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

Abstract

Wheat blast of wheat (Triticum aestivum), caused by Magnaporthe oryzae pathotype triticum (MoT; anamorph Pyricularia 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 of Magnaporthe isolates 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 of Magnaporthe spp. under greenhouse conditions showed a maximum disease severity of 55.3% and 66.7% for varieties BIOINTA 3004 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 of BIOINTA 3004 × 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 cultivars BIOINTA 3004 and Baguette 18, respectively. The disease affected grain germination, which fell to 65.9% for seeds infected with the PYAR22 isolate. Symptoms observed in infected grains were partial spotting, grain softening, and rot symptoms with the presence of a greyish mould.

Suitable methods for isolation, culture, storage and identification of wheat blast fungus Magnaporthe oryzae Triticum pathotype

“…There was no significant difference in the size of MoT conidia among the isolates tested. Furthermore, the size of conidia we isolated in Bangladesh was very similar with that from infected wheat fields of Brazil and Argentina (Castroagudin et al 2016;Perelló et al 2017). All of our isolates showed almost similar cultural and morphological characters indicating that the isolates probably originated from a single clade.…”

“…5236381.v1) also revealed that they belong to the same clonal type. Perelló et al (2017) reported that the growth of M. oryzae Triticum fungus was favored by temperatures ranging from 25 to 30°C in laboratory conditions. It has also been reported that the minimum and maximum temperatures required for the infection of wheat by MoT were 10°C and 32°C, respectively (Cardoso et al 2008).…”

“…The influence of several factors such as media composition, temperature, and pH of the medium on conidia production of M. oryzae isolates has been reported (Landraud et al 2013;Perelló et al 2017). However, the effect of incubation time on the conidia production rate of MoT has not been studied yet.…”

“…The MoT isolates were reported exhibiting cultural variabilities on different media (Castroagudin et al 2016;Perelló et al 2017), and the characteristic features commonly include concentric ring, abundant white aerial mycelia, dark centre with gray sporulation (Castroagudin et al 2016). Conidia are pyriform, hyaline with two septation, 25-30 μm long and 8-10 μm wide that arise from simple, short, erect conidiophore.…”

“…Several factors influence the rate of conidia production of M oryzae isolates in laboratory conditions. Among them, the influence of light duration and media composition are well documented (Lee et al 2006;Perelló et al 2017). Nevertheless, the effect of incubation period on MoT isolates needs further investigation to maximize conidia production.…”