Pathogenicity of Magnaporthe oryzae in varieties and wheat lines grown in Paraguay

Abstract

Wheat blast caused by Magnaporthe oryzae pathotype Triticum has become one of the most important crop production problems in South America. Given the availability of few sources of resistance, the identification of newer sources has become urgent. The present study was designed to evaluate the reaction of major wheat varieties grown in Paraguay to M. oryzae infection. Thirty-two wheat varieties and four advanced breeding lines were provided by the National Wheat Program of the Paraguayan Institute of Agrarian Technology. These varieties were spray inoculated with three isolates of M. oryzae using 5.10⁴ conidia mL^-1. The disease reaction was evaluated on a severity scale of 0-4, 15 days after inoculation. Data were analyzed using the Kruskal-Wallis test. Considering the median rating of infection, the materials were classified as Resistant (0-1), Moderately Resistant (1.1-2), Moderately Susceptible (2.1-3) and Susceptible (3.1-4). The variety Canindé 1 was resistant to all isolates, and CD 116 was resistant to one and moderately resistance to two isolates. All the remaining varieties were susceptible or moderately susceptible to the three isolates, showing the susceptibility of major wheat varieties grown in Paraguay, and an urgent need for widening the genetic basis of resistance to wheat blast disease in the National Wheat Breeding Program.