ABSTRACT

Pecan scab, caused by Venturia effusa, is the most prevalent disease of pecan in the southeastern United States. Recent characterization of the mating type (MAT) distribution of V. effusa revealed that the MAT idiomorphs are in equilibrium at various spatial scales, indicative of regular sexual recombination. However, the occurrence of the sexual stage of V. effusa has never been observed, and the pathogen was previously considered to rely entirely on asexual reproduction. We were able to generate the sexual stage by pairing isolates of opposite mating types on oatmeal culture media. Cultures were incubated at 24 C for 2 mo to allow hyphae from isolates of each mating type to interact. Culture plates were then incubated at 4 C for 4 mo, after which immature pseudothecia were observed. Following exposure to a 12-h photoperiod for 2 wk at 24 C, asci and ascospores readily developed. Pseudothecium and ascospore production was optimal when incubated for 4 mo at 4 C. We utilized progeny from a cross of an albino isolate and wild-type (melanized) isolates to determine that recombination had occurred. Multilocus genotyping using 32 microsatellite markers confirmed that progeny were the result of recombination, which was further supported by segregation of mating types and culture pigmentation. Albino progeny were all confirmed to contain the same mutation in the polyketide synthase (PKS1) melanin biosynthesis gene as the albino parent. The results of this study demonstrate the heterothallic nature of V. effusa. The impact of determining the source of the overwintering ascostroma will aid in management decisions to reduce the primary inoculum in the disease cycle.

摘要

山茱sc结Ven是由美国的南美白对虾（Venturia effusa）引起的，是美国东南部最流行的山核桃病。V. effusa的交配类型（MAT）分布的最新特征表明，MAT的独特性在各种空间尺度上处于平衡状态，表明有规律的性重组。但是，南半球野豌豆有性阶段的发生从未观察到，以前认为病原体完全依靠无性繁殖。通过在燕麦片培养基上配对相反交配类型的分离株，我们能够产生性阶段。将培养物在24°C下孵育2 mo，以使每种交配类型的分离物产生的菌丝相互作用。然后将培养板在4℃下温育4mo，之后观察到未成熟的假皮病。暴露于24小时的12小时光周期2 wk之后，asci和子囊孢子容易发育。当在4 C下孵育4 mo时，假孢子虫和子囊孢的产量最佳。我们利用来自白化分离株和野生型（黑色素化）分离株杂交的后代来确定已经发生重组。使用32个微卫星标记的多基因座基因分型证实了后代是重组的结果，交配类型和培养色素的分离进一步支持了这一点。白化病后代都被证实在聚酮合酶中含有相同的突变（PKS1）黑色素生物合成基因作为白化亲本。这项研究的结果证明了V. effusa的异质性。确定越冬虫草来源的影响将有助于管理决策，以减少疾病周期中的主要接种物。