Differentiation between Mycosphaerella dearnessii isolates from USA and China
In this paper, the situation of Mycosphaerella dearnessii (EPPO A2 quarantine pest) in USA and in China is recalled. In southern USA, M. dearnessii causes severe growth reduction or death of seedlings of Pinus palustris. Heavy infections in P. palustris stands can reduce pulpwood yields up to 60 %. In northern USA, defoliation of P. sylvestris can render Christmas trees unmarketable. In south-eastern China, severe damage occurred on P. taeda and P. thunbergii, but unlike in USA only slight damage on P. palustris was seen. In China, the disease was reported near Nanjing (Zhejiang province) in the early 1950s on P. thunbergii but no severe outbreak was seen before 1978. In the meantime, China started to import large amounts of P. elliottii from USA. Since 1978, many young plantations of P. elliottii have been damaged by M. dearnessii. The disease has been especially severe in Fujian Province and has spread to other provinces. Studies on genetic differences between isolates from USA and China were felt useful.
Isolates of M. dearnessii have been collected from northern and southern United States (Alabama, Florida, Louisiana, Mississippi, Iowa, Illinois*, Minnesota, Wisconsin) and from China (Fujian, Guangxi, Jiangsu, Jiangxi, Zhejiang*). These isolates have been analysed for differences in cultural morphology, growth rate, conidial germination at various temperatures and RADP markers. Differences in cultural morphology and conidial germination were detected between northern US isolates and other sources, but not between southern isolates and Chinese isolates. RADP analysis showed that northern US isolates composed a distinct 'northern group' while southern US and Chinese isolates composed a related 'southern group'. The authors felt that their results support a southern US origin of the current Chinese populations. Further studies are needed for a better understanding of the differences between northern and southern US isolates and also between American and European isolates (which so far appear to be closer to northern US isolates).
Sources
Huang, Z.Y.; Smalley, E.B.; Guries, R.P. (1995) Differentiation of Mycosphaerella dearnessii by cultural characters and RAPD analysis.
Phytopathology, 85(5), 522-527.