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A species-specific PCR assay was developed for rapid and accurate detection of the pathogenic oomycete Phytophthora capsici in diseased plant tissues, soil and artificially infested irrigation water. Based on differences in internal transcribed spacer (ITS) sequences of Phytophthora spp. and other oomycetes, one pair of species-specific primers, PC-1/PC-2, was synthesized. After screening 15 isolates of P. capsici and 77 isolates from the Ascomycota, Basidiomycota, Deuteromycota and Oomycota, the PC-1/PC-2 primers amplified only a single PCR band of c. 560 bp from P. capsici. The detection sensitivity with primers PC-1/PC-2 was 1 pg genomic DNA (equivalent to half the genomic DNA of a single zoospore) per 25- µL PCR reaction volume; traditional PCR could detect P. capsici in naturally infected plant tissues, diseased field soil and artificially inoculated irrigation water. Using ITS1/ITS4 as the first-round primers and PC-1/PC-2 in the second round, nested PCR procedures were developed, increasing detection sensitivity to 1 fg per 25- µL reaction volume. The results suggested that the assay detected the pathogen more rapidly and accurately than standard isolation methods. The PCR-based methods developed here could simplify both plant disease diagnosis and pathogen monitoring, as well as guiding plant disease management. [ABSTRACT FROM AUTHOR]

We determined DNA fingerprint haplotypes and pathotypes of the rice-blast fungus Magnaporthe grisea collected from 13 areas in China. This DNA fingerprinting analysis, using rep-PCR, of 381 haplotypes (482 isolates) from China indicated that the M. grisea populations cannot be delineated into region-specific groups. Analyses of the number of alleles ( na), Nei's gene diversity, unbiased genetic distance, and Shannon's Information index among 13 populations showed that clusters were not related to the geographic distance between populations with the exception of the Ningxia (NX) and Jilin (JL) cluster. Among northern populations, NX and JL were more similar to one another than to other populations. Pathogen populations consisting of 121 isolates from China were grouped into 53 pathotypes on the basis of disease reaction in differential rice lines. Isolates assayed for pathotypes were detected based on disease reactions. No correlation was observed between fingerprint groups and pathotypes of the pathogen. High frequency of virulence was found on the rice line Shin2 ( Pi-ks and Pi-sh) followed by PiNo.4 ( Pi-ta2 and Pi-sh) and K1 ( Pi-ta), while it was low on Kanto 51 ( Pi-k + ?), K3 ( Pi-kh), and Fujisaka ( Pi-i and Pi-sh). Virulence was rare on Toride 1 ( Pi-zt and Pi-sh). Tetep (Pi-kh + ?) was predicted to be a highly effective, as none of the isolates infected this line. These blast-resistant rice lines can be used in resistance breeding for the effective management of rice blast in the respective regions of China. [ABSTRACT FROM AUTHOR]