Department of Plant Pathology, CCS Haryana Agricultural University, Hisar–125 004
National Symposium on “Plant Pathology in the Changing Global Scenario” held at National Bureau of Plant Genetic Resources, New Delhi on February 27–28, 2009
Sclerotinia sclerotiorum (Lib.) de Bary is one of the most devastating and cosmopolitan plant pathogens. The fungus infects over 400 species of plants worldwide including important crops and numerous weeds. The disease causes serious and unpredictable yie1d losses in field which ranges from a trace to 100 per cent. Sclerotinia is generally considered to be a simple interest pathogen utilizing ascospores as the primary inoculum and plant infection by mycelial growth between stem bases or by contact between infected plants with neighboring healthy plants late in the growing season as secondary inoculum. The epidemiology of Sclerotinia diseases is dependent on several factors viz., soil inoculum; soil type; soil moisture; rainfall; soil and environmental temperature; host susceptibility; plant density and cultural practices adopted. Soil solarization through coverage of transparent polythene (0.1 mm) sheet for 45 days is a good control strategy. EPTC treatment significantly increases the degree of control irrespective of the depth of the sclerotia in the soil. Soil treatment with methyl bromide or formaldehyde has been used as effective pre-plant treatments for destroying sclerotia in the soil. Calcium cyanamide @ 500 kg/ha has been widely reported to prevent sclerotial germination and subsequent ascospore production. Methane sodium @ 35 ml/M2 or methyl bromide @ 50 g/M2 in the top 10 cm soil reduces apothecial production. The extracts of Bougainvillea spectabilis (Bougainvillea), Azadirachta indica (neem) and Allium sativum (garlic) were significantly effective in checking mycelial growth and sclerotia formation at 50 per cent concentration. Soil amendment with Bougainvillea, Jamun and Mehndi leaf were able to reduce the number of apothecia appearance, lesion length and disease intensity. Organic amendments with the use of cakes/organic manures have also been found to significantly reduce number of apothecia production in pots. Poultry manure was most effective and significantly better in reducing lesion length and disease intensity. Amount and duration of irrigation also affect the carpogenic germination and severity of the disease. Biological control of Sclerotinia is an alternative disease control strategy. Number of mycoparasites such as Coniothyrium minitans and Sporidesmium sclerotivorum. Coniothyrium minitans and Gliocladium virens parasitized on sclerotia have shown their potentiality against this pathogen. It has been observed that isolates of Trichoderma harzianum-3, T. harzianum-4 and Bacillus subtilis were most potent in decreasing the linear growth and number of apothecia production in in vitro conditions. T. harzianum was quite effective in reducing lesion length and disease intensity when applied simultaneously and seven days prior to the pathogen. Foliar application of spore suspension of C. minitans has been shown to reduce disease severity and application to crop residues occupied by S. sclerotiorum may reduce disease carry over inoculum. Growing the fungus in the plant debris and reintroducing it into the soil can conceivably hasten the destruction of sclerotia in the field. Systemic acquired resistance chemicals like INA, SA as seed treatment or spray @ 100 ppm could reduce seedling mortality, lesion length, disease intensity and disease incidence. Seed treatments with fungicides like carbendazim, thiophanate methyl, benomyl, thiram, mancozeb and organo-mercurials have been reported to be effective for the disease control. Foliar application to control this disease must be applied before infection occurs. Proper timing of spray and method of application have a great impact on the management of this disease. Several fungicides such as benomyl, chlorothalonil, thiophanate methyl, Iprodione and dicloran have been reported to be effective. Seed treatment, rotation between vegetable and cereal crops, fertilizers, rational close planting, pruning of old and infected leaves and 50 per cent carbendazole have been found effective as integrated disease control measures. Biotechnological approaches in enhancing disease resistance involve either exploitation of natural forms of resistance or genetic engineering approaches such as the introduction of chitinases, glucanases and other antifungal proteins.
