Lesser peachtree borer (Lepidoptera: Sesiidae) oviposition on Prunus germplasm

The lesser peachtree borer, Synanthedon pictipes (Grote and Robinson) (Lepidoptera: Sesiidae), is a serious pest of peach, Prunus persica (L.) Batsch, across the southeastern United States. We examined oviposition by S. pictipes on field-grown Prunus scion and rootstock cultivars and two endemic Prunus spp. when sawn limbs, not roots, were assayed in the laboratory. A choice test compared oviposition on the peach scion 'Harvester', peach rootstock 'Guardian', plum×peach hybrid rootstock 'MP-29', and the plum hybrid rootstock 'Sharpe'. A significantly lower percentage of eggs occurred on limbs of Sharpe rootstock than other choices. A choice test using two endemic hosts, black cherry (P. serotina Ehrh.) and Chickasaw plum (P. angustifolia Marsh.), along with Sharpe rootstock, found a lower percentage of eggs on limbs of Sharpe than either endemic host. However, when only limbs of Sharpe and a decoy were used, almost all eggs were laid on Sharpe. Interestingly, when Harvester and Sharpe limbs were paired side by side, a higher percentage of eggs were recovered from the Harvester limb than from the Sharpe limb. An analysis of volatiles from Sharpe may identify why fewer eggs were laid on it. Because S. pictipes attacks host trees above ground and Sharpe rootstock on grafted trees grows below ground, this rootstock might be a management option against the congeneric, root-attacking peachtree borer, S. exitiosa (Say). Our results suggest that high budding a peach scion onto Sharpe rootstock, thus allowing the rootstock to serve as the trunk, warrants further investigation against S. exitiosa under orchard conditions.     

Interspecific transfer of resistance to Plum pox virus from almond to peach by grafting

Grafting almond variety ‘Garrigues’ onto ‘GF305’ peach seedlings heavily infected by Plum pox virus (PPV) progressively produces the disappearance of viral symptoms and drastically reduces virus accumulation in ‘GF305’ rootstock, in most cases to undetectable levels. This response appears to be specific between almond and peach, as it was not consistently observed by grafting ‘Garrigues’ onto other Prunus species such as plum (‘Adesoto’) or apricot (‘Real Fino’). The ability to induce resistance to PPV in ‘GF305’ was transmitted to the sexual descendants of Garrigues. Furthermore, grafting ‘Garrigues’ onto ‘GF305’ before PPV inoculation completely prevented virus infection, showing that the resistance is constitutive and not induced by the virus. This fact suggests that resistance may be due to the transfer of a defence factor from ‘Garrigues’ almond through the graft union and its interaction with specific factors of ‘GF305’ peach to produce the antiviral response. These results open new avenues to potential protection against PPV in peach, the most economically important species among stone fruits.     

Nitrate Uptake Effectiveness and Utilization Efficiency of Two Plum Clones

Nitrate uptake and utilization efficiencies of two plum clones, Marianna 2624 (Prunus cerasifera×Prunus munsoniana?) and Myrobalan 3-J (Prunus cerasifera) in stirred solution cultures were investigated. Myrobalan 3-J had a significantly lower NO₃^- compensation point (i.e., greater capacity for nitrate depletion) but ceased growth earlier than Marianna 2624 under severe N stress. The maximum velocity of NO₃^- uptake was 33% higher in Marianna 2624 than Myrobalan 3-J. The nitrogen efficiency ratio (i.e., mg dry weight produced/mg nitrogen absorbed) of Marianna 2624 was 40% higher than Myrobalan 3-J when nitrogen was severely limiting (28 mg nitrogen per plant). Thus, Marianna 2624 plants may be capable of growth at lower mean nitrogen concentrations.     

Labile anion binding by roots of two plum clones

The anion-exchange capacities (AEC) of roots of intact plants of two plum clones [Marianna 2624 (Prunus cerasifera × P. munsoniana) and Myrobalan 3-J (P. cerasifera)] were assessed with an anionic dye, eosin Y. The positively charged eosin-specific adsorption sites were metabolically dependent and also affected by nutrient status. Myrobalan 3-J roots adsorbed twice as much exchangeable NO₃ as did Marianna 2624. Since we previously showed that net nitrate uptake by Myrobalan 3-J persisted at half the ambient nitrate concentration as that characteristic of Marianna 2624, the data provide circumstantial support for a functional role of labile anion binding in active uptake at dilute concentrations of ambient nitrate.     

