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Darush Struss, Riaz Ahmad, Stephen M. Southwick, and Manuela Boritzki

Simple sequence repeats (SSRs) and amplified fragment-length polymorphisms (AFLPs) were used to evaluate sweet cherry (Prunus avium L.) cultivars using quality DNA extracted from fruit flesh and leaves. SSR markers were developed from a phage library using genomic DNA of the sweet cherry cultivar Valerij Tschkalov. Microsatellite containing clones were sequenced and 15 specific PCR primers were selected for identification of cultivars in sweet cherry and for cross-species amplification in Prunus. In total, 48 alleles were detected by 15 SSR primer pairs, with an average of 3.2 putative alleles per primer combination. The number of putative alleles ranged from one to five in the tested cherry cultivars. Forty polymorphic fragments were scored in the tested cherry cultivars by 15 SSRs. All sweet cherry cultivars were identified by SSRs from their unique fingerprints. We also demonstrated that the technique of using DNA from fruit flesh for analysis can be used to maintain product purity in the market place by comparing DNA fingerprints from 12 samples of `Bing' fruit collected from different grocery stores in the United States to that of a standard `Bing' cultivar. Results indicated that, with one exception, all `Bing'samples were similar to the standard. Amplification of more than 80% of the sweet cherry primer pairs in plum (P. salicina), apricot (P. armeniaca) and peach (P. persica L.) showed a congeneric relationship within Prunus species. A total of 63 (21%) polymorphic fragments were recorded in 15 sweet cherry cultivars using four EcoRI-MseI AFLP primer combinations. AFLP markers generated unique fingerprints for all sweet cherry cultivars. SSRs and AFLP polymorphic fragments were used to calculate a similarity matrix and to perform UPGMA cluster analysis. Most of the cultivars were grouped according to their pedigree. The SSR and AFLP molecular markers can be used for the grouping and identification of sweet cherry cultivars as a complement to pomological studies. The new SSRs developed here could be used in cherry as well as in other Prunus species for linkage mapping, evolutionary and taxonomic study.

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Stephen M. Southwick and James T. Yeager

Heavy fruit set of apricot (Prunus armeniaca) cultivars grown in California often require hand thinning to insure that adequate fruit size is obtained. Alternatives to costly hand thinning would be welcome. GA treatments made during flower bud initiation/differentiation have been previously shown to inhibit the development of floral and vegetative buds in a number of different tree fruit species. The effects of post-harvest limb and whole tree aqueous gibberellic acid (GA) sprays on flower and fruit production were investigated over a 3 year period in `Patterson' apricot. Limb treatments indicated the potential for utilizing postharvest GA sprays to reduce the number of flowers produced in the following season. Harvest fruit size (June 1989) was increased by a 100 mg·liter-1 GA whole tree spray applied 7 July 1988 when compared to non-thinned and hand thinned trees. Yield per tree was reduced by that GA spray, but not enough to show statistical differences. No abnormal tree growth responses have been observed in GA-sprayed trees to date. These results and those from the 1989 and 1990 growing seasons will be presented in effort to identify a role for whole tree postharvest GA sprays in a chemical thinning program suitable for commercial apricots.

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Thomas M. Gradziel and Steven A. Weinbaum

The regulation of anther dehiscence by relative humidity (RH) was assessed for detached anthers and detached whole flowers from a limited selection of apricot (Prunus armeniaca L.), peach [P. persica (L.) Batsch], and almond [P. dulcis (Mill.) D.A. Webb, syn. P. amygdalus Batsch; P. communis (L.) Arcangeli, non Huds.] genotypes, as well as an almond X peach F2 progeny. Dehiscence was evaluated at 33, 64, 87, 93 and 97% RH for detached anthers, and at 33, 64 and 97% RH for whole detached flowers. Anther dehiscence was suppressed with increasing RH for all genotypes. Apricot anthers showed the greatest dehiscence at low RH and measurable dehiscence at high RH even when detached. Anther dehiscence in almond appeared more suppressed than in apricot at all RH levels tested, being completely suppressed by high RH in detached anthers. Peach genotypes exhibited the full range of variability between apricot and almond patterns. Evidence for transgressive segregation of RH-controlled anther dehiscence was observed in the occurrence of cleistogamy in an almond × peach F2 progeny. Rates of anther dehiscence were approximately linear with change in RH in detached anthers but exhibited a more buffered, step-wise response when detached whole flowers were tested. Results are consistent with field observations, and highlight the low but measurable risk of cleistogamy in these species, as well as opportunities to modify the breeding systems and crossing environments to facilitate controlled hybridization, and to reduce pollination vulnerability to adverse environments.

