HORTSCIENCE 42(3):712–714. 2007. planted in the field in 1983 and 1984. During their second year in the field, the trees were inoculated in the upper third of the main ‘Fiorente’ and ‘Arno’ Elm Trees stem. Inoculation was performed in the third Alberto Santini1, Alberto Fagnani, Fabio Ferrini, Luisa Ghelardini, week of May, when elms are at their highest susceptibility in Italy, by a single wound and Lorenzo Mittempergher through the bark to the younger wood using Istituto per la Protezione delle Piante–C.N.R., Via Madonna del Piano, a knife bearing two drops (0.2 mL) of a 1 · 10 50019 Sesto fiorentino, Italy 106/mL–1 fungal spore mixed suspension of yeast phase cells, so that the inoculum would Additional index words. tree breeding, Ulmus, Dutch elm disease, resistance, elm cultivars be absorbed by the tree’s rising sap. The Abstract. Dutch elm disease (DED) has spread through Europe since the beginning of the spore suspension consisting of two tester 20th century. Several independent genetic improvement programs for breeding DED- isolates of O. novo-ulmi subsp. novo-ulmi resistant elms have been established in Europe. The Italian elm breeding program began and subsp. americana (Brasier and Kirk, in the late 1970s with the goal of hybridizing susceptible European elms with resistant 2001), both found to be very aggressive in Asian species to select DED-resistant clones suited to the Mediterranean climate. Ulmus previous assays. The isolates were prepared ‘Fiorente’ and ‘Arno’ are two new releases selected for DED resistance, superior growth by inoculating 10 mL modified Tchernoff’s rate, attractive foliage, and upright habit. liquid medium (Brasier, 1981) in 50 mL Erlenmeyer flasks and incubating for 2 d on a shaker at room temperature. Spore concen- During the 20th century, two destructive lination of Heybroek’s ‘Plantyn’ (or Plantijn) tration was then adjusted with sterile water pandemics of Dutch elm disease (DED), elm (Heybroek, 1983) [(Ulmus glabra ‘‘Exo- to 1 · 106/mL–1. incited by the introduction of two very niensis’’ · Ulmus wallichiana p39) · (U. Searches for symptoms of disease (defo- different fungal pathogens [Ophiostoma ulmi minor 1 · U. minor 28)] with U. pumila S.2. liation and dieback) were undertaken at 4 (Buisman) and O. novo-ulmi (Brasier)], dev- Pollen from cultivars C.02 and S.2 was weeks, 3 months (not reported), and 8 months astated elm species native to Europe and collected in a warm room from flowering by three independent assessors. Seedlings North America. The severity and extent of twigs, filtered, and dried to 10% relative presenting less than 10% dieback were veg- the damage incited by the disease aroused the humidity (Mittempergher and La Porta, etatively propagated and planted out the concern of scientists and public alike, and the 1991). In January, the female flowers of following year in a completely randomized search for a solution to the problem was ‘Plantyn’ and S.10 were covered with tery- block design. Twelve rooted cuttings per considered imperative. The idea of screening lene bags for protection and the prevention of clone, divided into three blocks, were used. elms for resistance to DED and enhancing random pollination. The controlled pollina- Ramets of both the new clones were inocu- resistance through breeding first arose in the tion was effected by forced air injection of lated in 1990, together with 53 more clones Netherlands after the end of World War I. pollen into the bags, which were retained in from the best performing seedlings and four A second elm breeding program in situ until fruit maturity. control clones. Inoculations, disease evalua- Europe was initiated in Florence by the tions, and analyses were performed as before, Institute of Plant Protection (IPP), part of Cultivation and the symptoms compared with hybrids of the Italian National Research Council known DED responses. The resistance levels (C.N.R.), in the late 1970s when the second The seedlings and rooted cuttings were were comparable with those of ‘Lobel’ and more destructive DED pandemic incited by obtained at IPP’s Monna Giovannella exper- ‘Plantyn’, and were significantly higher than O. novo-ulmi reached Italy. The goal of the imental nursery at Antella (43°43#N, ‘Commelin’ (Table 1) during the inoculation Italian elm breeding program was the selec- 11°22#E, 170-m elevation), near Florence, year. During the next 10 years (i.e., until tion of elm cultivars resistant to DED but Italy, where the artificial inoculations were 2000), ramets were regularly checked for suited to the Mediterranean climate, unlike also performed. The trees were planted out in symptoms of DED, but not one showed the Dutch selections intended for northern 1993 in a fully randomized design with eight wilting or dieback. At the time of writing Europe. European elm species and selections