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Natural Selection During Germination in Wild Oat (Avena fatua) and California Burclover (Medicago polymorpha var. vulgaris) Populations

Published online by Cambridge University Press:  12 June 2017

S.K. Jain
Dep. of Agron. and Range Sci., Univ. of California, Davis, CA 95616
K.N. Rai
Dep. of Agron. and Range Sci., Univ. of California, Davis, CA 95616


Wild oat (Avena fatua L.) and California burclover [Medicago polymorpha L. var. vulgaris (Benth.) Shinners] are two important ruderal as well as rangeland species in California, with their wide adaptability correlated with several widespread genetic polymorphisms. In order to clearly demonstrate the role of genetic variation in their population dynamics, natural selection was studied at two of the polymorphic loci (B/b in wild oat and D/d in California burclover) which represent a useful class of marker genes governing seed coat morphology. Since parental seed coat often remains attached to the offspring seedling, two generations can be scored simultaneously during the population census in successive stages of the life cycle. Data are presented to provide direct evidence for natural selection at these loci and to argue for their wider use in such population studies. In wild oat, black lemma class (B-) germinated at a significantly higher rate than the gray class (bb) in mesic patches at one of the sites and seemed to be negatively density-dependent whereas density-dependent reproductive rates generally favored the gray class. Similarly, germination and seed output provided the balancing selection to maintain polymorphism at locus D/d in California burclover. Such processes of localized selection and population regulation may have significant implications in the management of weed populations.

Research Article
Copyright © 1977 by the Weed Science Society of America 

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