Studies on the control of downy mildow disease of maize in tropical countries of Asia

Technical bulletin of the Tropical Agriculture Research Center
ISSN 03889394
書誌レコードID(総合目録DB) AA00857848
In tropical and sub-tropical countries, downy mildew disease of maize seriously hampers maize production. The present study was carried out to investigate the extent of the damage produced, the characteristics of the appearance of the systemic symptoms, the mode of occurrence of the disease. On the basis of the results obtained, the author suggested effective control measures from the angle of maize cultivation under the present situation. The results can be summarized as follows:
1. More than 50 % among the infected plants with systemic symptoms caused by Sclerospora maydis died, while the growth of the other half was severely impaired with only 2 - 3 % ear production. Grain production was practically inexistant.
2. Small localized lesions were observed at the time of conidia penetration. The hyphae became elongated and reached the growing point. Subsequently they invaded the newly formed tissues. Newly formed leaves showed yellow streaks. As for the systemic symptoms they manifested themselves under 2 forms.
a) At first, local lesions were present on leaves at the point of invasion of the germtube of conidia (see Plate 6) and systemic symptoms were not observed before the 5th or 6th leaf stage (type I).
b) The systemic symptoms appeared in the middle or late growing stages (type II).
3. In tropical countries of Asia, control by fungicides is difficult to achieve since the growth rate of leaves is twice as fast as in Japan.
4. In Indonesia, the temperature and humidity level are conducive to the production and dissemination of conidia throughout the years. As a result, the damage is severe.
5. Transmission of the disease takes place by conidia and contaminated seeds originating from infected plants. However there are cases where the source of primary infection remains unclear.
6. In Indonesia, the author demonstrated that conidial dissemination of the disease occurred within a range of 42 m.
7. The sensitivity of maize plant to the disease was found to vary depending on the stage of growth. Sensitivity was maximum at the first leaf stge and decreased with advancing growth. It became difficult to infect plants after the plants reached the 6th leaf stage. As conidial production in infected plants chiefly developed from the 6th leaf stage, onward it became evident that the infection of plants located in the same plot and sown at the same time could not occur.
8. Results from field experiments showed that heavily infected maize plants produced abundant conidia enabling the infection of adjacent plots to take place. Conidial infection could occur within a short distance. Also, there were some instances where conidial production as a source of secondary infection could not be detected in the plot where maize plants showed mild infection.
In the case of maize cultivation in a field which had been heavily infected during the previous crop season, infected plants could be observed although conidia could not be recognized as a source of primary infection in adjacent fields. Therefore the author suggested that oospores or other pathogenic agents which tolerate dry conditions be considered as the source of the infection, although such structures have not been demonstrated hitherto. In that respect further stdies should be conducted.
9. On the basis of these investigations, control measures aimed at the prevention of the disease were proposed from the angle of crop production.
a) At the time of sowing, infected maize and sensitive plants should be removed in the adjacent plots within a range of 42 m so as to prevent conidial dissemination. Since maize is sensitive to the disease before reaching the 6th leaf stage, infected plants in adjacent fields should be removed to avoid the infection.
b) Within an area, sowing should take place at the same time to prevent crossinfection among plants at different stages of growth.
c) When maize plants become infected, they should be removed and burned, so as to prevent infection in the next sowing season via seeds or unknown agents acting as a source of primary infection.
d) Seeds should be used only after being dried (13 to 14 % moisture).
作成者 Haruo Mikoshiba
公開者 Tropical Agriculture Research Center
開始ページ 1
終了ページ 75
言語 eng