Date of Award:

5-2002

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Schuyler D. Seeley

Committee

Schuyler D. Seeley

Committee

Donald T. Jensen

Committee

Bruce Bugbee

Abstract

Manipulating bud dormancy in temperate fruit trees could reduce fruit loss due to early spring frosts. The relationship between moisture content and dormancy could provide a tool to better understand and ultimately manipulate the biochemical process of bud dormancy. Seeds have historically been used in research studies to predict bud dormancy because they have similar dormancy requirements and are easier to use. This study was conducted to quantify the relationship between seed water content and stratification efficiency for dormancy release. Seeds of peach, Prunus persica cv. 'Johnson Elberta,' and apple, Malus domestica cv. 'Golden Delicious,' were hydrated in vitro to various water contents, stratified, and germinated to determine threshold and optimal hydration levels for stratification. The threshold for stratification was 0.3 to 0.4 g H2O per g dry seed mass in peach, and 0.3 to 0.5 g H2O per g dry seed mass in apple. Stratification efficiency increased as hydration levels increased beyond this threshold level. As a result, percent emergence increased, time to emergence decreased, and normal seedling growth increased as evidenced by internode lengths. The optimal seed water content for peach seed stratification was 0.9 to 1.2 g H2O per g dry mass. The optimum seed water content for apple seed stratification was between 0.6 and 0.75 g H2O per g dry mass. However, water in excess of that needed for full seed hydration tended to improve germination, possibly because of leaching of inhibitors from the seed. Seed germination correlated with respiration rate during stratification at high seed water contents ( above 0.7 g H2O per g dry mass), but it was not correlated with post stratification respiration. Seed hydration in vitro was an effective method of hydrating seeds to a wide range of hydration levels. The hydration threshold greater than 0.3 g H2O per g dry mass suggested that free water in the seeds was necessary for stratification to occur. The optimum hydration included maximum imbibition of the seed plus additional water in the seed environment.

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