EVALUATION OF THE DOMESTICATION STATUS OF COW COCKLE (Vaccaria hispanica [P. Mill.] Rauschert) POPULATIONS
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Cow cockle (Vaccaria hispanica [P. Mill.] Rauschert) is a summer annual species introduced to North America from Europe. It has been investigated as a potential crop for the Canadian prairies because of its ultra–fine starch, cyclo–peptides, and saponins. However, cow cockle has a long history of being a weed in Canada and may need additional scrutiny of its weediness potential before initiating commercial production. In addition, cultivating poorly domesticated species may lead to further environmental and weed management risks; hence, an understanding of the domestication status is required. The objectives of this research were to evaluate available cow cockle germplasm i) to identify populations that are best adapted to cultivation as well as the traits responsible for such adaptation, ii) to determine seed dormancy levels in cow cockle populations and to determine how temperature and light affect seed dormancy and germination, and iii) to determine whether cow cockle populations are persistent and form a seed bank. A total of 15 cultivated, weedy, and wild cow cockle populations from different parts of the world were compared for agro–morphological, seed dormancy and seed persistence characters from 2009 to 2011. In the field persistence study, two populations including weedy (Scott weedy) and cultivated (Scott) lines were included. Cluster analysis revealed three main groups among the populations based on the traits studied. Physiological maturity, seed size, plant height and seed yield differed most among populations. The cultivated populations, Pink Beauty, Turkey, PB–87, Scott and a weedy population, UMan–89 had higher seed yield, larger seeds, and greater biomass compared to the other populations. Although weedy populations showed some adaptation to cultivation, characters relating to plant architecture, seed size and yield suggested a weedy habit. Freshly matured seeds of all the populations showed high levels of primary conditional dormancy except “Mongolia”. At optimum temperature conditions for germination (10 C), the effect of temperature regime (alternating and constant) and light on seed dormancy were insignificant. The variation in optimum temperature, light, and their interactions among the cow cockle populations may be due to the plants evolving to adapt to their local environments. In the field persistence study, the weedy population had higher seedling emergence at two out of three locations and a larger residual seed bank at all the locations. Despite the differences in seed persistence between the populations, considerable numbers of seed of both weedy and cultivated lines were recovered from the soil seed bank at the end of the study. This concurs with the results of the laboratory persistence study, as both the populations had greater seed longevity (p50 values > 50 days) which suggests a field persistence of over three years. In conclusion, higher seed yield, larger seeds, and greater biomass in cultivated populations may result from certain pre–adaptation towards domestication, which may have been acquired during the process of pre–domestication cultivation. From a domestication perspective, if cow cockle were grown as a crop, the conditional dormancy may not be considered a barrier to domestication and can be viewed as a physiological mechanism to avoid germination at harvest. The major concern in cow cockle domestication would be seed persistence, as it can form a reasonably long–term seed bank. This may pose some concerns for the production of cow cockle as a crop in the Canadian Prairies. The current research suggests that cow cockle populations from Canada, although they showed some adaptation to cultivation; are largely weedy and can be considered as variants of an early introduced species which might have evolved to adapt to non–native conditions.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorShirtliffe, Steve J.
CommitteeHucl, Pierre; Bai, Yuguang; Bedard-Haughn, Angela; Columan, Bruce
Copyright DateJuly 2014