|Budget Amount *help
¥2,600,000 (Direct Cost : ¥2,600,000)
Fiscal Year 1996 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1995 : ¥1,700,000 (Direct Cost : ¥1,700,000)
The presence of Geotrichum candidum, the citrus sour rot pathogen, was examined in soils of citrus groves and noncitrus fields of Japan. Soil samples were collected from 223 sites (118 sites in citrus groves, and 105 sites in fields cultivated with 33 species on nonvitrus plants and in evergreen broadleaved forest) in 11 main citrus growing prefectures, and Hokkaido, a noncitrus growing area. Standard isolates were isolated from the citrus sour rot fruit. The pathogenicity of all isolates obtained by using a selective medium were tested to lemon, orange and satsuma mandarin. Of 446 samples, 356 samples were citrus races which showed the pathogenicity to citrus. The isolates were identified as noncitrus race not to infect citrus fruits. This result suggests that the distribution of G.candidum citrus race is not restricted to the citrus-cultivating areas, but is also widely distributed in soils on noncitrus fields of diverse plant species.
The citrus race and noncitrus races were similar
morphologically, but differed in some physiological properties such as the radial growth rate on PDA and growth in autoclaved lemon juice at pH 2.2 Polygalacturonase activity and pathogenicity of citrus race were higher than that of noncitrus race. Citrus race showed 10 species of citrus and 6 species of vegitable and other fruits. Variation in susceptibility to sour rot pathogen was also found on satsuma mandarin fruit from varying maturity stages. The susceptibility of the fruit decreased with the advancement of maturity. The young, green fruits that contained less sugars and polyphanol, but more citric acid and water content than mature, yellow fruit was more susceptible to sour rot pathogen. Several volatile compounds which are known as constituents of citrus fruit were investigated for their effects on germination and growth of the citrus sour rot pathogen, both on PDA and lemon peel. Of them, alchols (heptanol, octanol, nonanol and decanol) at concentration of 1,000 ppm obviously inhibited the growth of this pathogen, both on PDA and on lemon peel. Fungicidal activities of Befran-25 and Chloramine-T were tested in relation with arthrospore germination and growth of G.candidum and development of sour rot on lemon fruit. Befran-25 at concentration of 1,000 ppm completely inhibited the growth and the development of sour rot on lemon fruit. Less