Hiromichi Nitta

Detection of viruses associated with rugose wood in Japanese grapevines and analysis of genomic variability of Rupestris stem pitting-associated virus

In Vitis labruscana ‘Pione’ and ‘Kyoho’, 57 grapevines with rugose wood (RW) symptoms and 31 asymptomatic grapevines were obtained from vineyards in Hiroshima and Okayama prefectures. We surveyed vines for RW-associated viruses and other viruses by reverse transcription-polymerase chain reaction with virus-specific primers and degenerate primers for simultaneous detection of viruses associated with RW or leafroll disease. Rupestris stem pitting-associated virus (RSPaV) was detected from all grapevines with RW symptoms and from eight asymptomatic grapevines. Grapevine leafroll-associated virus-1, -2, -3, Grapevine virus B, Grapevine fleck virus, and Grapevine asteroid mosaic-associated virus were detected from some of the grapevines tested. RSPaV isolates detected were clustered in four groups by phylogenetic analysis using the nucleotide sequences of coat protein gene. These results suggest that RSPaV with diverse genetic variants is highly related to RW in Japanese grapevine cultivars Pione and Kyoho.

Rainfall conditions inducing the dispersion of conidia of Botryosphaeria berengeriana.

The conditions inducing the peak dispersion of conidia of Botryosphaeria berengeriana were investigated using data collected during eight periods of continuous rainfall between 1991 and 1992. These rainfall events varied from 800 to 1540 minutes in duration. Conidia were collected about every two hours onto 2 glass microscope slides coated with glycerol jelly using a spore trap. The spore trap was set up in the midst of some naturally infected pear prunings about 20 cm in length at the height of 1 m from the groundside. This monitoring clearly showed that at least three hours from the beginning of a rainfall episode was needed before a large number of conidia of Botryosphaeria berengeriana dispersed under continuous rainfall. Moreover, it was shown that 60% or more of the total number of conidia produced by a rainfall event were released in the total period of 4-6 hours before and after the peak. Clarifying the rainfall conditions that induce maximal dispersion of conidia will help in understanding and so preventing disease outbreaks.

Effect of picking time and temperature on fruit corerot in Japanese pear caused by Phomopsis sp.

For Japanese pear the change in the temperature of fruit was monitored from the day before to the day after harvest and the resultant expression of fruit core rot after storage were compared for two handling regimes. Fruit were either harvested at 3 p.m., left in the field overnight and then moved indoors at 8 a.m. on the following morning, or moved indoors (25°C) immediately after being harvested at 8 a.m.. Fruit harvested at 3 p.m. and left in the field maintained a higher flesh temperature than fruit moved indoors (25°C) immediately after harvest. As well, the delay in moving fruit indoors resulted in a higher incidence of fruit core rot after storage.