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.

中文翻译：

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美洲山核桃疮痂病病原体文丘里氏菌有性阶段的首次描述

摘要 山核桃疮痂病是由文丘里菌引起的，是美国东南部最流行的山核桃病害。最近对 V. effusa 交配型 (MAT) 分布的表征表明，MAT 的特性在不同空间尺度上处于平衡状态，表明有规律的性重组。然而，V. effusa 的有性阶段的发生从未被观察到，病原体以前被认为完全依赖于无性繁殖。我们能够通过在燕麦培养基上配对相反交配类型的分离株来产生有性阶段。培养物在 24°C 下孵育 2 个月，以使来自每种交配类型的分离株的菌丝相互作用。然后将培养板在 4°C 下孵育 4 个月，之后观察到未成熟的假膜。在 24°C 下暴露于 12 小时光周期 2 周后，子囊和子囊孢子很容易形成。在 4 C 下孵育 4 个月时，假膜和子囊孢子的产生是最佳的。我们利用来自白化病分离物和野生型（黑化）分离物的杂交后代来确定重组已经发生。使用 32 个微卫星标记的多位点基因分型证实，后代是重组的结果，交配类型的分离和培养物色素沉着进一步支持了这一点。白化病后代都被证实在聚酮合酶 (PKS1) 黑色素生物合成基因中含有与白化病亲本相同的突变。这项研究的结果证明了 V. effusa 的异源性。