Bipen KumarRakesh Kumar2016-10-242016-10-242011http://krishikosh.egranth.ac.in/handle/1/81574Red rot caused by Colletotrichum falcatum Went is one of the most important disease of sugarcane and frequent breakdown of varietal resistance is due to variation in the pathogen. Keeping in view, seven stalk and midrib isolates of C. falcatum were obtained from different sugar mill areas of Punjab was studied for morphological and cultural characteristics like colony diameter, colony colour, growth pattern, sporulation and conidial size and also for pathological variability. The average conidial size of seven stalk and midrib isolates varied from 26.8-35.0 X 7.6-8.0 μm and 23.0-27.0 X 5.7-7.0. Two midrib isolates namely MR-5 and MR-6 from CoJ 85 and one stalk isolate CF-06 from CoJ 85 were relatively fast growing with an average colony diameter in the range of 13.3-13.6 mm, 36.5-36.9 mm and 84.1-84.2 mm and 13.5-13.9, 38.5 and 84.9 after 3, 5 and 7 days of incubation, respectively. All the midrib isolates showed low and stalk isolates low, medium and high sporulation which ranged from 2.08 to 16.67 X 105/ 9 mm disc (low), 16.67 to 29.17 X 105/ 9 mm disc (medium) and 29.17 to 41.67 X 105/ 9 mm disc (high). On the basis of morphological characters midrib isolates produced dark type and stalk isolates produced with light and dark type colony colour. Pathogenic variability in midrib and stalk isolates of C. falcatum was studied on fourteen host differentials. On the basis of reaction expressed by seven midrib red rot isolates were grouped into five pathotypes based on their virulence. Group I designated as MR Pb-1 from CoJ 85 (Isolate MR-5 and MR-6) was highly virulent and produced intermediate reaction on 6 differentials and stalk red rot isolates were grouped into four pathotypes based on their virulence. Group I designated as CF Pb-1 from CoJ 85 (Isolate MR-5 and MR-6) was highly virulent and produced susceptible reaction on 10 differentials. However, no differences among isolates from a particular variety were observed. Stalk and midrib red rot isolates produced crude toxic metabolite capable of inducing part of the disease symptom on the host. Their toxicity was increased with increasing days, susceptibility of variety and its concentrations. In vitro selection system for ameliorating problem like susceptibility to red rot through somaclonal variation can be successfully addressed, especially in popular genotype CoJ 64 which has desirable traits in all other aspects except resistance to red rot disease. Three to four months old calli of CoJ 64 were screened in vitro against different concentrations of crude pathogen culture filtrate (PCF) 5, 10, 15, 20 and 25% v/v for two selection cycles, each of three weeks duration. Calli survived and exhibited further proliferation at 5, 10, 15 and 20% v/v PCF concentrations whereas, at higher concentration (25% v/v) survival and/ or proliferation was completely inhibited. Shoot regeneration percent was higher in calli selected on 5% PCF concentration than those selected on 10, 15 and 20% concentrations. PCF had markedly inhibits survival and multiplication of sugarcane tissues at all stages viz., survival, proliferation and shoot regeneration of callus. Effect of PCF on callus survival, proliferation and shoot regeneration was observed to directly related to its concentration in the selection medium.. The plantlets regenerated from selected calli, after two selection cycles each of three weeks duration, using varied concentrations of PCF were likely to produce red rot resistant plantsendiseases, sugarcane, biological phenomena, fungi, pathogens, selection, planting, toxins, concentrates, regenerationsugarcaneThesis