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F.A. Bliss, P.L. Schuerman, A.A. Almehdi, A.M. Dandekar, and N. Bellaloui

Crown gall is an important disease of many fruit and nut crops, but little is known about sources of resistance. We screened germplasm from Prunus armeniaca L., P. angustifolia Marsh., P. argentia L., P. avium L., P. besseyi Bailey, P. bokhariensis Schneid., P. brigantica L., P. cerasifera Ehrh., P. cerasus L., P. dulcis (Mill.) D.A. Webb, P. fruiticosa Pall., P. hortulana Bailey, P. insititia L., P. japonica Thunb., P. mahaleb L., P. persica (L.) Batsch, P. serotina Ehrh., P. simonii Carr., P. sogdiana L., and P. webbii (Spach) Vieh. When either main stems or lateral branches of seedlings were inoculated with strains K12 and C58 of Agrobacterium tumefaciens (Smith and Townsend) Conn., the incidence of resistance was less than 10% except in some accessions of P. mahaleb L. where up to 30% of the plants were resistant. Some resistant plants were identified in other species, with P. insititia L. being the most promising. Symptoms based on presence and size of galls should be allowed to develop for up to 90 days after inoculation to reduce the likelihood of misclassifying plants as resistant when they are slightly susceptible.

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T.L. Creger and F.J. Peryea

Phosphate fertilizer additions to soils containing lead arsenate (LA) pesticide residues can increase As volubility. Apricot (Prunus armeniaca L.) rootstock liners were grown in nondraining pots containing Burch loam soil that received a factorial treatment combination: 1) LA enrichment [no added LA (-LA), and LA added at 138 mg Pb/kg and 50 mg As/kg (+LA)]; 2) fertilizer type [monoammonium phosphate (MAP) and its sulfur analog ammonium hydrogen sulfate (AHS)]; and 3) fertilizer anion rate (0-26.1 mol/m3 soil). Measured response variables were soil salinity and pH, plant biomass, and plant As and Pb concentrations. Both MAP and AHS increased soil electrical conductivity (EC) and decreased soil pH, with AHS usually being more salinizing and acidifying than MAP was at equivalent rates. Adding LA reduced shoot and root mass and increased As and Pb concentration in shoots and roots. Shoot and root mass were inversely related to soil EC in the -LA soil but not in the +LA soil. Adding MAP increased shoot and root As concentration in the +LA soil, but adding AHS had no effect. Fertilizer type and rate did not influence shoot As concentration or root Pb concentration in the -LA soil or shoot Pb concentration in either the +LA or -LA soil. Adding AHS to the +LA soil increased root Pb concentration. These results are consistent with a P-enhanced solid-phase As release mechanism, which consequently increases plant uptake of soil As. Phosphate amendment had no effect on soil Pb phytoavailability.

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Peter Sholberg, Paula Haag, Rod Hocking, and Karen Bedford

Vapors of several common vinegars containing 4.2% to 6.0% (= 2.5 to 3.6 mol·L-1) acetic acid effectively prevented conidia of brown rot [Monilinia fructicola (G. Wint.) Honey], gray mold (Botrytis cinerea Pers.:Fr.), and blue mold (Penicillium expansum Link) from germinating and causing decay of stone fruit (Prunus sp.), strawberries (Fragaria ×ananassa Duchesne), and apples (Malus ×domestica Borkh.), respectively. Fruit were fumigated in 12.7-L sealed containers in which vinegar was dripped on to filter paper wicks or vaporized by heating from an aluminum receptacle. Vapor from 1.0 mL of red wine vinegar (6.0% acetic acid) reduced decay by M. fructicola on `Sundrop' apricots (Prunus armeniaca L.) from 100% to 0%. Similarly, vapor from 1.0 mL of white vinegar (5.0% acetic acid) reduced decay in strawberries by B. cinerea from 50% to 1.4%. Eight different vinegars, ranging from 4.2% to 6.0% acetic acid, of which 0.5 mL of each vinegar was heat-vaporized, reduced decay by P. expansum to 1% or less in `Jonagold' apples. The volume of heat-vaporized white vinegar (5.0% acetic acid) necessary to reduce decay by P. expansum on `Jonagold' apples to zero was 36.6 μL·L-1 of air. Increasing the number of conidia on the apple surface reduced the effectiveness of vinegar vapor. The number of lesions caused by P. expansum on `McIntosh' apple decreased exponentially with increasing time of fumigation, approaching zero after about 6 hours. These results suggest that vinegar vapor could be an effective alternative to liquid biocides such as sodium hypochlorite for sterilization of surfaces contaminated by conidia of fungal pathogens.

