Phenology and Plant Species Adaptation to Climates of the Western United States
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Phenology and Plant Species Adaptation to Climates of the Western United States p Station Bulletin 632 September 1978 Agricultural Experiment Station Oregon State University, Corvallis Contents SUMMARY 1 Onset of Rest 2 INTRODUCTION 1 Chilling to Break Rest 2 LITERATURE REVIEW 1 Bud Break and Growth 3 Genetic Factors 1 MATERIALS AND METHODS 5 Sequential Phenology 2 RESULTS AND DISCUSSION 5 Cessation of Growth 2 LITERATURE CITED 14 About This Bulletin This bulletin was developed from the combined Colorado USDA efforts of the members of Western Region Cooperative M. J. Burke J. T. Raese project W-130, Improving Stability of Deciduous Fruit A. H. Hatch Production by Reducing Freeze Damage. M. W. Williams Cooperating agencies: The agricultural experiment Hawaii National Weather stations of California, Colorado, Hawaii, Idaho, Min- R. M. Bullock Service nesota, Montana, New Mexico, Oregon, Utah, Washing- E. M. Bates ton,theU.S.DepartmentofAgricultureFederal Idaho Research, and theU.S. Department of Commerce A. A. Boe Washington National Weather Service. W. J. Kochan D. 0. Ketchie Administrative Advisor: J. M. Lyons, California. Minnesota E. L. Proebsting, Jr. Technical Committee members: P. H. Li C. Stushnoff Oregon Montana M. N. Westwood H. N. Metcalf P. B. Lombard New Mexico W. M. Mellenthin J. N. Corgan Under the procedure of cooperative publications, c. Weiser this regional report becomes, ineffect, an identical T. Sullivan publication of each of the cooperating agencies, and California Utah is mailed under the frank and indicia of each. Limited G. C. Martin supplies of this publication are available at the sources J. L. Anderson K. Ryugo listed above.Itis suggested that requests be sent to A. Richardson one source only. S. D. Seeley D. R. Walker Oregon work was done under project 181. Summary the pertinent relationships between the phenomenon and the climate. The phenology and general hardiness of fruit cul- tivars and phenospecies were studied at 10 climatic GENETIC FACTORS sitesin the Western Region and one in Minnesota Plant evolution is essentially the selective accumu- during five years. Survival of several Pyrus species was lation of genes that adapt a species or ecotype to a related both to inherent hardiness and to the degree of given climate. Because a complete species model chiorosis sustained in soils with high pH. P. pashia and would be cumbersome, models are best used on de- P. fauriei were most susceptible to chiorosis and P. fined genotypes. For this reason, it is important to know amygdaliformis andP.e!aeagrifolia were the most such genetic adaptations of the plant being studied. tolerant of high pH soils. P. ussuriensis, P. fauriei and Some of these involve adaptations to: P. communis were hardiest, while P. pashia and P. Latitude (day length) amygdaliformis were least hardy. The bloom periods of most species were most pro- Temperature (both diurnal and seasonal) tractedinmarine climates andinlowerlatitudes, Radiation and light (quality, intensity) relative to continental sites. In the former case such Moisture (amount and time of year) protraction was due to cool spring temperatures, and in the latterit probably was due to suboptimal winter Examples of the importance of genetic factors were chilling. reported by Weiser (31) for processes relating to cold The implications of the data in fruit growing and acclimation of Cornus stolonif era Michx. Northern high- inthe continuing search for better predictive phe- latitude ecotypes ceased growth and became dormant nologic models are discussed. and entered the first stage of acclimation under the shortening days of late summer, while ecotypes from low latitudes or from mild marine climates did not cease growth nor enter first stage acclimation under Introduction similar short day conditions. Because of the mild win- ters, the latter ecotype (Seattle clone) evolved under As part of regional project W-86 (now W-130) on little or no selective pressure to stop growth early and dormancy and winter hardiness of deciduous fruit become physiologically prepared for a cold winter, al- trees, characteristics were charted for the climates of specific sites though such ecotypes are capable of developing sec- in cooperating states by establishing ond stage hardiness to temperatures as low as were phenological plots at ten sites in the Western Region the high-latitude ecotypes. This is a striking example and one in Minnesota. The objective was to gain a bet- of how the genetics of native species is influenced ter understanding of the interrelationships between cli- through natural selection to keep the plant physiologi- mate, soil, and plant development during the different cally suited to the dynamic climate in which it lives. seasons, and ultimately to develop models for predict- Another example of genetic adaptation as it relates ing phenological responses for given species and cli- to rest and winter chilling of seed of widely dispersed mates.Anunderstandingofseasonalsynchrony Pyrus