Masters Theses

Date of Award

8-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Carl E. Sams

Committee Members

David L. Coffey, Charles R. Graves

Abstract

High glucosinolate content in brassica meal is a limiting factor in utilization of rapeseed as livestock feed. In recent years canola cultivars of rapeseed with decreased glucosinolate content have been developed. However, environmental and nutritional factors are also believed to influence glucosinolate content. Two experiments were conducted to determine the relationships among water stress, boron nutrition, and glucosinolate content in cultivars of canola. Two canola cultivars ('Cyclone' and 'American A-112') were grown in a continuously recirculating hydroponic system with modified 'Hoagland solutions'. Boron (B) nutrition varied between experiments. During the Spring 1995 experiment (I) B concentration was 0.6 mg*l-1, and during the Spring 1996 experiment (II) 0.3 mg*l-1. Water stress was induced gradually (2% per day using polyethylene glycol 8000) starting when plants were four weeks old. Osmotic potential was maintained at -0.1 MPa (high stress treatment), -0.085 MPa (medium stress treatment), and -0.05 MPa (low stress treatment, without PEG). Treatments were arranged in a randomized incomplete block design, with three blocks, four replications, two cultivars, and three treatments. Upper leaves (#15 and up) were collected and analyzed by inductively coupled plasma emission spectrometry for boron content. Total and indole glucosinolate content of seeds were determined colorimeterically and individual glucosinolates were determined by gas chromatography.

For both cultivars, leaf B content decreased as water stress level increased, however, in experiment I, this change was not statistically significant. In experiment II with only 0.3 mg*l-1 B available in the solution, leaf B content decreased as in the experiment I and was statistically significant (P<.001). The difference between the two stressed treatments was not significant, suggesting that water stress greater then -0.085 MPa does not further decrease B uptake.

Water stress reduced leaf tissue B to about 50 µg*g-1 dry weight in experiment I but did not alter glucosinolate concentration. In experiment II, total glucosinolate concentration of seeds in "Cyclone" significantly increased (P<.01) with medium stress (-.085MPa), but water stress had no significant effect on glucosinolate content of "American-A112" seeds. Linear treatment contrasts showed that further increasing water stress from medium (-0.085 MPa) to high (-0.1 MPa) did not further increase glucosinolate content of seeds. Seed indole glucosinolate concentration was not significantly different among treatments or between cultivars in either experiment.

Both dry weight and yield were reduced as stress level increased (P<.001) for both cultivars in both experiments. However, severely stressed plants of "Cyclone" showed greater morphological variability than plants of "American-A112", producing malformed plants with few seeds.

Water stress decreased boron uptake in both cultivars. "Cyclone" was more susceptible to water stress, indicating genetic differences between the cultivars.

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