Attack by Hylobius warreni on grafted lodgepole pine and its relationships with monoterpene composition and scion : rootstock diameter ratio

1 A lodgepole pine seed orchard at the Prince George Tree Improvement Station (PGTIS), with up to 60% of grafted trees attacked by the Warren root collar weevil Hylobius warreni was investigated to determine whether relative monoterpene composition or scion : rootstock interactions of grafts affected susceptibility to attack. 2 There was a significant relationship between relative levels of α‐pinene, β‐thujene, β‐pinene, δ‐3‐carene and limonene in scion and rootstock in unattacked trees, indicating a potential effect of the scion monoterpene composition on their composition in the rootstock. 3 Relative content of δ‐3‐carene and β‐phellandrene differed significantly in root stocks of attacked and unattacked trees but, for individual clones, a significant difference was only detected for β‐phellandrene in one clone. δ‐3‐Carene levels may have been too low in the examined trees to exert a strong effect. 4 Interestingly, attack status was significantly associated with two scion monoterpenes: α‐thujene and α‐terpinolene, both of which had higher levels in unattacked than in attacked trees. 5 Warren root collar weevils appear largely unaffected by monoterpene content, but further study is required to determine whether high levels of δ‐3‐carene imparts some level of resistance to attack, and to verify whether the observed effects of scion monoterpenes are real or artefacts of the analysis. 6 Hylobius warreni‐attacked trees had smaller scion : rootstock diameter ratio (i.e. a large rootstock diameter relative to the scion diameter) than unattacked trees. This effect was consistent among clones, and was not due to the absolute diameter of the rootstock or the scion. Trees with increased diameter‐growth at the root collar (e.g. some grafted trees) may have increased susceptibility to attack by H. warreni, or diameter‐growth at the root collar is affected by the attack.     

Population Characteristics and Dosage Trajectory Analysis for Mesocriconema xenoplax in California Prunus Orchards

The Mesocriconema xenoplax population increased exponentially in a newly planted peach orchard. The rate of increase was greater on Nemaguard than on Lovell rootstock and was reduced by postplant nematicides. Population levels were more stable in an established almond orchard on Nemaguard rootstock. All life stages of the nematode were present year round; lower ratios of juveniles to adults in summer suggested adverse effects of temperature and dry soil. Also in summer, there was a smaller proportion of the population in the upper 30 cm of soil than at greater depths. Nematode dosage, average nematode density multiplied by accumulated degree-days (physiological time) of the sampling interval, was useful in quantifying nematode stress on trees and as an indicator of the nematode management effectiveness. The annual trajectory of the nematode dosage could be determined by two samplings, one in spring and one in fall. A nematode predator, the parasitic fungus Hirsutella rhossiliensis, did not regulate ring nematode populations in the newly planted orchard; a recovery period was necessary for increase in the prevalence of parasitism.     

Monitoring plum curculio, Conotrachelus nenuphar (Coleoptera: Curculionidae), populations in apple and peach orchards in the mid-Atlantic

We evaluated responses of plum curculio, Conotrachelus nenuphar (Herbst), to four trap types in commercial and unsprayed apple and peach orchards. Trap types included black pyramid and clear Plexiglas panel traps deployed outside the orchard 2 m from the border row, and branch-mimicking cylinder and trunk-mounted screen traps attached to trees in the border row. Bait treatments evaluated in conjunction with each trap type included the synthetic fruit volatile benzaldehyde, the aggregation pheromone grandisoic acid (GA), benzaldehyde in combination with GA, and an unbaited control treatment. In commercial apple orchards, significantly more plum curculio were captured in traps baited with benzaldehyde + GA compared with traps baited with other treatments. Furthermore, significantly more plum curculio were captured by screen traps baited with benzaldehyde + GA compared with unbaited control traps. Significantly more plum curculio were captured by screen traps compared with other trap types in an unsprayed apple orchard. Very few captures were recorded in commercial peach orchards. Dissections of trapped females indicate that bivoltine populations are present in the mid-Atlantic. In general, correlations between timing and amount of trap captures and timing and amount of fruit injury inflicted concurrently or 1 wk after trap captures were very weak for all trap types and bait combinations. Our results agree with previous studies in the northeastern United States in which trap captures are increased by presence of semiochemical baits but fail to serve as reliable tools to determine need for and timing of insecticide application against plum curculio.     

Decline and other effects of five virus infections on three varieties of plum (Prunus domestica L.)

