J. TARAFDAR, N. MANDAL AND H. SEN
Abstract
The field experiments were conducted in the University Horticultural Experimental field during 2000 and 2001 growing seasons to evaluate seven promi:-..ing cultivars of taro (Colocasia esculenta var. antiquorum) to study the resistance reaction to leaf blight disease caused by Pltutoplithora colocasiac and the tuber yield and the yield contributing characters. The preliminary findings on the interrelationships between the resistance reactions to Phytopht horn leaf blight, peroxidase (PO) isozyme profile and its activity in the cultivars were studied in response to inoculation by the pathogen. Significant differences were found among the cultivars for all characters studies. The cultivars 13CC-1 followed by Niuktakeshi, Jhankri and BCC-21 demonstrated very low intensity of blight disease, which ranged from 15.0 to 34.3% and 10.0 to 40.6% in both the seasons respectively. The cultivars Topi and BCC-15 showed low to moderate symptoms in the field but the intensity of the disease was low. The cultivar Telia had the highest disease severity, 81.6 and 95.0% respectively in the two seasons and was highly susceptible to Phylophthora Total side tuber yield, number of corms per five plants and dry matter !percentage exhibited a significant variation in both the years. BCC-1 showed highest yield (16.27 and 15.7 Ulla) and dry matter percentage (28.3 and 25.4%) in the respective years. Though the tuber yield of Jhankri, uktakeshi and topi were at par but the dry matter percentage was high in Jhankri followed by Muktakeshi and Topi. BCC-21 and BCC-15. The variation in the side tuber weight was also noticed among the cultivars. In comparison to these, the susceptibe cultivar Telia very low yield potential that was 9.88 and 7.29 !lila and dry matter was between 17.1 to 20.7%. Electrophoretic patterns of peroxidase (PO) isozyme profile of seven taro cultivars revealed the variation in band pattern of isoforms in non-inoculated and Phytoplithw.a colocasiac inoculated plants. The field resistance cultivar to blight disease showed four additional bands (Rin 0.12, 0.18, 0.22 and 0.27) 72 hours after infection with Phytopthora colocasiae, whereas the cultivars showing susceptibility to the blight were lacking of that isoforms. Both the common and additional bands of PO were absent in the highly susceptible cultivar Telia. PO activity was found very high in the resistant cultivars, which ranged from 2.36 to 4.01 (change in absorbance g leaf tissue-1 mind) and polyphenol oxidase activity was lowered down (0.16 to 1.18) in response to infection but the susceptible cultivars showed decreased level of PO.