Pyricularia blast - a threat to wheat cultivation

Abstract

Wheat blast disease caused by Pyricularia grisea (telemorph Magnaporthe grisea) has become a serious restriction on increasing the area and production of the crop, especially in the tropical parts of the Southern Cone Region of South America. First identified in 1985 in the State of Paraná in Brazil, it has become an endemic disease in the low lying Santa Cruz region of Bolivia, south and south-eastern Paraguay, and central and southern Brazil in recent years. Severe infections have also been observed in the summer planted wheat crop in north-eastern Argentina. So far, only sporadic infections have been seen in Uruguay, especially during the wet and warm years. Spike infection (often confused with Fusarium head blight infection) is the most notable symptom of the disease and capable of causing over 40% production losses. However, under severe infection, the loss of production can be almost complete in susceptible varieties. Wheat blast is mainly a spike disease but can also produce lesions on all the above ground parts of the plant under certain conditions. Depending upon the point of the infection on the rachis, the disease can kill the spike partially or fully. The infected portion of the spike dries out without producing any grain which can be visibly distinguished from the healthy portion. While virulence diversity in the fungus has been reported in the literature and is under further exploration, genetic resistance in the host species has been more difficult to identify. Earlier, Brazilian cultivars such as BH 1146, CNT 8, several IAC and OCEPAR selections were credited as demonstrating different levels of field resistance, but this was not confirmed under artificial inoculation studies. However, other cultivars such as BR18, IPR 85, CD 113, have shown moderate levels of resistance over the years in many locations. Recently, several cultivars and advanced lines derived from the CIMMYT line, Milan, have been observed to carry a high level of resistance to blast disease throughout the endemic region. However, to date, the genetic basis of this resistance is not very clear due to extreme variation in the pathogen. Cultivars showing complete resistance against a few isolates under controlled conditions in the glasshouse, may or may not show field resistance in commercial cultivation. Due to an increase of the area under Milan based resistant wheat cultivars in Bolivia, Brazil and Paraguay, it needs to be combined with other sources of resistance urgently to prevent the selection of a virulent pathotype in the fungus. Besides genetic resistance, avoidance of early dates of seeding and chemical control can reduce the disease severity. Fungicides combining triazols with strobilurins can, under some situations, be effective in disease control at the heading stage. Even when all components of integrated disease management of wheat blast are not in place yet, it is seen as an essential strategy to reduce production losses in this region. Given the threat that the blast disease may pose to world wheat growin...

Wheat Blast- A New Challenge to Wheat Cultivation in South Asia

“…The wet years; warm temperatures and high humidity were found associated with wheat blast epidemics (Kohli et al, 2011). The rains for several days and average temperatures ranging from 18-25°C during flowering, followed by sunny, hot, humid days is favourable for the epidemic of the wheat blast.…”

Cytological aspects of incompatible and compatible interactions between rice, wheat and the blast pathogen Pyricularia oryzae

“…Rice (Oryza sativa L.) and wheat (Triticum aestivum L.) are the most important staple crops produced worldwide (Kohli et al, 2011;Talbot, 2003). The fungus Magnaporthe oryzae (asexual phase Pyricularia oryzae) is the causal agent of blast disease on gramineous plants and poses a threat to world food security (Kohli et al, 2011;Talbot, 2003;Tosa et al, 2006;Valent and Chumley, 1991).…”

“…The fungus Magnaporthe oryzae (asexual phase Pyricularia oryzae) is the causal agent of blast disease on gramineous plants and poses a threat to world food security (Kohli et al, 2011;Talbot, 2003;Tosa et al, 2006;Valent and Chumley, 1991).…”

Wheat blast research: Status and imperatives

“…Ever since its first report, blast pathogen was variously named by researchers for example, Pyricularia oryzae Oliveira et al, 2015;Cruz et al, 2015a;Silva et al, 2015), Pyricularia grisea (Filha et al, 2011;Kohli et al, 2011;Rocha et al, 2014), Magnaporthe grisea (Urashima and Kato, 1994;Peng et al, 2011;Pagani et al, 2014) and M. oryzae Triticum (Cruz et al, 2015a). Blast pathogen has shown capability to evolve fast to adapt to new climates.…”

“…First detected in Brazil in 1985, wheat blast soon spread to other neighbouring countries like Bolivia, Paraguay (Kohli et al, 2011) and was detected in Argentina in 2012 (Perello et al, 2015). The blast causing fungal pathogen M. oryzae can spread through seed and can also survive on crop residues.…”