The effects of five different virus inocula on three varieties of plum (Prunus domestica L.) were studied in a field trial of 10 years duration. The viruses causing line pattern, ringspot, prune dwarf and bark split had no effect on the growth of Marjorie's Seedling and Cambridge Gage, and only that causing prune dwarf stunted Oullins Gage trees. However, these viruses diminished the fruit yield of one or more varieties, and prune dwarf virus seriously decreased the yield of all three. Decline disease, probably caused by a strain of Prunus necrotic ringspot virus, developed in Marjorie's Seedling but not in the other varieties. The symptoms first appeared after 5 years and then the trees declined progressively with necrotic ‘incompatibility’ between rootstock and scion.     

Characterization of Pseudomonas pathovars isolated from rosaceous fruit trees in East Algeria

A survey of bacterial diseases due to Pseudomonas on rosaceous fruit trees was conducted. In forty two orchards located in the Constantine region ( East Algeria). Pseudomonas isolates were identified on the bases of their cultural and biochemical characteristics . A total of fifty nine phytopathogenic bacteria were isolated from diseased pome and stone fruit trees. Thirty one strains comparable to Pseudomonas syringae pv. syringae were isolated from cherry (Prunus avium L.), plum (P. domestica L.), apricot (P. armeniaca L.), almond (P. dulcis L.) and pear trees (Pirus communis L.); sixteen strains comparable to Pseudomonas syringae pv. morsprunorum were obtained from samples of cherry and plum. Twelve strains of Pseudomonas viridiflava were isolated from cherry, apricot and peach (Prunus persica L.).     

Possible roles of auxin and zeatin for initiating the dwarfing effect of M9 used as apple rootstock or interstock

Endogenous indole-3-acid (IAA) and zeatin (t-Z) may play important roles in the dwarfing mechanisms of rootstocks. The concentrations of IAA and t-Z, as well as the expression of the genes PIN1 and IPT3 were measured in leaves, barks, and roots from nine treatments: M9, Malus X micromalus Makino, Red Fuji/M9/Malus X micromalus, Red Fuji/M9, Red Fuji/Malus X micromalus, M9 rootstock substitution above and below the original graft union, interstock bridging, and interstock bark substitution of M9. The results show that there were greater amounts of t-Z and expressions of IPT3 in invigorated trees (Malus X micromalus and Red Fuji/Malus X micromalus) when compared with dwarfing trees (M9, Red Fuji/M9/Malus X micromalus and Red Fuji/M9) during the period of fast shoot growth (early June to mid-August). Moreover, the variation of IAA contents and PIN1 expressions shared the same pattern with t-Z contents and IPT3 expressions in all the tested locations. IAA content was extremely high in the bark of M9 interstock when compared with that of the scion and the rootstock, yet PIN1 expression in corresponding tissues was very low. After M9 rootstock were substituted above and below the original graft union, contents of t-Z, IAA, and PIN1 expressions in leaves and branch-barks recovered gradually to standard tree levels. However, there is no significant difference between the two treatments. We conclude graft union has no obvious influence on hormone transport. After M9 interstock and its bark were substituted, the hormone measurement of every index was consistent with that of rootstock substitution.     

Association of Tobacco Ringspot Virus with a Union Incompatibility of Apple

A virus-like disease of apple was observed for the first time in Canada in 1974 in a three year old planting. The disease was characterised by stem pitting, necrosis and breaking or separation of scion/rootstock at the graft union. Foliage was sparse and leaves were chlorotic and diffusely mottled. Using both frozen and freshly harvested leaves of infected apple trees from rootstock suckers as inoculum, a virus was transmitted to herbaceous indicator hosts. Based on host range symptoms, serology and electron microscopy, this virus was identified as tobacco ringspot virus. Initial counts of nematodes in the rhizophere of apple trees affected with union necrosis showed high densities of Xiphinema americanum Cobb., a known vector of nepoviruses. Reports of similar symptoms have indicated that the disease, apple union necrosis and decline was associated with the recovery of tobacco ringspot virus from infected rootstocks. This is the first report associating a union incompatibility condition of apple and tobacco ringspot virus.     

Factors promoting infestation of newly planted, nonbearing apple orchards by dogwood borer (Lepidoptera: Sesiidae)