replicates per clone at two sites of differing (2007), none of the clones have displayed any with desirable morphological and physiolog- topography in the Province of Ravenna, symptoms of either DED or elm yellows ical characteristics were hybridized with Northern Apennines (Presiola: 44°08#N, infections (Mittempergher, 2000), and their DED-resistant Asian species (Smalley and 11°36#E, 599-m elevation; Purocelo: Guries, 1993) that had thrived in the Medi- 44°10#N, 11°40#E, 312-m elevation). The Presiola site is characterized by a poor clay terranean climate, broadening genetic resour- Table 1. Descriptive statistics of defoliation ces (Simmonds, 1993). ‘Fiorente’ and soil on a steep northeast-facing slope, (symptoms assessed 4 weeks after inoculation) ‘Arno’, following ‘San Zanobi’ and ‘Plinio’ whereas Purocelo is flat with a marly (cal- and dieback (symptoms assessed 8 months after (Santini et al., 2002), are the two latest results careous) clay soil of poor permeability. inoculation) of ‘Plinio’, ‘LUTE` CE’, ‘Lobel’, of this research. ‘Plantyn’, ‘Fiorente’, ‘Arno’, and ‘Commelin’ Analysis grown and inoculated at Antella (Florence) Origins in 1990. Biometric data were measured in 2005 Mean defoliation Mean dieback ‘Fiorente’ (patent RM 2006 NV000005) and analyzed using one-way analysis of Clone (%)z (%)y was selected from seedlings obtained by variance. Mean values were compared using Plinio 15.53 ax 10.05 ax controlled pollination of U. pumila S.10 with Duncan’s test. Statistical analysis was per- LUTE`CE 19.75 a 11.70 a U. minor C.02. ‘Arno’ (patent RM 2006 formed used Statistica 6.0 (StatSoft Italia srl Lobel 27.87 b 21.55 b NV000004) was obtained by controlled pol- 1984–2001, Italy) software, and color deter- Plantyn 27.97 b 20.47 b minations were made using the Royal Horti- Fiorente 32.34 bc 19.89 b cultural Society color chart (Royal Arno 35.40 c 21.04 b Commelin 83.54 d 88.16 c Horticultural Society, 1966). Received for publication 21 Dec. 2006. Accepted zF = 118.74, P = 0.0000. for publication 26 Feb. 2007. yF = 140.97, P = 0.0000. We gratefully acknowledge the field work of Disease-resistance Testing xMeans not sharing the same letters are Mr. Abdellah Dahmani. significantly different according to Duncan’s test. 1To whom reprint requests should be addressed; Two-year-old seedlings from the two Angles were used as a normalizing transformation e-mail [email protected] controlled crosses raised in the nursery were for statistical analysis. 712 HORTSCIENCE VOL. 42(3) JUNE 2007 susceptibility to elm leaf beetle remains comparatively late for a hybrid, from the tive buds are small (<2 mm Ø), ovoid, comparable with that of U. minor. fourth or fifth year of age on self-rooted trees. covered by only three or four hairy perulae, It should also be noted that strong Fruits are ovate-roundish sessile samarae and are brown (RHS66 200B/177A) and winds have not injured any of these measuring 1.4 · 1.7 cm. Flushing is earlier rounded at the base of the shoot. Apical buds selections. than in Ulmus minor Mill. of the short shoots are larger than the sub- ‘Arno’ is monocormic, with erect habit, dominant buds, typically oblique, and inward ascending branches, and an upright oval folded. Leaves are alternate and deciduous, Descriptions of the Cultivars crown (Fig. 2). Adaptation field trials indi- remaining green into the fall and shedding cate that ‘Arno’, although slower than ‘Fior- late. The leaf margins are often undulate, and ‘Fiorente’ is monocormic and shows ente’, is among the fastest growers ever tested green–yellow (RHS66 147A). The second exceptionally rapid growth, significantly (Table 2). Trials of this clone have now been leaf of the shorter shoots is ovate or lanceolate, greater than the other cultivars cultivated at made at many sites of differing topography 5 to 9 cm long · 3 to 5 cm broad, the base the same site, suggesting that it could also be and geology. The trunk is straight, branching uneven, and the apex acute to acuminate; the used for timber production (Table 2). Its habit at a height of 3 m. The wood characteristics central vein is convex. The base is more is conical with pronounced apical domi- of this clone (previously encoded as FL 090) asymmetric on the leaves of the shorter nance, a result of the limited lateral branching are not different from those known for field shoots. The petiole is glabrous, 7 mm and 8 on the developing shoots of the current elm (Santini et al., 2004). The bark is gray– mm long on short and long shoots respec- season’s growth (Fig. 1). The crown is green (RHS66 198B/198C) with cracks of tively. therefore slender and columnar. The trunk gray–orange (RHS66 177C). Twigs are slen- Flowering starts relatively late, at 5 years is straight, long, and the bark is gray–green der, glabrous, and gray–green (RHS66 of age on self-rooted trees.