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Abstract

The effectiveness of (2 chloroethyl)phosphonic acid (ethephon) in inducing defoliation and in delaying spring bud growth of red-osier dogwood was related to the time of application. Plants treated with ethephon before they matured were not effectively defoliated. Mature plants were effectively defoliated and ethephon’s effectiveness increased progressively at subsequent treatment dates. Ethephon treatments applied on September 29, October 6 and 13, delayed spring bud break by 7, 5, and 3 days respectively. Hand defoliation on the same dates induced identical delays in spring growth.

The purpose of this presentation is to discuss the value of identifying growth stages of bud dormancy numerically. The Degree Growth Stage Model (°GS Model) will be used to quantify the annual growth stages and the various developmental stages of endo-, eco-, and paradormancy. The model is divided into 360°GS's, illustrated either as a sine curve or a circle, that serve as a timeline for the cyclical passage of temperate woody plants, through five distinct point events (growth stages). The sine curve illustrates the relative degree of development of the segment events between the point events. This paper will focus on the °GS model as a relative method of quantifying the various segment events and improving our communication of the annual physiological processes of temperate woody plants. In addition, recent evidence on altering dormancy, and its impact on dormancy models, will be presented.

Abstract

Plants of red-osier dogwood (Cornus sericea L.) treated with 2,4-dichlorophenoxy-acetic acid (2,4-D) or l,1’-dimethyl-4,4’-bipyridium ion (paraquat) after reaching vegetative maturity were much less affected by the herbicides than plants treated earlier. Data support the hypothesis that vegetative maturity is a distinct physiological stage in the development of woody plants, and that inconsistencies in herbicide efficacy can, in part, be explained by this phenomenon.

New roots of Malus domestica Borkh MM106 apple rootstock were divided into two categories, 1) feeder roots and 2) extension roots based on morphology and their ability to take up NH₄ ⁺, were studied. The roots were harvested in August from 1-year-old potted plants growing under natural conditions in Corvallis, Ore. Extension roots were thicker and longer than feeder roots. Average diameter and length were 0.89 and 45.29 mm for extension roots and 0.27 and 5.36 mm for feeder roots. Root special length (cm/g FW) and surface area (cm²/g FW) were 11.94 and 33.17 for extension roots and 108.97 and 93.38 for feeder roots. Maximum uptake rate, I_max, K_m, an_d root absorption power, α (α = I_max•1/K_m), for NH₄ ⁺ absorption were 6.875, 0.721, and 9.48 for extension roots and 4.32, 0.276, and 15.63 for feeder roots. Feeder roots had stronger affinity to NH₄ ⁺ (low K_m) and higher NH₄ ⁺ absorption power (high α value) than extension roots. The feeder roots were better able to uptake NH₄ ⁺ at lower external solution concentrations than extension roots according to the nutrient depletion curve, which indicates feeder roots being more efficient than extension roots in nutrient absorption when NH₄ ⁺ availability was low.

Previously, we reported that plant recovery from “near-lethal” (NL) (sublethal) stresses depended on stage of development and poststress environment (PSE). Dormant red-osier dogwood (Cornus sericea) plants exposed to NL heat, freezing, and hydrogen cyanamide either died or were severely injured when stored at 0C or recovered at 23C and nautral condition. Exposure of dormant stem tissues of red oak (Quercus rubra), paper birch (Betula papyrifera) and European mountain ash (Sorbus aucuparia), to heat stress also resulted in higher ion leakage when they were stored at 0C PSE for 3 weeks. Soaking NL-heat-stressed (49C for 1 hour) stem tissue of red-osier dogwood in double distilled water for 48 hours before incubating at 0C PSE for 2 and 12 weeks resulted in lower ion leakage and 80% tissue survival. NL-stressed tissue had higher sodium and similar potassium leakage at 0C PSE. At 23C, PSE NL stress had no effect on leakage of these specific ion.

The nutrient uptake kinetics by new roots of 1-year-old potted clonal apple rootstocks (M7, M9, M26, M27, MM106, and MM111) were determined by the ion depletion technique at the stable development stage of trees in August. The total roots of five of the rootstocks (except MM111) consisted of more than 60% feeder roots and less than 12% extension roots. MM111, the most vigorous rootstocks tested, had 60.7% feeder roots and 24.5% extension roots. Root: top ratio was negatively related to the growth inhibiting character of the rootstock. Nutrient uptake by excised new roots was found to fit into Michaelis-Menton kinetic model for all rootstocks tested. The kinetic characteristics (maximum uptake rate, I_max, apparent Michaelis-Menton constant, K_m, and root absorption power, (α = I_max•1/K_m) between rootstocks differed significantly. MM111 had the highest I_max for NH₄ ⁺ absorption and M9 for NO₃ ^-. Root affinity to ions was highest with MM106 for NH₄ ⁺ and with M26 for NO₃ ^-. Root absorption power (α = I_max•1/K_m) was greatest in MM106 for NH₄ ⁺ and M9 for NO₃ ^-. At this developmental stage the data suggest no relationship between nutrient uptake and dwarfing character of the rootstocks.

“Near-lethal” (NL) stresses from varied sources, e. g. NL-heat (47°C-lhr), NL-freeze (-7°C -lhr), and NL-hydrogen cyanamide (0.5-1 M), overcame endo-dormancy in red-osier dogwood (Cornus sericea L.) plants. Near-lethal heat stress applied at early rest (Oct.) had a slight effect on cold acclimation, whereas at late rest (Dec.), NL-stress resulted in the rapid loss of hardiness at warm or natural environment conditions. Recovery of plants from NL-stresses was dependent on the stage of development and temperature. Less dieback occurred with later stage of endo-dormancy, and at warmer temperatures. Dormant plants in October exposed to other NL-stresses, e. g., freezing temperature and hydrogen cyanamide, also caused plant dieback at 0°C and recovered at 23°C post-environment treatment. Conditions that favored recovery also favored production of glutathione.

Abstract

Xylem water potential (XWP) and electrical impedance ratios were used to determine the time of vegetative maturity in red-osier dogwood (Cornus stolonifera Michx.) grown under 2 temperature and a short-day dormancy inducing regime in growth chambers and a lathhouse under natural conditions. The decline in XWP correlated with the development of vegetative maturity as measured by tip dieback after defoliation. Under growth chamber conditions, average XWP values reached a minimum at the time of vegetative maturity. In all cases, however, variability within samples was so large as to preclude the use of XWP as an accurate, reliable index of vegetative maturity. A change in electrical impedance ratios at and after vegetative maturity caused the impedance meter to go “off scale.” Compared with XWP values, changes in electrical impedance ratios were more consistent and show promise in predicting vegetative maturity.

Abstract

Red-osier dogwood (Cornus stolonifera Michx.) plants were grown outdoors in a lathhouse to study the relationship between vegetative maturity and the first stage of cold acclimation. Both microscopic observations and electrical impedance ratios used to measure damage of frozen stem sections verified the close association of the onset of the first stage of cold acclimation and vegetative maturity. The relationship of these processes to dormancy development is discussed.

Abstract

Potted plants of red-osier dogwood (Cornus sericea L., syn. C. stolonifera Michx) were grown under 3 different dormancy-inducing regimes. Each week 5 plants per group were defoliated and placed in a warm greenhouse. Plants were checked daily for regrowth and new leaves were removed. When defoliation ceased to induce bud break, the plants were considered to be in a state of winter dormancy. Plants were observed for damage the following spring to determine when they had reached vegetative maturity, and it was found that vegetative maturity corresponded to winter dormancy development in all 3 growing conditions.