'San Zanobi' and 'Plinio' Elm Trees

Abstract

Additional index words. tree breeding, Ulmus, Dutch Elm Disease diam.), covered by only 3–4 perules; dark brown (RHS 200/b); rounded at the base of the long shoot and in the short shoot. The apical bud of the short shoot is larger than the subdominant buds and it is typically oblique and inward-folded. Corky wings are absent. Flowering starts late, only from the fifth year of age on selfrooted trees. Fruits are ovateroundish sessile samara measuring 1.5 × 1.8 cm. Flushing occurs at the same time or only slightly later than in Ulmus minor Mill.. The name ‘San Zanobi’ comes from the reported prodigious flushing of a dead elm, acknowledgement of the passage of the relics of the saint bishop St. Zenobius, coming from outside town to the Florence (Italy) Cathedral during the year 429 C.E.; the event is commemorated by a marble stele flanking the Baptistry. ‘Plinio’ grows rapidly, although slightly slower than ‘San Zanobi’, roughly similar to that of fast-growing benchmark ‘Lobel’ (Table 1). It adapts readily to Mediterranean mountainous climates of Northern Italy (unpub. data). ‘Plinio’ is used as an ornamental shade tree (Fig. 2). The crown is about oval in 5-year-old trees. In isolated trees, the width of the crown can be up to 70% of its height. The trunk is straight, at times slightly sinuous, short. Branching begins at a height of 2–3 m. The bark is grey-green (RHS 198/ a) and is still smooth in 5-year-old trees. Leaves are alternating and deciduous, remaining green and active on the tree longer than is usual in other elms. The leaf blade is glabrous on both surfaces. Tertiary venation is rare. The leaf has a biserrate margin; an acute apex, and a noticeably asymmetric base. Color = yellowish green (RHS 147/a). The second leaf of the short shoot is broadly elliptic or oval. The petiole is glabrous and 6– 9 mm long. The branches are rather slender; the glabrous twig is grey-green in color (RHS 197/a). Vegetative buds are fairly large (2–3 mm diam.), ovoid, with a non-pointed tip, and dark brown in color (RHS 200/a). The apical bud of the short branch is inwardfolded. Corky wings are absent. Flowering starts early, from the third year of age and is abundant. Fruits are ovate-roundish sessile samara with central seed measuring 2 × 2 cm. Flushing occurs a few days after that of Ulmus minor. Elm (Ulmus L.) has been utilized by humans since prehistoric times for food, medicine, fiber, fodder for cattle, timber for construction, firewood, and [in the Mediterranean Basin from ancient Roman times (Columella ≈60 C.E.) to the mid-20th century] as a living support for grapevine. In the last three centuries, elm has also been widely used as an ornamental tree to embellish the avenues and gardens of Europe, North America, and China. However, during the past century, this tree suffered major losses, with near-total disappearance of adult trees in some areas of the world as a result of two epidemic outbreaks of Dutch Elm Disease (DED), caused by two ascomycetes, Ophiostoma ulmi (Buisman) Nannf. and Ophiostoma novo-ulmi Brasier. The European elm species, U. glabra Huds., U. laevis Pall., U. procera Salisb. and U. minor Mill., are generally susceptible, although rare individuals of the last species and its hybrid U. ×hollandica Mill. showed enough resistance to form the main basis of a breeding program (Heybroek, 1993). Ulmus pumila L., an Asian species introduced as an ornamental tree in the Mediterranean areas, proved to be moderately to highly resistant. Another source of genes for resistance to the fungus that causes DED has been found in several species growing in central-eastern Asia, one of the most important centers of genetic diversity of Ulmus (Smalley and Guries, 1993). Unfortunately, the Asian species do not always meet ornamental and production requirements, or do not adapt easily to different environmental conditions. Consequently, the main breeding programs set up in Europe and in North America to develop DED-resistant trees involve cross-breeding of Asian with other indigenous species in order to produce individuals that combine the disease resistance of Asian elm with the growth characteristics and higher degree of environmental adaptability of European elm. ‘San Zanobi’ and ‘Plinio’ are two recent results of such research.