EFFECTS OF ISOLATION DISTANCE ON CONTAMINATION IN SWEETCLOVER

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Abstract
The recessive low coumarin gene cu was used as a marker to study the effects of isolation distance on contamination levels in sweetclover pollinated by honey bees. A 46-m isolation distance was found inadequate to maintain a high level of genetic purity. Considerable contamination from crossing resulted with isolation distances from 46 to 804 m when there was little competitive bloom from other entomophilous crops. A highly attractive and competitive crop of rapeseed appeared to serve as a very effective isolation barrier to minimize contamination. A higher amount of contamination occurred in the borders of the low-coumarin isolation plots of one test. The results of this study are sufficient to question the existing isolation standards for sweetclover, but are not adequate to formulate new standards.