TITLE:
Early Growth and Development of Horseweed (Conyza canadensis (L.) Cronq.)
AUTHORS:
William T. Molin, Katherine Parys, Christine L. Beck
KEYWORDS:
Horseweed, Conyza canadensis, Germination
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.11 No.1,
January
9,
2020
ABSTRACT: Horseweed (Conyza canadensis (L.) Cronq.)
produces thousands of small elongated seeds which are botanically defined as
achenes; yet, relative to the quantity of achenes produced, few seedlings
survive to produce mature plants. The developmental progression from achene to
4 mm seedlings was documented, and seedling response to moisture deprivation
was described. Radical protrusion through the pericarp occurred between 18 and
30 hours after onset of imbibition in water or when germinated on soil at or
greater than field capacity. A ring of root hair initials formed immediately
after radical emergence at the interface of what was to become the separation
between the root and hypocotyl. By 48 hours post imbibition, radicals
differentiated into a distinct root with root cap and a hypocotyl, and root
hairs elongated. By 72 hours post imbibition, seedlings had emerged from the
pericarp, and had: expanded photosynthetic cotyledons, a clearly defined
hypocotyl, a ring of elongated root hairs exceeding 1 mm in length, and a root
equal or longer than the hypocotyl. The epicotyl had not yet emerged, and the
total seedling length was approximately 3 to 4 mm. Germination was delayed on
soil at or below field capacity. More than 95% of two- and four-day-old seedlings that had been
desiccated for more than 24 hours died after being rehydrated.