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SIMULTANEOUS SELECTION OF WHEAT PLANTS WITH RESISTANCE TO
ROOT-LESION NEMATODES, CROWN ROT AND YELLOW SPOT
J.G. Sheedy, J.P. Thompson and R.A. Reen
Leslie Research Centre, PO Box 2282, Toowoomba, 4350, Queensland. Email: jason.sheedy@daff.qld.gov.au
ABSTRACT. Root-lesion nematodes (Pratylenchus thornei [Pt] & P. neglectus [Pn]), crown rot (CR; Fusarium
pseudograminearum) and yellow spot (YS; Pyrenophora tritici-repentis) are four economically important diseases of wheat
that commonly occur in combination and cost northern growers $137 M annually. Therefore, we need to develop germplasm
with combinations of disease resistance to minimise yield loss in these situations. To achieve this, the established screening
methods for each disease were combined and where necessary modified, to allow testing of up to 4 diseases simultaneously.
Initial experiments tested every disease combination on up to 42 fixed cultivars covering resistant to susceptible disease
reactions to develop a procedure that could be used to select individuals with resistance to Pt, Pn, CR and YS. This procedure
was used to select resistant individuals in an experiment of 21 check cultivars and 132 segregating F 3 ’s exposed to all 4
diseases. The check cultivars in the F 3 experiment were significantly correlated with long-term rankings for YS (r = 0.96***),
CR (r = -0.61**) Pt (r = 0.84**) and Pn (r = 0.52*) and we were able to select nine F3’s (7%) with resistance to all four
diseases. This procedure will likely hasten the development of multiple-disease resistant parents, suitable for introduction
into commercial breeding programs.
INTRODUCTION
Root-lesion nematodes (Pratylenchus thornei [Pt] & P.
neglectus [Pn]), crown rot (CR; Fusarium
pseudograminearum) and yellow spot (YS; Pyrenophora
tritici-repentis) are four economically important diseases that
commonly occur in combination and cost the northern wheat
industry $137 M annually. To help minimise these losses we
conducted 14 experiments that evaluated disease
combinations, inoculum types and rates and timing of
disease assessment on fixed wheat cultivars to develop a
procedure that could be used to select individuals with
resistance to Pt, Pn, CR and YS simultaneously. We then
applied that procedure to a segregating wheat population and
selected individuals with resistance to all 4 diseases.
MATERIALS AND METHODS
Germplasm 21 check cultivars ranging from resistant (R) to
susceptible (S) for each disease were compared to 132 F 3 ’s
of DH83/Wylie selected from 14 F 2 families previously
identified as moderately resistant (MR) to Pt. DH83 is a
doubled haploid line derived from a cross between the
synthetic hexaploid CPI133872 and Janz and is MR to Pt, Pn
and YS. Wylie is MR-MS to CR.
Procedure The experiment consisted of 4 blocks, each with
21 check cultivars and 33 F 3 ’s in a partially replicated design
and was grown in an evaporatively-cooled glasshouse with
soil temperature maintained at 22°C by under-bench heating.
Plants were grown in 330 g of an Irving Series vertosol
partially sterilized by steam at 70°C for 45 minutes and then
inoculated at planting with 1650 each of Pt and Pn. Each pot
was fertilized with 1 g of Osmocote® Native Gardens slowrelease
fertilizer. Pots were watered using a self-regulated
capillary watering system at 2cm water tension. Seven days
after planting (DAP) 10 mL of CR mycelial suspension was
applied at the plant base and a YS spore suspension was
applied by aerosol sprayer to the leaves. YS symptoms were
rated 18 DAP on a 1 to 9 scale and CR damage (% browning
of leaf sheaths) was rated 21 DAP. Then, 20mL/plant of
Benomyl® [1 g/L] was applied 3 times at 2-week intervals.
Nematodes were extracted from the soil and roots of each
entry 16 weeks after inoculation using a 48hr Whitehead tray
method. Nematode counts were transformed by ln(x+1)
before REML analysis in GenStat 11th Ed. The predicted
means were back-transformed after analysis and expressed
as Pratylenchus/kg oven-dry soil. Reproduction factor (RF)
was calculated by dividing the final nematode population/kg
by the initial population/kg.
RESULTS
The disease ratings of the check cultivars were correlated
with established ratings for each disease (YS, r = 0.96***;
CR, r = -0.61**; Pt, r = 0.84**; Pn, r = 0.52*). Pt
multiplication was lower than expected but the relative
performance of R and S checks were maintained. By
comparing the performance of F 3 ’s with MR check cultivars
for each disease we were able to select 9 F 3 ’s (7%) with
resistance to all 4 diseases (Table 1).
Table 1. Nine F 3 ’s moderately resistant to YS, CR, Pt and
Pn were identified using a simultaneous selection procedure.
Genotype YS CR Pt-RF Pn-RF
DH_83 (Parent) 4.7 58 0.8 5.1
EGA Wylie (Parent) 3.9 55 5.7 6.9
DH_83/EGA Wylie-016-02 8.0 35 1.3 5.0
DH_83/EGA Wylie-016-05 7.6 13 1.3 7.1
DH_83/EGA Wylie-070-07 4.6 41 2.0 5.7
DH_83/EGA Wylie-071-01 7.2 41 1.1 6.5
DH_83/EGA Wylie-150-03 6.1 19 1.0 3.8
DH_83/EGA Wylie-150-06 5.6 16 1.4 6.7
DH_83/EGA Wylie-156-01 5.6 35 1.4 6.5
DH_83/EGA Wylie-244-07 4.8 41 1.2 5.5
DH_83/EGA Wylie-244-09 4.5 39 1.4 5.4
CPI133872 (MR – YS,Pt,Pn) 7.6 22 0.7 5.2
Leichhardt (MR – YS) 7.1 44 2.1 9.2
2_49 (MR – CR) 5.7 33 3.9 16.8
Janz (S – YS,CR,Pt,Pn) 2.8 55 4.6 14.8
Banks (S – YS,CR,Pt,Pn) 3.2 64 6.3 20.8
DISCUSSION
Traditional plant pathology and breeding have dictated that
selection of disease-resistant germplasm must be done one
disease at a time to avoid disease interactions, the possibility
of acquired resistance and to have the most precise
assessment of resistance. Consequently, developing cultivars
with multiple-disease-resistance has been slow and in many
cases ineffective. The procedure we have developed can be
applied to breeding populations with suitable genetics to
“fast-track” the development of wheat cultivars with superior
levels of resistance to Pt, Pn, CR and YS than is currently
available in commercial cultivars.
© State of Queensland, Department of Agriculture, Fisheries
and Forestry, 2012.
7th Australasian Soilborne Diseases Symposium 69