Diurnal variations in the chemical composition of xylem fluid have been established for many plant species exhibiting positive root pressure; similar patterns have not been well documented in transpiring plants. Diurnal changes in plant water status and xylem fluid chemistry were investigated for `Flordaking' peach [Prunus persica (L.) Batsch], `Suwannee' grape (Vitis hybrid), and `Flordahome' pear (Pyrus communis L.). Xylem tension was maximum at 1200 or 1600 hr and declined to <0.5 MPa before dawn. Xylem fluid osmolarity ranged from 10 to 27 mm and was not correlated with diurnal patterns of xylem tension. The combined concentration of amino acids and organic acids accounted for up to 70%, 45%, 55%, and 23% of total osmolarity for irrigated P. persica, nonirrigated P. persica, Vitis, and P. communis, respectively. The concentration of total organic compounds in xylem fluid was numerically greatest at 0800 or 0900 hr. For irrigated P. persica the osmolarity of xylem fluid was reduced by 45% from 0800 to 1200 hr, 1 h after irrigation, compared to only a 12% reduction from 0800 to 1200 hr for nonirrigated trees. Asparagine, aspartic acid, glutamine, and glutamic acid were mainly responsible for diurnal changes in the concentration of total amino acids and organic N for P. persica; the diurnal variation in organic N for Vitis was due to glutamine. Arginine, rather than the amides, was the primary source of organic N in xylem fluid of P. communis, and there was no consistent diurnal change in the concentration of amino acids or organic N. The predominant organic acids in all species examined were citric and malic acids. No consistent diurnal trend occurred in the concentration of organic acids or sugars in xylem fluid.
Fruit color is a commercially important quality for sand pear ( Pyrus pyrifolia Nakai). Sand pear can be divided into russet, semi-russet, and green types based on the color of the peel, which is typically composed of a cuticle layer, an epidermis
Abstract
‘Flordahome’ pear was released by the University of Florida Agricultural Experiment Station in 1981 and fills the need for a pear with a low-chilling requirement that produces fruit which acquires a buttery, melting texture upon ripening. It is recommended for local use, but should be valuable germplasm for breeding pear cultivars with low chilling and resistance to fireblight and leafspot.
Abstract
A computer program was written to allow fast tracing of pedigrees from a computer file of parentage records and which lists the pedigree of any requested individual or progeny in 2 forms. The first output format is a listing adapted to integration with another program which calculates inbreeding coefficients and coefficients of coancestry; the second output format is a family tree.
Abstract
The age at which flowering began and the stem diameter at various ages were recorded for more than 9,000 pear seedlings planted in orchards at Beltsville. The juvenile period for individual seedlings varied from 2 to 10 years, with a number of seedlings still not flowering after 8 to 10 years. An overall negative correlation of stem diameter with length of the juvenile period was found. Within planting years, this relation was significant only in certain years; within progenies, the relation was significant less than half the time; within a specific cross repeated in different years, the relation varied considerably from year to year. Stem diameter can be successfully used as a preselection criterion for early flowering (short juvenile period) only when these two characteristics are significantly correlated. Since this condition does not exist in most crosses under the growing conditions at Beltsville, stem diameter is not a valid predictor of early flowering.
The culture of meristems, shoot tips, and axillary buds leads to the method of in vitro multiplication that is easily used and safe to obtain uniform copies with no undesirable variations. This work aimed to propagate five in vitro pear cultivars: Housui, Carrick, Nijisseiki, Packham's Triumph, and Red Bartlett. The work was carried out in the Tissue Culture Laboratory at Embrapa Temperate Climate. The plants were sprayed with benomyl (1.0 mg./L) and agrimicine (2.4 mg/L) in the fields, 2 weeks before the shoots were collected. The shoots were then cut with two buds with no leaves and desinfested with alcohol 70% for 10 s and 1% sodium hypochloride for 20 min, 50 explants, 25 buds, and 25 meristems, were then transferred to test tubes containing MS salts and vitamins, myo-inositol (100.0 mg/L), sucrose (30.0 g/L), agar (6.0 g/L), added to in mg/L: BAP (1.0), GA3 (0.1), and NAA (0.01). Three pear cultivars were used for in vitro multiplication (`Nijisseiki', `Red Bartlett', and `Housui') by using the same basal salt with N reduced to strength, added to (in mg/L): BAP (1.6), NAA (0.16). The material was kept in growth room under 16-h photoperiod, 25 ± 2 °C and 19 μMol·m-2·s-1 of flux radiation. The in vitro contaminations were mainly due to bacteria derived from the bud material (71.5%). Higher oxidation for meristem material was observed for `Carrick' and `Packham`s Triumph'. `Red Bartlett' showed the best results for all the variable studied, although all cultivars in general presented low response.
