Genetic Improvement and Crop Management Strategies to Minimize Yield Losses in Warm Non‐traditional Wheat Growing Areas due to Spot Blotch Pathogen Cochliobolus sativus

Abstract

Spot blotch caused by Cochliobolus sativus emerged as a major threat to wheat production in the warmer nontraditional wheat growing areas in the late 1980s. This foliar disease causes significant yield losses annually (15-20% on average in South Asia) endangering the livelihoods of millions of small farmers. Effective measures in the field are needed to mitigate the impact of spot blotch on food security in affected areas. This review summarizes the global knowledge on genetic improvement and crop management strategies to minimize yield losses based on latest field research. Recent studies have shown that spot blotch severity is highly influenced by stress factors affecting crop physiology which in turn affects host tolerance and resistance to the pathogen. Soil nutrient and water stress aggravate spot blotch-induced grain yield losses. Heat stress which is gradually increasing in Asia causes higher levels of disease damage. Genetic improvement is the cornerstone of a sustainable control of spot blotch in all affected regions. Resistance is essentially based on Chinese and South American sources and inter-specific crosses with broadly adapted semi-dwarf germplasm. A list of genotypes consistently reported in the last 10 years to harbor at least partial resistance to spot blotch, along with their inheritance of resistance, has been compiled to help breeding programmes. As the fungus is aggressive under conditions of high relative humidity and heat which in turn influences plant susceptibility, a synthesis of the different tools for scoring disease severity is given. Because resistance is incomplete, the ultimate goal is the accumulation of minor genes of resistance in adapted high yielding genotypes. This paper shows how the use of resistant varieties, timely seeding, adequate fertilization, crop rotation, and the judicious use of fungicides can be part of an integrated management strategy for controlling yield losses due to spot blotch.

Assessing Effects of Climatic Change, Region and Agronomic Practices on Leaf Spotting of Bread and Durum Wheat in the Western Canadian Prairies, from 2001 to 2012

“…For each climate cell, the average temperature and total precipitation for each month is determined. To determine the climate characteristics for each field sample site, the samples were overlain on to the gridded climate cells in ArcMap 10.1 (ESRI, 2013). A buffer of 10 km around each sample site was used to find the nearest climate cells resulting in a minimum of two and a maximum of four climate cells found for each sample site.…”

“…In Manitoba, Gilbert et al (1998) reported that the isolation frequency of this pathogen was positively correlated with temperature, being higher in years with high minimum temperatures (warm nights). In regions where this pathogen is more prevalent than in the western Prairies, Acharya et al (2011) and Duveiller and Sharma (2009) reported that the development and severity of C. sativus infections are related, among other factors, to high temperatures and relative humidity favoring long duration (>12 h) of leaf wetness.…”

Crops that feed the world 10. Past successes and future challenges to the role played by wheat in global food security

“…Among foliar leaf pathogens affecting food security in developing countries, spot blotch caused by Cochliobolus sativus is of major importance in warm wheat growing areas of South Asia and in particular the eastern Gangetic plains where millions of resource-poor farmers grow wheat after rice and can face up to 15 % yield reduction (Duveiller and Sharma 2009). This chronic wheat disease is exacerbated by abiotic stresses and typically affects marginal farmers who are less able to sow crops in a timely manner or apply adequate level of fertilizer.…”

Characterization of Wheat and Barley Entries for Foliar Blight Resistance

“…In Gangetic plains of India, it is the major biotic constraint in wheat production where ricewheat cropping systems were adopted . Besides, the extensive use of conservation tillage practices may possibly be favourable for the higher intensity of spot blotch incidence in the South East Asia (Duveiller and Sharma, 2009). The yield losses of 27 to 56.6 per cent during 1998-99 were reported in North Eastern and North Western Plains of India due to the leaf blight (Satvinder et al, 2002) and 6.3 to 50.6 per cent of yield losses have been reported due to foliar blight influenced by cultivars and agro climatic zones (Singh et al, 2004).…”

“…The yield losses of 27 to 56.6 per cent during 1998-99 were reported in North Eastern and North Western Plains of India due to the leaf blight (Satvinder et al, 2002) and 6.3 to 50.6 per cent of yield losses have been reported due to foliar blight influenced by cultivars and agro climatic zones (Singh et al, 2004). The most economical and effective strategy to manage the disease is planting of resistant cultivars (Duveiller 2004;Duveiller and Sharma 2009;Sharma et al, 2007).…”