Using tests based on serological, chemical and pathological aspects Ralstonia solanacearum strains
(of brown rot disease) were identified in 10 strains were isolated from infected potato tubers grown in Egypt
with biovar II pathogenicity and hypersensivity on leaves of tobacco and sugar utilization. , ISSR markers
were used to differentiate the strains .Total number of amplified fragments was 68 bands and polymorphic
bands were 38 representing 56% polymorphism. Twenty one bands were monomorphic and 9 were
uniquely amplified DNA fragments of DNA which ranged between 7 to 16. The number of polymorphic
fragments ranged between 1 to 13 for each primer. Values of genetic similarity among genotypes ranged
from 63 to 92%. A dendrogram separated the strains into two major clusters. Pathogenicity tests showed
QB.4, BK.5, BK.7 and Gk.8 isolates being highly virulent on tobacco in hypersensitivity test (HR) study.
Virulence degree were between low and high on seedlings of tomato and potato and tomato seedlings. R.
solanacearum (QB.4, QB.5, BK.7 and BK.8) showed highest disease incidence of 25.0, 24.6, 25.3 and
28.5%, respectively. Recorded wilt disease severity were 6.5, 6.2, 6.1 and 7.5 %, respectively at 42 days.
Only the four isolates QB.4, QB.5, BK.7 and BK.8 were highly pathogenic to all of the studied seven potato
cultivars of Accent, Alpha, Kara, Spunta, Draga, Sntana and Monalisa.
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