New Zealand Journal of Agricultural Research abstracts
Progress in recurrent selection and in crossing cultivars with
white clover resistant to the clover root-knot nematode
Meloidogyne trifoliophila
C. F. MERCER
J. VAN DEN BOSCH*
K. J. MILLER
AgResearch Grasslands
Private Bag 11-008
Palmerston North, New Zealand
*Present address: Wrightson Research, P.O. Box 939, Christchurch.
Abstract New Zealand pastures are generally deficient in
clover content due in part to root-invading nematodes. A recurrent selection
programme for resistance to the clover root-knot nematode (Meloidogyne
trifoliophila) assessed individual white clover (Trifolium repens)
genotypes for the number of root galls and root dry weight. Low galling
(resistant) and a few high galling (susceptible) genotypes were crossed to
provide divergent selections and progeny screened. In the sixth generation, the
resistant selections (n = 581) averaged 45% of the susceptible
selections (n = 146) for number of galls per gram of root dry weight.
The seventh generation equivalent figure improved to 38% (n = 112
resistant and n = 81 susceptible genotypes). In the seventh generation,
survival of the resistant group of lines was poorer than other groups.
Resistant genotypes were crossed with established cultivars and progeny
screened and crossed. The resistant x cultivar progeny averaged 83% of the
susceptible x cultivar progeny's galls per gram in the first cross (ns), 58%
(P < 0.001) in the second, and 44% (P < 0.001) in the third
cross. Progeny of Sustain x resistant crosses had fewer galls per gram than
progeny of crosses with other cultivars. Foliage dry weights were assessed
every 3 weeks for 6 months from M. trifoliophila-infected and
nematode-free pairs of resistant and susceptible white clover lines. Yields of
all four lines were reduced by the invasion of the M. trifoliophila
second-stage juveniles but the two resistant lines outyielded the
susceptible ones. There was little yield from infected susceptible lines from
127 to 191 days after inoculation. More M. trifoliophila eggs were
recovered from one resistant line mainly because it survived and grew better
than the other lines.
Keywords breeding; Meloidogyne trifoliophila;
screening; selection; resistance; Trifolium repens; root-knot nematode;
white clover
New Zealand Journal of Agricultural Research, 2000, Vol. 43: 41-48
0028-8233/00/4301-0041 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (566K); (scanned from paper original: notes about this process)
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