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  • Author or Editor: M. N. Westwood x
  • Journal of the American Society for Horticultural Science x
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Abstract

Growth and performance of ‘Anjou’ pear, Pyrus communis L., were reduced by infection with severe vein yellows virus (VYV) tested in 2 plots for 10 years. Bloom density and yield with some selections were reduced by the virus. Overall performance was affected by scion source as well as by VYV content. Inconsistencies resulted apparently from either undetected viruses, different strains of VYV, or from differences in genetic strains of the pear cultivar.

Open Access

Abstract

Growth and yield of ‘Montmorency’ cherry varied greatly both within and between species of rootstock clones. Trees on FI2/1 mazzard (Prunus avium L.) were very vigorous and less productive than those on other stocks. Some growth control was found within each species or hybrid group but was most pronounced with P. mahaleb L. clones PI 193688, PI 163091 and PI 193693. Yield efficiency was not necessarily related to tree size but tended to be better with smaller trees. The 3 P. mahaleb clones listed above and the vigorous clones OCR-3 (P. mahaleb × P. avium) and PI 194098 (P. mahaleb) had high yield efficiencies. Trees on F12/1 and P. mahaleb PI 193703 had the lowest yield efficiencies. Based upon ideal orchard spacing for tree size, calculated annual yields exceeded 10 metric tons per ha for 6 of the clonal stocks.

Open Access

Abstract

‘Golden Delicious’ and ‘Starking Delicious’ apple (Malus domestica Borkh.) on Mailing 9 (M 9) rootstock were planted in 1956 in alternate rows 4.57 m (15 ft) apart, with in-row spacings of 1.22, 1.83 and 2.44 m (4, 6, and 8 ft). Average annual yield was higher at the closest spacing (1794 trees/ha) during the entire 18 years of the test. The pattern of yield was similar for the 2 cultivars but was higher for ‘Golden Delicious’ because of the lower fruit set of ‘Starking’ in some years due to adverse weather. Pruning during the last 6 years of the test was done by mechanical shearing of tops and sides, with no detailed pruning within the fruiting wall. This type of pruning on dwarf trees resulted in adequate fruit size, color, and quality with normal fruit thinning practices.

Open Access

Abstract

Deep supercooling was found in the stem tissues of all the Pyrus species studied. There was more than 1 low temperature exotherm resulting from the freezing of supercooled water in stem tissue, and these exotherms were associated with the tissue injury. The supercooled water in the stems of P. nivalis Jacq., P. cordata (Desv.) Schneider and P. elaeagrifolia Pall, was found in both xylem and bark tissues. The supercooling characteristics of vegetative and flower buds are also described. The hardiest and least hardy species found were P. caucasica Fed. and P. pashia D. Don., respectively.

Open Access

Abstract

Controlled freezing tests showed no hardiness differences between comparable floral developmental stages on weak and vigorous ‘Bartlett’ (Pyrus communis L.) pear trees. Bloom delay through evaporative cooling resulted in a loss of hardiness beyond that found earlier in the season on non-misted trees for similar stages of development, although a certain degree of frost protection was gained through bloom delay.

Open Access

Abstract

Simulated frost injury to ovaries at intervals after full bloom significantly increased fruit malformation, reduced fruit weight, and increased fruit drop in ‘Bartlett’, ‘Bosc’, and ‘Comice’ pear (Pyrus communis L.). Time of injury did not affect fruit weight and malformation in most cases, but did significantly affect fruit drop. Significant positive correlations were found between fruit weight and seed content, while negative correlations were found between fruit malformation and seed content for all cultivars.

Open Access

Abstract

Decline- and fire blight-resistant clonal rootstock selections of Old Home × Farmingdale (OH×F), Pyrus communis L. were compared during a 12-year period with Bartlett seedling, P. calleryana Decne. seedling and clonal Old Home as understocks for ‘Bartlett’. Some OH×F clones were found to be more vigorous than Old Home rootstock, while others were much less vigorous. Only OH×F 51 was as dwarfing as East Mailing (EM) Quince A. Trees on some clones of each vigor class were more efficient (yield per unit of tree size) than others of the same class. Yield efficiency was not well correlated with rootstock vigor, but the semi-dwarf clones tended to induce more efficient yield than vigorous ones.

Open Access

Abstract

Field and laboratory studies of host preference and resistance of Pyrus species and cultivars to the pear psylla, Psylla pyricola, were conducted in Southern Oregon from 1964–1968. Asian species were generally less attractive to oviposition than those from Asia Minor, North Africa or Europe. Attractiveness of P. pyrifolia and P. communis cultivars was higher than for P. ussuriensis.

Susceptibility of Pyrus was based on differences between total egg deposition and resulting nymphal populations. Using this nymph/egg ratio the results indicated that Asian material was more resistant than material from Asia Minor or Europe. The Asian species P. fauriei and P. calleryana exhibited both a high degree of unattractiveness to oviposition and resistance to nymphal development.

Open Access

Abstract

Potted seedlings and cuttings of various tree species were submerged to 5–10 cm above the soil level for up to 20 months in order to determine flood tolerance based on leaf conductance (kl), growth, and survival. Flooding induced a decline in kl at soil oxygen diffusion rates of 30, 22, 20, and 15 × 10−8g cm−2 min−1 for Prunus persica (L.) Batsch, Halford seedlings (peach), Pyrus communis L. cv. Bartlett (Bart), Pyrus calleryana Decne (Call), and Pyrus betulaefolia Bunge (Bet), respectively. The leaves of some species, particularly Pyrus communis L. cv. Old Home × Farmingdale 97 (OH × F 97), abscised shortly after a decline in kl, yet leaves of most other Pyrus species did not abscise despite months of maintaining a kl near zero. Growth rates were reduced for all fruit tree species except Bet and Call after one month of spring flooding. One month of fall flooding reduced the growth of all fruit tree species the following spring. Bet survived 20 months of continuous submergence; however, only Salix discolor Muhl. (willow) grew well under these conditions. Flooding promoted adventitious rooting of willow, Cydonia oblonga Mill. cv. Provence BA 29 (quince) and Malus domestica Borkh. cv. MM 106 (apple); anthocyanin pigmentation in leaves of apple and all Pyrus species; leaf chlorosis of quince, apple, and peach; and hypertrophied lenticels on the submerged stems and roots of all species. The tolerance, based upon kl, growth, and survival, was: willow > Bet > Call = quince > Bart > OH × F 97 = Pyrus pyrifolia (Burm.) Nak. (Pyri) = Pyrus ussuriensis Maxim. (Ussuri) = apple > peach. Although the survival of pear rootstocks with and without a ‘Bartlett’ scion were similar, flooding symptoms often were quite different.

Open Access

Abstract

Freezing studies on ‘Bartlett’ pear (Pyrus communis L.) bouquets of buds, flowers, and small fruit showed injury increased with decreasing temperature, increasing developmental stage, and increasing duration of frost. At the minimum temperature, 30 and 60 minutes of frost exposure in all stages increased injury, however, in the small fruit stage injury at −2°C increased for up to 2 hours exposure. The effect of freezing rate was dependent on minimum temperature and dry florets were injured slightly more than florets misted just prior to freezing.

Open Access