Low temperature is acknowledged to be the single most important factor limiting the distribution of plants (70). Freezing damage to horticultural crops is a ubiquitous problem of major economic significance even in sub-tropical regions. Among the more commonly recognized types of freezing injury are sunscald and frost splitting of tree trunks, winter burn on conifer foliage, blackheart in stems of trees and shrubs, soil heaving damage and crown kill of herbaceous perennials, die-back in citrus, mid-winter kill of dormant flower buds, and spring and autumn frost damage of tender annuals, flowers and fruits.
An organization can be effective only when its value system is congruent with and complementary to its central mission(s). The value system of a university is most clearly described by its promotion and tenure policies, processes, and the criteria it uses in evaluating a faculty member's performance. Professorial-rank faculty members at universities are required to perform assigned duties in teaching, research, extension, advising, administration, etc., that are unique to their position. All faculty members are required to make scholarly contributions and are encouraged to perform service that is relevant to their assignment and of value to their institution and profession. The balance of emphasis between assigned duties and scholarship varies from one faculty position to another—ranging from faculty with few assigned duties who engage predominantly in scholarship, to faculty with extensive assigned duties who devote a small, but significant, effort to scholarly achievement. A university's effectiveness can be compromised, and its faculty inappropriately evaluated, if this reality is not recognized; if scholarship is too narrowly interpreted; or if undue weight is given to individual achievement rather than to the achievements of individuals—including those that resulted from team efforts. Changes that are evolving at Oregon State Univ. to address these three issues will be described, including: adoption of a broader definition of scholarship as intellectual work that is validated by peers and communicated; a description of four fundamental forms of scholarship: discovery, development, integration, and creation; incorporation of a dynamic description of position responsibilities for each faculty member into annual and promotion and tenure evaluations; and addition of a category entitled, Results of team efforts into the format for faculty documentation of achievements.
Rooted cuttings of a clonal selection of Salix purpurea L. were grown in perlite, in a warm greenhouse at natural daylengths and irrigated daily with one of 10 different mineral nutrient solutions. Plants from each of the nutrient treatments were hand defoliated at weekly intervals beginning in August to assess the effects of mineral nutrients on vegetative maturity development. Vegetative maturity was quantified the following spring by measuring stem dieback. Plants in some nutrient treatments ceased growing 9 weeks earlier in the autumn, and became vegetatively mature several weeks sooner than plants in other treatments. Specifically, treatments such as the distilled water control and Hoagland solution -N,-P, and -S induced early growth cessation, resulted in less stem growth, and induced early onset of vegetative maturity as evidenced by reduced stem dieback the following spring. Development of vegetative maturity was slower in plants irrigated with complete Hoagland solution or Hoagland solution -Ca, -Mg, and -K, which continued growing until October when natural defoliation and growth cessation occurred on control plants treated with complete Hoagland solution. The study demonstrates that vegetative maturity in S. purpurea can be hastened by witholding N, P, and S.
It has been necessary for perennial plants to develop systems for sensing and reacting to environmental parameters. Their survival and perpetuation is determined, in large measure, by the timing of vital processes in relation to favorable and unfavorable cycles of environment. While the regulation of flowering by environmental stimuli has been extensively researched little is known about the control of cold acclimation. Recent studies show striking similarities between the control mechanisms for flowering and cold acclimation in temperate zone plants.
The relationship of environmental temperature to the cold resistance of apple bark tissue was studied on mature orchard trees in the field during natural spring dehardening and on 3 and 4 year old trees in the containers which were dehardened under controlled conditions. Field studies showed day to day fluctuations in dehardening and rehardening during the spring in each of 2 years. These short term changes in cold resistance were closely related to the air temperatures of the preceding day. In controlled studies, hardy plants during the winter dehardened as much as 15°C in one day in a warm greenhouse, and rehardened 15° in 3 days when they were held at −15°. The dehardening process was only partially reversible. Once dehardening began, the bark did not reharden beyond a certain base level. This base level raised with each successive day of dehardening. The base level usually corresponded to the minimum killing temperature on the day preceding the final day of dehardening.
A simple reproducible procedure is described for assessing frost injury of potato foliage, involving controlled freezing of excised leaflets and measurement of leached electrolytes. Test results are shown for 5 tuber-bearing Solarium species representing a wide range of frost tolerance. The test can be used in selection and breeding for frost tolerance in potato.
The highbush blueberry cultivars, ߢRancocasߣ and ߢEarliblueߣ, failed to acclimate in time to avoid low temp injury to stems exposed above the snow level during the 1st year seasonal change in hardiness was studied. In the 2nd year, however, they hardened to temp as low as -40°C and survived the winter. Acclimation occurred earlier in a native selection of Vaccinium angustifolium Aiton and in ߢRancocasߣ. Selections of V. angustifolium and natural hybrids of V. angustifolium and V. cormybosum L. were found to be hardier than any of the highbush cultivars. A selection of V. constablaei Gray and V. membranaceum Douglas, respectively, were also hardier than the highbush types. A low temp exotherm was found to be present in blueberry stems, but it was associated only with xylem injury which was not as critical for survival as the bark tissues. The bark was injured at temp higher than the xylem and was not associated with any exotherm.
During controlled freezing as many as 4 exotherms were detected in apple twigs by differential thermal analysis (DTA). Three of the exotherms usually occurred at relatively high temperatures above the killing point of stem tissues. There was no apparent association between any of these exotherms and freezing injury to cambium, cortex, phloem, or vegetative buds. The temp of the fourth exotherm (D), however, coincided with the killing temp of xylem ray and pith parenchyma as hardiness changed during the season. DTA studies and hardiness tests performed on whole and dissected twigs indicated that the fourth exotherm arose from the xylem and pith tissues; that injury to xylem and pith occurred when twigs were frozen below the initiation temp of the fourth exotherm independent of cooling rate and that bud and bark tissues were considerably hardier than xylem in mid-winter while in early autumn and late spring xylem and pith were hardier than buds and bark.
The results suggest that freezing injury to xylem and pith cells is caused by a specific freezing event, and that it is different from freezing injury to other stem tissues. Measurements of the fourth exotherm may provide a convenient way of studying freezing injury and resistance in xylem – a recurring problem in many fruit species.