ABSTRACT

Neofusicoccum species are endophytes and pathogens of woody hosts and members of the Botryosphaeriaceae. Leaf dieback is a new disease resulting in death of compound leaves and extensive defoliation of pecan trees (Carya illinoinensis) throughout the southeastern United States. Currently, the disease is consistently most severe on trees that are not managed with fungicides for pecan scab. Preliminary observations of the fungus isolated from symptomatic leaves indicated that it was a member of the genus Neofusicoccum. Our objectives were to confirm that this is the causal organism of leaf dieback disease of pecan and to determine whether this disease is caused by a new or previously described species of Neofusicoccum. Morphological observations of pure cultures, conidiomata, conidiogenous cells, and conidia were consistent with members of the genus Neofusicoccum. Using Koch’s postulates, we established that Neofusicoccum sp. isolated from symptomatic leaves caused the disease. We sequenced the internal transcribed spacer of the rDNA (ITS), elongation factor 1-α (EF1-α), the second largest subunit of RNA polymerase II (RPB2), and β-tubulin (TUB2) of 11 isolates collected from Georgia and Texas. Phylogenetic and network analyses of these sequences combined with publicly available sequences of 40 members of the N. parvum–N. ribis species complex and the outgroup N. australe revealed that this fungus is a member of the species complex but is genetically distinct from previously described species. We determined that leaf dieback of pecan is caused by a novel species, named herein N. caryigenum.

摘要

Neofusicoccum物种是木本宿主和葡萄球菌科成员的内生菌和病原体。叶枯萎病是一种新病害，可导致美国东南部的山核桃树 ( Carya illinoinensis ) 的复叶死亡和大面积落叶。目前，这种疾病在没有用杀菌剂处理山核桃疮痂病的树木上一直是最严重的。从有症状的叶子中分离出的真菌的初步观察表明它是新粘孢子菌属的成员。我们的目标是确认这是山核桃叶枯死病的致病生物，并确定该病害是由新的或先前描述的新镰孢菌引起的. 纯培养物，分生孢子，分生孢子细胞和分生孢子的形态学观察与属的成员一致Neofusicoccum。使用 Koch 的假设，我们确定了Neofusicoccum sp。从有症状的叶子中分离出引起该病的。我们对 rDNA (ITS) 的内部转录间隔区、延伸因子 1 - α ( EF1-α )、RNA 聚合酶 II ( RPB2 )的第二大亚基和 β-微管蛋白 ( TUB2 ) 的 11 个分离株进行了测序德克萨斯州。这些序列的系统发育和网络分析与N. parvum – N. ribis的 40 个成员的公开可用序列相结合物种复合体和外群N. australe揭示了这种真菌是物种复合体的成员，但在遗传上与先前描述的物种不同。我们确定山核桃的叶子枯死是由一种新物种引起的，在此命名为N. caryigenum。