DETECTION AND IDENTIFICATION OF PERONOSCLEROSPORA-SACCHARI IN MAIZE BY DNA HYBRIDIZATION

The causal organism of an incidence of maize downy mildew in Southern China proved difficult to classify by standard techniques. The pathogen, subsequently identified as Peronosclerospora sacchari, was detected by DNA hybridization in endosperm, pericarp, and pedicel tissues, but not in embryos of infected maize seeds. Plasmid pCLY83, which had been selected from a P. maydis DNA library, served as the probe. No evidence for hybridization was detected between the probe and DNAs extracted from ten common seedborne fungi of maize: Colletotrichum graminicola, Acremonium strictum, Curvularia lunata, Fusarium moniliforme, Bipolaris maydis, Macrophomina phaseolina, Rhizoctonia sp., Rhizopus sp., Penicillium sp., and Alternaria sp. Hybridization was also not detected with DNAs isolated from plant tissues infected with Sclerospora graminicola or Sclerophthora macrospora. The hybridizing DNA of the corn pathogen from China was readily distinguished from P. sorghi and P. maydis by differences in EcoRI, PvuI, BamHI and HindIII restriction patterns. RFLP patterns on blots of DNA from the plants showing symptoms of downy mildew in this case were the same as those for P. philippinensis and P. sacchari, now believed to be conspecific.