FONDO DE GARANTÍAS DE INSTITUCIONES FINANCIERAS
FONDO DE GARANTÍAS DE ENTIDADES COOPERATIVAS
J.A. Davidson{ XE "Davidson, J.A." }A, L. McMurrayB and M. LinesB
A
South Australian Research and Development Institute (SARDI), GPO Box 397, Adelaide, 5001, SA
B
South Australian Research and Development Institute (SARDI), GPO Box 822, Clare, 5453, SA
INTRODUCTION
Field pea production in South Australia has remained constant at
approximately 120,000 ha since the mid 1990s, although
plantings have increased in medium to low rainfall areas.
Blackspot, caused by a complex of fungi i.e. Mycosphaerella pinodes, Phoma medicaginis var. pinodella, Ascochyta pisi and Phoma koolunga (1), is the most common disease in field peas.
Research on blackspot in the 1990s, based in traditional areas
and on traditional late‐maturing trailing type peas i.e. cv. Alma,
found that foliar fungicides were uneconomic but delaying
sowing minimised blackspot infection from airborne spores.
Delayed sowing is still a major recommendation for the pea
industry across South Australia (2). Given the expansion into low
rainfall areas and increasing frequency of low rainfall seasons,
the potential yield loss through delayed sowing is often now
greater than the loss from blackspot. Furthermore, fungicide
costs have reduced and this practice may now be economic in
some environments. The pea industry has also adopted higher
yielding cultivars including early maturing erect semi‐leafless
types i.e. cv. Kaspa. Agronomic trials were conducted in 2007
and 2008 to identify economic strategies to control blackspot in
new improved pea cultivars, and to identify optimum sowing
dates in low to medium rainfall areas for these cultivars.
MATERIALS AND METHODS
Trials were sown at three sites each season, viz. high rainfall
(450mm per annum) at Kingsford in 2007 and Turretfield in
2008; medium rainfall (400mm per annum) at Hart in both
seasons; low rainfall (325 mm per annum) at Minnipa in both
seasons. The high and medium rainfall sites had three sowing
times and the low rainfall site had two sowing times. First sowing
occurred within a week of the break of the season (first week of
May) at each site and subsequent sowing times were at intervals
of three weeks. Trials were split plot design, with time of sowing
as the main block, with three replicates. Cultivars included the
conventional trailing types Alma and cv. Parafield (the latter at
Minnipa only), and the new erect semi‐leafless types including
the current commercial cultivar Kaspa and advanced breeding
lines WAPEA2211 and OZP0602 (the latter in 2008 only).
Fungicide treatments were the seed treatment P‐Pickel T® (thiram plus thiabendazole, 200 ml/100kg seed), a foliar
application of mancozeb (2 kg/ha) at 9 node growth stage, foliar
applications of mancozeb at 9 nodes plus early flowering growth
stage, P‐Pickel T® seed dressing plus a foliar application of
mancozeb at 9 nodes, foliar applications of chlorothalonil (2
L/ha) every fortnight (i.e. disease control) and an untreated
control. Disease was assessed regularly, 2 or 3 weeks apart,
throughout the growing season, and recorded as % leaf area
diseased (%LAD) in the early stages of the epidemic, or as % of
nodes infected (%ND) in the later stages of the epidemic. Plot
yields were recorded as tonnes per hectare. Significant
differences identified by analyses of variance were separated on
P<0.05.
RESULTS
Disease severity reached between 25% and 60%ND in medium
and high rainfall trials but lack of rainfall during spring stopped
further disease progress in both seasons. Low rainfall trials
developed less than 5% LAD due to dry conditions. Delayed
sowing reduced disease levels by 30% less than the untreated
controls throughout the season. P‐Pickel T® reduced disease
levels by 50% for 6–8 weeks after sowing but no differences
were detected by the end of the season. Foliar fungicides
resulted in a small (6–12%) reduction in disease severity, but this
did not translate into additional grain yield due to the dry spring.
Infection appeared earlier in Alma and disease remained at
higher levels than in the other varieties. Kaspa had higher
disease levels than WAPEA2211 which in turn had higher levels
than OZP0602.
Yield in early sown plots was significantly higher than later sown
plots in 2007, but not in 2008 due to erratic high temperatures
and frosts in spring. However a variety interaction occurred. In
2008 the early flowering line, OZP0602, was the highest yielding
line when sown at the mid sowing time, and it had similar
highest yield to Kaspa at the early sowing time. Kaspa yield
decreased with later sowing. The older conventional variety
Alma was the lowest yielding variety and showed a variable
response to sowing date.
DISCUSSION
Blackspot was reduced in new cultivars and breeding lines,
indicating that improved blackspot resistance is becoming
available to the Australian pea industry. The semi‐leafless more
erect pea types are better adapted to earlier sowing dates than
the older conventional types due to a combination of reduced
biomass, more erect plant type and slower disease development
in the early growth stages. Maximum grain yields of Kaspa were
achieved by sowing early but this exposes Kaspa to higher
disease and frost risks. The breeding line, OZP0602, was equally
as high yielding in first and second time of sowing. Consequently,
this line does not need to be sown early to maximise yields,
providing a safer option when sowing needs to be delayed. Foliar
fungicides slightly reduced disease, but this did not translate into
yield gains in these trials due to the dry springs. Anecdotal
evidence, from commercial crops grown in average rainfall
seasons, has shown that similar small reductions in disease lead
to economical yield gains. Further research is required to
confirm this in trials with more favourable spring rainfall.