In the 1980' s, a Bartlett pear giant fruit sport was found in Pingdu, Shandong. The characteristics of mutation are larger fruit, thicker branch, shorter internode and much more spur. By grafting propagation, the clones began to bear fruit in 1990, and maintain the characteristics of variable mother plant.
From microspore formation to blossom and spreading pollen, the cytohistological observation of sport flowering organs indicates: in every phase of pollen development, the size of florets, anthers and pollen grains are similar to CK; their pollen types both belong to tricolporat, pollen grains are nearly equal in size. This indicates that sport sporogenous tissue do not mutate. The observation of shoot apex sections showes: for CK, the cells of three histogenic layers range regularly; the size of cells, nuclei, and nucleoli among LI, LII, LIII are similar. For sport, the cells of LI, LII are no difference from CK, but in LIII and inner tissue, cells, nuclei, nucleoli all become larger clearly. This indicates LIII had mutated. So this sport is a 2–2–4 type chimera.
1-Methylcyclopropene (1-MCP), a gaseous synthetic cyclic hydrocarbon, has been shown to have potential to become an important new tool in controlling the response of plants sensitive to ethylene. Due to its irreversible binding to the ethylene receptor(s) and its subsequent prevention of the physiological action of ethylene for extended periods, 1-MCP may prove also to have effective commercial application in the control of ethylene effects in detached organs such as fruit. Our objective was to investigate the effectiveness of 1-MCP in controlling ripening in pear. Two commercial cultivars (Bosc, Anjou) and one numbered cultivar from Agriculture and Agri-Food Canada's breeding program (Harrow 607) were harvested at commercial maturity. Immediately after harvest, fruit were exposed for 24 h at 20 °C to 1-MCP ranging from 0 to 100 μL•L-1 then placed in air at 0 °C and 90% relative humidity for 5 and 10 weeks. Following treatment and after 5 weeks storage plus a 7- or 14-day post-storage ripening period, fruit softening and ethylene evolution were inhibited and fruit volatile evolution was reduced significantly by exposure to 1-MCP at or above 1.0 μL•L-1 in all three cultivars. Concentrations exceeding 1.0 μL•L-1 were required to maintain initial firmness and inhibit ethylene production after 10 weeks storage in air. Evolution of alpha-farnesene and 6-methyl-5-hepten-2-one was related to low temperature stress and chlorophyll loss as a result of ripening, respectively, and were affected by 1-MCP exposure. The pattern of evolution and amounts of other volatiles was also affected by 1-MCP treatment. These results indicate a huge potential for commercial use and application of 1-MCP in controlling fruit ripening and senescence.
Variegated `Louise Bonne' (LB) pear is a periclinal chimera in which the LIII layer is albino. Chimeral shoots propagated in vitro segregate spontaneously into green, albino, pale, or rearranged chimeral types, making them difficult to maintain in culture. We investigated the role of growth regulators on chimeral stability and destability to find a combination that would maintain the chimera through repeated subcultures. 70 to 90% of shoots remained chimeral on Lepoivre (LP) medium supplemented with 8 μM BA or less. Only 36 to 58% of shoots grown at concentrations greater than 8 μM were stable. Shoots grown on LP with thidiazuron (TDZ) were very unstable (4 to 44%). NAA had no significant effect on chimeral stability. While shoots multiplied better on LP, the chimeral pattern was more obvious on MS, making it a good screening medium. Selection and subculturing chimeral shoots on a good medium (LP with 2 to 4 μM BA) increased the percentage of chimeral shoots from 26% at the 4th subculture to 84% at the 27th subculture.
To maintain appropriate tree shapes for Asian pear trees, multi-leader system would be more suitable, which could be obtained from the proper training systems. Controlling apical dominance should be the major factor for tree shape management and this might be modified by branch bending or pruning methods. When the tree shape was managed with Alternate Fan System, too narrower branch angle depressed flower bud formation because of the vigorous shoot growth but too wider angle also decreased that formation because of the numerous water sprouts. The tree with 75 degrees of internally deviated angle performed superior result in fruiting process. Additionally, heading-back pruning could be another for water sprout emerging. For that reason, the severer heading-back pruning stimulated the more water sprout emerging. The proper pruning method could be obtained by considering the relation between main stem width and sum of remained branch width.