Marchant Wendy G, Gautam Saurabh, Hutton Samuel F, Srinivasan Rajagopalbabu
Department of Entomology, University of Georgia, Tifton, GA, United States.
Department of Entomology, University of Georgia, Griffin, GA, United States.
Front Plant Sci. 2020 Dec 7;11:599697. doi: 10.3389/fpls.2020.599697. eCollection 2020.
is a species in the genus and family . Tomato yellow leaf curl virus (TYLCV) infection induces severe symptoms on tomato plants and causes serious yield losses worldwide. TYLCV is persistently transmitted by the sweetpotato whitefly, (Gennadius). Cultivars and hybrids with a single or few genes conferring resistance against TYLCV are often planted to mitigate TYLCV-induced losses. These resistant genotypes (cultivars or hybrids) are not immune to TYLCV. They typically develop systemic infection, display mild symptoms, and produce more marketable tomatoes than susceptible genotypes under TYLCV pressure. In several pathosystems, extensive use of resistant cultivars with single dominant resistance-conferring gene has led to intense selection pressure on the virus, development of highly virulent strains, and resistance breakdown. This study assessed differences in TYLCV genomes isolated from susceptible and resistant genotypes in Florida and Georgia. Phylogenetic analyses indicated that Florida and Georgia isolates were distinct from each other. Population genetics analyses with genomes field-collected from resistant and susceptible genotypes from Florida and/or Georgia provided no evidence of a genetic structure between the resistant and susceptible genotypes. No codons in TYLCV genomes from TYLCV-resistant or susceptible genotypes were under positive selection, suggesting that highly virulent or resistance-breaking TYLCV strains might not be common in tomato farmscapes in Florida and Georgia. With TYLCV-resistant genotypes usage increasing recently and multiple tomato crops being planted during a calendar year, host resistance-induced selection pressure on the virus remains a critical issue. To address the same, a greenhouse selection experiment with one TYLCV-resistant and susceptible genotype was conducted. Each genotype was challenged with TYLCV through whitefly-mediated transmission serially 10 times (T-T). Population genetics parameters at the genome level were assessed at T, T, and T. Results indicated that genomes from resistant and susceptible genotypes did not differentiate with increasing transmission number, no specific mutations were repeatedly observed, and no positive selection was detected. These results reiterate that resistance in tomato might not be exerting selection pressure against TYLCV to facilitate development of resistance-breaking strains. TYLCV populations rather seem to be shaped by purifying selection and/or population expansion.
是属和科中的一个物种。番茄黄化曲叶病毒（TYLCV）感染会在番茄植株上引发严重症状，并在全球范围内导致严重的产量损失。TYLCV由烟粉虱[Bemisia tabaci (Gennadius)]持续传播。通常种植具有单个或少数抗TYLCV基因的品种和杂交种，以减轻TYLCV造成的损失。这些抗性基因型（品种或杂交种）对TYLCV并非免疫。在TYLCV压力下，它们通常会发生系统感染，表现出轻微症状，并且比易感基因型能产出更多适销对路的番茄。在几个病理系统中，广泛使用具有单个显性抗性基因的抗性品种，导致对病毒的选择压力增大，高毒力菌株的出现以及抗性丧失。本研究评估了从佛罗里达州和佐治亚州的易感和抗性基因型中分离出的TYLCV基因组的差异。系统发育分析表明，佛罗里达州和佐治亚州的分离株彼此不同。对从佛罗里达州和/或佐治亚州抗性和易感基因型田间采集的基因组进行群体遗传学分析，未发现抗性和易感基因型之间存在遗传结构的证据。TYLCV抗性或易感基因型的TYLCV基因组中没有密码子受到正选择，这表明高毒力或抗性突破型TYLCV菌株在佛罗里达州和佐治亚州的番茄种植环境中可能并不常见。随着最近抗性基因型的使用增加以及在一个日历年内种植多季番茄作物，寄主抗性对病毒产生的选择压力仍然是一个关键问题。为解决此问题，使用一种抗TYLCV和易感基因型进行了温室选择实验。每种基因型通过粉虱介导的传播连续10次（T1-T10）用TYLCV进行挑战。在T1、T5和T10时评估基因组水平的群体遗传学参数。结果表明，抗性和易感基因型的基因组不会随着传播次数的增加而分化，没有反复观察到特定突变，也未检测到正选择。这些结果重申，番茄中的抗性可能不会对TYLCV施加选择压力以促进抗性突破菌株的发展。相反，TYLCV群体似乎是由纯化选择和/或群体扩张塑造的。
