Abstract
Brown lesions, a symptom of concave stem canker, were found on Citrus junos (Yuzu) in Hijikawa-cho, Ehime Prefecture, Japan in July 2000. The fungus isolated from the brown lesions by single-spore isolation was pathogenic on C. junos. By morphological characteristics of the specimen and culture and analysis of the ITS (internal transcribed spacer) region of the rDNA, the causal fungus was identified as Lachnum abnorme (Mont.) J. H. Haines & Dumont, and the disease was confirmed as concave stem canker of citrus. Based on small nucleotide differences in the ITS regions of seven isolates of L. abnorme, including pathogenic isolates on C. junos and eight other species of Lachnum, species-specific primers LAF (5'-CCTACCCTTGTGTATTATAACAAT-3') and LAR (5'-ATCCGAGGTCAACCTAAG-3') were selected. Primer pairs LAF and LAR amplified a fragment of 449 bp containing a portion of the ITS region in all the L. abnorme isolates tested, which originated from different hosts and regions of Japan, but did not amplify a fragment of any other species of Lachnum. In a PCR assay for concave stem canker, DNA was extracted from diseased branches of C. junos from Tokushima, Kochi and Ehime Prefectures using magnetic silica beads. Only a 449-bp fragment was amplified from DNA extracted from the brown lesions. The method developed may be useful for the rapid detection and identification of L. abnorme from both culture and plant tissue.
