Sivager Gary, Calvez Leny, Bruyere Saturnin, Boisne-Noc Rosiane, Brat Pierre, Gros Olivier, Ollitrault Patrick, Morillon Raphaël
CIRAD, UMR AGAP Institut, Equipe SEAPAG, Petit-Bourg, Guadeloupe, French West Indies-UMR AGAP Institut, Univ. Montpellier, CIRAD, INRAE, Institut Agro, Montpellier, France.
CIRAD UMR Qualisud Dpt PERSYST-Qualisud, Univ. Montpellier, Avignon Université, CIRAD, Institut Agro, IRD, Université de La Réunion, Montpellier, France.
Front Plant Sci. 2021 Aug 26;12:685679. doi: 10.3389/fpls.2021.685679. eCollection 2021.
Huanglongbing (HLB) is presently a major threat to the citrus industry. Because of this disease, millions of trees are currently dying worldwide. The putative causal agent is a motile bacteria belonging to Liberibacter spp., which is transmitted by psyllids. The bacteria is responsible for the synthesis of callose at the phloem sieve plate, leading to the obstruction of the pores that provide connections between adjacent sieve elements, thus limiting the symplastic transport of the sugars and starches synthesized in leaves to the other plant organs. The Persian triploid lime () is one of the most HLB-tolerant citrus varieties, but the determinants associated with the tolerance are still unknown. HLB-infected diploid Mexican lime () and Persian lime were investigated. The leaf petiole was analyzed using scanning electron microscopy (SEM) to observe callose deposition at the phloem sieve plate. Leaf starch contents and detoxification enzyme activities were investigated. In the field, Persian lime leaves present more limited symptoms due to HLB than the Mexican lime leaves do. Photosynthesis, stomatal conductance, and transpiration decreased compared with control plants, but values remained greater in the Persian than in the Mexican lime. Analysis of the petiole sieve plate in control petiole samples showed that pores were approximately 1.8-fold larger in the Persian than in the Mexican lime. SEM analyses of petiole samples of symptomatic leaves showed the important deposition of callose into pores of Mexican and Persian limes, whereas biochemical analyses revealed better detoxification in Persian limes than in Mexican limes. Moreover, SEM analyses of infected petiole samples of asymptomatic leaves showed much larger callose depositions into the Mexican lime pores than in the Persian lime pores, whereas biochemical traits revealed much better behavior in Persian limes than in Mexican limes. Our results reveal that polyploids present specific behaviors associated with important physiological and biochemical determinants that may explain the better tolerance of the Persian lime against HLB compared with the Mexican lime.
黄龙病（HLB）目前是柑橘产业面临的主要威胁。由于这种病害，全球数以百万计的树木正在死亡。假定的病原体是一种属于韧皮部杆菌属的运动细菌，由木虱传播。这种细菌会导致在韧皮部筛板处合成胼胝质，从而阻塞相邻筛管分子之间的连接孔，限制了叶片中合成的糖类和淀粉向其他植物器官的共质体运输。波斯三倍体酸橙（）是最耐黄龙病的柑橘品种之一，但与之相关的耐受决定因素仍不清楚。对感染黄龙病的二倍体墨西哥酸橙（）和波斯酸橙进行了研究。使用扫描电子显微镜（SEM）分析叶柄，以观察韧皮部筛板处的胼胝质沉积。研究了叶片淀粉含量和解毒酶活性。在田间，与墨西哥酸橙叶片相比，波斯酸橙叶片因黄龙病出现的症状更有限。与对照植株相比，光合作用、气孔导度和蒸腾作用均下降，但波斯酸橙的这些值仍高于墨西哥酸橙。对对照叶柄样本的筛板分析表明，波斯酸橙的筛孔比墨西哥酸橙大约1.8倍。对有症状叶片的叶柄样本进行SEM分析表明，胼胝质大量沉积在墨西哥酸橙和波斯酸橙的筛孔中，而生化分析显示波斯酸橙的解毒能力优于墨西哥酸橙。此外，对无症状感染叶柄样本的SEM分析表明，墨西哥酸橙筛孔中的胼胝质沉积比波斯酸橙筛孔中的大得多，而生化特性显示波斯酸橙的表现比墨西哥酸橙好得多。我们的结果表明，多倍体具有与重要生理和生化决定因素相关的特定行为，这可能解释了波斯酸橙比墨西哥酸橙对黄龙病具有更好耐受性的原因。