The initiation and level of infestation by dogwood borer, Synanthedon scitula (Harris), was tracked over three consecutive years in two nonbearing apple (Malus spp.) orchards in West Virginia and Virginia. The orchards were planted on a number of rootstock-variety (approximately cultivar) combinations and grown using different cultural practices. Infestations were detected during the first season after planting and continued to increase annually. The amount of burr knot tissue had the greatest impact on dogwood borer populations, because increasing amounts of burr knot tissue resulted in higher infestation rates. The use of plastic spiral wrap tree guards seemed to increase the development of burr knot tissue, resulting in significantly greater infestation compared with trees without tree guards in the West Virginia orchard. Variety also had a significant effect, because 'Idared' trees on M.26 had significantly greater levels of infestation compared with 'Buckeye Gala' on M.26, with or without tree guards, in the Virginia orchard. Mounding soil around the rootstock to a height just above the graft union prevented or tremendously curtailed infestation by dogwood borer, but it led to scion rooting that seemed to have an impact on size-controlling features of dwarfing rootstocks. Removal of the mounds at the beginning of the third growing season resulted in infestation of the rooted tissue during the same season. As long as apple cultivars continue to be planted on size-controlling rootstocks, dogwood borer will likely remain a serious pest, requiring either chemical treatments or a behavioral control strategy, such as mating disruption, to protect trees from infestation and damage.     

Effects of the root-lesion nematode Pratylenchus vulnus and the vesicular-arbuscular mycorrhizal fungus Glomus mosseae on the growth of three plum rootstocks

The effects of Pratylenchus vulnus and the endomycorrhizal fungus Glomus mosseae on growth of Myrobalan 605, Marianna 2624 and San Julian 655-2 plum rootstocks were measured under shadehouse conditions in the field for two growing seasons (1990–91). Shoot dry weights were higher in the majority of the vesicular-arbuscular mycorrhizal (VAM) alone inoculated plants after both growing seasons. Root weights of mycorrhizal Myrobalan and Marianna were higher than root weights of the same rootstocks lacking mycorrhizae, inoculated with P. vulnus, and VAM in combination with the nematode. Mycorrhizal Marianna inoculated with the nematode showed a considerably higher final nematode population in relation to non-inoculated VAM treatments. No correlation was found in the number of nematodes per gram of root between mycorrhizal and non-mycorrhizal treatments. P. vulnus adversely affected the mycorrhizal colonization in Marianna, but not in Myrobalan and San Julian. Marianna appears to be more mycorrhizal dependent than the two other rootstocks.     

<Emphasis Type="Italic">Prunus</Emphasis> microsatellite marker transferability across rosaceous crops

A total of 145 microsatellite primer pairs from Prunus DNA sequences were studied for transferability in a set of eight cultivars from nine rosaceous species (almond, peach, apricot, Japanese plum, European plum, cherry, apple, pear, and strawberry), 25 each of almond genomic, peach genomic, peach expressed sequence tags (EST), and Japanese plum genomic, 22 of almond EST, and 23 of apricot (13 EST and 10 genomic), all known to produce single-locus and polymorphic simple-sequence repeats in the species where they were developed. Most primer pairs (83.6%) amplified bands of the expected size range in other Prunus. Transferability, i.e., the proportion of microsatellites that amplified and were polymorphic, was also high in Prunus (63.9%). Almond and Japanese plum were the most variable among the diploid species (all but the hexaploid European plum) and peach the least polymorphic. Thirty-one microsatellites amplified and were polymorphic in all Prunus species studied, 12 of which, covering its whole genome, are proposed as the “universal Prunus set”. In contrast, only 16.3% were transferable in species of other Rosaceae genera (apple, pear, and strawberry). Polymorphic Prunus microsatellites also detected lower levels of variability in the non-congeneric species. No significant differences were detected in transferability and the ability to detect variability between microsatellites of EST and genomic origin.     

Bacillus thuringiensis protein transfer between rootstock and scion of grafted poplar

Bacillus thuringiensis (Bt) Cry1Ac protein is a toxin against different leaf‐eating lepidopteran insects that attack poplar trees. In the present study, the mode of migration of the Bt‐Cry1Ac protein within poplar grafts was investigated. Grafting was done using Pb29 (transgenic poplar 741 with cry1Ac genes), CC71 (transgenic poplar 741 with cry3A genes), non‐transgenic poplar 741 and non‐transgenic Populus tomentosa, either as scion or as rootstock. In order to detect migration of Bt‐Cry1Ac protein from one portion of the graft union to different tissues in the grafted plant, ELISA analysis was employed to assess the content of Bt‐Cry1Ac protein in the phloem, xylem, pith and leaves of the grafted poplar. To further verify migration of Bt‐Cry1Ac protein, Clostera anachoreta larvae, which are susceptible to Bt‐Cry1Ac protein, were fed leaves from the control graft (i.e., graft portion that originally did not contain Bt‐Cry1Ac protein). The results showed that Bt‐Cry1Ac protein was transported between rootstock and scion mainly through the phloem. Migration of Bt‐Cry1Ac protein in the grafted union was also evidenced in that the leaves of the control graft did have a lethal effect on C. anachoreta larvae in laboratory feeding experiments.     

