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The levels of mRNA transcripts of genes for several pathogenesis-related proteins were examined in cotton stems after infection of the plants with the soil-borne, vascular wilt pathogen Verticillium dahliae . Reverse transcription PCR was used to estimate mRNA levels corresponding to particular transcripts. In order to determine if differences in timing or levels of gene activation were likely to account for differences in the susceptibility of Gossypium hirsutum cultivars to Verticillium wilt, we compared the gene activation patterns in the relatively resistant commercial cultivar, Sicala V2 with those exhibited by the susceptible cultivar, CS50. A non-defoliating, Australian isolate of V. dahliae was used and infection was achieved by stem-puncture inoculation with a conidial suspension of the pathogen. Levels of mRNA for genes for cadinene synthase, acidic chitinase, basic chitinase, β-1,3-glucanase, and at least one member of the family of cotton Ypr10 gene homologues coding for potential PR10 proteins increased after inoculation with V. dahliae , while levels of mRNA for a gene for phenylalanine ammonia lyase were similar in all samples. Even though leaf necrosis symptoms were found to be less severe in Sicala V2 after V. dahliae infection, no differences in the timing or in the extent of activation of gene expression were observed between the two cultivars used. Significant gene activation was not observed after treatment of CS50 with bion ® (benzo-(1,2,3)-thiadiazole-7-carbothioc acid S -methyl ester, BTH) or methyl jasmonate, but there was a reduction in the severity of leaf necrosis of both cultivars after bion ® treatment, which was marginal in CS50 but clearly evident in Sicala V2. Thus the enhanced partial resistance of cotton to Verticillium wilt observed here, whether due to cultivar or bion ® treatment, is not accompanied by a change in the timing or levels of expression of the genes investigated. Therefore it is likely that some other factors are responsible for the degree of resistance observed. |
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