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Jorge Pinochet, Cinta Calvet, Adriana Hernández-Dorrego, Ariadna Bonet, Antonio Felipe, and Marian Moreno

Two trials involving 20 Prunus rootstocks were conducted under greenhouse conditions to screen for resistance to root-knot nematode [Meloidogyne javanica (Treub.) Chitwood]. Many of the tested materials are interspecific hybrid rootstocks and represent new commercial peach (P. persica Batsch) and plum (Prunus sp.) releases or experimental genotypes of Spanish, French, and Italian origin. In the first trial, the rootstocks Adesoto 101 (P. insititia L.), Bruce (P. salicina Lindl. × P. angustifolia Marsh.), Ishtara, AC-952 (P. insititia), Garnem [P. dulcis (Mill.) D.A. Webb × P. persica], Cadaman [P. persica × P. davidiana (Carr.) Franch], and Orotava (P. salicina) were immune or resistant to a mixture of 10 isolates of M. javanica. The remaining rootstocks, Myrocal (P. cerasifera Ehr.), Montclar (P. persica), and Adafuel (P. dulcis × P. persica), were susceptible. In the second screening trial, the plum rootstocks Adesoto 101, Adara (P. cerasifera), Myro-10 (P. cerasifera), Constantí (P. domestica L.), and AD 105 (P. insititia) were immune to the root-knot nematode. Cadaman, G × N No. 17 (P. dulcis × P. persica), and Tetra (P. domestica) were resistant. Laroda F1OP (P. salicina), Myro-almond (P. cerasifera × P. dulcis), and the peach–almond hybrids Mayor, Adafuel, and Sirio were susceptible.

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D. Esmenjaud, J.C. Minot, R. Voisin, J. Pinochet, and G. Salesses

Resistance variability was evaluated for five rootstock: three Myrobalan plum (Prunus cerasifera Ehr.) genotypes (P.1079, P.2175, and P.2032) grown from in vitro plantlets, one peach (P. persica (L.) Batsch `GF 305') grown from seeds, and one peach-almond hybrid (P. persica × P. amygdalus Batsch `GF 557') grown from rooted cuttings. Twenty-two root-knot nematode populations from different origins were used: Meloidogyne arenaria (Neal) Chitwood (six populations), M. incognita (Kofoid and White) Chitwood (eight populations), M.javanica (Treub) (four populations), M. hispanica Hirschmann (one population), M. hapla Chitwood (two populations), and an unclassified root-knot species (one population). The study was conducted under greenhouse conditions for 1 and 2 months. No galling or nematode reproduction was observed in P.1079 and P.2175, which should be considered immune; P.2032 showed the highest galling and nematode counts when inoculated with M. hispanica and M. javanica. In P.2032, a high proportion of males was recovered in populations that had a limited development. Because the populations of the first four Meloidogyne species reproduce by obligatory mitotic parthenogenesis, high sex ratio maybe the expression of a late form of resistance. Host suitability of `GF 305' was highly variable among M. arenaria and M. incognita populations. A lower relative variation was observed in M. javanica. `GF 557' was resistant to M. arenaria and M. incognita except for one population of M. arenaria that was weakly aggressive and susceptible to M. javanica. Consequently, resistances specific to the genus Meloidogyne for the Myrobalan plum genotypes P.1079 and P.2175, specific to the nematode species for `GF 557', and specific to the nematode population for `GF 305', were evidenced. This study indicates that, in rootstock selection procedures, it is important to test resistance to several populations within the same nematode species.

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J.D. Norton, G.E. Bovhan, D.A. Smith, and B.R. Abrahams

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B.L. Topp and D.M. Russell

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B.L. Topp and D.M. Russell

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J.D. Norton, G.E. Boyhan, D.A. Smith, and B.R. Abrahams

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J.D. Norton, G.E. Boyhan, D.A. Smith, and B.R. Abrahams

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J.D. Norton, G.E. Boyhan, D.A. Smith, and B.R. Abrahams

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Dangyang Ke, Leonor Rodriguez-Sinobas, and Adel A. Kader

Fruits of `Granny Smith' and `Yellow Newtown' apples (Malus domestica Borkh), `20th Century' pear (Pyrus serotina L.), and `Angeleno' plum (Prunus domestica L.) were kept in air and in 0.25% or 0.02% O2 at 0, 5, or 10C for 3, 7, 14, 25, or 35 days to study the effects of low-O2 atmospheres on their postharvest physiology and quality attributes. Soluble solids content (SSC), pH, and external appearance were not significantly influenced, but resistance to CO2 diffusion was increased by the low-O2 treatments. Exposures to the low-O2 atmospheres inhibited ripening, including reduction in ethylene production rate, retardation of skin color changes and flesh softening, and maintenance of titratable acidity. The most important detrimental effect of the low-O2 treatments was development of an alcoholic off-flavor that had a logarithmic relation with ethanol content of the fruits. The ethanol content causing slight off-flavor (Eo) increased with SSC of the commodity at the ripe stage, and it could be estimated using the following formula: (Log Eo)/SSC = 0.228. Using SSC of ripe fruits and average ethanol accumulation rate per day (VE) from each low-O2 treatment, the tolerance limit (Tl) of fruits to low-O2 atmospheres could be predicted as follows: Tl = Eo/VE = (100.228SSC)/VE.

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P. Martínez-Gómez, M. Rubio, F. Dicenta, and T.M. Gradziel

Sharka [(plum pox virus (PPV)] mainly affects Prunus species, including apricot (Prunus armeniaca L.), peach (Prunus persica L.), plum (Prunus salicina Lindl., Prunus domestica L.), and, to a lesser degree, sweet (Prunus avium L.) and sour cherry (Prunus cerasus L.). Level of resistance to a Dideron isolate of PPV in seven California almond [P. dulcis (Miller) D.A. Webb], five processing peach cultivars, and two peach rootstocks was evaluated. In addition, almond and peach selections resulting from interspecific almond × peach hybridization and subsequent gene introgression were tested. Evaluations were conducted in controlled facilities after grafting the test genotypes onto inoculated GF305 peach rootstocks. Leaves were evaluated for PPV symptoms during three consecutive cycles of growth. ELISA-DASI and RT-PCR analysis were also employed to verify the presence or absence of PPV. Peach cultivars and rootstocks showed sharka symptoms and were ELISA-DASI or RT-PCR positive for some growth cycles, indicating their susceptibility to PPV. Almond cultivars and almond × peach hybrids did not show symptoms and were ELISA-DASI and RT-PCR negative, demonstrating resistance to PPV. Two (almond × peach) F2 selections as well as two of three backcrossed peach selections also showed a resistant behavior against the PPV-D isolate. Results demonstrate a high level of resistance in almond and indicate potential for PPV resistance transfer to commercial peach cultivars.