Articles
AGROMETEOROLOGICAL ZONING IN CHINA AND DAMAGES OF THE POTATO CROP BY BACTERIAL WILT
Through analysis of geographic and climatic conditions, the potato-growing areas in China are classified into four cropping zones with different meteorological characteristics, i.e. a northern single crop zone, a central double crop zone, a southern double crop zone and a southwestern single and double mixed crop zone (Ke-shan Agri.
Institute, 1982, Song Bo Fu, 1986) (Figure 1 and Table 1). More than eighty per cent of the potato fields are located in the northern single crop zone and the southwestern single and double mixed crop zone.
Bacterial wilt in potatoes was firstly reported in Shanghai suburbs in the 1960s and then observed in a few provinces in the 1970s, restricted to the lowlands of the southern double crop zone and the southwestern single and double mixed crop zone (He and Hua, 1985). But now this disease is found in at least 17 provinces or regions of the four potato cropping zones and has become a serious threat for the potato production in China (Table 2).
Based upon studies on strains of Pseudomonas solanacearum, collected from different potato cropping zones, two races have been observed, race 1 and race 3 (He, 1986). It is known that race 1 has a high optimum growth temperature of 35-37°C, whereas race 3 possesses a low optimum growth temperature of 27-28°C (Hayward, 1976). Of 46 potato isolates examined in China, 41 belonged to race 3, these were mostly obtained from the highlands or hills of the southwestern mixed cropping zone, i.e. the highland single mixed cropping zone, where the temperature in the summer is relatively low and precipitation is high.
Four of the five isolates of race 1 were collected from plains or lowlands on the southern, southwestern and central cropping zones.
Since the highlands or hills of the southwestern mixed cropping zone are major potato producing areas in China, the rapid increase in the presence of race 3 has become a challenging problem for potato production in these areas.
Although race 3 has spread into the northern single cropping zone, the most important potato producing zone in China, the bacterial wilt there is not severe so far.
For the control of potato bacterial wilt, integrated management strategies are applied in China.
The strategies include avoidance of water flowing in potato fields after heavy rainfall, and prevention of high moisture.