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Title: Analysis of mode of reproduction of guayule (Parthenium argentatum A. Gray) using flow cytometry and identification of polyhaploids for breeding

Author
item CRUZ, VON MARK - Bridgestone Americas Tire Operations
item PANTEL, AMBER - Bridgestone Americas Tire Operations
item RAY, DENNIS - University Of Arizona
item NIAURA, WILLIAM - Bridgestone Americas Tire Operations
item Purdy, Phil
item DIERIG, DAVID - Bridgestone Americas Tire Operations

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2017
Publication Date: 7/1/2017
Citation: Cruz, V.V., Pantel, A., Ray, D.T., Niaura, W., Purdy, P.H., Dierig, D.A. 2017. Analysis of mode of reproduction of guayule (Parthenium argentatum A. Gray) using flow cytometry and identification of polyhaploids for breeding. Industrial Crops and Products. https://doi.org/10.1016/j.indcrop.2017.07.004.
DOI: https://doi.org/10.1016/j.indcrop.2017.07.004

Interpretive Summary: Guayule may potentially be used as a source of solid rubber for tire manufacture in North America. Crop improvement and breeding efforts on guayule enable improved germplasm to be developed and deployed on commercial fields. One difficulty in guayule breeding is identification of the mode of reproduction. To overcome this we compared leaf tissue and seed tissues to determine the mode of reproduction. Results from this study indicated that off-type progeny (seed) would not have been identified if only leaf samples were used, resulting in either an over-estimate of the rate of apomixis for the accession or misclassification of the type of reproduction.

Technical Abstract: Guayule (Parthenium argentatum Gray) is a promising crop to obtain a domestic source of solid rubber for tire manufacture in North America. Crop improvement and breeding efforts on guayule enable improved germplasm to be developed and deployed on commercial fields. One difficulty in guayule breeding is identification of the mode of reproduction, particularly in polyploids which exhibit a mixed mode due to their facultative nature. Guayule polyploids range from triploids (3n = 3x = 54) to octaploids (8n = 8x = 144). Polyploids are known to reproduce by facultative apomixis while diploids (2n=2x=36) follow a sexual mode of reproduction. Flow cytometry is a useful tool to assess ploidy levels of plants. One objective of this study was to estimate the rate of apomixis occurring in different USDA germplasm lines, as well as whether or not there was meiotic reduction in the megaspore mother cell, and whether or not there was fertilization to form an embryo. We examined leaf tissue of maternal plants and 100 progeny seeds from these plants to estimate their rate of apomixis. The seed provided additional insight due to the ploidy levels in two different tissues (embryo and endosperm). Flow cytometric analysis of polyhaploids was also conducted to enable validation of their mode of reproduction which have not previously been identified in the literature. Results from this study indicated that off-type progeny (seed) would not have been identified if only leaf samples were used, resulting in either an over-estimate of the rate of apomixis for the accession or misclassification of the type of reproduction. All identified polyhaploids were analyzed for genetic diversity and compared to existing diploid germplasm.