Phenotypic virulence analysis of Pyricularia grisea isolates from Brazilian upland rice cultivars

Abstract

_ Phenotypic virulence analysis was made on population of Pyricularia grisea isolates collected from 10 upland cultivars in three distinct rice breeding sites, with the objective of studying the degree of similarity in the phenotypic virulence among the isolates, the composition of races, and their virulence pattern. Sixteen races were identified based on the reaction type on eight standard international differentials, the predominant ones being IB-9 and IB-41. The virulence frequency was high on IAC 47 and IAC 165 among medium and early maturing cultivars, respectively. The frequency of isolates virulent was greater on upland rice cultivars (51.1%) than on irrigated rice cultivars (21.8%). Both virulent and avirulent isolates were present in the population of P. grisea to the known genes in the near isogenic lines. Of 72 test isolates, 94.4% were virulent for genes Pi-3 and Pi-4a. The virulence frequencies were relatively lower in decreasing order on Pi-1, Pi-4b and Pi-2. The coefficient of similarity ranged from 0.28 to 1.0 among the isolates pertaining to different races, while within the race IB-9, it varied from 0.56 to 1.0. Considering the coefficient of similarity of 0.81, 72% of isolates of race IB-9 exhibited similar pattern of virulence.Index terms: pathotype, Oryza sativa, Magnaporthe grisea, physiologic races, pathogenicity. Análise fenotípica da virulência dos isolados de Pyricularia grisea, coletados em cultivares de arroz de terras altasResumo _ Foi conduzido um estudo de virulência fenotípica da população de Pyricularia grisea, coletada de 10 cultivares de arroz de terras altas, em três locais distintos, objetivando determinar o grau de similaridade entre virulência fenotípica de isolados, a composição de raças fisiológicas e seu padrão de virulência nas cultivares de arroz. Identificaram-se 16 raças, com base no tipo de reação nas oito diferenciadoras internacionais, das quais IB-9 e IB-41 foram as predominantes. A freqüência de virulência foi alta nas cultivares IAC 47 e IAC 165 entre as de ciclo médio e precoce, respectivamente. A freqüência dos isolados virulentos nas cultivares de terras altas foi maior (51,1%) do que nas cultivares irrigadas (21,8%). Ambos os isolados virulentos e avirulentos às linhas isogênicas estavam presentes na população de P. grisea testada. Dos 72 isolados estudados, 94,4% foram virulentos aos genes Pi-3 e Pi-4a. A freqüência de virulência foi relativamente baixa, em ordem decrescente, em Pi-1, Pi-4b e Pi-2. O coeficiente de similaridade variou de 0,28 a 1,0 entre as diferentes raças dos isolados. O coeficiente de similaridade entre os isolados pertencentes ao grupo IB-9 variou de 0,56 a 1,0. Considerando o coeficiente de similaridade de 0,81, 72% dos isolados IB-9 apresentaram o mesmo padrão de virulência.Termos para indexação: patótipo, Oryza sativa, Magnaporthe grisea, raça fisiológica, patogenicidade.

Indução de resistência à brusone em folhas de arroz por isolado avirulento de Magnaporthe oryzae

“…Os isolados indutores foram pulverizados nas concentrações de 0 (água), 10 5 , 3x10 5 e 6x10 5 conídios.mL -1 , e nos períodos de 24, 48 e 72 horas que antecederam a inoculação com o isolado virulento, que foi inoculado na concentração 3x10 5 conidíos.mL -1 , conforme metodologia descrita por Filippi & Prabhu (2001).…”

Virulence and rep-PCR analysis of Pyricularia grisea isolates from two Brazilian upland rice cultivars

“…Maravilha were identified as pathotypes IB-41 and IB-9 (Prabhu et al, 2003). The predominance of the pathotypes IB-9 and IB-41 among isolates of Maravilha was also encountered among isolates of P. grisea retrieved from other upland rice cultivars (Filippi & Prabhu, 2001). The pathotype IC-1 was encountered at a high frequency only among isolates of cv.…”

“…The Mycelial growth, sporulation on culture medium and inoculation procedure were adapted as described earlier (Filippi & Prabhu, 2001). Leaf blast reactions were assessed as compatible and incompatible, seven to nine days after inoculation.…”

“…Barr] is the major yield constraint in upland rice in Brazil. It is widely recognized that when a cultivar with moderate resistance is extensively grown, pathotypes matching their resistance genes will increase in frequency resulting in greater susceptibility (Filippi & Prabhu, 2001). The susceptibility of the widely grown upland rice cultivars Maravilha and Primavera has increased since their release, and currently the grain yield losses are considered significant.…”

Potential for using crude extract of Sarocladium oryzae for suppression of rice blast

“…The solution was sprayed at twenty oneday old plants. One hour after spraying, the plants were inoculated with a M. oryzae conidial suspension (3 × 10 5 conidia.mL -1 ) of isolate CNPAF Py 435 as described by Filippi & Prabhu (2001). After inoculation, the plants were incubated in a humid chamber for 24 hours and transferred to greenhouse benches at temperatures varying from 27ºC to 30ºC and under high humidity until disease evaluation.…”