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How many experiments are needed to characterize sunflower
cultivars for resistance against Sclerotinia
head rot under assisted inoculation?
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C.B. Troglia, F.J. Quiroz and A.R. Escande
Department of Agronomy, Unidad Integrada INTA-University of Mar del
Plata,
CC 276, 7620 Balcarce, Argentina. |
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Introduction
The characterization of sunflower cultivars
for resistance against Sclerotinia head rot (SHR) caused by
Sclerotinia sclerotiorum is highly affect by the
environment.
The assisted inoculation by spraying
ascospores, reduce part of the environmental effect. The goal of
this work is to search the amount of experiments needed to
characterize cultivar resistance. |
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Materials and Methods
Nine field experiments were carried out. Twenty
six commercial cultivars were tested. Each cultivar was tested in at
least five experiments. Heads were inoculated according to Quiroz
et al (1998). Disease incidence (DI) (diseased heads/ total heads)
was evaluated at physiological maturity. For each experiment cultivars
were separated in three groups: i) those that do not differ from the
lowest DI (Waller-Duncan, =
a
0.05), ii) those that differ from the lowest and the highest DI
and iii) those that do not differ from the highest DI (Table 1 A).
Cultivars were characterized as moderately susceptible (MS, group iii
in at least one experiment) and moderately resistant (MR, groups i or
ii through all the experiments) (Table 1 A). The same
characterization was done by using a random combination of one to
eight of these experiments (an example is shown in Table 1 B) and was
compared with that of all experiments. Percentage of coincidence (PC)
was calculated among these characterizations (Table 1 B). PC
average and standard deviation were calculated.
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Click para ampliar |
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Table 1: Sclerotinia head rot Incidence (%,
DI) in eight experiments with assisted inoculation. Experiments
without significant differences between cultivars were not
included. Green boxes: cultivars that do not differ from
the lowest DI of each experiment (Waller-Duncan,
a=0.05),
yellow boxes: cultivars that differ from the lowest
and the highest DI of each experiment and red boxes:
cultivars that do not differ from the highest DI. Characterization:
MS- moderately susceptible (red boxes in at least one
experiment), MR- moderately resistant (green or yellow
boxes through all the experiments).
A) Cultivar's characterization through all
the experiments.
B) Characterization of cultivars based on a random
combination of three experiments (An example of more than eighteen
combination tested); comparison with the characterization based on
all the experiments and percentage of coincidences. |
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Figura 1. Click para ampliar |
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Results
Percentage of coincidence (PC) increased with the
number of experiment according to a negative exponential curve (Y
= 98.91
(1-e-0,72 X); R2=0,97, P<0.0001) (Fig.1).
The PC of one experiment was 56±20 and that of
seven was 100. From four experiments on, PC was equal or higher than
92±10. | |
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Conclusion
At least four experiments with assisted
inoculation are needed to characterize sunflower cultivar resistance
against Sclerotinia head rot.
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Reference
Quiroz FJ, Pereyra VR, Escande AR 1998.
Comportamiento de cultivares de girasol frente a infecciones de
Sclerotinia sclerotiorum inducidas por pulverización de
ascosporas o por inóculo natural. III Reunión Nacional de Oleaginosas.
Bahía Blanca, Argentina. pp 35-36. | |
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13th International Sclerotinia
Workshop. Monterey, California, USA 12-16 June, 2005 |
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