The significance of inter- and intraspecific DNA content variation in agriculturally important species

This dissertation examined the total nuclear DNA content variation in agriculturally important plant species and determined any differences. The nuclear DNA content of 40 Malus species and hybrids was examined using flow cytometry. Estimates of total nuclear DNA content for this collection ranged from 1.45 pg for a diploid variety to 2.57 pg for a triploid variety. The total DNA content variation of the genus Cucurbita was examined both intra- and interspecifically. Flow cytometry was used to calculate the estimates of total nuclear DNA content for the selected pumpkin species ranged from 0.92 pg for a giant variety, to 1.14 pg for a miniature variety. There was also a significant positive linear correlation (P = 0.004) between stomatal length and genome size in the pumpkin varieties. Indicating that nucleotypic selection does appear to be involved in determining fruit size. A technique for providing substantial, thick root formation from weedy Amaranthus species was also examined. No changes in total DNA content were observed by flow cytometric analysis, and the in vitro procedure did produce significantly larger roots, in higher quantity, containing 32 chromosomes of normal morphology. The effects of interspecific hybridization events between Amaranthus hybridus and A. tuberculatus, putative F1, BC1, and BC 2 hybrids were also examined. The parental plants had micropollen of 0.28% or lower, whereas the F1 hybrids had an average of 23.6% micropollen. The BC1 hybrids had six fold lower micropollen percentages than the F1 hybrids, but at least 13% higher than the parental types. The BC2 plants had four fold more micropollen than the parental types, but at least nine fold lower than those of the F1 hybrids and half of the percentage of micropollen of the BC1 hybrids. Finally, one of the mechanisms that could be involved with abnormal meiosis in maize was examined. By comparing the St1 mutant maize with a non-mutant Pa91 line it was determined that knob regions are not associated with increased chromosomal stickiness. This research found that there is a great deal of DNA content variation both within and between numerous agriculturally important species.