Morphological characterization of Amaranthus palmeri x A. spinosus hybrids

Authors: Molin, William; Nandula, Vijay

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2017
Publication Date: 5/27/2017
Citation: Molin, W.T., Nandula, V.K. 2017. Morphological characterization of Amaranthus palmeri x A. spinosus hybrids. American Journal of Plant Sciences. 8:1499-1510.

Interpretive Summary: The rapid and widespread adoption of glyphosate-resistant crops, associated with the intense use of glyphosate and lack of rotation with non-glyphosate-resistant crops has resulted in evolution of several glyphosate-resistant weed species, including spiny amaranth in Mississippi. The glyphosate-resistant spiny amaranth was proven to be a hybrid, formed from interspecific hybridization of spiny amaranth and glyphosate-resistant Palmer amaranth. Scientists from the Crop Production Systems Research Unit (USDA-ARS) conducted greenhouse studies to compare growth of several hybrids to Palmer amaranth and spiny amaranth. Palmer amaranth had the highest magnitude in several growth parameters with spiny amaranth having the least. The hybrids had intermediary growth rates and days to flowering, but differed from each other with regard to sex identity. Thus, hybridization between Palmer amaranth and spiny amaranth resulted in hybrids akin to evolution of a new species. These findings will profoundly change how resistant weed populations, with interspecific hybridization potential, are managed.

Technical Abstract: The growth of clones of seven Amaranthus palmeri x A. spinosus hybrids was compared to type specimens of A. palmeri and A. spinosus. The hybrids came from the field where they were originally discovered and clones of the type specimens and hybrids were established under greenhouse conditions and used to compare growth rates. A. palmeri had the highest growth rate and A. spinosus the lowest growth rate based on height, node counts, and dry weight accumulation. A. palmeri also had the greatest number of days to flowering and A. spinosus the fewest. Hybrids had intermediary growth rates and days to flowering, but differed from each other with regard to sex identity. The hybrids were either dioecious like A. palmeri or, if monoecious, had patterns unlike A. spinosus. Spine length and texture also varied in hybrids and some were without spines. Hybrid 16Ci was short compared to all others and had succulent leaves and stems, which easily separated from the plant body. These hybridizations resulted in morphologically distinct types with acquisition of physical traits intermediate to the type specimens which may drive evolution of these species.