Ecological Studies on Lettuce Drop Disease Occurring under Controlled Cultivation Conditions in Drained Paddy Fields

답리작 상치 시설재배지에서의 균핵병 발생생태에 관한 연구

Incidence of lettuce drop was observed throughout the growing season in the vinylhouse at the southern part of Korea, Kimhai. Occurrence of this disease was especially severe at the seedling stage. Number of sclerotia in surface soil $(30\times30\times5cm)$ was 22.0 at the seedling stage, and 5.3 at harvest in the infected area. Temperature for mycelial growth ranged from 5 to $30^{\circ}C$ with optimum temperature at $25^{\circ}C$. Sclerotia were formed fewer at low temperature, but their size was larger resulting in heavier dry weight than that at high temperature. The apothecia were formed from the sclerotia that were buried in March, April and September upto 3cm soil depth, but formed from those buried only 1 em soil depth in October. Sclerotia buried in June and December did not form apothecia regardless of soil depth by 90 days. The sclerotia buried in the 5cm of soil depth did not form apothecia. Sclerotia that were embedded in wet or flooded soil at $25^{\circ}C$ and $30^{\circ}C$ for 5 weeks lost their viability. Infection of lettuce was possible with mycelia originated from sclerotia on autoclaved lettuce plant fragments. The fungus was pathogenic on 25 plant species in 8 families in artificial inoculation tests. Lettuce seedlings appeared to be infected by airborne ascospore originated from sclerotia on crops and weeds around paddy fields, because sclerotia existing in soil might perish under long flood conditions during rice cultivation.

답후작으로 시설재배되는 상치에 발생한 균핵병의 발생생태에 대하여 조사연구한 결과, 상치 균핵병은 전생육기간을 통하여 발생하였는데, 특히 유묘기에 피해가 심하였다. 후병지$(30\times30\times5cm)$내의 균핵수는 유묘기에 22.0개, 수확기에는 5.3개가 검출되었다. 이상치 균핵병 (S. sclerotiorum)의 균사생장적온은 $25^{\circ}C$였고, $15^{\circ}C$이하의 온도에서는 $20^{\circ}C$이상의 온도에서보다 균핵의 형성수는 적었으나 큰 균핵을 형성하였고 건물중도 높았다. 토양깊이 및 시기별로 균핵을 매몰하였을 때 3월, 4월 9월의 매몰구에서는 토양깊이 3cm구까지 자양반을 형성하였으나, 6월, 12월의 매몰구에서는 90일간의 조사기간내에는 자 반을 형성하지 않았다. 그리고 중력수만 제거한 토양과 담수토양내에서 균핵을 $25^{\circ}C$와 $30^{\circ}C$로 5주간 처리하였을 때 $100\%$의 균핵이 사멸하였다. 고압멸균된 상치 식물체절편과 함께 균핵을 상치에 접종하였을 때 균핵의 균사형성에 의한 감염이 일어났으며, 포장주위식물에 대한 병원성 조사에서는 조사식물 9과 31종중 화본료 식물을 제외한 8과 25종의 식물에 병원성을 나타냈다. 그러므로 답리작으로 시설재배되는 상치에 발생한 균핵병의 전염원은 포장주위의 기주식물에 형성된 균핵이라고 생각된다.