Induction of pathogenesis-related gene 1 (PR-1) by acibenzolar-s-methyl application in pineapple and its effect on reniform nematodes (Rotylenchulus reniformis)

Abstract

The induction of systemic acquired resistance (SAR) in pineapples (Ananas comosus) was studied as shown by the up-regulation of the PR-1 gene (the SAR marker) and examination of the SAR effect on the reniform nematode, Rotylenchulus reniformis. Real-time polymerase chain reaction assay was performed using degenerate primers designed from the PR-1 genes of several monocotyledonous (monocots) and dicotyledonous (dicots) plants. A 266 bp cDNA band was evident only in plants treated with the SAR inducer, acibenzolar-s-methyl. This 266 bp cDNA was sequenced and found to be highly homologous to a number of PR-1 genes from monocots. In addition, the amino acid sequence deduced from the 266 bp cDNA showed a high identity to PR-1 proteins from both monocots and dicots. Therefore, it was highly likely that this cloned fragment was part of the A. comosus PR-1 gene, indicating that A. comosus has an SAR pathway. The time course of PR-1 expression was studied. The results showed that PR-1 induction was initiated as early as 1 d after acibenzolar application and continued through 3 wk thereafter. The effect of SAR on the nematodes, R. reniformis, in pineapples was also elucidated. The results showed that the reproduction of nematodes on the pineapples treated with 100 mg/L or 200 mg/L was 55% lower than that on pineapples treated with 0 mg/L or 50 mg/L. Nematode reproduction on pineapples treated with the same concentration but inoculated at different times was not significantly different (p > 0.05).