Twenty-nine commercial and experimental Prunus rootstocks, most with incorporated root-knot nematode [Meloidogyne javanica (Traub.) Chitwood] resistance, were evaluated against mixtures comprising nine populations of the root-lesion nematode Pratylenchus vulnus Allen and Jensen. Nearly all tested materials were susceptible. Five cultivars with high resistant levels were further challenged with seven P. vulnus populations individually. `Redglow' (Prunus salicina Lindl. × P. munsoniana Wight and Hedrick) was the only rootstock that showed broad resistance to all populations. The rootstocks `Torinel' (P. domestica L.), AC-595 (P. domestica × P. insititia L.), `Marianna 4001' (P. cerasifera Ehr. × P. munsoniana), and `Felinem' [P. dulcis (Mill.) D. A. Webb × P. persica (L.) Batsch] showed resistance to one or a few P. vulnus populations. Several supposedly resistant sources proved to be susceptible. Tests of crosses made between parents of diverse genetic background with partial resistance to P. vulnus indicate that a descendant with potential P. vulnus resistance is difficult to obtain. Pathogenic diversity among P. vulnus populations appears to be high.
Jorge Pinochet, Carolina Fernández, Cinta Calvet, Adriana Hernández-Dorrego, and Antonio Felipe
S. Kadir and E. L. Proebsting
Flower buds of 20 Prunus species representing 4 subgenera were collected during winter and spring of 1989-90. Buds were preconditioned at +3° or 7°C to test their minimum hardiness level (MHL) or the rate of hardiness increase. DTA revealed that most of the prunus species have flower primordia that supercool. The subgenus Padus have racemose inflorescences and do not deep supercool during dormancy. P. besseyi, P. nigra and P. americana had small exotherms between -22° and -27°C while P. davidiana and P. subhirtella had larger exotherms at higher temperatures. Exposure of flower buds to -7°C shifted LTES to lower temperatures and/or reduced the size of LTE, which became undetectable for many species including P. nigra and P. americana. P. davidiana and P. subhirtella increased hardiness by 6°/day at -7° while dormant. Deacclimation coincided with an increase in LTE50 and the development of xylem vessel elements in the bud axis, calyx and filaments as indicated by dye movenent. P. davidiana was the least hardy species and required only 700 chill units to satisfy the chilling requirement, while P. nigra and P. americana had LTE average of -26°C at MHL and required over 1000 chill unit accumulation.
Yvonne Ottman and David H. Byrne
A nondestructive method for evaluating the salt tolerance of Prunus seedlings was devised for greenhouse sand-culture with 60 days of saline drip irrigation. The treatments contained half-strength Hoagland's solution using distilled water and supplementary chloride and sulfate salts of Na, Ca, and Mg to reach 1.5 dS·m–1 for control, 4.5 dS·m–1 for the first trial, and 6.0 dS·m–1 for the second and third trial screenings. After 60 days of irrigation with 6.0 dS·m–1 Nemaguard, the standard peach [P. persica (L.) Batsch] rootstock averaged 46% of the fresh weight, 53% of the volume, 66% of the height, and 74% of the foliar health ratings of the control seedlings. Percent of control values were compared for a tentative ranking of salt tolerance: ‘Titan’ almond × Nemaguard and P. mexicana Wats. > Nemaguard and Nemared > Myrobalan plum (P. cerasifera J.F.Ehrh.) and bitter almond (P. amygdalus var. amara Focke.). Correlation coefficients were used in selecting useful sets of evaluation parameters. Height was rejected as a screening parameter. Final fresh weight and a final foliar health rating are recommended for cursory screenings of Prunus germplasm. The last three weekly foliar health scores are useful for comparing rates of decline. Volume displacements are useful for comparing root vs. shoot growth.
Salvador Perez and James N. Moore
Eighteen species of Prunus and 4 interspecific hybrids from the 3 main subgenera were used to ascertain the prezygotic mechanisms that maintain reproductive isolation. The percentage of pollen germination of pure species was very high (82% to 97%), and ranged from 1% to 97% for interspecific hybrids. Pollen tube growth rates differed greatly among species and ranged from 3.8 to 8.7 mm/day in vitro, and from 3 to 12 mm/day in vivo. These values were highly correlated with pistil length (r = 0.90) and pollen volume (r = 0.91). Evidence was obtained suggesting the existence of additional incompatibility mechanisms, the 1st preventing interspecific fertilization in the subgenus Cerasus. In P. avium L., the pollen tubes of some species are inhibited and finally arrested before they reach the first half length of the style. In crosses involving P. cerasus L. and P. serotina Ehrh., the use of the latter as the seed parent showed a 10-fold increase in fruit set when compared to the reciprocal. Secondly, differences in pistil length and in pollen tube growth rate among species provide a sound basis for explaining the phenomenon of unilateral incompatibility in Prunus. The use of male-sterile genotypes of P. persica L., which had a prolonged period of receptivity, gave increased fruit set and showed increased potential for overcoming the prezygotic incompatibility barriers.
