Identification of a major QTL for Xanthomonas arboricola pv. pruni resistance in apricot

Xanthomonas arboricola pv. pruni causes bacterial spot of stone fruit resulting in severe yield losses in apricot production systems. Present on all continents, the pathogen is regulated in Europe as a quarantine organism. Host resistance is an important component of integrated pest management; however, little work has been done describing resistance against X. arboricola pv. pruni. In this study, an apricot population derived from the cross “Harostar” × “Rouge de Mauves” was used to construct two parental genetic maps and to perform a quantitative trait locus analysis of resistance to X. arboricola pv. pruni. A population of 101 F1 individuals was inoculated twice for two consecutive years in a quarantine greenhouse with a mixture of bacterial strains, and disease incidence and resistance index data were collected. A major QTL for disease incidence and resistance index accounting respectively for 53 % (LOD score of 15.43) and 46 % (LOD score of 12.26) of the phenotypic variation was identified at the same position on linkage group 5 of “Rouge de Mauves.” Microsatellite marker UDAp-452 co-segregated with the resistance, and two flanking microsatellites, namely BPPCT037 and BPPCT038A, were identified. When dividing the population according to the alleles of UDAp-452, the subgroup with unfavorable allele had a disease incidence of 32.6 % whereas the group with favorable allele had a disease incidence of 21 %, leading to a reduction of 35.6 % in disease incidence. This study is a first step towards the marker-assisted breeding of new apricot varieties with an increased tolerance to X. arboricola pv. pruni

Tolerância de gemas floríferas, flores e frutos de pessegueiro a temperaturas de ocorrência de geadas.

Na região produtora de pêssegos do sul do Brasil, não é rara a ocorrência de geadas nos meses de julho, agosto e, em alguns anos, até setembro. Este período coincide com a floração do pessegueiro e com o início do desenvolvimento dos frutos. Com a finalidade de testar possíveis diferenças entre cultivares quanto à tolerância a baixas temperaturas foram conduzidos experimentos, em delineamento inteiramente casualizado, nos anos de 2009 e 2010. Foram testados dois fatores (genótipo e estádio da gema floral), com três repetições e 20 botões forais por parcela. Os genótipos testados foram os cultivares 'Chimarrita', 'Coral' e 'BR-1' e a seleção Cascata 730. Em 2010, foi acrescentado o cv. 'Charme'. Os estádios fenológicos testados foram: o de botão prateado, botão rosado, balão e flor aberta. Ramos destacados dos genótipos a serem testados foram submetidos, por 16 horas, a temperaturas entre -2,2 e -5,5 ºC. Ramos com frutos, antes e após o endurecimento do caroço, foram testados em outro experimento. As diferenças entre genótipos foram pequenas e parecem estar mais ligadas ao pré-condicionamento das gemas. A seleção Cascata 730 mostrou ser das mais sensíveis ao frio. As gemas florais são, geralmente, menos sensíveis a temperaturas negativas (próximas a -3 ºC), nos estádios de botão rosado e balão. Frutos com endocarpo macio são sensíveis a danos de frio, independentemente do genótipo. Temperaturas próximas a 2 ºC negativos não causam problemas em frutos com endocarpo já endurecido

Effects of different rootstocks on aroma volatile constituents in the fruits of peach (Prunus persica L. Batsch cv. ‘Cresthaven’)

The consumption of peaches is dependent on fruit quality. Aromatic compounds directly affect the sensorial quality and consumer acceptance of peaches. This study evaluated the fruit quality and aroma volatile constituents of the peach cultivar Cresthaven' grafted on to five different rootstocks in 2012 and 2013. The rootstocks used were Uzunoglu Seedling' (Prunus persica), GF677' (P. persicaxP. dulcis), Nemaguard' (P. persicaxP. davidiana), Cadaman' (P. persicaxP. davidiana) and St. Julien GF 655/2' (P. insititia). Fruits were sampled at the commercial maturity stage around mid-August. Fruit quality characteristics and aroma volatiles differed significantly in peaches grown on different rootstocks. The largest fruits and highest titratable acidity were obtained from Cadaman'. The major volatile constituents of Cresthaven' fruits were acetaldehyde, hexanal, benzaldehyde, ethanol, 1-hexanol, (Z)-3-hexenol, (E)-2-hexen-1-ol, linalool, ethyl acetate, hexyl acetate, (Z)-3-hexenyl acetate, (E)-2-hexenyl acetate, 6-methyl-5-hepten-2-one, (E)--ionone, -decalactone and limonene. The type and concentration of volatile compounds showed great variability in Cresthaven' peach grafted on to different rootstocks. A total of 91 volatile compounds were detected and the highest volatile content was found in GF677'