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Montoya, Ma*.,
Troglia, C.a, Escande, A.a
aDept. of Agronomy, Unidad Integrada
Balcarce INTA University of Mar del Plata,
CC 276 (7620),
Balcarce, Argentina. *Corresponding author:
mmontoya@balcarce.inta.gov.ar |
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Click para ampliar |
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Materials and Methods
A small set of genotypes (10) differing in their
reaction to SSR in preliminary tests were included in field and
greenhouse trials at Balcarce (Argentina). PGA plugs, brown rice and
wheat kernels were used as inoculum supports. Sclerotia formed on
soybean plants in the previous season and preserved at 4°C were used
to obtain the mycelium on PGA. Brown rice and wheat kernels were
autoclaved in glass bottles before inoculation with PGA plugs,
incubated and shaked daily. The improved technique involves a unit of
the mentioned mycelium-colonized support placed on a little piece of
moistened cotton and attached with a tape onto a flower of the main
stem of R2-R3
soybean plants. Sprinkler irrigation was provided in all trials after
inoculation. The lesion length on the main stem (LLMS, in cm) and wilt
severity (WS, scale of Kolkman and Kelly, 2000) were registered.
Disease incidence (DI, in %) was calculated for two field trials.
Evaluations were made since the third or seventh day after inoculation
(dai) and repeated three times every three to seven days. |
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Figura 1. Click para ampliar
Figura 2. Click para ampliar
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Results
Regardless of the inoculum support, effectivity
for reproducing the disease has been proved both in field and
greenhouse experiments (no escape: all cultivars got diseased).
Phenotypic differences (0.06 > p > 0.0003) were detected for LLMS (two
field trials), WS (two field and one greenhouse trials) and DI (two
field trials) between 2003 and 2005 (Fig
1). Brown rice method was better than two other inoculations
using ascospores on blossoming plants (fig
1a). In a greenhouse trial (fig
1b), the same method detected significant differences among
cultivars in WS 22 dai, but earlier evaluation dates seemed necesary
for LLMS. This was proved in 2003-2004 field trials (evaluations at 3,
6 and 9 dai; PGA plugs) (fig 1c).
Wheat kernels worked better as inoculum support (fig
1d). Moreover, expected reaction from most cultivars was
confirmed in the field experiments.
Discussion and Conclusions
All these techniques differ from others
previously described in that mycelial inoculum is put onto the flower
with no wounding of plant tissues. Evaluation of disease must be done
soon after inoculation (since the third day), otherwise differences
could go undetectable later for some variables. Wheat kernels resulted
even better than brown rice and PGA plugs (fig 2).
They are a rich nutrient source; grains keep as a
whole after autoclaving and shaking for homogenization; assembling of
the inoculum device (tape, cotton and kernel) is friendly; mycelium
accumulates inside the crease, which makes visualization and selection
of the best kernels easier and quicker. More replications,
environments and genotypes must be tested and complementation with
other inoculation methods made, in order to test the wheat kernel
method. However, this technique promises more suitable than others for
screening soybean germplasm with partial resistance to SSR.
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