of conidiogenous hyphae varied between 1.17 l and 9.56 l, with maximum in the Va-5 and Ma isolates. Most of the isolates showed smooth mycelial growth with circular and irregular margin and without concentric zonation. Sporulation was not found in any of the isolates on four different nutrient media, whereas conidiogenous hyphal length was observed in V-8 juice agar medium only. Based on the pathogenicity, isolates of A. solani were rated as virulent or less virulent based on percentage disease incidence data. Molecular variability studies were also done to find out the best annealing temperature and eighty-six primers were screened to select for maximum polymorphism of DNA. The best annealing temperature was recorded between 32.5°C and 34.0°C for the pathogen, and most efficient amplification and polymorphism of DNA was found with random primer 5 0 -CGCGTTCCTG-3 0 .

Actinomycetes, a Gram positive bacteria, well reported as a source of antibiotics, also possess potential to control various plant pathogens, besides acting as plant growth promoting agent. Chemicals in different forms are extensively being used in vegetable farming, adversely affecting the environment and consumer health. Microbial agent like actinomycetes can substantially replace these harmful chemicals, and have now started finding a place as an important input in to farming practices. Only selected vegetable crops belonging to 11 different families have been explored with use of actinomycetes as biocontrol and plant growth promoting agent till now. It provides ample opportunities to vegetable researchers, to further explore with use of this very important group of microorganisms, in order to achieve even higher production level of safe vegetables. Mycostop and Actinovate are two actinomycetes based formulations globally available for use in vegetable farming as a substitute for chemical formulations. Present review article has summarized the literature available on use of actinomycetes in vegetable farming. Existing wide gap in knowledge, and potential thrust areas for future research have also been projected.

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