Multi-environment assessment of fungicide performance for managing wheat head blast (WHB) in Brazil and Bolivia

Abstract

This study aimed to evaluate the performance of fungicides against wheat head blast (WHB) under various environments and to determine scenarios best suited for fungicide applications. Field experiments were conducted at 23 environments in Brazil and Bolivia from 2012 to 2015. Data from all trials within the same country were combined for estimating mean WHB control efficacy and yield benefits from using a set of fungicides. Experiments were classified, based on disease index in the check treatment, as having low (CDI = 10), moderate (CDI = 40), and high (CDI = 70) disease pressure and this variable was tested as a covariate in the model. In Brazil, greater disease reduction and yield increase, in trials with moderate to high disease pressure, were obtained when using mancozeb-based fungicides, but with yield gains below 1276 kg/ha. In Bolivia, all fungicides reduced the disease at moderate to high disease pressure, but specific QoI + DMI premixes led to higher yield gains averaging 1834 kg/ha. Based on the evidence provided, we concluded that current WHB chemical strategies could have radically different results depending on country and disease pressure. Although WHB chemical control can be effective even under environmental conditions that favor the disease, integrated management strategies should be explored. Our results are useful for aiding decisions on fungicide application and identifying priorities for future research.

Genome‐wide association reveals limited benefits of pyramiding the 1B and 1D loci with the 2NvS translocation for wheat blast control

“…No significant SNPs identified in this study were common between the MoT isolates, suggesting that the resistance might be isolate specific, which is in agreement with previous studies (Cruppe et al., 2020; Cruz et al., 2016). In fact, we only identified significant SNPs using MoT isolate T‐25, which could be explained by (a) the resistance identified using the older and less aggressive MoT isolate T‐25, was already overcome by the newer and more aggressive MoT isolates (i.e., B‐71); and/or (b) the lower number of wheat genotypes tested with isolate B‐71 has limited the discovery of significant associations.…”

“…Despite more than 30 yr of intensive efforts investigating wheat genetic resistance to MoT, reliable resistance resources are still scarce (Cruppe et al. 2020; Cruz & Valent, 2017; Cruz et al., 2016). Several wheat genotypes were identified as resistant to specific races of MoT (Cruppe et al., 2020; Cruz et al., 2016); however, the majority of the reported resistance is based on the same source, the 2N V S translocation (Cruz et al., 2016).…”

“…Thus, the genetic mechanism behind the 2N V S‐based WSB resistance trait remains unknown. Based on field and controlled environment experiments, the 2N V S‐based varieties exhibit characteristics of both qualitative (i.e., complete resistance controlled by a single gene or a few genes with large effects) and quantitative (i.e., incomplete resistance controlled by multiple genes of small effects) resistance (Cruppe et al., 2020; Cruz et al., 2012, 2016). Qualitative resistance, such as that conferred by NBS‐LRR genes, is often known for its large effects and usually provides a strong selection pressure on the pathogen, leading to the pathogen's rapid evolution and consequent resistance breakdown (Poland, Balint‐Kurti, Wisser, Pratt, & Nelson, 2009).…”

“…The hypersensitive‐like response in 2N v S‐based varieties often begins as small dark flecks, which remain as small random spots or grow into larger coalescing lesions depending on the level of resistance. Second, the 2N v S‐based resistant varieties often show strong isolate × cultivar interactions, which are generally associated with qualitative resistance (Cruz et al., 2016; Maciel et al., 2014). Specifically, experiments with near‐isogenic lines (NILs; i.e., with vs. without the 2N v S translocation) demonstrated that not all the NILs carrying the 2N V S translocation had a significant reduction in WSB when tested against newer and more aggressive MoT isolates, suggesting that the genetic background may influence levels of 2N V S resistance (Cruz et al., 2016).…”

Genome-wide association mapping for wheat blast resistance in CIMMYT’s international screening nurseries evaluated in Bolivia and Bangladesh

“…Management of wheat blast using fungicides is possible, but has been reported to be elusive, because of the inefficiency of fungicides in offering complete control under high disease pressure, the resistance in MoT populations to some classes of fungicides, and the high cost of the fungicides that cannot be afforded by resource-poor farmers 4 , 6 , 9 , 26 – 28 . While other potential blast control measures including altering the sowing time 5 , 29 , suspending the cultivation of wheat in disease-prone areas and declaring a ‘wheat holiday’ will help to mitigate the disease spread to some extent, the development and deployment of wheat varieties with genetic resistance to blast has been resorted to as the most sustainable and farmer-friendly approach 4 , 30 , 31 .…”