Physiological and molecular studies on bacterial wilt disease Potato

Bacterial wilt (BW) disease caused by Ralstonia solanacearum (Yabuuchi et al. 1995) is one of the most important bacterial disease over the world, this study was planned to develop physiological and molecular RAPD marker linked with resistance or susceptibility to B.W, among six of commonly cultivated potato (Solanum tuberosum,L.) cultivars. Nicola and Lady rosetta cultivars were high by susceptible to bacterial wilt disease, but Santana and Valor cultivars were moderately susceptible and/or resistance to the disease. Also, Diamont and Lady balfor cultivars appeared resistance to bacterial wilt disease. The enzymes phenylalanine ammonia-layse (pAL), pyroxidase (PO) and polyphenol oxidase (PPO showed high activity in infected plants compared with healthy ones Phenylalanine ammonia-layse and polyphenol oxidase activity have increased with increasing the period after R. solanacearum inoculation .On the contrary, activity of pyroxidase was decreased with increasing the period after inoculation. There was positive correlation between enzymatic activities and resistance of potato cultivars to bacterial wilt disease. Phenylalanine ammonia-layse showed high activity in Nicola and Lady rosetta (susceptible cultivars) but showed moderate activity in Santana and Valor (moderately resistance cultivars). Also, Lady balfor and Diamont (resistance cultivars) showed less activity with Phenylalanine ammonia-layse. There was no significant differerence in activity of peroxidaes and polyphenol oxidase in healthy potato cultivars but significant differerence were found between potato cultivars in case of infected plants. However, peroxidase and polyphenol oxidase showed high activity in Nicola compared with Lady rosetta, Santana,Diamont, Valor, and Lady balfor cultivars which showed moderate and/or lower activity in peroxidase and polyphenol oxidase. Total phenolic compounds content in shoots was higher than in roots and the highest content is also related with the resistant cultivars in shoots and roots, but in Nicola roots was high too. Steriodal glycoalkaloids (SGAs) content in shoots was determined at 25 days after inoculation, the highest value of SGAs content was in Valor and Lady rosetta and the lowest content was in resistant cultivar, generally, it is in healthy more than in infected except in Valor and Santana. Four kinds of phytoalexine were detected in all infected cultivars and just one in healthy cultivars. Lignin content of roots in resistant cultivars was higher than in susceptible cultivars and moderate in moderately susceptible and/or resistant cultivars. In general its higher in healthy roots than in infected. Proteomic and isozyme profiles were very different in comparison between healthy and infected potato cultivars. Genetically, seven RAPD primers gave polymorphism with the studied genotypes using RAPD-PCR technique. Only three primers exhibited molecular markers among these genotypes. Where, three molecular markers were detected in primer (C20); the first was positive marker linked with susceptible cultivars, meanwhile, second was detected positively with moderate and/or susceptible cultivars to BW, and negatively with resistance cultivars. Only one positive marker was detected in primer (A14) linked with susceptible cultivars. Two molecular markers were detected in Primer (Cll) positively liked with resistance cultivars. Genetically, these cultivars were divided to three cluster groups Diamont and Lady blfor in the first cluster as resistance cultivars, Santana and Valor in the second cluster as moderately resistance and/or susceptible cultivar, Nicola and Lady rosetta were in the third cluster as susceptible cultivars. As well as, SRAP- technique results showed genetic variation among these cultivars.