A simple and convenient inoculation method using small wooden chips made of disposable chopsticks for Rosellinia necatrix, the causal fungus of white root rot disease on fruit trees.

A simple and convenient inoculating method for Rosellinia necatrix , the causal fungus of white root rot disease of fruit tree, was developed. The R. necatrix W563 was incubated on potato dextrose agar medium (PDA) plate for 1 - 2 weeks at 25 o C. The wooden chips (ca. 30 x 5 x 5mm) made of disposable chopsticks were autoclaved at 120 o C for 20 minutes and placed on the colony of W563 and incubated for 1 week at 25 o C. Each infected wooden chip was cut off into uniform length of 20mm, and was attached onto the stem base of one year old of Chinese crab apple ( Malus prunifolia ) seedling grown in the small plastic pot and tightly fixed with a Parafilm tape. The inoculated region was covered with soil and the seedling was incubated in the air-conditioned greenhouse at 25 o C. Three weeks after inoculation, four of five seedlings inoculated with W563 showed decline in newly developed twigs followed by wilt and fall of the leaves resulting in total death by 6 weeks after inoculation. In another trial, the small wooden chips (ca. 10 x 5 x 5mm) placed and incubated on W563 colony for 2 weeks were perpendicularly inserted into the soil nearby the stem base of the seedlings of yellow lupine ( Lupinus luteus ), apple ( Malus x domestica ) and Japanese pear ( Pyrus pyrifolia ). All the plants inoculated through the insertion of wooden chips showed almost the same symptoms as those of the first experiment, by 6 weeks after inoculation. The above mentioned inoculation methods, especially by means of infested wooden chip insertion, were very stable in their pathogenic effect, simpler and more convenient than the traditional way using the infested soil prepared by mixing with infested wheat bran.