Fine root dry matter relative to mango (<Emphasis Type="Italic">Mangifera indica</Emphasis>) tree scion size grafted on size-controlling rootstocks,is negatively related to scion growth rate

Key message

The effects of mango rootstock cultivars on scion vigour may be predicted by scion growth rate being negatively related to fine root dry matter/scion trunk cross sectional area.

Abstract

Knowledge of root dry matter (DM) allocation, in relation to differing vigour conferred by rootstock cultivars, is required to understand the structural relationships between rootstock and scion. We investigated the mass of roots (four size classes up to 23 mm diameter) by coring proximal to five polyembryonic mango rootstock cultivars known to differ in their effects on the vigour and productivity of scion cultivar ‘Kensington Pride’, in a field trial of 13-year-old trees. Significant differences in fine (<0.64 and 0.64–1.88 mm diameter) and small (1.88–7.50 mm) root DM contents were observed between rootstock cultivars. There was a complex relationship between the amount of feeder (fine and small size classes) roots and scion size (trunk cross sectional area, TCSA), with intermediate size trees on rootstock MYP having the most feeder roots, while the smallest trees, on the rootstock Vellaikulamban had the least of these roots. Across rootstock cultivars, tree vigour (TCSA growth rate) was negatively and significantly related to the ratio of fine root DM/scion TCSA, suggesting this may be a useful indicator of the vigour that different rootstocks confer on the scion. In contrast non-ratio root DM and scion TCSA results had no significant relationships. The significant rootstock effects on orchard root growth and tree size could not be predicted from earlier differences in nursery seedling vigour, nor did seedling vigour predict root DM allocation.

     

Overwintering sites and winter mortality of Euseius finlandicus (Acari: Phytoseiidae) in a peach orchard in northern Greece

In peach orchards of northern Greece Euseius finlandicus Oudemans overwinters in various sites on the trees, usually in groups of 5–15 females. Overwintering females were mostly found in bark crevices near the hibernation cocoons of the peach moth Adoxophyes orana (Fischer von Rosslerstamm), and also in small crevices of the bark and in pedicels left after fruit harvesting. Empty scales of dead diaspidids and dead coccids, cocoons of lacewings and mummies of parasitized aphids sporadically found on trees, were less common overwintering sites for females of the mite. In two successive years, mortality of overwintering females was very low, approximately 4 and 4.5% which could be due to the mild climate of northern Greece and the high cold tolerance of the mite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interaction dynamics between saprobic lignicolous fungi and Armillaria in controlled environments: Exploring the potential for competitive exclusion of Armillaria on peach

Armillaria root rot, caused by Armillaria tabescens and Armillaria mellea, is a major cause of premature tree death in peach orchards in the southeastern United States. The root systems of infected trees can become entirely colonized by Armillaria, serving as an inoculum source for adjacent trees and providing massive inoculum levels in replant situations. If dead or dying trees could be colonized by an effective competitor of Armillaria before their removal, the extent of root colonization by the pathogen could be reduced, thus decreasing the threat to adjacent trees and/or subsequent plantings. Interactions between five species of saprobic lignicolous fungi (Ganoderma lucidum, Hypholoma fasciculare, Phanerochaete velutina, Schizophyllum commune, and Xylaria hypoxylon) and the two Armillaria species were examined in controlled conditions to provide proof of concept for competitive exclusion of Armillaria from peach roots. On agar-coated glass slides, all five potential antagonists induced detrimental reactions in >58% of the Armillaria hyphae observed, with the majority resulting in hyphal swelling or granulation. On poplar wood blocks, all antagonists consistently either overgrew Armillaria colonies or—in the case of S. commune—engaged in deadlock reactions; in all cases, the viability of Armillaria colonies was reduced to <30% of that of unchallenged controls. When inoculated simultaneously onto opposite ends of peach root segments, all antagonists consistently reduced growth and viability of Armillaria on and under the bark, whereby reduction of pathogen growth underneath the bark, Armillaria’s primary ecological niche, was most pronounced for G. lucidum, S. commune, and X. hypoxylon. When root segments were allowed to be colonized entirely by Armillaria before being inoculated with the antagonists, the latter were able to overgrow the pathogen on the root surface but unable to pre-empt it from underneath the bark. In summary,G. lucidum, S. commune, and X. hypoxylon caused strong hyphal and mycelial interference reactions and the most pronounced reductions in growth of Armillaria above and below the bark, indicating that they would be the most promising candidates for field-scale evaluations to restrict colonization of dead or dying peach trees by Armillaria in the orchard.