Department of Plant Pathology and Ecology, Connecticut Agricultural Experiment Station, P. O. Box 1106, New Haven, Connecticut 06504, USA.
Mycologia. 2011 Jul-Aug;103(4):806-19. doi: 10.3852/10-155. Epub 2011 Apr 6.
Sudden vegetation dieback (SVD) is the loss of smooth cordgrass (Spartina alterniflora) along intertidal creeks in salt marshes of the Atlantic and Gulf states. The underlying cause of SVD remains unclear, but earlier work suggested a contributing role for Fusarium spp. in Louisiana. This report investigated whether these or other Fusarium species were associated with S. alterniflora dieback in mid- to north-Atlantic states. Isolations from seven SVD sites yielded 192 isolates of Fusarium spp., with more than 75% isolated from aboveground tissue. Most isolates (88%) fell into two undescribed morphospecies (MS) distinguished from each other by macroconidial shape, phialide ontogeny and growth rates. Pathogenicity tests on wound-inoculated S. alterniflora stems and seedling roots revealed that isolates in MS1 were more virulent than those in MS2 but no single isolate caused plant mortality. No matches to known species of Fusarium were revealed by DNA sequence queries of translation elongation factor 1-α (tef1) sequences. A phylogenetic analysis of partial sequences of three genes, β-tubulin (β-tub), calmodulin (cal) and tef1, was conducted on representative isolates from MS1 (n = 20) and MS2 (n = 18); it provided strong evidence that the MS1 isolates form a clade that represents a heretofore undescribed species, which we designate Fusarium palustre sp. nov. Isolates from the more variable MS2 clustered with the F. incarnatum-equiseti species complex as F. cf. incarnatum. Although a strong association exists between both species and declining S. alterniflora in SVD sites, neither appears to play a primary causal role in SVD. However, our findings suggest that F. palustre might play an important secondary role in the ecological disruption of the salt marshes.
突发性植被衰退（SVD）是指大西洋和墨西哥湾各州盐沼潮间带沟渠中光滑大米草（Spartina alterniflora）的消失。SVD 的根本原因仍不清楚，但早期的研究表明，镰刀菌属（Fusarium spp.）在路易斯安那州起了一定作用。本报告研究了这些或其他镰刀菌属物种是否与中大西洋至北大西洋各州的大米草衰退有关。从七个 SVD 地点分离得到 192 株镰刀菌属菌株，其中 75%以上分离自地上组织。大多数分离株（88%）分为两个未描述的形态种（MS），彼此之间通过大分生孢子形状、瓶梗发生和生长速度来区分。对创伤接种的大米草茎和幼苗根进行的致病性测试表明，MS1 中的分离株比 MS2 中的分离株更具毒性，但没有单个分离株导致植物死亡。通过翻译延伸因子 1-α（tef1）序列的 DNA 序列查询，未发现与已知镰刀菌属物种相匹配的序列。对来自 MS1（n = 20）和 MS2（n = 18）的代表性分离株的三个基因，β-微管蛋白（β-tub）、钙调蛋白（cal）和 tef1 的部分序列进行的系统发育分析提供了强有力的证据，表明 MS1 分离株形成了一个代表迄今为止未描述物种的分支，我们将其命名为腐皮镰刀菌（Fusarium palustre）。来自更具变异性的 MS2 的分离株与 F. incarnatum-equiseti 种复合体聚类，为 F. cf. incarnatum。虽然这两个物种与 SVD 地点的衰退大米草之间存在很强的关联，但它们似乎都没有在 SVD 中起主要的因果作用。然而，我们的研究结果表明，腐皮镰刀菌可能在盐沼生态破坏中发挥重要的次要作用。
