Identificação da compatibilidade, sexualidade, fertilidade e avirulência em populações de Magnaporthe oryzae, de lavouras de arroz brasileiras
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2014-08-15
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Universidade Federal de Goiás
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Rice is a worldwide cultivated and consumed grain, playing an important role on the diet of half of the
world’s population. Several losses in production and grain quality have been reported due to biotic factors,
such as rice blast, caused by Magnaporthe oryzae, which is the major disease in rice crops. One of the most
effective ways to control this disease is the use of resistant cultivars. However, the high genetic variability
of the pathogen results in a rapid resistance loss. The discovery of highly fertile, hermaphrodites individuals
outside of the rice center of origin, suggests that sexual reproduction may contribute to this genetic
variability, which influences the appropriate control strategies. M. oryzae reproduction studies begins with
the determination of mating types, controlled by two idiomorphic genes (MAT1-1 e MAT1-2), along with
the sexuality (hermaphrodite, female or male) and fertility (number of perithecia). Another important
approach under investigation for this crop is the detection of avirulence genes from M. oryzae, to understand
the pathogen variability. Our study focused on the investigation of MAT1-1 or MAT1-2 genes, and the
presence of the avirulence gene AVR1-CO39in field isolates collected from all rice production regions from
Brazil. Sexuality and fertility were also characterized. 208 selected isolates were cultivated in PDA medium
and the fungus mycelia were used for DNA extraction and PCR detection of the above-mentioned genes.
For the sexual characterization, 106 field isolates were paired in Petri dishes containing rice bran medium
with two reference isolates: KA-3 (MAT1-1) and GUY11 (MAT1-2), known worldwide for their mating type
and high fertility. The AVR1-CO39 gene was only detected in two field isolates. One of them was able to
infect the rice cultivar CO39, which has the resistance gene Pi-CO39(t). A mutation on AVR1-CO39 gene
could impair the recognition of its effector by Pi-CO39(t) protein. Only one mating type (MAT1-2) was
observed on the 208 field isolates. It was also observed that, among the 106 analyzed isolates, one (0,94%)
was identified as a female; three (2,8%) as hermaphrodite, 62 (57,9%) as male; and 41 (38,3%) were not
determined, considered infertile. We also observed the formation of perithecia inside of rice leaves. Despite
the predominance of one mating type among rice field isolates, there is a possibility that sexual reproduction
may occur as the other idiomorphic gene (MAT1-1) is present on field isolates collected from other Poaceae.
The identification of highly fertile hermaphrodites and fertile-female individuals in this study also highlight
this possibility.
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PEIXOTO, L. F. Identificação da compatibilidade, sexualidade, fertilidade e avirulência em populações de Magnaporthe oryzae, de lavouras de arroz brasileiras. 2014. 76 f. Dissertação (Mestrado em Agronomia) - Universidade Federal de Goiás, Goiânia, 2014.