species was reported by Westwood and Bjorn- between plant and climate is recognized as a key stad (33). Not only did low-latitude species have shorter requisite to temperate fruit production. chilling requirements to break rest, but they also had This work describes various predictive models some higher optimum temperatures for chilling than did spe- of which were developed by W-130 cooperators, but cies from middle latitudes. Thus seeds of the subtrop- none of which seem to characterize all situations. Data ical Pyrus pashia D. Don. required only 380 hours chill- presented are not complete enough to develop a re- ing at an optimum temperature of 10°C, while the mid- vised model now, but it is hoped that this can be done temperate P. communis L. required 2060 hours chilling during the next phase of work in project W-130. at an optimum of 5°C. A special adaptation was found with the subarctic species P. ussuriensis Max., indige- nous to areas where the tempeatures average below Literature Review freezing for five winter months. Because temperatures much below 0°C are ineffective in breaking winter rest, The complexity of the relationship between climate P. ussuriensis apparentlyischilledinearly spring and plant development is compounded by the fact that rather than in winter, and has an optimum chilling tem- both factors are made up of many distinct components perature of 7°C, somewhat higher than middle latitude and both are dynamic, i.e. continuously changing. Any species. The genetic basis for differences in chilling model describing such a plant-climate relationship must requirements was shown to be multigenic and inheri- include genetic characteristics of the plant, sequential tance was quantitative. Seed from crosses of long chill plant processes, sequential changes in climate, and x long chill species showed only 5 percent germination transitions between sequential processes. Also, such after 770 hours chilling; while for long chill x short a model depends on the types of standard climatic data chill (and the reciprocal)it was 31 percent; and for used and how they relate to the environment of the short chill x short chill species, germination was 76 plant or plant part. Phenology models can be very sim- percent. pie or very complex. Some, like flower initiation, can be Because genetic controls result indifferent tem- triggered by only one aspect of the climate, daylength; perature optima (maxima, minima, and intermediate while others, shoot growth for instance, depend on temperature responses) and in different day-length re- many aspects of the environment for total development sponse, etc., predictive models must not assume that and thus require complex models. Generally, a model all species are constant in these respects. When possi- should be as simple as possible as long as it shows ble, one should know the details of the indigenous cli- 1 mate for a species being studied; this will provide clues the known effects of environment on onset and depth of to critical sequential changes required by the plant to rest. survive a given climatic situation. Tropical climates lack the environmental cues for the onset of rest, so full rest is not attained with tem- perate species. Thus, some have assumed that temper- SEQUENTIAL PHENOLOGY ate cultivars such as apple, which sometimes grow in the tropics, have genetically fixed low chilling require- Cessation of Growth ments. Actually, they don't need the usual chilling to break rest because under those conditions they do not The first general change in a growing plant which enter deep rest. In Taiwan, grapes are grown continu- helps adapt it to an adverse winter season is the cessa- ously by defoliating and pruning the plants after harvest tion of growth. Many species undergo a grand period of growth up to early or mid-summer, then stop shoot to start a new cycle of growth, resulting in two to three elongation, set terminal buds, and "mature" their tis- crops per year with no rest period or chilling in the sues prior to winter. As discussed above, termination annual cycle. Two crops of pears and apples are grown of growth may result from genetic control relating to there, too, but yield and quality are poor. Janick (23) shortening day length even though the day length is reported that Rome Beauty apple is grown successfully in tropical Indonesia. Leaves are stripped off one month still quite long or later from a combination of shorter after harvest in April, resulting in a second cycle of days and cooler temperatures. For domestic plants flowering and growth, with the second crop maturing lacking such genetic controls, however, growth cessa- tion can be achieved by growth controlling rootstocks in October. The natural climate there lacks completely and by various cultural manipulations (32). Reduced the environmental cues to induce winter rest. In Peru, apples are grown with avocado, mango, and papaya by nitrogen nutrition and reduced irrigation in late sum- withholding water and pruning during the summer sea- mer often are used to stop growth of young vegetative son, then using pruning, irrigation, nitrogen fertilizer, trees.