Bulletin of Insectology 60 (2): 301-302, 2007 ISSN 1721-8861 Malus sieboldii-based rootstocks mediate apple proliferation resistance to grafted trees 1 2 1 Erich SEEMÜLLER , Eckard MOLL , Bernd SCHNEIDER 1Federal Biological Research Center for Agriculture and Forestry, Institute for Plant Protection in Fruit Crops, Dossenheim, Germany 2Federal Biological Research Centre for Agriculture and Forestry, Central Data Processing Group, Kleinmachnow, Germany Abstract Over a period of 24 years, three trials were carried out in which open pollinated apomictic seedlings were examined for apple pro- liferation (AP) resistance in comparison with several clonal rootstocks. The screening was performed under experimental inocula- tion and natural infection conditions. Criteria for the resistance rating were occurrence of AP symptoms, percentage of affected trees, incidence of the small fruit symptom and the effect of the disease on vigor. In all trials, similar results were obtained. Satis- factory resistance was only identified in trees grown on progenies of M. sieboldii and M. sieboldii-derived experimental root- stocks. The screening also showed that rootstocks with M. sieboldii parentage are often highly susceptible to latent apple viruses. Key words: Apple proliferation, ‘Candidatus Phytoplasma mali’, apple, resistance. Introduction clonal rootstocks of the Budagovsky series B, the Polish series P and rootstocks M 9, M 11 and M 13. The root- Apple proliferation (AP) phytoplasma disease is diffi- stocks were graft-inoculated with Golden Delicious sci- cult to control. Phytosanitary measures such as the use ons or were budded with healthy Golden Delicious and of healthy planting material and uprooting of diseased grown under natural infection conditions. Over a period trees are often unsatisfactory, because infections by in- of 24 years, three trials were carried out which where sect vectors are difficult to prevent. Currently, spraying observed for 9 to 14 years. against the vectors is the most promising method to re- duce infection. However, sprays cannot always be ap- plied, for example during flowering, so that insecticide Results and discussion treatment is often not fully efficient. The most promising approach to control AP would be In the three trials carried out, different sets of apomictic the use of resistant plants. Previous work has shown that seedling rootstocks were examined for AP resistance in ‘Ca. P. mali’ is eliminated in the aerial parts during win- comparison to various nonapomictic clonal rootstocks. ter due to degeneration of phloem sieve tubes on which The overall results obtained were similar. They showed the pathogen is depending. Over wintering occurs in the that the rootstock-mediated resistance of grafted trees roots where intact sieve tubes are present throughout the differs greatly. A high level of resistance was only in- year. From the roots the stem may be recolonized in duced by progenies of M. sieboldii in 12 out of 14 selec- spring when new phloem is being formed (Schaper and tions with M. sieboldii in their parentage. Thus, M. sie- Seemüller, 1982; Schaper and Seemüller, 1984; Seemül- boldii appears to be the only resistance source known at ler et al., 1984). Due to this fluctuation in the coloniza- present. More affected were trees on progenies of clonal tion pattern many clonal rootstocks and a wide range of stocks M9 and M11. High susceptibility showed trees wild and ornamental Malus species were examined for on progenies of M. sargentii, most selections with M. AP resistance. However, most genotypes showed suscep- sargentii parentage, clonal stocks of the P series, most tibility for AP. Resistance was only observed in some ex- clonal stocks of the B series and M13. perimental apomictic rootstock selections derived from Under all resistance criteria the group of resistant M. crosses between the apomictic species M. sieboldii and sieboldii-derived stocks performed better than the clonal genotypes of the nonapomictic species M. x domestica or stocks. Of particular importance is that incidence of un- M. purpurea (Kartte and Seemüller, 1991; Seemüller et dersized fruits in trees grafted on resistant apomictic al., 1992). To examine the M. sieboldii-derived resistance plants is significantly lower than the one of trees grafted in more detail, long-term trials were carried out. on M9, the most employed commercial rootstock in Europe. The results obtained in this study largely confirm the Materials and methods data of previous work in which, however, mainly other criteria including foliar symptoms, phytoplasma persis- AP resistance of open pollinated seedlings from 22 tence and phytoplasma concentration were examined apomictic rootstock selections and the apomictic parents (Bisognin et al., 2007; Kartte and Seemüller, 1991; M. sieboldii and M. sargentii was compared with that of Seemüller et al., 1992). The screening also showed that rootstocks with M. SCHAPER U., SEEMÜLLER E., 1982.- Condition of the phloem sieboldii and M. sargentii in their parentage are often and the persistence of mycoplasmalike organisms associated highly susceptible to latent apple viruses including ap- with apple proliferation and pear decline.- Phytopathology, ple chlorotic leaf spot virus, apple stem grooving virus 72: 736-742. SCHAPER U., SEEMÜLLER E., 1984.- Recolonization of the stem and apple stem pitting virus. Furthermore, apple trees of apple proliferation and pear decline-diseased trees by the grafted on most of the M. sieboldii-based progenies causal organisms in spring.- Zeitschrift für Pflanzenkrank- were more vigorous and less productive than trees on heiten und Pflanzenschutz, 91: 608-613. standard rootstock M9. SEEMÜLLER E., SCHAPER U., ZIMBELMANN F., 1984.- Seasonal variation in the colonization patterns of mycoplasmalike or- ganisms associated with apple proliferation and pear de- References cline.- Zeitschrift für Pflanzenkrankheiten und Pflanzen- schutz, 91: 371-382. BISOGNIN C., SCHNEIDER B., SALM H., GRANDO M. S., JA- SEEMÜLLER E., KARTTE S., KUNZE L., 1992.- Resistance in es- RAUSCH W., MOLL E., SEEMÜLLER E., 2007.- Apple prolif- tablished and experimental apple rootstocks to apple prolif- eration resistance in apomictic rootstocks and its relation- eration disease.- Acta Horticulturae, 309: 245-251. ship to phytoplasma concentration and SSR genotypes.- Phytopathology, in press. Corresponding author: Eric SEEMÜLLER (e-mail: KARTTE S., SEEMÜLLER E., 1991.- Susceptibility of grafted [email protected]), Federal Biological Research Center for Malus taxa and hybrids to apple proliferation disease.- Jour- Agriculture and Forestry, Institute for Plant Protection in Fruit nal of Phytopathology, 131: 137-148. Crops, D-69221 Dossenheim, Germany. 302 .