PATHOGEOGRAPHIC STUDIES OF SUGARCANE DOWNY MILDEW IN TAIWAN III. A COMPARATIVE STUDY OF VARIETAL DISEASE PATTERNS IN THREE PATHOGEOGRAPHIC REGIONS

Abstract

The downy mildew disease patterns of 7 major sugarcane varieties in 3 pathogeographic regions were compared based upon the disease survey records from 1965-1978. The varieties studied were F155, F156, F146, F160, F161, F167 and NCo31O. The regions compared were Huwey (a region of sporadic occurence), Hsinying (a region of severe disease) and Pingtung (a region of marginal damage). The attributes to disease development pattern considered are the amount of disease-conducive varieties which determines an infection spectrum as well as the inoculum source in the population. Susceptibiliy and resistance of the variety are conditioned by. environmental influence in the different regions. It was found the susceptibility rating of varieties based on historical records was similar to that based on field testing. F155 was found highly susceptible. F156, F161 and F146 were found resistant. The primary factor associated with disease on these varieties appeared to be per cent of the planted area. Other factors such as per cent of disease conducive varieties planted, potential inoculum, susceptibility of the variety and environment may play secondary role. Infection of F160, F167 and NCo3IO in the different regions varied. It is speculated that disease intensity on these varieties depend on environment, while per cent of the variety planted and per cent of disease-conducive varieties planted were secondary factors. The primary factors associated with variety infection in Huwey was the availability of disease-conducive variety and potential inoculum; in Hsinying, the per cent of the variety planted; and in Pingtung, environment seemed to play the primary role. 取自臺糖公司1965至1978年來之病害調查資料，比較三個不同病害地理區域即虎尾（偶發病區）、新營（主要受害區）及屏東（邊際受害區），其中七個主要甘蔗品種(F155, F156, F146, F160, F161, F167及NCo310)之露菌病發病情形。根據歷年發病資料估計之品種抗感病等級，大致與田間試驗測定之結果相等。F155極為感病。F156, F161及F146均為抗病，影響各品種發病之主因似為該品種所佔之栽種百分比，其他因子如助長發病之品種栽種百分比，潛在之發病源、品種之感病性及環境可能亦有影響。各區之F160, F167及NCo310之發病情形不一。該等品種之發病主要可能受環境影響，各品種及助長發病品種之栽種百分比亦有影響，故推測影響各區發病情形之主因大致如下：(1)虎尾：助長發病之寄主組織及潛在感染源之多寡；(2)新營：品種之栽種百分比；(3)屏東：環境因子。