Genetic improvement of crop plants via incorporation and introgression of exotic alleles

Introgression and incorporation are strategies used in plant breeding to exploit exotic alleles for the purpose of improving crop production. Methods of possible value for increasing the efficiency of these pursuits were evaluated in this research. Exotic maize (Zea mays L.) germplasm may allow for increased flexibility and greater long-term progress from selection if it can be incorporated into U.S. breeding programs. Experiments were conducted to develop and evaluate maize inbred lines derived from crosses between a temperate line, NC262A, and each of eight lines consisting of 100%-tropical germplasm. Testcrosses of several inbred lines with the stiff stalk tester FR992/FR1064 were competitive in yield trials with three commercial hybrids. Simple sequence repeat (SSR) genotypes of the better-performing lines showed the estimated genetic contribution from the tropical parent to range from 0.32 to 0.70. These experiments collectively demonstrated that tropical maize germplasm can be incorporated at high rates into a temperate line via pedigree methods to improve the combining ability of the line. A second set of experiments was conducted to transfer genetic resistance to potato virus Y (PVY) to the tobacco (Nicotiana tabacum) genome from a N. africana chromosome in the alien addition line NC152-dhfr-996 (2n = 50). One introgression event was obtained using conventional backcrossing, and six were obtained using a scheme that involved exposure of NC152- dhfr-996 explants to tissue culture. Fifty-one random amplified polymorphic DNA (RAPD) markers specific to the intact addition chromosome were identified and used to characterize 2n = 48/PVY-resistant genotypes. Variability was present among these plants with respect to the total number of N. africana RAPD markers that were present. A small molecular assisted backcrossing effort allowed for selection of a 2n = 48/PVY-resistant individual possessing only six of the 51 original N. africana RAPD markers. At least three of the seven introgression events involved the same N. tabacum recipient chromosome and segregated independently of the PVY-resistance locus Va. In vitro culture may be valuable for increasing rates of alien gene transfer in tobacco. Successful transfer of PVY resistance from N. africana may allow for an increased level and range of resistance to this virus in tobacco.