Pathogenicity of isolates ofMagnaporthespp. from wheat and grasses infecting seedlings and mature wheat plants in Argentina

Abstract

Wheat blast of wheat (Triticum aestivum), caused byMagnaporthe oryzaepathotypetriticum(MoT; anamorphPyricularia oryzae) is a destructive disease in the South American countries of Brazil, Paraguay and Bolivia. In Argentina, the fungus was recently recorded on wheat and barley plants in the northeast part of the country, Buenos Aires and Corrientes Provinces, with a potential for spreading. This work aimed to study, for the first time, the morphocultural and pathogenic characteristics ofMagnaportheisolates collected from wheat and other herbaceous species in Argentina and three neighbouring countries (Paraguay, Brazil and Bolivia) and determine their aggressiveness on wheat varieties. Statistical differences among isolates, culture media, and development conditions were found for conidia colour, growth rate, size and sporulation rate. Pathogenicity tests performed on seedlings with 19 isolates ofMagnaporthespp. under greenhouse conditions showed a maximum disease severity of 55.3% and 66.7% for varietiesBIOINTA3004 and Baguette 18, respectively. Weed and grass isolates were infectious on wheat, demonstrating their potential epidemiological role on the disease. Spike disease severity was 34.6% for the host × pathogen interaction ofBIOINTA3004 × PY22. Observed symptoms included partial or total spike bleaching, and glume and rachis discolouration. The 1000‐grain weight was significantly reduced to 38.5% and 63.1% for cultivarsBIOINTA3004 and Baguette 18, respectively. The disease affected grain germination, which fell to 65.9% for seeds infected with thePYAR22 isolate. Symptoms observed in infected grains were partial spotting, grain softening, and rot symptoms with the presence of a greyish mould.