Resistance of Peach and Plum Rootstocks from Spain, France, and Italy to Rootknot Nematode Meloidogyne javanica

Two trials involving 20 Prunus rootstocks were conducted under greenhouse conditions to screen for resistance to root-knot nematode [Meloidogyne javanica (Treub.) Chitwood]. Many of the tested materials are interspecific hybrid rootstocks and represent new commercial peach (P. persica Batsch) and plum (Prunus sp.) releases or experimental genotypes of Spanish, French, and Italian origin. In the first trial, the rootstocks Adesoto 101 (P. insititia L.), Bruce (P. salicina Lindl. x P. angustifolia Marsh.), Ishtara, AC-952 (P. insititia), Garnem [P. dulcis (Mill.) D.A. Webb x P. persica], Cadaman [P. persica x P. davidiana (Carr.) Franch], and Orotava (P. salicina) were immune or resistant to a mixture of 10 isolates of M. javanica. The remaining rootstocks, Myrocal (P. cerasifera Ehr.), Montclar (P. persica), and Adafuel (P. dulcis x P. persica), were susceptible. In the second screening trial, the plum rootstocks Adesoto 101, Adara (P. cerasifera), Myro-10 (P. cerasifera), Constantí (P. domestica L.), and AD 105 (P. insititia) were immune to the rootknot nematode. Cadaman, G x N No. 17 (P. dulcis x P. persica), and Tetra (P. domestica) were resistant. Laroda F1OP (P. salicina), Myro-almond (P. cerasifera x P. dulcis), and the peach–almond hybrids Mayor, Adafuel, and Sirio were susceptible. since the late 1980s and seems to have stabilized in the mid-1990s (Badenes et al., 1998). In general, root-knot nematodes are common and tend to be a serious problem in warm, well-drained, sandy soils. High susceptibility of peach and plum seedling rootstocks, and the widespread use of the susceptible peach–almond hybrid GF-677 as a rootstock have significantly contributed to an increase in the incidence of replant problems caused by rootknot nematodes in Spain, thus seriously affecting the competitiveness of the fresh peach and plum industry. A significant effort has been made in Spain to incorporate resistance to root-knot nematodes into new peach, peach–almond hybrid, plum, and interspecific Prunus rootstocks (Esmenjaud et al., 1993, 1994; Fernández et al., 1994; Marull et al., 1991), with the intention of replacing the widely used seedling rootstocks. Seedling rootstocks often lack homogeneity, tend to suffer badly from root asphyxia and iron chlorosis, and are susceptible to root-knot infestation (Felipe, 1989; Socías, 1990). This breeding effort has been constant in the last decade resulting in the introduction of new material that has multiple resistance and/or tolerance to several biotic and abiotic stresses (Felipe et al., 1990). The root-knot nematode resistance trait is easy to transmit by hybridization. It is apparently controlled by one major gene or a few dominant genes (Cook and Evans, 1987; Esmenjaud et al., 1997). Screening procedures in rootstock selection involve repeated testing of plant material with mixtures of populations involving one or several species of Meloidogyne to ensure broad resistance (De Guiran, 1993; Marull et al., 1994; Scotto La Massese et al., 1984). Some of the rootstocks tested in this study have been bred specifically for root-knot nematode resistance and have been evaluated in the past against M. incognita Kofoid and White (Pinochet et al., 1996) but not against M. javanica. This last species attacks rootstocks that are supposedly resistant to root-knot nematode, especially peach and peach–almond hybrids, indicating differences in virulence between Meloidogyne species (Esmenjaud et al., 1994). The purpose of our study was to evaluate new commercial releases and experimental Prunus genotypes in their late stages of selection from Spanish, French, and Italian breeding programs to determine their response to M. javanica, using mixtures of many isolates of the nematode (large pathogenic diversity). Materials and Methods Rootstock material. Seeds, hardwood cuttings, and micropropagated material were supplied by Spanish and French public research institutes and private sources (Table 1). Seeds of the peach rootstock Montclar were treated with a 5% solution of copper oxychloride for 36 h, rinsed with running water, covered with a moist paper towel, and stratified in perlite on trays that were kept in a storage room at 4 °C for 60 d. Seeds were then moved to ambient temperature in a greenhouse to induce germination. Hardwood cuttings of the rootstocks G x N No. 17, AD 105, Constantí, Bruce, Orotava, Myro-almond, Myro-10, and Adara were treated for 6–10 s with a 50% alcohol solution that contained 1000 mg·L of indole butyric acid (Hansen and Hartman, 1967). Cuttings then were planted in 200-mL minipots containing a pasteurized (80 °C) 2 sand : 1 peat (v/ v) mixture. Montclar seeds were provided by Viveros Orero, Villaverde del Río, Sevilla. Hardwood cuttings were provided by the Dept. de Fruticultura of the Servicio de Investigación Agraria in Zaragoza, Spain, and by the Dpto. de Fruticultura, Estación Experimental Aula Dei, Zaragoza, Spain. Micropropagated Adafuel, Cadaman, Garnem, Adesoto 101, Mayor, Myrocal, Ishtara, Laroda F1OP, and AC-952 were provided as plantlets in 300-mL minipots by Agromillora Catalana S.A., Sant Sadurní d’Anoia, Barcelona, Spain, in a Moor peat and clay substrate (Stender Bassis Substrate 3, Blumenerdenwerke Stender GmbH, Schermbeck, Germany). Micropropagated Tetra and Sirio rootstocks were supplied by Vivai Battistini, Diegaro di Cesena, Italy. Plantlets with uniform growth arising from germinated seeds, rooted cuttings or microRoot-knot nematodes (Meloidogyne sp.) can become a limiting factor in peach and plum production in Mediterranean environments (Lamberti, 1981, McKenry, 1989; Nyczepir and Halbrendt, 1993; Pinochet, 1997), especially in replant sites that have a history of nematode infestation (García de Otazo, 1992; Scotto La Massese, 1989). Several species of root-knot nematodes are present in Spain, but M. javanica is predominant in the warmer areas of the Levante Region (Valencia, Alicante and Murcia) and Andalucía, where most of the peaches, nectarines, and plums for export are produced. The area of production, especially for peach, has steadily increased