Morphological Characteristics and URP-PCR Analysis of Hypocrea sp., a Weed Mould of Oyster Mushroom Cultivation

Recently a serious outbreak of weed mould caused by a species of Hypocrea occurred in oyster mushroom (Pleurotus ostreatus) substrates in Korea. The disease was characterized by a rapid infestation of the oyster mushroom substrates by Hypocrea sp. and subsequent inhibition of fructification of the mushroom. In spite of it's serious losses to the oyster mushroom industry in Korea, etiology and ecology of the disease have not been studied. Morphological characteristics of the fungus were examined and molecular characteristics of the fungus were compared with those of the green moulds (Trichoderma spp.) isolated from oyster mushroom bed. Stromata formed superficially on suface of the substrates were pulvinate to effuse or irreguler, initially white but becoming yellowish brown, measuring $6.0{\sim}13.0{\times}3.0{\sim}11.0mm$. Perithecia were globose to subglobose, immersed in stroma, $223{\sim}263\;(Ave.239.9){\times}167.3{\sim}231\;(Ave.204.1){\mu}m$ in size. Asci were unitunicate, cylindrical, nonamyloid, $82.7{\sim}124.8\;(Ave.103.3){\times}4.1{\sim}5.1\;(Ave.4.9){\mu}m$ in size, 16 part-spored. Ascospores were bullet-shaped or somewhat oblong, hyaline, bicellular, roughened or warted, $5.4{\sim}7.4\;(Ave.6.5){\times}3.6{\sim}5.5\;(Ave.4.7){\mu}m$ in size. This fungus readily form the stroma on PDA. Mycelia on PDA nearly invisible and without cottony aerial mycelium. Optimum temperature for mycelial growth of this fungus was $25^{\circ}C$ on PDA and its growth rate was 15 mm per day. This species did not grow at below 10 and above $35^{\circ}C$. Phialides in culture enlarged in the middle and aggregated to penicillate type. They were very variable, shorted ampulliform and occasionally curved when matured, but cylinderical when young, measuring $11.9{\sim}24.3\;(Ave.\;14.7){\times}2.9{\sim}3.9\;(Ave.\;3.4){\mu}m$ when matured and $7.2{\sim}14.0\;(Ave.\;10.8){\times}2.8{\sim}4.9\;(Ave.\;3.5){\mu}m$ when young. Phialosopres were ovoid to ellipsoid, smooth, measuring $3.5{\sim}7.2\;(Ave.\;4.5){\times}2.6{\sim}3.3\;(Ave.\;2.9){\mu}m$. Nineteen isolates of Hypocrea sp. were analyzed on the basis of molecular characteristics and classified into phenotypic groups. On the basis of RAPD, URP-PCR, the fungus was confirm to monoclonal, and was classified as a different taxon from reported species of Hypocrea and Trichoderma and supposed to be a new species not previously reported in literature.

느타리버섯 유해균 Hypocrea sp.의 형태 및 URP-PCR 분석

느타리버섯 균상에 발생하는 Hypocrea속 균의 분류학적 위치를 확립하기 위하여 유성세대 및 무성세대의 형태적 특징을 조사하였고, 국내 분리 균주의 RAPD, RFLP, URP-PCR 분석 등 분자생물학적 특징을 조사하였다. 1. 충남과 전남 일대의 8개 시, 군의 느타리 재배사에서 19 균주를 분리하였으며 이들 균주간의 형태적, 발생생태학적 변이는 없었고, 기존 보고된 Hypocrea 종들과는 다른 형태적 특징을 나타내었다. 2. Hypocrea 자좌의 크기는 $6.0{\sim}13.0{\times}3.0{\sim}11.0mm$이었고, 위유조직으로 구성되어 있으며 대부분 군생하고 처음엔 백색이지만 성숙되면 노란빛을 띤 갈색을 나타내었다. 자낭각은 구형으로 크기가 평균 $239.9{\times}204.1{\mu}m$이었으며, 자낭에는 16개의 자낭포자(part ascospores)를 형성하였고, 자낭과 장낭포자의 크기는 각각 $103.3{\times}4.9{\mu}m$와 $6.5{\times}4.7{\mu}m$이었다. 3. 무성세대의 phialide는 보통 Trichoderma virens와 유사한 형태로 모여서 형성되나 때때로 penicillate의 형태도 관찰되었다. T. virens형 phialide의 크기는 $10.8{\times}3.5{\mu}m$이었고 penicilliale형은 $14.7{\times}3.4{\mu}m$이었다. 분생포자는 계란형에서 타원형으로 표면은 매끈하고 크기는 $4.5{\times}2.9{\mu}m$이었다. 4. Hypocrea 균주들의 배양적 특징 조사한 결과, PDA 배지에서 균사생장 최적 온도는 $25^{\circ}C$이었고 자좌는 $15{\sim}25^{\circ}C$ 범위에서 발생하였으며 자좌 발생 최적 온도는 $20^{\circ}C$였다. 5. RAPD 및 RFLP 분석을 실시한 결과 Hypocrea속 균은 공시균주는 모두 단일 유전 개체군으로 느타리 재배사에서 발생하는 Trichoderma속 균 및 기존에 보고된 Hypocrea spp.와는 다른 분류군으로 나타났다.