Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Timothy O. Croughan

Abstract

Three tissue culture techniques, somaclone evaluation, in vitro screening of suspension cells, and in vitro screening of protoplasts were evaluated for their potential to produce aluminum (Al) tolerant rice. For somaclone evaluation, a collection of 9,000 rice somaclones was screened. After 11 days of germination in 200 uM Al, the length of the primary root was measured and used as the criterion for selection since a principal effect of Al toxicity is inhibition of root growth. Four superior lines were identified. Root length of the most tolerant line was 50% greater than its control following germination in screening solution. A genetic study indicated that Al tolerance in one of the somaclones fits a single dominant gene model. Aluminum tolerance in two of somaclones is possibly governed by more than one gene. The genetics of the tolerance trait in the fourth somaclone could not be clearly determined. For screening suspension cells, Al was added to a 30 gL$\sp{-1}$ sucrose solution with a pH of 4.0. Two Al concentrations (10 and 20 mM) and two exposure periods (4 and 7 days) were evaluated. More than 1,425 fertile plants were recovered from the various Al treatments. Cells selected with 20 mM Al for 7 days yielded a regenerated plant with progeny root growth twice that of the parental cultivar following germination in Al solution. Pretreatment with ethyl methanesulfonate increased the survival rate of cells following exposure to Al but induced a higher frequency of sterility in regenerated plants. Two different screening approaches, direct screening of protoplasts and indirect screening of protoplast-derived calli, were evaluated in the third study. A total of 484 fertile plants were recovered from the various Al treatments. The most Al tolerant line was derived from indirect selection, producing progeny whose seedling root length was improved 50% compared with that of the parental check when germinated in Al solution. Among the methods evaluated, in vitro screening using suspension cultures appeared to be the most effective method for developing rice germplasm with improved Al tolerance. Somaclone evaluation and in vitro screening of protoplasts also yielded improvements, but not as great as that resulting from in vitro screening of suspension cells.

Pages

96

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