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Wang Zu-Hua and Lu Zhen-Xiang

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Zhen-Xiang Lu, G.L. Reighard, W.V. Baird, A.G. Abbott, and S. Rajapakse

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].

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Zhen-Xiang Lu, Gregory L. Reighard, Andrew P. Nyczepir, Thomas G. Beckman, and David W. Ramming

Two F1 hybrid Prunus rootstocks, K62-68 and P101-41, developed from a cross of `Lovell' [susceptible to both Meloidogyne incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood] and `Nemared' (resistant to both root-knot nematode species), were selfed to produce two F2 seedling populations. Vegetative propagation by herbaceous stem cuttings was used to produce four or eight self-rooted plants of each F2 seedling for treatment replications. Eggs of M. incognita and M. javanica were inoculated into the potted media where plants were transplanted, and plants were harvested and roots examined for signs and symptoms associated with root-knot nematode infection ≈120 days later. Segregation ratios in both F2 families suggested that resistance to M. incognita in `Nemared' is controlled by two dominant genes (Mi and Mij) and that to M. javanica by a single dominant gene (Mij). Thus, Mij conveys resistance to both M. incognita and M. javanica.

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Zhen-Xiang Lu, G.L. Reighard, W.V. Baird, and A.G. Abbott

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.