Use of Entomopathogenic Nematodes for Control of Grape Phylloxera (Homoptera: Phylloxeridae): A Laboratory Evaluation

The effectiveness of 2 species of entomopathogenic nematodes was examined in the laboratory against the root-form of grape phylloxera Daktulosphaira vitifolia (Fitch). Our basic unit of measurement was survival of grape phylloxera established on root pieces of the cultivated grape Vitis vinifera L. variety ‘Cabernet Sauvignon' in the presence or absence of nematodes. In petri dish trials, the Oswego strain of Heterorhabditis bacteriophora Poinar reduced survival of attached grape phylloxera by up to 80% relative to the control treatment, whereas Steinernema glaseri Steiner (isolate 326) had no measurable impact and was not used in further experiments. Hb Oswego significantly reduced survival of grape phylloxera on root pieces placed in small cups filled with soil, but only when soil moisture was high (>13% water content wt:wt) and when high densities of infective nematodes were used (>15,000/g soil). Grape phylloxera exposed to Hb Oswego often turned a brick-red color, indicating successful infection. However, we did not detect any evidence that Hb Oswego could successfully reproduce within the bodies of grape phylloxera hosts. Therefore, although Hb Oswego can exert significant mortality in the laboratory, their use in the field in an augmentative release program may be constrained by the need to use high densities, their dependence on moist soils, and their inability to propagate themselves within grape phylloxera host

EST contig-based SSR linkage maps for Malus × domestica cv Royal Gala and an apple scab resistant accession of M. sieversii , the progenitor species of domestic apple

Malus sieversii is a progenitor species of domestic apple M.×domestica. Using population "GMAL 4595” of 188 individuals derived from a cross of Royal Gala×PI 613988 (apple scab resistant, M. sieversii), 287 SSR (simple sequence repeats) loci were mapped. Of these SSRs, 80 are published anchors and 207 are newly developed EST (expressed sequence tag) contig-based SSRs, representing 1,630 Malus EST accessions in GenBank. Putative gene functions of these EST contigs are diverse, including regulating plant growth, development and response to environmental stresses. Among the 80 published SSRs, 18 are PI 613988 specific, 38 are common and 24 are Royal Gala specific. Out of the 207 newly developed EST contig-based SSRs, 79 are PI 613988 specific, 45 are common and 83 are Royal Gala specific. These results led to the construction of a M. sieversii map (1,387.0cM) of 180 SSR markers and a Royal Gala map (1,283.4cM) of 190 SSR markers. Mapping of scab resistance was independently conducted in two subsets of population "GMAL 4595” that were inoculated with Ventura inaequalis races (1) and (2), respectively. In combination with the two major resistance reactions Chl (chlorotic lesions) and SN (stellate necrosis) to each race, four subsets of resistance data, i.e., Chl/race (1), SN/race (1), Chl/race (2) and SN/race (2), were constituted and analyzed, leading to four resistance loci mapped to the linkage group 2 of PI 613988; SNR1 (stellate necrosis resistance to race (1)) and SNR2 are tightly linked in a region of known scab resistance genes, and ChlR1 (Chlorotic lesion resistance to race (1)) and ChlR2 are also linked tightly but in a region without known scab resistance genes. The utility of the two linkage maps, the new EST contig-based markers and M. sieversii as sources of apple scab resistance are discusse

Variation in host and pathogen in the Neonectria/Malus interaction; toward an understanding of the genetic basis of resistance to European canker

Apple canker caused by the phytopathogenic fungus Neonectria ditissima is an economically important disease, which has spread in recent years to almost all pome-producing regions of the world. N. ditissima is able to cross-infect a wide range of apple varieties and causes branch and trunk lesions, known as cankers. Most modern apple varieties are susceptible and in extreme cases suffer from high mortality (up to 50%) in the early phase of orchard establishment. There is no known race structure of the pathogen and the global level of genetic diversity of the pathogen population is unknown. Resistance breeding is underway in many global breeding programmes, but nevertheless, a total resistance to canker has not yet been demonstrated. Here we present preliminary data from a survey of the phylogenetic relationships between global isolates of N. ditissima which reveals only slight evidence for population structure. In addition we report the results of four rapid screening tests to assess the response to N. ditissima in different apple scion and rootstock varieties, which reveals abundant variation in resistance responses in both cultivar and rootstock material. Further seedling tests show that the segregation patterns of resistance and susceptibility vary widely between crosses. We discuss inconsistencies in test performance with field observations and discuss future research opportunities in this area

New Insight into the History of Domesticated Apple: Secondary Contribution of the European Wild Apple to the Genome of Cultivated Varieties

The apple is the most common and culturally important fruit crop of temperate areas. The elucidation of its origin and domestication history is therefore of great interest. The wild Central Asian species Malus sieversii has previously been identified as the main contributor to the genome of the cultivated apple (Malus domestica), on the basis of morphological, molecular, and historical evidence. The possible contribution of other wild species present along the Silk Route running from Asia to Western Europe remains a matter of debate, particularly with respect to the contribution of the European wild apple. We used microsatellite markers and an unprecedented large sampling of five Malus species throughout Eurasia (839 accessions from China to Spain) to show that multiple species have contributed to the genetic makeup of domesticated apples. The wild European crabapple M. sylvestris, in particular, was a major secondary contributor. Bidirectional gene flow between the domesticated apple and the European crabapple resulted in the current M. domestica being genetically more closely related to this species than to its Central Asian progenitor, M. sieversii. We found no evidence of a domestication bottleneck or clonal population structure in apples, despite the use of vegetative propagation by grafting. We show that the evolution of domesticated apples occurred over a long time period and involved more than one wild species. Our results support the view that self-incompatibility, a long lifespan, and cultural practices such as selection from open-pollinated seeds have facilitated introgression from wild relatives and the maintenance of genetic variation during domestication. This combination of processes may account for the diversification of several long-lived perennial crops, yielding domestication patterns different from those observed for annual species