Studies on the Effect of Plant Growth Promoting Rhizobacteria on Mulberry Leaf Yield, Disease Management and Cocoon Productivity under Semi-Arid Condition

摘要

Extensive use of chemicals in the area of plant growth promotion and disease management has become an issue of public worry and scrutiny owing to their detrimental effects on environment and man-kind as well. In recent years, the concept of PGPR mediation on plant growth promotion and disease management is gaining importance and acceptance world wide. Activation of the host plant defense by the application of various agents including plant growth promoting rhizobacteria is one of the potenial areasof research.PGPR are free-living bacteria having beneficial effects on plant growth and represent the potential useful tool for environmental sound pest management (Zehnder et al., 1997).The objective of this study was to evaluate and identify suitableisolate of PGPR on growth promotion and leaf spot disease management in mulberry.Two isolates viz., Azotobacter chroococcum (CMNR) and Azotobacter chroococcum (MYS) were evaluated for their bio efficacy as growth promoters and resistance inducers againstleaf spot disease with different fertilization doses covering seven treatments under semi-arid field conditions for a period of three years(2000 - 2003) at Regional Sericultural Research Station Chamarajanagar. Different growth and yield parameters suchas number of shoots/plant, length. of shoots, number of leaves/plant and leaf yield kg/ha were recorded. Effect of Azotobacter strains on leaf spot disease was also recorded during rainy season (June-Sept). Results indicated that the plants treated withAzotobacter showed considerable enhancement in growth though 50% of N application was curtailed. Varying degrees of leaf spot disease severity suppression were observed in different treatments. 20 kg of CMNR isolate recorded minimum disease severity of17.72 % and the corresponding leaf yield loss was 4.92 % followed by T-5 (MYS)and T-6 (CMNR). Maximum disease severity was recorded in control plots(41.22%) with proportionate loss of 19 % with full dose of N application with out Azotobacter. Regressionanalysis of leaf yield loss on PDI indicated less percentage of loss in treated plots ranging from 0.19 to 0.53% as against the control (0.83%) for every unit of disease level.Bioassay studies also revealed that the incorporation of PGPR of either CMNR isolate or MYS isolate had significant influence on the post cocoon parameters such as cocoons by number, cocoons by weight, single shell weight and shell ratio percentage. The present investigation suggests that the application of PGPR as a biostimulantand bio-protectant for the spot disease management is an advantage for the sustainable quality leaf and cocoon productivity under semi-arid condition.