Mahmoud Lamiaa M, Dutt Manjul
Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States.
Plant Breeding Graduate Program, University of Florida, Gainesville, FL, United States.
Front Plant Sci. 2025 Jun 13;16:1614845. doi: 10.3389/fpls.2025.1614845. eCollection 2025.
Citrus greening disease, or Huanglongbing (HLB), is the most destructive disease affecting citrus crops worldwide. All commercially cultivated citrus varieties are highly susceptible to HLB, and currently, no effective treatments exist. Several Australian lime species have demonstrated significant HLB tolerance, making them promising candidates for developing HLB-tolerant rootstocks and scions through conventional breeding and biotechnological approaches. Herein, we report the successful development of HLB-tolerant citrus hybrids via integrating Australian lime genetics using traditional breeding methods and protoplast fusion techniques. To test the HLB tolerance of these hybrids as rootstocks, they were clonally propagated through cuttings and divided into two groups: one grafted with Las-free 'Valencia' sweet orange budwood and the other grafted with Las-infected 'Valencia' budwood. The performance of these hybrids was compared to similar Las-infected and free 'Valencia' budded onto Swingle rootstock. Total DNA was isolated from the 'Valencia' leaves at 6, 12, 18, and 24 months post-grafting to assess Las titers using quantitative PCR. After two years, significantly higher Ct values (ranging from 29.11 to 35.00) was observed in 'Valencia' trees grafted onto the experimental hybrids than in those grafted onto Swingle, which presented a Ct value of 22.25 ± 1.11. Compared with other hybrids, the mandarin (UF304) × finger lime hybrid (MFL1-98) and pummelo × finger lime hybrid (PFL2-61) exhibited improved graft-take, enhanced growth, and lower Las titers. Additionally, we analyzed the biochemical and molecular changes in the leaves of 'Valencia' grafted onto these Australian lime-derived hybrids. Biochemical analyses revealed significant alterations in chlorophyll content, starch accumulation, and levels of phenolic and flavonoid compounds. These results demonstrate the practical benefits of using Australian lime-derived hybrids as rootstocks to increase HLB tolerance in citrus, offering a promising approach for the sustainable management of HLB in commercial citrus production.
柑橘黄龙病（HLB）是全球影响柑橘作物最具毁灭性的病害。所有商业化种植的柑橘品种对HLB都高度易感，目前尚无有效的治疗方法。几种澳大利亚酸橙品种已表现出对HLB的显著耐受性，使其有望通过传统育种和生物技术方法培育出耐HLB的砧木和接穗。在此，我们报告了通过传统育种方法和原生质体融合技术整合澳大利亚酸橙基因成功培育出耐HLB柑橘杂种。为了测试这些杂种作为砧木对HLB的耐受性，通过扦插进行无性繁殖，并分为两组：一组嫁接无黄龙病菌（Las）的‘伏令夏橙’甜橙接穗，另一组嫁接感染Las的‘伏令夏橙’接穗。将这些杂种的表现与嫁接在枳柚砧木上的类似感染Las和未感染Las的‘伏令夏橙’进行比较。在嫁接后6、12、18和24个月从‘伏令夏橙’叶片中提取总DNA，使用定量PCR评估Las滴度。两年后，嫁接在实验杂种上的‘伏令夏橙’树中观察到的Ct值显著更高（范围为29.11至35.00），而嫁接在枳柚上的Ct值为22.25±1.11。与其他杂种相比，宽皮橘（UF304）×指橙杂种（MFL1 - 98）和柚×指橙杂种（PFL2 - 61）表现出更好的嫁接成活率、更强的生长势和更低的Las滴度。此外，我们分析了嫁接在这些源自澳大利亚酸橙的杂种上的‘伏令夏橙’叶片中的生化和分子变化。生化分析显示叶绿素含量、淀粉积累以及酚类和黄酮类化合物水平有显著改变。这些结果证明了使用源自澳大利亚酸橙的杂种作为砧木来提高柑橘对HLB耐受性的实际益处，为商业柑橘生产中HLB的可持续管理提供了一种有前景的方法。
