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Unaroj Boonprakob and David H. Byrne

Diploid plums such as Prunus salicina, P. simonii, P. cerasifera, P. americana, P. angustifolia, P. mexicana, and their hybrids have a high level of RAPD polymorphisms. Of 71 successfully used primers, there are 417 reproducible RAPD markers and only 55 (13%) markers are not polymorphic. Genetic relationships of these diploid plums based on RAPD data is estimated using genetic distance (GD) defined as GDij = 1 – Sij, where Sij is similarity coefficient. Two similarity coefficients, Jaccard's and simple matching coefficient, are compared. Simple matching always yields higher similarity coefficients. Genetic distance within and between each gene pool: California, southeastern U.S., foreign, is estimated. Genetic distances of these diploid plums ranged from 0.32 to 0.68, and agreed well with the natural geographic distribution of the species. The cluster analysis using unweighted pair-group methods using arithmetic averages (UPGMA) was used to construct phenograms to summarize the relationships among these cultivated diploid plums and plum species.

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Esmaeil Fallahi, Brenda R. Simons, John K. Fellman, and W. Michael Colt

Influence of various concentrations of hydrogen cyanamide (HC) on fruit thinning of `Rome Beauty' apple (Malus domestica Borkh.), `Friar,' and `Simka' plums (Prunus salicina Lindley) were studied. A full bloom application of HC at all tested concentrations decreased `Rome Beauty' apple fruit set and yield, and increased fruit weight. Hydrogen cyanamide at 0.25% (V/V) resulted in adequate apple thinning, indicated by the production of an ideal fruit weight. Prebloom and full bloom applications of HC at greater than 0.75% reduced plum fruit set and yield in `Friar.' Full bloom application of HC at 0.25% to 0.50% showed a satisfactory fruit set, yield, and fruit size in `Friar' plum. Full bloom application decreased fruit set and yield in `Simka' plum. Hand thinning, as well as chemical thinning, is recommended for plums.

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Ana Pina, Pilar Errea, Ana Wünsch, and Rafael Gella

‘Monrepos’ is a Prunus -plum rootstock developed at the Agri-Food Research and Technology Center of Aragón (CITA), Zaragoza, Spain, for use as a rootstock for sweet cherry ( Prunus avium L.). Cherry rootstock research over the last decade has been

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Bruce R. Abrahams and Joseph D. Norton

The transmission of plum leaf scald or phony peach, Xylella fartidiosa, Wells is compared by the slip and chip budding with peach and plum scions on two peach rootstocks, `Lovell' and `Nemaguard'. ELISA was used to determine mean concentrations of the bacteria in scion leaf petioles. There was a greater level of transmission of the pathogen using chip budding over slip budding in plums but not in peach. Further analysis of slip budding showed no difference to unbudded rootstocks wheras chip budding caused a significantly higher incidence of transmission.

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G.E. Boyhan, B.R. Abrahams, J.D. Norton, and Hongwen Huang

Detection of Xylella fastidiosa Wells et al. by enzyme-linked immunosorbent assay indicated that plums (Prunus hybrids) had higher absorbance values than peaches [Prunus persica (L.) Batsch]. The slip-budded trees had lower readings than those that were chip budded; however, the scion × method interaction was significant. Further comparison of slip vs. chip budding indicated that the lower absorbance value of slip budding occurred in plums only; there was no difference between budding methods in peach.

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Gregory L. Reighard, David W. Cain, and William C. Newall Jr.

More than 400 genotypes of Prunus were evaluated for “in field” rooting and survival from fall-planted hardwood cuttings treated with 2000 ppm IBA. Cultivars of European and Japanese plums originating from species and interspecific hybrids of the section (sect.) Prunus had the highest survival. Cuttings from cultivars of sand cherry (sect. Microcerasus) and peach (sect. Euamygdalus) averaged 28% to 54% lower survival than European and Japanese plums. Few cultivars of almonds (sect. Euamygdalus), apricots (sect. Armeniaca), and American plums (sect. Prunocerasus) rooted from hardwood cuttings. Chemical name used: 1H-indole-3-butyric acid (IBA).

