Abstract
Wheat blast caused by Magnaporthe oryzae pv. Triticum is an upcoming threat to wheat cultivation worldwide. The disease crossing over to wheat first gained attention in South America, with increasing interest coming from its more recent appearance in the big wheat-growing areas of Asia. The increasing economic relevance of the disease and the lack of genetic resistance in current wheat breeding material, besides fungicide resistance already present in fungal pathogen populations, highlighted the need to evaluate the potential of isotianil as an alternative plant protection measure. Isotianil is already registered in Asia for the protection of rice against M. oryzae, but because the agronomic practices and disease development of blast differ between rice and wheat, the efficacy of isotianil against wheat blast was hard to predict. Testing isotianil in the currently available formulations, applied either as seed treatment or soil drench, resulted in a significant reduction of disease severity. The efficacy was comparably high, on different wheat cultivars and using several fungal isolates with different degrees of virulence. Microscopic analyses revealed that isotianil treatment can prevent invasive growth of the pathogen. No phytotoxicity from isotianil treatment was observed on wheat plants. Importantly, isotianil not only protects wheat plants at the seedling stage but also on spikes thereby preventing losses due to this most severe disease syndrome. In summary, the results showed the high potential of isotianil to protect against wheat blast.
Highlights
Soon after humans began to cultivate plants, devastating plant pathogens emerged, hanging over the heads of farmers like the sword of Damocles
Seed treatment was made prior to sowing using two different concentrations of isotianil which equals 10 or 50 g a.i. per dt seed as suggested by the supplier (IST 10 and IST 50, Fig. 1 and Online Resource 1). Plants derived from these seeds and plants from untreated seeds which served as control (UTC) were inoculated with fungal conidia 17 days after sowing, on the third fully expanded leaf
Disease severity was scored 1 week after inoculation by quantification of the diseased leaf area using digital imaging. Both the area and length of disease symptoms caused by M. oryzae pathotype Triticum (MoT) on inoculated leaves of isotianil-treated plants were significantly reduced compared to untreated control plants (Online Resource 1a)
Summary
Soon after humans began to cultivate plants, devastating plant pathogens emerged, hanging over the heads of farmers like the sword of Damocles. A particular example adding to the above-mentioned scenarios is the occurrence of wheat blast, a disease caused by a specific lineage of the Magnaporthe species complex (Gladieux et al 2018). This group is best known because of Magnaporthe oryzae, a pathogen of rice causing dramatic yield losses of about $66 billion annually, equivalent to the amount needed to feed 60 million people (Pennisi 2010). Wheat blast was first observed in South America in 1985 and spread throughout the whole continent reaching Bolivia in 1996 and Argentina in 2012 (Cruz and Valent 2017).
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