4-D TOLERANCE IN RED-CLOVER RECURRENT HALF-SIB FAMILY SELECTION FOR 2

1989, Crop Science Society of America. All rights reserved. Low profit potential as well as environmental residue and toxicology concerns make it difficult for chemical companies to develop and register herbicides for forage crops. Selection of forages with tolerance to currently labeled herbicides may be an alternative. The objective of this research was to develop a 2,4-D [(2,4-di-chloro-phenoxy) acetic acid] tolerant red clover (Trifolium pratense L.) population, using recurrent half-sib family selection. A 20 000 plant base population of equal parts of Nolins, Kenstar, and a Florida population (QC5) was sprayed with 1.12 kg ha-1 2,4-D and 63 individuals were selected and intercrossed. Four cycles of half-sib family selection were conducted with from 63 to 276 families evaluated in a cycle. Family selections were based on mean visual top and root damage scores using a 1 to 5 visual rating scale. Four cycles of recurrent selection increased levels of 2,4-D tolerance in red clover by approximately 35% with an average change of 0.30 score units per cycle. The narrow-sense heritability of the 2,4-D tolerance trait was near 50% and inbreeding depression was apparently minimal. These results showed that significant progress has been made and that future progress leading to economically valuable field tolerance should be possible.

RECURRENT HALF-SIB FAMILY SELECTION FOR 2,4-D TOLERANCE IN RED-CLOVER Academic Article