New Zealand Journal of Agricultural Research abstracts
Genetic differentiation in white clover (Trifolium repens)
populations during 8 years of contrasting phosphorus supply in New
Zealand hill country
M. E. Wedderburn1
D. J. Barker2
D. F. Chapman3
S. J. Orr1
N. Dymock1
1AgResearch Limited
Ruakura Agricultural Centre
Private Bag 3123
Hamilton, New Zealand
2Department of Horticulture
and Crop Services
The Ohio State University
202 Kottman Hall
2021 Coffey Road
Columbus OH 43210-1086, USA
3Department of Animal
Production
Institute of Land and Food Resources
University of Melbourne
Parkville, Victoria 3052, Australia
Abstract Genetic differentiation under the
selection force of variable soil P availability was measured in
populations of two white clover cultivars introduced to a grazed, low
fertility grassland site. The resulting mixed grass-clover pastures
subsequently received contrasting levels of phosphorus (P) fertiliser
for 8 years. A field-based reciprocal transplant experiment and two
controlled-environment experiments were conducted using plants removed
from the 8-year field experiment and appropriate controls to test the
hypotheses that: (1) genetic differentiation occurred within the white
clover populations in response to variation in P supply; and (2)
surviving plants which demonstrated genetic differentiation under
high-P conditions would continue to do this when grown in mixtures with
plant material removed from unsown pasture. This study demonstrated
that genetic differentiation did occur. In the reciprocal transplant
experiment, when returned to a low-P environment the mean of the
populations removed from a low-P site yielded more than the mean
population removed from a high-P site. Genetic differentiation was
demonstrated most strongly with ‘Grasslands Huia’. ‘Huia’ survivors
growing in the high-P source environment retained the potential of the
original seed line to respond to P additions, but this potential was
lost in ‘Huia’ populations grown under low-P fertility. In contrast,
‘Grasslands Tahora’ did not retain the potential of the original seed
line to respond to additional P and behaved similarly to the resident
material. High-P inputs led to the retention of ‘Huia’ genotypes with
the capacity for high growth rates and superior competitive ability.
This competitive ability was demonstrated when resident plants grown in
a mixture with ‘Huia’ plants removed from the high-P source treatment
suffered reductions in yield compared with their yield in pure pots.
The drift by both ‘Tahora’ and ‘Huia’ away from the potential of the
original seed attributes towards the resident type demonstrates the
adaptive nature of the traits found in the resident population that
favour a conservative growth strategy. P availability does not appear
to be a dominant selection factor where new germplasm has been
introduced to pastures with the objective of stimulating production;
maintenance of fertility levels may assist in retaining a full
complement of P-responsive genotypes.
Keywords genetic differentiation; white clover;
phosphorus
A04007; Received 20 January 2004; accepted 24 September 2004; Online
publication date 21 March 2005
New Zealand Journal of Agricultural Research, 2005, Vol. 48:
63–74
0028–8233/05/4801–0063 © The Royal Society of New Zealand 2005
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