Hot spots for diversity of Magnaporthe oryzae physiological races in irrigated rice fields in Brazil

Justino José Dias Neto,Paulo Hideo Nakano Rangel,Gil Rodrigues Dos Santos,Marcio Elias Ferreira,Liamar Maria Dos Anjos

doi:10.1590/s0100-204x2010000300004

Justino José Dias Neto, Paulo Hideo Nakano Rangel + Show 3 more

Open Access

https://doi.org/10.1590/s0100-204x2010000300004

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Abstract

The objective of this work was to evaluate the Magnaporthe oryzae pathotype diversity in new commercial irrigated rice fields in the Araguaia River Valley, state of Tocantins, Brazil. The causal agent of rice blast has heavily affected rice production in the region. Despite the efforts of breeding programs, blast resistance breakdown has been recorded shortly after the release of new resistant cultivars developed for the region. Among the causes of resistance breakage is the capacity of the fungus to rapidly develop new pathotypes. A sample of 479 M. oryzae monosporic isolates was obtained and tested using the international rice blast differential set. Isolate collections were made in small areas designed as trap nurseries and in scattered sites in their vicinity. Analysis of 250 M. oryzae isolates from three trap nurseries indicated the presence of 45 international M. oryzae races belonging to seven pathotype groups (IA-IG). In the isolates tested, 61 M. oryzae pathotypes belonging to all but the IH group were detected. The new areas of irrigated rice in the Araguaia River Valley have the highest diversity of M. oryzae pathotypes reported so far in Brazil.

Highlights

Irrigated rice accounts for approximately 70% of the rice produced in Brazil
Two blast traps were located in Formoso do Araguaia (FA‐1 and FA‐2, approximately 20 km apart) and one in Lagoa da Confusão (LC, approximately 110 km from FA‐1 and FA‐2), each surrounded by extensive commercial rice fields
A total of 479 M. oryzae monosporic isolates were obtained from new areas of irrigated rice production located in the Araguaia River Valley, state of Tocantins, Central Brazil

Summary

Introduction

Irrigated rice accounts for approximately 70% of the rice produced in Brazil. New commercial irrigated rice fields have been installed in the last 25 years in the Araguaia River Valley, state of Tocantins, Central Brazil, and blast disease is the most important problem for rice production in the area.The blast‐causing fungus Pyricularia grisea (Cooke) Sacc., an anamorph of Magnaporthe oryzae (Hebert) Barr is a yield‐limiting factor for irrigated and upland rice. Irrigated rice accounts for approximately 70% of the rice produced in Brazil. New commercial irrigated rice fields have been installed in the last 25 years in the Araguaia River Valley, state of Tocantins, Central Brazil, and blast disease is the most important problem for rice production in the area. The blast‐causing fungus Pyricularia grisea (Cooke) Sacc., an anamorph of Magnaporthe oryzae (Hebert) Barr is a yield‐limiting factor for irrigated and upland rice. Fungicide control of rice blast is not cost effective. Breeding programs for blast resistance have developed numerous resistant cultivars. Due to break of resistance, the useful lifespan of commercial cultivars has been short in blast‐prone areas.

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