Plant pathogenic Magnaporthales in Australia, with particular reference to Pyricularia oryzae on wild and cultivated rice

Abstract

The Magnaporthales is an order of fungi that contains plant pathogens and saprobes. This order consists of three families, Pyriculariaceae, Magnaporthaceae and Ophioceraceae, which are phylogenetically, morphologically and ecologically distinct. To date, about 200 species have been described in Magnaporthales, of which approximately 50% are plant pathogens. Some species are important pathogens of grasses and cereals such as the rice blast fungus Pyricularia oryzae (syn. Magnaporthe oryzae) and the take-all pathogen of cereals Gaeumannomyces graminis. The study of classification and identification of Magnaporthales in Australia and pathogenicity of Pyricularia oryzae are reported in this thesis.The genus Pyricularia comprises species that cause blast diseases on various hosts, especially grasses (Poaceae) that include crops such as rice, wheat, barley and grasses. This study used morphology, phylogenetic concordance, ecology and pathogenicity, to study Pyricularia and allied genera in the Magnaporthales. The fungi associated with blast diseases on eleven monocot hosts in Australia were identified by morphological characters and DNA sequence analysis in Chapter 2. Three species of Pyricularia, namely, Pyricularia angulata, Pyricularia pennisetigena and Pyricularia oryzae, were confirmed as present in Australia.Another species, Pyricularia rabaulensis was found to belong to a recently established genus Barretomyces. A formal transfer of this fungus to Barretomyces has been proposed.In Chapter 3, the phylogenetic relationships of some other Australian Magnaporthe-like fungi were investigated based on morphology and DNA sequence analysis of multiple genes. The root pathogenic fungi of Cynodon dactylon and Agrostis stolonifera as well as holotype specimens of Magnaporthe garrettii and Magnaporthe griffinii were examined. Two novel genera, Budhanggurabania and Wongia, were described as well as a new species, Magnaporthiopsis agrostidis.Rice (Oryza sativa L., Poaceae) is the most important cereal crop globally and a primary source of starch for more than half the world's population. The major constrain to rice production worldwide is rice blast disease, which is caused by the fungus Pyricularia oryzae Cavara (syn. Magnaporthe oryzae Hebert). Rice blast disease is a problem in over 85 countries in all continents where rice is cultivated in both paddy and upland situations.Unpredictable epidemics can cause significant economic losses.

Rice Blast, A Major Threat to the Rice Production and its Various Management Techniques

“…Generally, horizontal and vertical resistance is used in developing disease resistant cultivars (Rijal & Devkota, 2020). Due to the high genetic variability of the fungus, resistance to infection by Pyricularia oryzae can be short-lived (Khemmuk, 2017). The breakdown of resistance to Pyricularia oryzae results from evolution of genetic variants (races) in the pathogen populations (Liu et al, 2011).…”

“…Therefore, emphasis must be taken to minimize, mitigate and control the infestation of blast disease worldwide so that global food security can be ensured. For this, different available management techniques should be followed and also many strategies should be developed in accordance with the time as the pathogen shows variable behavior according to the environmental conditions (Khemmuk, 2017). In this limelight, a brief information about the blast disease is presented along with its various management practices to minimize its infestation so that global rice production can be increased and the global food security can be ensured.…”