PATHOGEOGRAPHIC STUDIES OF SUGARCANE DOWNY MILDEW IN TAIWAN III. A COMPARISON OF CLIMATIC CONDITIONS IN FOUR PATHOGEOGRAPHIC REGIONS

Abstract

The climatic conditions of four pathogeographic regions of sugarcane downy mildew as represented by Huwey (sporadic region), Hsinying .(main damae region), Pingtung (marginal damage region) and Taichung (nonepidemic region) were compared. No striking difference in the annual means of different climatic factors and the climatic patterns for the different months can be identified to account for the difference in disease intensities in the pathogeographic regions. The dynamic disease patterns of the period studied (1965-1978) does not correspond to the dynamic of climatic conditions. In a qualitative analysis of the records, none of the weather variables of the four months (the disease onset period) studied can be used to distinguish epidemic and nonepidemic years and no distinct climatic trend can be found in epidemic years that deviate from the climatic conditions of normal years. Quantitative analysis of the relationship between infection on F160 and F155 and climatic factors in Pingtung was conducted. Disease on F160 appeared to be associated with the amount of sunshine while high temperature and low humidity appeared to be associated with lower level of disease on F155. Failure to identify the relationship between climate and disease was attributed to the irrelevancy of macroclirnatic data since the downy mildew pathogen is highly sensitive to microenvironment which is crucial to disease development. It is also suggested that host factor may play a more important rote other than the climatic factors in the sugarcane downy mildew disease. 虎尾（偶發病區）、新營（主要受害地區）、屏東（邊際受害地區）及臺中（非流行病區）等糖廠區域自1965至1978年氣象條件之比較顯示：(1)各區之氣象因子之年平均或各月份之氣象相大致相似。(2)病害與氣象之變遷並不吻合。(3)根據歷年資料之定性分析，初期發病月份之氣象趨勢亦與常年無太大偏差。(4)相關分析之結果顯示，F160品種之發病似與日照量有關，而F155之發病則與溫度高低及低濕度有關。因為露菌對氣象因子極為敏感，故從大氣象資料無法洞測氣象因子與發病之關係，微氣象與發病之關係較為密切，而且露菌病寄主因子可能較氣象因子為重要。