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Rawia El-Motaium, Hening Hu, and Patrick H. Brown

The influence of B and salinity [3 Na2SO4 : 1 CaCl2, (molar ratio)] on B toxicity and the accumulation of B, sodium, and SO4 in six Prunus rootstocks was evaluated. High salinity reduced B uptake, stem B concentrations, and the severity of toxicity symptoms in five of the six rootstocks. Forward and backward stepwise regression analyses suggested that stem death (the major symptom observed) was related solely to the accumulation of B in the stem tissue in all rootstocks. The accumulation of B and the expression of toxicity symptoms increased with time and affected rootstock survival. No symptoms of B toxicity were observed in leaf tissue. The Prunus rootstocks studied differed greatly in stem B accumulation and sensitivity to B. The plum rootstock `Myrobalan' and the peach-almond hybrid `Bright's Hybrid' were the most tolerant of high B and salinity, whereas the peach rootstock `Nemared' was very sensitive to high B and salinity. In all rootstocks, adding B to the growth medium greatly depressed stem SO4 concentrations. In every rootstock except `Nemared' peach, adding salt significantly depressed tissue B concentrations. A strong negative correlation between tissue SO4 and B was observed. Grafting experiments, in which almond was grafted onto `Nemared' peach or `Bright's Hybrid', demonstrated the ability of rootstocks to influence B accumulation and scion survival.

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K.V. Kommineni, J.M. Gillett, and D.C. Ramsdell

In a greenhouse study, fifty 1-year-old `Stanley'/`Myrobalan 29C' plum (Prunus sp.) trees were inoculated with tomato ringspot nepovirus (ToRSV) by either nematode inoculation or slash inoculation to compare how inoculation effects the onset of the prune brown line (PBL) disease. In six tests (over 2 years), slash-inoculated trees had a higher percentage of ToRSV infection than nematode-inoculated trees when root and bark samples were tested by enzyme-linked immunosorbent assay (ELISA). ELISA differences between the two treatments were significant by chi-square analysis. None of the ToRSV positives by ELISA developed a brown line at the graft union. In a second experiment, five rootstock (`Myrobalan 29C', `Marianna 4001', `Marianna 2624', `Marianna GF8-1', and `St. Julian 655-2') and five scion (`Carolyn Harris', `New York 58.900.12', `Stanley', `Valor', and `70031') combinations (total combination = 25) were established in a field plot in Traverse City, Mich., and infected with ToRSV by slash and nematode inoculation. All five rootstocks were infected, with incidences of 40% to 60% ToRSV infections after 3 years. `Marianna 2624' had the lowest incidence of PBL (5%) compared to `Myrobalan 29C', which had the highest incidence (30%). The scion 70031 in combination with either `Myrobalan 29C' or `Marianna 4001' rootstocks, produced PBL in 100% of the trees. ToRSV was detected by ELISA and northern hybridization assays. ELISA consistently detected more positives when root or bark tissues were tested, and northern hybridization assay consistently detected more positives when rootstock sucker leaves were used.

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Randy G. Gardner and Dilip R. Panthee

Plum Regal’ is a fresh-market plum (Roma type) tomato ( Solanum lycopersicum L.) with crimson fruit color; resistance to verticillium wilt ( Verticillium dahliae ), fusarium wilt [ Fusarium oxysporium f.sp. lycopersici (Sacc.) W.C. Snyder and

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Eun Young Nam, Ji Hae Jun, Kyeong Ho Chung, Jung Hyun Kwon, Seok Kyu Yun, Ik Koo Yun, and Kang Hee Cho

between ‘Soldam’ japanese plum ( Prunus salicina Lindl., female parent) and ‘Harcot’ apricot ( Prunus armeniaca L., male parent). It was released for commercial use in the Republic of Korea in 2011. ‘Tiffany’ has a red-fleshed fruit similar to that of