Alves Mônica N, Raiol-Junior Laudecir L, Girardi Eduardo A, Miranda Maéva, Wulff Nelson A, Carvalho Everton V, Lopes Sílvio A, Ferro Jesus A, Ollitrault Patrick, Peña Leandro
Fundo de Defesa da Citricultura, Araraquara, Brazil.
Faculdade de Ciências Agrárias e Veterinárias (FCAV), Universidade Estadual Paulista (UNESP), Jaboticabal, Brazil.
Front Plant Sci. 2022 Sep 9;13:1009350. doi: 10.3389/fpls.2022.1009350. eCollection 2022.
Huanglongbing (HLB), the most destructive citrus disease, is associated with unculturable, phloem-limited Liberibacter species, mainly L. asiaticus (Las). Las is transmitted naturally by the insect . In a previous study, we determined that the Oceanian citrus relatives , , , and and three hybrids among them and were full-resistant to Las. After 2 years of evaluations, leaves of those seven genotypes remained Las-free even with their susceptible rootstock being infected. However, Las was detected in their stem bark above the scion-rootstock graft union. Aiming to gain an understanding of the full-resistance phenotype, new experiments were carried out with the challenge-inoculated Oceanian citrus genotypes through which we evaluated: (1) Las acquisition by fed onto them; (2) Las infection in sweet orange plants grafted with bark or budwood from them; (3) Las infection in sweet orange plants top-grafted onto them; (4) Las infection in new shoots from rooted plants of them; and (5) Las infection in new shoots of them after drastic back-pruning. Overall, results showed that insects that fed on plants from the Oceanian citrus genotypes, their canopies, new flushes, and leaves from rooted cuttings evaluated remained quantitative real-time polymerase chain reaction (qPCR)-negative. Moreover, their budwood pieces were unable to infect sweet orange through grafting. Furthermore, sweet orange control leaves resulted infected when insects fed onto them and graft-receptor susceptible plants. Genomic and morphological analysis of the Oceanian genotypes corroborated that and are pure species while our accession is an × hybrid and probably a × hybrid. × hybrid was found coming from a cross between and mandarin or tangor. × hybrid is a complex admixture of , , and while the last hybrid is an × admixture. Confirmation of consistent full resistance in these genotypes with proper validation of their genomic parentages is essential to map properly genomic regions for breeding programs aimed to generate new -like cultivars yielding immunity to HLB.
黄龙病（HLB）是最具破坏性的柑橘病害，与不可培养的、韧皮部受限的韧皮杆菌属物种有关，主要是亚洲韧皮杆菌（Las）。Las通过昆虫自然传播。在之前的一项研究中，我们确定大洋洲柑橘近缘种、、、以及它们之间的三个杂种和对Las完全抗性。经过2年的评估，即使其易感砧木被感染，这七个基因型的叶片仍未检测到Las。然而，在接穗 - 砧木嫁接结合处上方的茎皮中检测到了Las。为了了解完全抗性表型，对接种挑战的大洋洲柑橘基因型进行了新的实验，通过这些实验我们评估了：（1）取食它们的昆虫获取Las的情况；（2）用它们的树皮或芽条嫁接的甜橙植株中Las的感染情况；（3）顶部嫁接到它们上的甜橙植株中Las的感染情况；（4）它们的生根植株新梢中Las的感染情况；（5）大幅回缩修剪后它们新梢中Las的感染情况。总体而言，结果表明，取食大洋洲柑橘基因型植株、其树冠、新梢以及评估的生根插条叶片的昆虫，经实时定量聚合酶链反应（qPCR）检测仍为阴性。此外，它们的芽条片段无法通过嫁接感染甜橙。此外，当昆虫取食甜橙对照叶片并嫁接受体易感植株时，甜橙对照叶片被感染。对大洋洲基因型的基因组和形态分析证实，和是纯合物种，而我们的种质是×杂种，可能是×杂种。×杂种被发现来自与柑橘或橘橙的杂交。×杂种是、和的复杂混合物，而最后一个杂种是×混合物。在这些基因型中确认一致的完全抗性并正确验证其基因组亲本对于为旨在培育对HLB具有免疫力的新类品种的育种计划正确定位基因组区域至关重要。
