Submitted to: Plant Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/1998
Publication Date: N/A
Interpretive Summary: Guayule, a desert plant, considered as a potential domestic source of natural rubber and latex, produces seed through the normal sexual process, and also through one not involving cross pollination, similar to cloning, called apomixis. Although Seeds resulting from both processes, look the same, they can be distinguished only through lengthy testing. It is critical to know from which process the seeds resulted to breed better plants. In this experiment, we developed a simple test to identify the origin of a plant's seeds. Hormone treated flowers responded with developed or undeveloped seed depending on the type of reproductive process that occurred. These results could greatly increase research progress and efficiency of plant breeding for rubber and latex improvement.
Technical Abstract: Guayule (Parthenium argentatum, Gray, Asteraceae) is a latex-producing perennial desert shrub that is potentially of economic importance as an industrial crop for the desert Southwest. It is known to possess complex reproductive modes. Diploids are predominantly sexual and self- incompatible, while polyploids show a range of apomictic potential and self compatibility. This paper describes the development of a relatively rapid and simple technique for characterizing reproductive modes of breeding lines of P. argentatum. Initial field experiments were based on an auxin test used successfully to characterize reproductive mode in the Poaceae. The application of 2,4-dichlorophenoxyacetic acid inhibited embryo formation in P. argentatum, but this was not the case with other auxins tested. Results of field experiments were ambiguous because the floral structure of P. argentatum is such that auxins might not have penetrated to the ovules, and there was potential self fertilization by pollen released within isolation bags. Therefore, in vitro culture of flower heads was tested because it provided much better control of environmental conditions, growth regulator application, and pollen release. Auxin alone, or in combination with giberrellic acid or kinetin, inhibited parthenogenesis in vitro. Embryo production did not vary using two substantially different nutrient media. In-vitro flower head culture using Nitsch and Nitsch liquid nutrient medium without growth regulators permitted characterization of the reproductive mode of seven breeding lines, ranging from predominantly sexual to predominantly apomictic. The results of this technique were substantiated using RAPD analyses of progeny arrays from controlled crosses.