Phytopathology. 1999 Oct;89(10):851-60. doi: 10.1094/PHYTO.1999.89.10.851.
ABSTRACT Alternaria spp. were sampled from two rough lemon (RL) and two Minneola tangelo (MIN) groves in a limited geographic area in central Florida to test for host-specialized forms of the pathogen. Isolates of Alternaria spp. were scored for variation at 16 putative random amplified polymorphic DNA (RAPD) loci and for pathogenicity on both hosts. Subpopulations on each host were differentiated genetically and pathogenically, which was consistent with the hypothesis of host specialization. Highly significant genetic differentiation was detected among all four subpopulations (Nei's coefficient of gene differentiation [G(ST)] = 0.292, P = 0.000); most of the differentiation occurred between hosts (G(ST) = 0.278, P = 0.000). Phenograms of qualitative similarities among isolates within subpopulations revealed two or three distinct clusters of isolates within each subpopulation. The majority of isolates sampled from RL were pathogenic on RL and not on MIN, although a few RL isolates were able to induce disease on MIN, and 44% were nonpathogenic on either host. In contrast, isolates from MIN were pathogenic only on MIN, never on RL, and only 3% of the isolates were nonpathogenic. Overall, three genetically distinct clusters of isolates were detected on both hosts. One of the clusters (cluster A) sampled from RL was pathogenic on RL and not on MIN and consisted almost entirely of one RAPD genotype. This cluster also contained two isolates that were 93% similar to the majority genotype but were pathogenic on MIN and not RL. In isolates from MIN, two distinct clusters of isolates were found in one subpopulation (clusters B and C), and three distinct clusters were found in another subpopulation (clusters A, B, and C). Clusters A and B were found on both hosts, while cluster C was limited to MIN. Populations of Alternaria spp. sampled from RL and MIN showed a high degree of host specificity; however, the specificity obscured a high level of genetic variation within subpopulations.
从佛罗里达州中部一个有限地理区域的两个粗糙柠檬（RL）和两个 Minneola 橘柚（MIN）果园中采集了 Alternaria spp. 菌株，以测试病原体的宿主专化形式。对 Alternaria spp. 菌株在 16 个假定的随机扩增多态性 DNA（RAPD）基因座的变异和在两种宿主上的致病性进行了评分。在每个宿主上的亚种群在遗传和致病性上都有所不同，这与宿主专化的假设一致。在所有四个亚种群中都检测到高度显著的遗传分化（Nei 的基因分化系数[G(ST)]=0.292，P=0.000）；大部分分化发生在宿主之间（G(ST)=0.278，P=0.000）。在亚种群内的菌株之间定性相似性的 phenograms 显示，每个亚种群内有两个或三个不同的菌株簇。从 RL 中采集的大多数菌株对 RL 具有致病性，但对 MIN 没有致病性，尽管有少数 RL 菌株能够在 MIN 上引起疾病，并且 44%的菌株对两种宿主均无致病性。相比之下，来自 MIN 的菌株仅对 MIN 具有致病性，从未对 RL 具有致病性，并且只有 3%的菌株对两种宿主均无致病性。总体而言，在两种宿主上均检测到三个遗传上截然不同的菌株簇。从 RL 中采集的一个菌株簇（A 簇）对 RL 具有致病性，对 MIN 没有致病性，并且几乎完全由一个 RAPD 基因型组成。该簇还包含两个与大多数基因型相似但对 MIN 具有致病性而对 RL 无致病性的菌株。在来自 MIN 的菌株中，在一个亚种群中发现了两个截然不同的菌株簇（B 和 C 簇），而在另一个亚种群中发现了三个截然不同的菌株簇（A、B 和 C 簇）。A 簇和 B 簇在两种宿主上均有发现，而 C 簇仅限于 MIN。从 RL 和 MIN 采集的 Alternaria spp. 种群表现出高度的宿主特异性；然而，这种特异性掩盖了亚种群内高水平的遗传变异。
