Date of this Version
Thesis (M.S.)—University of Nebraska—Lincoln, 1950. Department of Horticulture.
In breeding apples for a region where winter hardiness is an important consideration, the desirability of having some rapid and reliable means of separating the few winter hardy seedlings produced from the great number of less hardy ones is obvious.Any elimination that can be made in the first year or two of seedling growth is economical from the standpoint of both time and cost.
From previous investigations, it is apparent that many factors are involved in working with the electro-conductivity method as a measurement of winter hardiness.Several of these factors are discussed in this paper.
Studies were begun in the spring of 1949 and carried through the fall of the same year.The material used throughout this investigation consisted of shoots from 16 standard horticultural varieties of apples.All of the material used in the experiment were obtained from the University of Nebraska fruit farm at Union, Nebraska.
The varieties were grouped as follows starting with the variety showing the least amount of resistance to cold and ending with the variety of greatest resistance:Cortland, Grimes Golden, Joan, Golden Delicious, Sharon, Secor, Winesap, Hawkeye, Wealthy, Haralson, Jonathan, Beacon, Red Duchess, Virginia Crab, and Hibernal.
Two year old shoots were found to have nearly twice as much resistance to a temperature of 15° F. as the one-year old shoots had.It was found that waxing the cut ends of a sample reduced the electrolyte loss to almost 50 percent less than that of a sample with unwaxed ends.There was a greater spread in specific conductance readings between varieties when the ends of each piece were waxed.Very little difference was found between varieties when shoots were allowed to exosmose without being frozen.
The rapidity with which the estimation of injury can be accomplished and the convenience of the precise numerical values obtained by electrical conductance makes the application of this method very valuable in studying winter hardiness of plants.
Advisor: Victor Miller