The effects of genetically engineered chlorsulfuron resistance genes on yield and chlorophyll concentration of potato, Solanum tuberosum cv. Iwa: A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Horticultural Science (Honours) at Lincoln University

Abstract

Genes for chlorsulfuron resistance and the reporter gene β-glucuronidase were incorporated into potato using the Agrobacterium tumefaciens plasmid vector pKIWI 110. Three lines, Sci I, Sci II, and Sci IV of transformed Solanum tuberosum cultivar Iwa containing one copy, three copies, and two copies of these genes respectively, and a single non-transformed line of Iwa were grown in the field. The effects of four weed control treatments, no spraying with chlorsulfuron, no spraying with chlorsulfuron and hand weeding, one spray of chlorsulfuron (field rate, 20 grams a.i/hectare, and two sprays of chlorsulfuron (two sprays of field rate 20 grams a.i/hectare) were assessed on the different lines. The main hypothesis being investigated was whether expression of chlorsulfuron resistance was related to the number of copies of resistance genes present in the lines. This was assessed by the analysis of chlorophyll concentration, yield, and β-glucuronidase expression. Measurements were made of mean leaf chlorophyll concentration four weeks after each application of chlorsulfuron, and final yield was measured in terms of three size classes of tubers,< 40 grams, between 40 and 110 grams, and> 110 grams. Results were also obtained for β-glucuronidase expression in each of the lines using a fluorimetric assay. There was at least a 20 percent yield penalty associated with possession of genes for chlorsulfuron resistance genes in the unsprayed treatment. Iwa (80.1 tonnes/hectare) yielded at least 15 tonnes/hectare more than any transformed line. Iwa showed an overall yield trend over treatments of unsprayed> hand weeded> one spray> two sprays. The transformed lines had stable yield characteristics over all treatments, but line Sci I was variable, and in general yielded less than the other two lines. Results obtained for mean leaf chlorophyll content and β-glucuronidase reflected the trend of chlorsulfuron resistance between lines. The trend was Sci II = Sci IV > Sci I> Iwa. Thus both the expression of β-glucuronidase and analysis of chlorophyll content provided a good measure of chlorsulfuron resistance expression in Solanum tuberosum. Thus chlorsulfuron resistance was found to be higher in the lines that possessed two or three copies of genes for resistance, than in the line that possessed only one copy of the gene. However, because the level of chlorsulfuron resistance conferred by two or three copies of resistance genes was not significantly different, it can be said that greater than one copy of these genes is optimal.