Centro APTA Citros Sylvio Moreira, Centro de Citricultura Sylvio Moreira, Instituto Agronômico (IAC), CP 04, Cordeirópolis, SP, 13490-970, Brazil.
Departamento de Genética, Instituto de Biociências, UNESP, Caixa Postal 510, CEP, Botucatu, SP, 18618-000, Brazil.
BMC Genomics. 2018 Jul 3;19(1):516. doi: 10.1186/s12864-018-4888-2.
Phytophthora nicotianae Breda de Haan (Phytophthora parasitica Dastur) causes severe damage to citrus crops worldwide. A population of citrandarins was created from the cross between the susceptible parent Citrus sunki Hort. Ex Tan. and the resistant parent Poncirus trifoliata (L.) Raf. cv. Rubidoux, both parents and two reference rootstocks (Rangpur lime and Swingle citrumelo) were grafted in a greenhouse on Rangpur lime. Inoculations were performed at 10 cm and 15 cm above the grafting region and the resulting lesions were evaluated by measuring the lesion length 60 days after inoculation. As control, non-inoculated plants of each genotype were used. In addition, we evaluated the expression of 19 candidate genes involved in citrus defense response 48 h after pathogen infection by quantitative Real-Time PCR (qPCR). We mapped genomic regions of Quantitative Trait Loci (QTLs) and Expression Quantitative Trait Loci (eQTLs) associated with resistance to P. parasitica in the linkage groups (LGs) of the previously constructed maps of C. sunki and P. trifoliata.
We found disease severity differences among the generated hybrids, with lesion lengths varying from 1.15 to 11.13 mm. The heritability of the character was 65%. These results indicate that there is a great possibility of success in the selection of resistant hybrids within this experiment. The analysis of gene expression profile demonstrated a great variation of responses regarding the activation of plant defense pathways, indicating that citrandarins have several defense strategies to control oomycete infection. The information of the phenotypic and gene expression data made possible to detect genomic regions associated with resistance. Three QTLs and 84 eQTLs were detected in the linkage map of P. trifoliata, while one QTL and 110 eQTLs were detected in C. sunki.
This is the first study to use eQTLs mapping in the Phytophthora-citrus interaction. Our results from the QTLs and eQTLs mapping allow us to conclude that the resistance of some citrandarins to the infection by P. parasitica is due to a favorable combination of QTLs and eQTLs transmitted by both parents.
烟草疫霉（Phytophthora parasitica Dastur）对世界各地的柑橘作物造成严重破坏。通过易感性亲本甜橙（Citrus sunki Hort. Ex Tan.）和抗性亲本枳（Poncirus trifoliata（L.）Raf. cv. Rubidoux）杂交产生了一个甜橙枳杂种群体，两者的亲本和两个参考砧木（莱姆和莱檬杂种）都在温室里嫁接到莱姆砧木上。在嫁接区域上方 10cm 和 15cm 处进行接种，接种后 60 天通过测量病变长度来评估病变。作为对照，使用每个基因型的未接种植物。此外，我们还通过定量实时 PCR（qPCR）在病原菌感染后 48 小时评估了 19 个与柑橘防御反应相关的候选基因的表达。我们在先前构建的甜橙和枳图谱的连锁群（LG）中定位了与对 P. parasitica 抗性相关的数量性状位点（QTL）和表达数量性状位点（eQTL）的基因组区域。
我们发现所产生的杂种之间存在疾病严重程度的差异，病变长度从 1.15 到 11.13mm 不等。该性状的遗传力为 65%。这些结果表明，在本实验中，成功选择抗性杂种的可能性很大。基因表达谱分析表明，植物防御途径的激活存在很大的差异，表明甜橙枳具有几种控制卵菌感染的防御策略。表型和基因表达数据的信息使得检测与抗性相关的基因组区域成为可能。在枳图谱中检测到 3 个 QTL 和 84 个 eQTL，而在甜橙图谱中检测到 1 个 QTL 和 110 个 eQTL。
这是首次在柑橘与疫霉的相互作用中使用 eQTL 作图。我们从 QTL 和 eQTL 作图中得到的结果使我们能够得出结论，一些甜橙枳对 P. parasitica 感染的抗性是由于由双亲传递的有利的 QTL 和 eQTL 组合所致。
