Browsing by Subject "pollen tube"
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Item Method of pollination and heritability for seedling vigor in switchgrass(Texas A&M University, 2005-08-29) Ramirez de Leon, HectorSwitchgrass (Panicum virgatum L.) is a warm-season perennial bunchgrass native to North America. In addition to its importance as a forage grass, it has promise as a biofuel crop. However, its use is limited because the grass is difficult to establish. Improving seedling vigor is one approach for improving establishment. The objectives of this study were to: 1) select for increased seedling mass through half-sib family selection; 2) calculate an estimate of heritability for seedling mass; and 3) determine the mode of pollination of switchgrass. One cycle of selection was completed using a half-sib methodology. Seedling mass was determined in a series of growth chamber studies. The seed was produced in different space planted field nurseries in the College Station, TX area. Mean seedling weight of the base population (C0) was 0.014 gm seedling-1, while the mean seedling weight from the C1 cycle of selection was 0.029 gm seedling-1. Unfortunately, bulked seed from the base population was old and did not germinate well. Therefore, a new base population was recreated, and the C0 seedlings from this population were heavier than the C1 seedlings, 0.020 and 0.016 gm seedling-1, respectively. The calculated heritability estimate was H2 = 0.6. Since the C0 and C1 nurseries were not grown on the same soil type, the lack of a positive response for seedling weight may be due to the different soil types. However, it may require another cycle of selection to determine if seedling mass can be positively impacted via half-sib selection. The mode of pollination of the species was determined by 1) observing pollen germination and tube growth in the pistils using fluorescent microscopy and 2) determining seed set with selfed plants. When self-pollinated, the pollen tubes never grew into the ovaries but when cross-pollinated the tubes readily grew to the micropyle. Also, when switchgrass plants were self-pollinated, viable seed were not produced. These findings indicate that switchgrass is highly self-sterile because a self-incompatibility mechanism prevents the pollen tubes from growing into the ovary of the same genotype.Item Survey for Intergeneric Pollen Tube Growth in Intergeneric Pollinations Utilizing the iap Allele in Sorghum bicolor(2012-02-14) Bartek, Matthew ScottHybridization within Sorghum bicolor (L.) Moench has been the primary means of creating genetic diversity needed for sorghum crop improvement. While significant variation exists within S. bicolor, there are several traits that can be improved and potential opportunities to improve S. bicolor if secondary and tertiary germplasm pools could be accessed. Recently, the discovery of the iap (Inhibition of Alien Pollen) mutant and its introgression into more breeding-amenable genetic background has facilitated the development of S. bicolor germplasm with genetic diversity not previously seen within Sorghum. The key to producing this variation is the homozygous recessive mutant gene iap which removes an important reproductive isolation barrier to hybridization. Development of a S. bicolor accession (Tx3361) containing the mutant allele iap and ms3 has allowed introgression of genomic regions from divergent sorghum species into S. bicolor. Given the success with divergent sorghum species, there is a real interest in assessing the potential of this mutant to facilitate intergeneric hybridization. The objective of this study was to determine the range and effectiveness of the iap mutant to allow pollen tubes of Poaceae species outside of the genus Sorghum to grow into S. bicolor pistils. Accessions from the genera Zea, Miscanthus, Pennisetum, and Sorghastrum were used as pollen donors onto Tx3361 and fluorescent microscopy was used to determine the distance through the pistils that foreign pollen tubes grew. Results indicate high levels of pollen tube growth into the ovaries of S. bicolor pistils for two accessions of Pennisetum ciliare (L.) Link and four accessions of Zea mays L. Pollen tubes of other accessions tested did grow to the ovary but in very small numbers. While the recovery of embryos was not attempted in this study, the results indicate that there is potential for hybridization, but the specific pollinator within a species is critical in this attempt.