Abstract
A wilt disease on lettuce was observed in 2006 and 2007 in commercial plastic house at main production areas of lettuce in Icheon, Yongin and Goyang of Gyeonggi Province. The disease was characterized by the wilting of lower leaves, accompanied by stunting symptoms of the whole plants. Old affected stems showed the black streak in the vascular system. The pathogen, Fusarium oxysporum f. sp. lactucae was isolated from stems and roots of diseased plants. Isolated pathogen also produced the microconidia and macroconidia with chlamydospores on carnation leaf agar medium. The pathogen easily invaded and made many chlamydospores on the roots of lettuce and also made dark streaking through the vascular in the lettuce stems. The density of Fusarium sp. in the severely diseased field soil was more higher populations than that in the healthy and less diseased field soil. The minimum population of pathogen would be above $10^3$cfu/g soil to induce the Fusarium wilt on lettuce in plastic house. The results of pathogenicity test showed 'Sunpung' and 'Mipungpochap' was high susceptible to Fusarium pathogen isolates while some cultivar 'Mihongjeokchukmyeon' and 'Jinjachukmyeon' showed moderate resistance. Disease development for some lettuce was related to treated temperature, so the symptom was more severe above $25^{\circ}C$. Selection of appropriate lettuce cultivar and planting time should be related for the successful control of Fusarium wilt.
경기도내 주요 상추 시설재배지에서의 Fusarium 시들음병 발생을 2006년과 2007년에 걸쳐 조사한 결과 3월부터 11월까지 발생하였으며, 특히 여름철에 발병주율이 크게 증가하였다. 발병된 상추는 잎이 황화되고 포기 전체가 위축되는 증상을 보였고, 줄기 부위에 뚜렷한 도관부 갈변 증상이 관찰되었다. 시들음증상을 나타내는 상추 줄기에서 Fusarium균을 분리하였고, 균학적 특징을 분석했을 때 Fusarium oxysporum f. sp. lactucae로 동정되었다. 분리된 F. oxysporum을 토양에 접종한 결과 뿌리를 통해 쉽게 균사가 침입하였고, 점차 도관부를 통해 전체 줄기로 진전되었으며, 뿌리 주변에서 후막포자를 형성하였다. 병 발생이 높은 하우스의 토양 내 Fusarium균의 밀도는 건전 또는 병 발생이 낮은 토양보다 밀도가 높고, 병 발생을 일으키는 최소 병원균 밀도는 $10^3$cfu/g 이상으로 추정하였다. 병원균에 대하여 '선풍'과 '미풍포찹' 품종이 가장 감수성이었고, '미홍적축면'과 '진자축면'이 중도저항성 이었으며, 발병은 $25^{\circ}C$ 이상의 온도에서 더 빨리 진전되었다.