Jose X. Chaparro, Ronald R. Sederoff, and Dennis J. Werner
Total cellular DNA has been extracted from leaves and\or seed of Prunus dulcis, P. persica, P. mira, P. davidiana, P. persica subsp. ferganensis, and P. triloba. Chloroplast restriction fragments have been visualized by Southern blot analysis using heterologous probes from a petunia chloroplast library. Analysis of preliminary data separates the species into three groups. The first contains P. dulcis, P. mira, and P. davidiana; the second P. kansuensis, P. persica, and P. persica subsp. ferganensis; and the third P. triloba.
PCR amplification using oligos for cytosolic glyceraldehyde-3-phosphate dehydrogenase yields genomic fragments approximately 1kb in size from P. dulcis and P. triloba. Sequence analysis will be performed to determine species relationships at the gene level.
Ali A. Almehdi and F.A. Bliss
Crown gall incited by Agrobacterium tumifaciens is an important problem for nursery and field production of stone fruit and nut crops. Genotypes reportedly differ for crown gall reaction, but there is little information about resistance of Prunus accessions used as rootstocks. From among four wild-type strains of A. tumifaciens-virulent on apricot and almond, K12 was selected for inoculation of 6-month-old seedlings of cherry, plum, peach, almond, apricot, and miscellaneous species. The large majority of seedlings were very susceptible to crown gall, but some had few or no galls. Cherry, especially some lines of P. mahaleb, showed the most resistant or moderately resistant seedlings, while some accessions of plum, especially P. cerasifera, P. angustifolia, and P. insititia had the most resistant seedlings. Plants with different reactions were propagated to determine adult plant resistance and to study the heritability of crown gall reaction.
Zhi-Hong Gao, Zhi-Jun Shen, Zhen-Hai Han, Jing-Gui Fang, Yu-Ming Zhang, and Zhen Zhang
Sequencing amplification fragments produced using simple-sequence repeat (SSR) primer pairs pchgms2 and UDP96008 in `Dayezhugan' japanese apricot showed that SSRs obtained included a microsatellite locus originally identified in peach. The microsatellite sequence homogeneity between UDP96008 in japanese apricot in this study and UDP96008 in the peach in GenBank was 98%. Twenty-four japanese apricot genotypes originating in diverse geographic areas had been identified with 14 SSR primer pairs developed in different species of Prunus. In total, 129 alleles were obtained and per primer pairs detected 2.5 alleles on the average. The results from cluster analysis showed that the genetic distance between `Nanhong' and `Zhonghong' was the closest, and cultivars from China and from Japan could not be separated completely.
T. Baba, G. Como, T. Ohtsubo, F. Ikeda, and M.C.C. Lizada
Physical and physiological changes in mume (Prunus mume Sieb. et Zucc.) subjected to a 10-minute hydrostatic high-pressure treatment at 5, 10, 50, 100, 150, and 200 MPa were investigated. Mume fruit exhibited substantial injury at pressures >5 MPa. All treatments induced color changes, which became more apparent at pressures >100 MPa. Fruit subjected to pressures ≥100 MPa deteriorated and were rendered commercially unacceptable. After transfer to atmospheric pressure all treated fruit exhibited lower CO2 evolution rates compared with control fruit. Only fruit subjected to 5 MPa exhibited an increase (27%) in titratable acidity. Ethylene production rate in mume fruit was very high, but consistently and dramatically decreased after treatment, regardless of the pressure applied. The decline in ethylene production was associated with a decrease in ACC oxidase activity. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC).
Sorkel A. Kadir and Ed L. Proebsting
Differential thermal analysis (DTA) was used to measure deep supercooling in flower buds of Prunus dulcis Mill., P. armeniaca L., P. davidiana (Carr.) Franch, P. persica (L.) Batsch, three sweet cherry (P. avium L.) selections, and `Bing' cherries (P. avium L.) during Winter 1990-91 and 1991-92. Low temperatures in Dec. 1990 killed many flower buds. After the freeze, dead flower primordia continued to produce low-temperature exotherms (LTEs) at temperatures near those of living primordia for >2 weeks. In Feb. 1992, cherry buds that had been killed by cooling to -33C again produced LTEs when refrozen the next day. As buds swelled, the median LTE (LTE50) of dead buds increased relative to that of living buds, and the number of dead buds that produced LTEs decreased. LTE artifacts from dead flower priimordia must be recognized when DTA is used to estimate LTE50 of field-collected samples.
Yan Shi and D. H. Byrne
A standardized screening procedure for tolerance to bicarbonate-induced Fe chlorosis using a commercial fertilizer mix (Plantex) as the nutrient source, high solution pH (8.5) and 1.5 m m bicarbonate to simulate a calcareous soil situation was used with a 1 vermiculite:1 perlite (v/v) support media, small pots and topping (pinching back the tops of shoots). The tolerance level of peach [Prunus persica (L.) Batsch] rootstock could be assessed by leaf visual-chlorosis ratings and Spad-502 chlorophyll readings instead of extractable leaf-chlorophyll concentration or plant Fe concentration. Although most of the tolerant genotypes had almond [P. amygdalus (Mill.) D.A. Webb] in their parentage, a few peaches (`Swat', NJ672281007) showed high to moderate levels of tolerance.