Sr. Dahanayake et Nw. Galwey, Diallel analysis of vernalisation responses in spring rape (Brassica napusL.): a basis for adaptation to a Mediterranean environment, AUST J AGR, 50(8), 1999, pp. 1417-1423
The capacity for vernalisation varies among genotypes of spring rape, Brass
ica napus L., and any vernalisation response reduces their suitability for
cultivation in the Mediterranean environment of south-western Western Austr
alia. The genetic basis of this variation was studied in the F-1 generation
of a diallel cross among 5 inbred genotypes derived from a cross between 2
cultivars differing in sensitivity to vernalisation. In non-vernalised pla
nts the number of leaf nodes at flowering, time to flowering, stem height a
t flowering, and time to initiation of stem elongation showed substantial g
enetic variation, both additive and dominance effects being significant. Th
e time to initiation of stem elongation was not vernalisation-sensitive, bu
t for the other 3 characters the response to vernalisation showed significa
nt genetic variation, largely additive. The genetic effects controlling the
number of leaf nodes at flowering were clearly different from those contro
lling stem height at flowering, and hence could be manipulated independentl
y by selection. Moreover, the genetic effects controlling these characters
in the absence of vernalisation were different from those controlling the r
esponse to vernalisation. Discontinuities in the distributions of the paren
t means and other statistics for the number of leaf nodes at flowering sugg
ested that major Mendelian genes may largely control this character and its
response to vernalisation. Comparison of the number of leaf nodes at flowe
ring in the presence and absence of a vernalising stimulus is therefore sug
gested as a selection criterion for the elimination of vernalisation respon
se. However, in the absence of a vernalising stimulus, the time to flowerin
g will be the character easiest to influence by selection.