We determined the mating system of the pathogen of Japanese pear dwarf, Fomitiporia sp., in pairing tests of single basidiospore isolates from two vegetative strains isolated from decayed wood and from another vegetative strain from a fruiting body produced on a Japanese pear tree. Each basidiospore usually had a single nucleus. Number of nuclei per hyphal cell varied from two to six for vegetative strains and one to six for single basidiospore isolates. Thus, it was difficult to distinguish between primary and secondary hyphae based on nucleus number. In pairing tests using 15–20 single basidiospore isolates from each strain, compatible reactions were characterized by tuft formation at the junction between two mycelia. Tuft isolates, analyzed by inter-simple sequence repeat (ISSR) markers using a PCR primer (GTG)₅, were found to be composed of secondary hyphae. In incompatible pairing reactions, no tufts formed. Mating patterns based on tuft reactions were complex and ambiguous for determining polarity; however, the fungus was inferred to be bipolar or tetrapolar. Most inter-strain combinations were compatible. In conclusion, the pathogen of Japanese pear dwarf, Fomitiporia sp., was predominantly heterothallic.

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Citrus greening (CG), also called huanglongbing, was found on Tokunoshima, Okinoerabu and Yoron islands of Kagoshima in southern Japan in 2002. Because inter- and intra-island transportation of citrus trees has been banned since April 2007, new CG infections that developed after the ban can be attributed to transmission by the vector, Diaphorina citri. Since the first record of the disease on the islands, disease spread on these islands has been studied at 10,176 sites on a total of 63,295 trees. Using data from before April 2011, CG infection pressure was evaluated by analyzing the spatiotemporal distribution of CG on the infected trees in the studied areas. Newly confirmed area with infected trees amounted to 75% on Tokunoshima within 21 m, Okinoerabu within 90 m and Yoron within 241 m of areas with infected trees confirmed in the past 2 years. Areas were classified into three infection pressure ranks (IPRs; low to high): IPR-1, ≤ 0.5; IPR-2, >0.5 to 2.0; IPR-3, >2.0. The frequencies of uninfected/infected trees in each rank during the 2 years after April 2007 were calculated and compared between infection ranks. Odds ratios indicated that the infection risk of trees in IPR-2 was seven times higher than in IPR-1 and six times higher in IPR-3 than in IPR-2. For the predicted risk, monitoring of CG is discussed.

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A bacterial disease, causing black spot of leaves and fruits, was found on European pear, Pyrus communis L. var. sativa de Candolle, in Yamagata Prefecture, Japan, in 2008 and 2009. The bacterium that was isolated from affected tissues was identified as Pseudomonas syringae pv. syringae. This is the first report of bacterial black spot on European pear in Japan.

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