The xylophagous leafhopper Homalodisca coagulata Say is an important vector of diseases caused by the bacterium, Xylella fastidiosa (e.g., Pierce's disease, phony peach disease, plum leaf scald, etc.). Neither leafhoppers or X. fastidiosa can be controlled by chemical sprays. For many plant species there is no resistant germplasm. H. coagulata is highly polyphagous, and within Prunus spp. host preference ranges from moderate (plum) to low (peach). The abundance, feeding and performance of H. coagulata on many unrelated plant species have been previously correlated with the amino acid profile, and particularly the amides in xylem fluid. We tested Prunus scion/rootstock combinations, which provided for a range of xylem fluid chemistry, on the behavior (abundance, feeding) and performance (survivorship, fecundity, body weight and body composition) of H. coagulata. Leafhopper abundance on various rootstock/scion combinations was determined seasonally. During the period of peak abundance (June 14 to 30) feeding rates and performance indices were determined. Leafhopper abundance and feeding increased with an increased concentration of amino acids. Abundance and feeding rate were most highly correlated with the amides in xylem fluid; performance indices were influenced by the amides and certain essential amino acids. Lower consumption rates decreased survivorship, reduced body dry weight and the carbon concentration of surviving insects.
Forty eight cultivars, species, and their progeny including Prunus americana P. angustifolia, P. cerasifera P. munsoniona, P. salicina, P. simoni, and P. triflora were evaluated for resistance to Xylella fastidiosa based on percent of scalded leaves and tree longevity. Observations indicate that resistance is heritable and controlled by recessive genes. Further, X. fastidiosa transmission was evaluated in plum and peach by chip and slip budding. Transmission as measured by enzyme-linked immunoabsorbant assay indicated that chip budding resulted in a higher level of transmission over slip budding in plum but not in peach. Neither Lovell nor Nemaguard rootstock had an effect on transmission.
Effects of scion inclination on root growth and distribution were studied on INRA GF 677 (Prunus persica × Prunus amygdalus) and apple/M.9 trees. At planting, central leaders were positioned vertically (0°) or inclined 45° or 60° to the north and south. Three years after planting, root total dry weight of inclined trees was lower than that of the control (0°, vertical central leader). Five years after planting, the isotropic distribution of the normal root systems was distorted by inclination in both species. Roots were more numerous and more elongated in the direction of inclination. Statistical analysis of root density data, using a polar coordinate system, confirmed that the trunk inclination reduced root development and redirected root distribution. The major effect was induced on GF 677 by 60° inclinations. Tree orientation did not seem to influence root distribution.
Armillaria spp. associated with root disease in peach orchards in the State of Mexico, Mexico For. Pathol. 43 390 401 Guillaumin, J.J. Pierson, J. Grassely, C. 1989 The susceptibility of different Prunus species used as stone fruit rootstocks to
strong indication that Unknown 7 from Goldridge is a cultivar of P. rivularis . Sister to the previous monophyletic group is ‘Chalco’ (DPRU.431) (WEO), which is listed as Prunus spp. in the USDA-ARS-NCGR GRIN Global database ( Figs. 2 , 4 , and 5
Abstract
Ethanol treatment broke dormancy in Gladiolus spp., Freesia spp., Lilium longiflorum Thunb., Zingiber myoga Rose., Platycodon grandiflorum A. DC., Paeonia suffruticosa Andr., and Prunus persica (L.) Batsch. Effectiveness of ethanol depended on species and stage of dormancy.
Educational and research opportunities utilizing native plant species are being developed by the LSU Agricultural Center through the recent establishment of a native plant arboretum at the Calhoun Research Station. Plants indigenous to Louisiana and surrounding states are being collected and planted in the arboretum for evaluation of potential values for landscaping, in food industries, and/or wildlife management. Native trees being studied include species of oak (Quercus), maple (Acer), hickory (Carya), and dogwood (Cornus). Lesser known species of holly (Ilex) and hawthorn (Crataegus), are being evaluated for commercial production and landscape potential. Fruit being collected for field orchard studies include mayhaw (Crataegus opaca), pawpaw (Asimina triloba), and several native plums (Prunus spp.).
Nearly 5000 seedling trees representing more than 100 peach [Prunus persica (L.) Batsch.] and plum (Prunus spp.) lines were planted at a 4 × 0.6-m spacing in Jan. 1983, on a site with a known history of peach tree short life (PTSL) and Armillaria root rot (ARR). Trees were arranged in a randomized complete-block with eight replicates of six trees each. Beginning in Spring 1984 and each year thereafter the cause of tree death was determined. At the end of 9 years, 50% of the trees had succumbed to PTSL and 35% had been killed by ARR apparently caused by Armillaria tabescens. Analysis of the data for trees killed by ARR showed a wide range in mortality, some peach lines appeared significantly more tolerant to ARR than others. Plum lines derived from native North American species also appeared to be a potential source of improved tolerance. We did not establish whether ARR tolerance is affected by PTSL.
Trials were established at Aula Dei Experimental Station (EEAD-CSIC, Zaragoza, Spain) to assess graft compatibility between peach cultivars [Prunus persica (L.) Batsch] and new Prunus spp. rootstocks or selections. Peach cvs. `Catherina' and `Tebana' and nectarine cvs. `Big Top' and `Summergrand' were grafted on peach seedlings, plum rootstocks, almond × peach hybrids, and other interspecific rootstocks. Part of the evaluated material belongs to the EEAD-CSIC selection program, which has showed good adaptation to Mediterranean growing conditions. Other rootstocks such as Bruce, Evrica, Hiawatha, Ishtara, Tetra, and Krymsk-1 have been recently introduced in Spain. A peach and a plum source, GF 677 and Adesoto 101, respectively, were used as compatible reference rootstocks. Both are widely used for peach and nectarine production in the Mediterranean area.
Japanese plum (Prunus salicina Lindel. `Casselman') trees exposed to three atmospheric ozone partial pressure treatments were sprayed with a summer application of Volck Supreme oil (1% aqueous solution) to control an outbreak of spider mites (Tetranychus spp.). Phytotoxic effects were observed on the foliage of trees in the plots exposed to ambient or higher atmospheric ozone partial pressures 5 days following spray application. Foliage on trees exposed to 0.044 and 0.081 μPa·Pa-1 ozone [12-h mean (8 Apr. to 12 June 1992)] partial pressures developed water spotting and more foliage abscission than trees exposed to charcoal-filtered air (0.024 μPa·Pa-1 ozone). Thus, ozone air-pollution stress may predispose plants to increased phytotoxicity from summer oils.