Peres N A, Mackenzie S J, Peever T L, Timmer L W
University of Florida, Department of Plant Pathology, Gulf Coast Research and Education Center, Wimauma 33598, USA.
Phytopathology. 2008 Mar;98(3):345-52. doi: 10.1094/PHYTO-98-3-0345.
Colletotrichum acutatum causes two diseases of citrus, postbloom fruit drop (PFD) and Key lime anthracnose (KLA). PFD is a disease restricted to flowers of sweet orange and most other citrus, and symptoms include petal necrosis, abscission of developing fruit, and the formation of persistent calyces. KLA is a disease of foliage, flowers, and fruits of Key lime only, and symptoms include necrotic lesions on leaves, fruits, twigs, flowers, and blight of entire shoots. The internal transcribed spacers 1 and 2 and the gene encoding the 5.8S ribosomal RNA subunit within the nuclear ribosomal cluster (ITS) and intron 2 of the glyceraldehyde-3-phosphate dehydrogenase gene (G3PD) were sequenced for isolates from PFD-affected sweet orange and KLA-affected Key limes collected in the United States (Florida), Brazil (São Paulo), Mexico, Belize, Costa Rica, and the Dominican Republic to determine if there are consistent genetic differences between PFD and KLA isolates over the geographic area where these diseases occur. Based on the sequence data, isolates clustered into two well-supported clades with little or no sequence variation among isolates within clades. One clade (PFD clade) contained PFD isolates from all countries sampled plus a few isolates from flowers of Key lime in Brazil. The other clade (KLA clade) contained KLA isolates from Key lime foliage from all countries sampled and one isolate from flowers of sweet orange in Mexico. In greenhouse inoculations with PFD and KLA isolates from Florida, isolates from both clades produced PFD symptoms on Orlando tangelo flowers, but KLA-clade isolates produced significantly less severe symptoms. PFD-clade isolates were not pathogenic to Key lime foliage, confirming previous studies. The differentiation of PFD and KLA isolates into two well-supported clades and the pathogenicity data indicate that PFD and KLA are caused by distinct phylogenetic lineages of C. acutatum that are also biologically distinct. PFD is a recently described disease (first reported in 1979) relative to KLA (first reported in 1912) and it had been proposed that strains causing PFD evolved from strains causing KLA eventually losing pathogenicity to Key lime foliage. We reject the hypothesis that PFD strains have diverged from KLA strains recently based on estimated divergence times of haplotypes and it appears that PFD and KLA strains have been dispersed throughout the Americas independently in association with each host.
尖孢炭疽菌可引发柑橘的两种病害，即花期后落果病（PFD）和墨西哥莱檬炭疽病（KLA）。PFD仅局限于甜橙及大多数其他柑橘类的花朵，症状包括花瓣坏死、发育中果实脱落以及宿存萼片的形成。KLA仅发生于墨西哥莱檬的叶片、花朵和果实，症状包括叶片、果实、嫩枝、花朵上的坏死斑以及整枝枯萎。对从美国（佛罗里达州）、巴西（圣保罗）、墨西哥、伯利兹、哥斯达黎加和多米尼加共和国采集的受PFD影响的甜橙和受KLA影响的墨西哥莱檬的分离株，对其核糖体DNA内转录间隔区1和2、编码5.8S核糖体RNA亚基的基因（ITS）以及甘油醛-3-磷酸脱氢酶基因（G3PD）的内含子2进行测序，以确定在这些病害发生的地理区域内，PFD和KLA分离株之间是否存在一致的遗传差异。基于序列数据，分离株聚为两个得到充分支持的分支，分支内分离株之间的序列变异很少或没有。一个分支（PFD分支）包含来自所有采样国家的PFD分离株以及巴西少数来自墨西哥莱檬花朵的分离株。另一个分支（KLA分支）包含来自所有采样国家墨西哥莱檬叶片的KLA分离株以及墨西哥一个来自甜橙花朵的分离株。在温室中用来自佛罗里达州的PFD和KLA分离株进行接种试验时，两个分支的分离株在奥兰多橘柚花上均产生了PFD症状，但KLA分支的分离株产生的症状明显较轻。PFD分支的分离株对墨西哥莱檬叶片无致病性，这证实了先前的研究。PFD和KLA分离株分化为两个得到充分支持的分支以及致病性数据表明，PFD和KLA是由尖孢炭疽菌不同的系统发育谱系引起的，在生物学上也有差异。相对于KLA（1912年首次报道），PFD是一种最近才描述的病害（首次报道于1979年），有人提出引起PFD的菌株是由引起KLA的菌株进化而来，最终失去了对墨西哥莱檬叶片的致病性。基于单倍型的估计分化时间，我们拒绝PFD菌株最近从KLA菌株分化而来的假说，而且似乎PFD和KLA菌株已与各自的寄主独立地在美洲各地传播。