ACKNOWLEDGEMENTS
This research was funded by South Australian Grains Industry
Trust.
REFERENCES
1. Davidson, J.A., Hartley, D., Priest, M., Krysinska‐Kaczmarek, M., Herdina, McKay, A. and Scott, E.S. (2009) A new species of Phoma causes ascochyta blight symptoms on field peas (Pisum sativum) in South Australia. Mycologia, 101(1): 120–128.
2. Hawthorne W, Davidson JA, McMurray L, Armstrong E, MacLeod W, Bretag TW (2003) Field Pea Disease Management Strategy for southern and western regions. Disease Management Guide Series. Pulse Australia, Sydney, Australia.
Posters
63 Dispersal potential of Gibberella zeae ascospores
P.A.B. Davies{ XE "Davies, P.A.B." }A, L.W. BurgessB, R. TrethowanA, R. TokachichuA, D. GuestB
A
Plant Breeding Institute, University of Sydney, PMB 11, Camden, NSW, 2750
B
Faculty of Agriculture, Food and Natural Resources, University of Sydney, NSW, 2006
INTRODUCTION
Fusarium head blight (FHB) of wheat, caused by the fungus
Gibberella zeae (anamorph Fusarium graminearum) is a disease
that occurs sporadically in the Liverpool Plains region of
Northern NSW. The fungus is also a pathogen of maize, causing
Gibberella stalk and ear rots, and an asymptomatic endophyte of
sorghum. The pathogen survives in the residues of these hosts,
and in spring and autumn, perithecia form on these residues and
forcibly discharge ascospores into the air (1).
The potential for long distance dispersal of these ascospores has
been examined in North America (1, 2, 3), where spores have
been recovered at least 3km from the nearest inoculum source
and at 60m above the earth’s surface (2). This suggests that
where there is a significant regional source of inoculum,
localised control of infested residue through rotation or tillage
practices may not effectively reduce the risk of FHB in individual
fields (1).
While inoculum levels and potential for dispersal are
traditionally greater in North America compared to Australia,
due to more favourable climatic conditions and the greater
presence of maize within the farming system, evidence to
support longer distance dispersal has been observed in the
Liverpool Plains during 2005, when wheat crops free of inoculum
had moderate levels of FHB.
To determine the potential for long distance dispersal of
ascospores under Australian conditions, a spore trapping
experiment was established during October, 2008.
MATERIALS AND METHODS
A centre pivot irrigation field (80ha) in Spring Ridge (latitude 31°
31'2.1''S longitude 150°14'6.3''E) was identified as a source of
inoculum due to significant amounts of G. zeae perithecia on 6
month old maize residue and high levels of FHB and perithecia
on a cv. Beaufort wheat crop.
Spore traps, standing 1m in height were placed at 50m intervals
in a north easterly direction into a field 12 months fallow from
Chickpeas, to a distance of 250m from the inoculum. Traps were
also placed at 50m intervals into the wheat crop to a distance of
250m into the crop. Traps consisted of four 90mm petri dishes
containing Fusarium‐selective medium with increased rates of
antibiotics, exposed to the atmosphere from sunset to sunrise
the following morning. Exposure of the plates was timed to
follow an irrigation event to the wheat crop of equivalent to
15mm of rainfall 24 hours prior.
Plates were recovered and incubated for 3 days under
alternating light and dark conditions with temperatures at 24°C
and 22°C respectively. A random subset of the colonises were
subcultured from each plate and identified morphologically.
Spore counts were taken from each plate and used to determine
the number of G. zeae ascospores intercepted.
RESULTS
Ascospores of G. zeae were recovered at all locations and ranged
from 90 cfu per plate at 250m from the inoculum source to 750
cfu per plate within the wheat crop. The pattern of dispersal of
spores away from the source of inoculum closely fitted an
exponential curve (R2 =0.97) (Figure 1).
Figure 1. G. zeae ascospore deposition away from inoculum source. The
pattern of deposition closely follows the exponential curve y = 1.52 + 56.99 x 0.99x R2 = 0.97
DISCUSSION
The pattern of ascospore dispersal agrees with previous reports
of the incidence of disease away from an inoculum source being
described by an exponential model (3). The results also suggest
that recovery of spores at distances greater than 250m is likely.
Extrapolation of the model to 500m suggests that 4000
spores/m2 would be deposited nightly. Whether this level of
deposition is sufficient to initiate disease however is yet to be
established.
This experiment demonstrated that spore release events can be
triggered by overhead irrigation events. The timing of irrigation
events on wheat crops following maize should attempt to avoid
irrigating during anthesis, at which wheat is susceptible to
infection. Residue management may also be necessary to reduce
the risk of FHB in such situations.
ACKNOWLEDGEMENTS
The research was completed with the assistance of a GRDC
Grains Research Scholarship.
REFERENCES
1. Schmale, D.G., III, E.J. Shields, and G.C. Bergstrom, Night‐ time spore deposition of the fusarium head blight pathogen, Gibberella zeae, in rotational wheat fields. Canadian Journal
of Plant Pathology, 2006. 28(1).
2. Maldonado‐Ramirez, S.L., et al., The relative abundance of viable spores of Gibberella zeae in the planetary boundary layer suggests the role of long‐distance transport in regional epidemics of Fusarium head blight. Agricultural and Forest
Meteorology, 2005. 132(1/2): p. 20–27.
3. Paulitz, T.C., et al., A generalized two‐dimensional Gaussian model of disease foci of head blight of wheat caused by Gibberella zeae. Phytopathology, 1999. 89(1): p. 74–83.