An evaluation of an index method of selection for high yield in turnip rape, Brassica campestris L. ssp. oleifera Metzg

Summary

Substantial variation in yield, its primary components and several vegetative characters which influence yield was observed among a series of families drawn at random from a low erucic acid variety of turnip rape. A sib analysis of family means showed all characters to have relatively high heritabilities, although yield was, together with seed weight and specific leaf weight, in a group having the lowest values.

Several characters, including flowering time, leaf area and leaf weight, had appreciably higher heritabilities than yield, however, none appeared to be a suitable alternative criterion for selection as the expected correlated responses to selection for these characters were lower than the direct response to selection for yield. The expected genetic advance in yield from the simultaneous selection for a number of these characters using a selection index technique, was significantly greater than that expected from selection for yield alone. Selection indices based either on yield components or vegetative characters were, at best, only as efficient as selecting directly for yield. Several indices including measurements of both yield components and vegetative characters were, however, expected to facilitate a greater rate of advance in yield than direct selection.

The practical value of such indices in improving rapeseed yields in Western Australia was discussed with reference to the additional costs involved in their use and their accuracy in environments where genotype x environment interactions are likely to be high.