In order to establish an assay for bacterial wilt resistance in vitro for potato plants, we examined the assay conditions of inoculation with Ralstonia solanacearum. The suitable plant stage and bacteria concentration as inoculum were the 4-5 leaf stage and 102 CFU/ml in this assay. The suitable incubation temperature was also 28℃ after inoculation. The validity of this assay was assessed using six cultivars and two breeding lines of potato plants with known resistance to R.solanacearum in field screening. Cultivars（or breeding lines） with fewer dead plants in the assay（lower dead plant rates）had stronger resistance in the field test. In addition, this assay was able to distinguish statistical differences between the resistant cultivars（or breeding lines）and the susceptible cultivars in the field screening. These results suggest that this assay system is effective for evaluating bacterial wilt resistance in potato plants.
Citrus greening disease （CG） caused by 'Candidatus Liberibacter asiaticus' （Las） was investigated on Amamioshima, Tokunoshima, Okinoerabu and Yoron islands of Kagoshima in Southern Japan. Based on the distribution of infected trees in the second investigation from April 2006 to March 2009, citrus trees on four islands were categorized. A total of 143,782 citrus trees were investigated at 22,866 areas on four islands during the third investigation from April 2009 to March 2012. A total of 8,694 symptomatic trees at 6,569 areas were examined for Las infections by polymerase chain reaction （PCR）. As a result, 258 trees at 120 areas were confirmed to be infected. Infected trees and newly confirmed areas with infected trees in this survey were fewer than those in the second one on Tokunoshima and Yoron islands. The frequencies of uninfected/infected trees during this survey were calculated and compared with those during the second one. Odds ratios indicate that infected trees and newly confirmed areas with infected trees in this survey were fewer than those in the second one on Tokunoshima and Yoron islands. In order to detect latent infected trees, monitoring of CG is discussed.
To develop an effective method for controlling post-harvest stem-end rot of mango, we investigated the efficacy of heat treatment of mango peduncle using a soldering iron. Examination of pathogen progression from the peduncle to fruit interior in fruits of varying degrees of maturity revealed that the pathogen developed more quickly in mature fruit than in immature fruit, with the pathogen in the former advancing to a depth of 15 mm from the peduncle 12 h after inoculation with the pathogen. Heat treatment of the peduncle was accomplished by cutting the tip of the soldering iron flat and pressing the heated tip against the peduncle for 10 s. Following heat treatment of peduncles 3, 6, 12, or 24 h after inoculation with the pathogen, disease was significantly inhibited only in fruits that were heat treated 3, 6 or 12 h after inoculation, but not in those that were heat treated 24 h after inoculation. These results demonstrated that it is necessary to perform heat treatment of peduncles within 6 h of harvest in order for the treatment to be effective. In addition, in field experiments in which peduncles were heat treated 4 h after harvest, we observed marked inhibition of disease in heat-treated fruit compared to untreated fruit, with no deterioration in quality of heat-treated fruit.
Blight-like symptoms on Cleyera japonica Thunb. were first found on plants growing on the shrine in Omura, Nagasaki, Japan on June 19, 2009. White mycelia and brown, spherical,rapeseed-sized sclerotia were observed on the diseased plants. A fungus similar to Sclerotium rolfsii Saccardo was isolated from infected plants. The optimum growth temperature of these isolates, on potato dextrose agar, was 25℃for mycelial growth and 30℃for sclerotium formation.The mycelial tufts were white to grayish brown, and the main hyphal width ranged from 4.5-7.8μm（avg. = 6.6μm）with clamp connections. These mycological characters are identical to those of S. rolfsii reported in other plants. The isolates were found to be pathogenic to C. japonica in artificial inoculation test, and could be re-isolated from infected tissue. It is proposed that the disease should be referred to as southern blight of C. japonica caused by S. rolfsii.
The geographical distribution of the sweetpotato weevil, Cylas formicarius and the West Indian sweetpotato weevil, Euscepes postfasciatus were investigated on sweetpotato, Ipomoea batatas and wild host plants, I. india and I. pes-caprae on the Amami Islands except Kikai Island during 2010 to 2011. The number of C. formicarius male adults was determined using simple sticky traps with synthetic sex pheromone at 235 sites during November 2010 to February 2011. The occurrence of the two weevils were investigated at 109 sweetpotato fields and 97 creeping colonies of wild host plants, I. india and I. pes-caprae, sites during November 2010 to February 2011. Both weevil species were found in all islands of the Amami Islands. This was consistent with the result of 1997-1998, and the distribution of both weevils species have not changed on the Amami Islands. The occurrence of E. postfasciatus was on the increase from 1997. On Okinoerabu Island, the number of male adults of C. formicarius captured using pheromone traps were fewer than the other islands.