Abstract
1. The present paper deals with a method of disease resistance trials of sugar cane varieties to red rot caused by Colletotrichuin falcatum WENT and with the results hitherto obtained by this method at the Government Sugar Experiment Station, Tainan, Formosa.
2. The sugar cane varieties improved in our station and other imported ones are tested for the resistance to red rot by inoculating the causal fungus to the stalks of the growing canes.
3. The main points of the method of inoculation and measurement of the size of affected part of the stalks are as follows:
(1) The fungus cultured at 28°C for four days on cane juice agar is used for the inoculum.
(2) A small portion of the fungus culture is inserted into the hole, bored by a kind of punch with an opening 7 mm in diameter, in the center of the internode of the cane stalk.
(3) The inoculated stalks are split lengthwise at the harvest time and the size of the affected tissues is measured.
(4) The inoculation is performed at the time two to three months prior to the harvest.
(5) About thirty to fourty stalks of each varieties may be sufficient for one trial.
4. The resistance of each variety to red rot is judged by the theoretical figure derived from the number of the diseased internodes. When the area of the affected portion of the inoculated stalks holds more than 2/3 part of an internode, it is collected under sign + + +, between 2/3 and 1/3, it is collected under sign + +, and below 1/3 under sign + respectively. The number of diseased internodes belonging to the class + + + is then multiplied by 3/3, the number of the class + + by 2/3, and the number of the class + by 1/3. The degree of damage (b) will be obtained when total sum of the figure of three classes of each variety is divided by the number of stalks measured. Then the ratio (b'), quotient of the figure of damage of each variety by that of the standard one, may be the theoretical figure to compare the resistance of each variety. If the figure of ratio (b') of one variety is above 1 the variety may be less resistant than the standard one, on the contrary, if the figure of ratio of another variety is below 1, the variety may be more resistant than the standard one.
5. The varietal resistance of sugar cane to red rot obtained by this method are tabulated elsewhere, which has been carried out since 1936.
6. For the selection of the resistant varieties of sugar cane to red rot this inoculation technique together with the field observation are now put in practice at our station.
Government Sugar Experiment Station,
Tainan, Formosa
