Screening and biochemical characterization of tomato genotypes for resistance to bacterial wilt

Abstract

Investigation on 'Screening and biochemical characterization of tomato genotypes for resistance to bacterial' wilt' was carried out in the Department of Olericulture, and Biochemistry Laboratory, College of Horticulture, Vellanikkara 1 during 1997-99. The objectives of this study were to identify tomato genotypes resistant to bacterial wilt and to find the possibility for biochemical cataloguing of bacterial wilt resistant tomato genotypes. Evaluation for bacterial wilt resistance revealed that Sakthi, Mukthi and LE-474 were consistently resistant to bacterial wilt. Four additional sources of bacterial wilt resistance were identified, viz. LE-214, LE-415, LE-470 and LE-421. Based on the percentage wilting the twenty four genotypes included in this study were classified into four groups, viz. Resistant, Moderately Resistant, Susceptible and Highly susceptible. -.: All the bacterial wilt resistant and moderately resistant genotypes had a higher content of total phenols in roots and leaves at 45th and 60th day of plant growth; O.D. phenol content in roots of resistant varieties were higher than susceptible varieties. In leaf, the O.D. phenol content was high in moderately resistant genotypes at 45th and 60th day. All the genotypes were studied for isozyme variation with respect to two enzymes, viz. polyphenol oxidase and peroxidase. 10 general the roots had more number of bands compared to leaves at both the stages. '.. The root samples at 45th day showed two polyphenol oxidase bands, viz. PPO-I (~=0.074) and PPO-12 (Rm=0,414) which were specific to resistant varieties alone. This combination along with high total phenols may be considered as a biochemical marker for resistance to bacterial wilt in tomato. In 60 days old roots of resistant and moderately re istant genotypes the protein band PPO-9 (Rm=0.851) was predominantly present Regarding peroxidase, 45 . days old leaf samples had a combination of protein bands, viz. PRX-7 (Rm=0.361) and PRX-8 (Rm=O.382) in resistant and moderately resistant varieties. But at 60 days the roots and leaves did not show any specific band for resistance. In general at 45 days both leaf and root samples had more number of bands for polyphenol oxidase and peroxidase in resistant varieties compared to susceptible varieties. The study revealed that it was possible to arrive at a combination of specific isozyme bands at a particular growth stage, which can be used as a marker for bacterial wilt resistant tomato genotypes.