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Peter Sholberg, Paula Haag, Rod Hocking, and Karen Bedford

Vapors of several common vinegars containing 4.2% to 6.0% (= 2.5 to 3.6 mol·L-1) acetic acid effectively prevented conidia of brown rot [Monilinia fructicola (G. Wint.) Honey], gray mold (Botrytis cinerea Pers.:Fr.), and blue mold (Penicillium expansum Link) from germinating and causing decay of stone fruit (Prunus sp.), strawberries (Fragaria ×ananassa Duchesne), and apples (Malus ×domestica Borkh.), respectively. Fruit were fumigated in 12.7-L sealed containers in which vinegar was dripped on to filter paper wicks or vaporized by heating from an aluminum receptacle. Vapor from 1.0 mL of red wine vinegar (6.0% acetic acid) reduced decay by M. fructicola on `Sundrop' apricots (Prunus armeniaca L.) from 100% to 0%. Similarly, vapor from 1.0 mL of white vinegar (5.0% acetic acid) reduced decay in strawberries by B. cinerea from 50% to 1.4%. Eight different vinegars, ranging from 4.2% to 6.0% acetic acid, of which 0.5 mL of each vinegar was heat-vaporized, reduced decay by P. expansum to 1% or less in `Jonagold' apples. The volume of heat-vaporized white vinegar (5.0% acetic acid) necessary to reduce decay by P. expansum on `Jonagold' apples to zero was 36.6 μL·L-1 of air. Increasing the number of conidia on the apple surface reduced the effectiveness of vinegar vapor. The number of lesions caused by P. expansum on `McIntosh' apple decreased exponentially with increasing time of fumigation, approaching zero after about 6 hours. These results suggest that vinegar vapor could be an effective alternative to liquid biocides such as sodium hypochlorite for sterilization of surfaces contaminated by conidia of fungal pathogens.

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W.T. Liu, C.L. Chu, and T. Zhou

Fumigation with 1 mg·L-1 of thymol vapor retarded mycelial growth of Monilinia fructicola (G. Wint.) Honey. Mean colony diameter was reduced from 49 mm in the control to 13 mm when the conidia were cultured on potato dextrose agar. Fumigation of apricots (Prunus armeniaca L.) with 2 mg·L-1 of thymol vapor reduced the germination of M. fructicola conidia to 2% compared with 98% on untreated fruit. Microscopic observations showed that the spores fumigated with thymol were shrunken and had collapsed protoplasts. In in vivo experiments, surface-sterilized apricots and plums (Prunus salicina L.) were inoculated with conidia of M. fructicola by applying 20 μL of a spore suspension to wounds on the fruit, and then were fumigated with thymol or acetic acid. The incidence of brown rot was reduced to 3% and 32% when `Manch' apricots were fumigated with thymol or acetic acid at 5 mg·L-1, respectively, compared with 64% incidence in untreated fruit. Fumigation of `Violette' plums with thymol or acetic acid at 8 mg·L-1 reduced brown rot from 88% in the control to 24% and 25%, respectively. Fumigation of `Veeblue' plums with thymol at 4 mg·L-1 reduced brown rot from 56% in the control to 14%. Fumigation of apricots with thymol resulted in firmer fruit and higher surface browning, but total soluble solids and titratable acidity were not affected. Fumigation of plum with thymol resulted in higher total soluble solids, but firmness and titratable acidity were not affected. Thymol fumigation caused phytotoxicity on apricots but not on plums.

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Qijing Zhang and Dajun Gu

Prunus (Rosaceae) is a large genus with significant economic importance, since it includes a variety of popular stone fruit species [e.g., peach ( Prunus persica ), apricot ( Prunus armeniaca ), almond ( Prunus dulcis ), and sweet cherry ( Prunus

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Mariem Bouhadida, Juan P. Martín, Gennady Eremin, Jorge Pinochet, María Á. Moreno, and Yolanda Gogorcena

). The basic chromosome number of Prunus is x = 8. Almond [ P. dulcis D.A. Webb (formerly P. amygdalus Batsch)], peach [ P. persica (L.) Batsch], apricot ( P. armeniaca L.), and sweet cherry ( P. avium L.) are diploids with 2 n = 2 x = 16