Abstract

Populations of Ulmus minor in Europe were severely damaged by Dutch elm disease (DED) pandemics. However, elm breeding programmes have permitted selection of resistant elm varieties currently used for reforestation. In restored elm forests, resistant (R) and susceptible (S) trees interbreed, but little is known about resistance in their offspring. In this work, growth, DED resistance and xylem anatomy in the offspring of two resistant U. minor trees (R₁ and R₂) were studied. To verify whether transmission of traits in offspring is determined by maternal or paternal trees, a complete randomized plot was established with clonal material from controlled crosses (R₁ × S and R₂ × S) and parent trees (R₁, R₂ and S). Trees were inoculated with O. novo-ulmi firstly at age 4 years and again at 5 years. Growth, susceptibility to DED and vessel size in offspring were closer to the traits of maternal than of paternal trees. This association disappeared after the second inoculation when symptoms increased. The more resistant trees in R₁ × S and R₂ × S had wide and narrow earlywood vessels, respectively, suggesting that water-conducting strategies and resistance mechanisms vary in offspring. Tylosis formation was related to resistance only in R₂ × S offspring, possibly due to the narrow earlywood vessles of trees. Latewood vessels were normally narrower in the more resistant trees. This study sheds light on anatomical resistance mechanisms of elms against DED: (1) offspring exhibit high variability in responses among individuals, (2) narrow earlywood vessels are not a prerequisite for DED resistance and (3) barrier zones are not fully associated with tree resistance in offspring.

中文翻译：

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表征荷兰榆树抗病树的后代（Ulmus minor Mill。）

摘要

欧洲榆树未成年人种群受到荷兰榆病（DED）大流行的严重破坏。但是，榆树育种计划允许选择目前用于重新造林的抗性榆树品种。在恢复的榆树林中，抗性（R）树和易感性（S）树相互杂交，但对其后代的抗性知之甚少。在这项工作中，研究了两种抗性U. minor树（R ₁和R ₂）的后代的生长，DED抗性和木质部解剖。为了验证性状在后代中的传播是由母本还是父本树决定的，建立了一个完整的随机图，其中包含来自受控杂交的克隆材料（R ₁  ×S和R ₂ ×S）和父树（R ₁，R ₂和S）。树木被接种O. NOVO-螨首先在4岁，并再次在5年以上。与父本树相比，后代的生长，对DED的敏感性和血管大小更接近母本的性状。症状增加后，第二次接种后该关联消失。R ₁  ×S和R ₂  ×S中抗性较强的树木分别具有较宽和较窄的早木容器，这表明后代的导水策略和抗性机制各不相同。上凸的形成仅与R _2中的抗性有关 ×S后代，可能是由于树木较早的木质小血管所致。在耐力较强的树木中，晚材船通常较窄。这项研究揭示了榆树抗DED的解剖学抗性机制：（1）后代在个体之间表现出高度的变异性；（2）狭窄的早材血管不是抗DED的先决条件；（3）障碍区与树没有完全关联后代的抵抗力。