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A treatment to inhibit browning and maintain quality of fresh-cut `Anjou' and `Bartlett' pears (Pyrus communis L.) was developed. Slices of ŒAnjou, and ŒBartlett, pears with a range of initial firmness values were dipped in mixtures of 4-hexylresorcinol, isoascorbic acid, potassium sorbate, and N-acetylcysteine before refrigerated storage. Browning, as indicated by visual observation and by colorimeter readings, was inhibited for 14 d. Pears receiving the antibrowning treatment maintained firmness as well or better than the control slices.
Cluster analyses of 20 peach rootstocks by 40 RAPD markers produced a dendrogram of genetic relationship in good agreement with their putative pedigrees. BY520-9, BY520-8, SL1089, and SL1090, which are selections derived from a common ancestor, clustered together, with the normalized average distance (NAD) ranging from 0.20 to 0.55. Similarly, the clustering of Lovell with Halford and Boone County with Harrow Blood, whose respective NADs were 0.19 and 0.22, implied a high degree of genetic relatedness between each pair of genotypes. Okinawa and Yunnan, both introduced from eastern Asia, tied in a close group (NAD = 0.63) and share relatively similar phenotypes. The first major bifurcation in the dendrogram divided the 20 rootstocks into two groups. One group (Lovell, Halford, Montclar, Bailey, Harrow Blood, Boone County, Tennessee Natural, and GF 305) is susceptible to root-knot nematodes, whereas the second group (BY520-9, BY520-8, SL1089, SL1090, Higama, Nemaguard, Flordaguard, Yunnan, Okinawa, and Nemared), with the exception of Rubira and Siberian C, is tolerant or resistant.
Eighteen peach rootstock cultivars, most of Prunus persica (L.) Batsch, were screened for diagnostic random amplified polymorphic DNA (RAPD) markers using synthetic decamer oligonucleotide primers. Twenty of the 80 primers were informative, and 40 amplified DNA bands from the informative primers were selected as RAPD markers. Based on combined banding patterns, all 18 rootstock cultivars were identified with only six of the 20 informative primers. Cluster analysis of the 18 peach rootstock cultivars using 40 RAPD markers produced a dendrogram of genetic relatedness in good agreement with their putative pedigrees. The first major bifurcation in the dendrogram divided these rootstock cultivars into two groups according to their resistance or susceptibility to root-knot nematodes [Meloidogyne incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood].
We have developed a highly saturated genetic linkage map in peach (diploid, 2n = 16) using two separate crosses. The first population consists of 48 randomly selected F2 individuals which were generated by selfing an F1 from the cross of `New Jersey Pillar' x KV 77119. This progeny set exhibits segregation for gross morphological traits including: canopy shape, fruit flesh color, and flower petal color, size, and number. The second population contains 48 F2 progeny derived from the cross of `Suncrest' x `Bailey'. These progeny segregate for quality traits such as fruit diameter, weight, flesh color, cling vs. free stone, soluble solids, pH of juice extract, and fruit developmental period. Nine linkage groups were identified in the first cross, which cover 590 cM of the genome. In the second cross, eight linkage groups were found that contain several significant chromosomal intervals contributing to fruit quality characteristics by QTL analysis. Anchor loci present in both maps were used to join the linkage groups to create a single combined map of the peach genome. Physical mapping is currently underway to assign the each linkage group to the appropriate chromosome.
We have constructed a genetic linkage map of peach consisting of RFLP, RAPD, and morphological markers, based on 78 F2 individuals derived from the self-fertilization of four F1 individuals originating from a cross between `New Jersey Pillar' and KV 77119. This progeny set was chosen because parental genotypes exhibit variation in canopy shape, fruit flesh color, and flower petal color, size, and number. The segregation of 81 markers comprised of RFLP, RAPD and morphological loci was analyzed. Low copy genomic and cDNA probes were used in the RFLP analysis. The current genetic map for the WV family contains 57 markers assigned to 9 linkage groups, which cover 520 cM of the peach nuclear genome. The average distance between two adjacent markers was 9 cM. Linkage was detected between Pillar (Pi) and double flowers (Dl). RFLP markers loosely linked to Pi, flesh color (Y), and white flower (W) loci were found. Twenty-four markers remain unassigned.