Critical-point yield loss models based on incidence and severity of wheat head blast epidemics in the Brazilian Cerrado

Abstract

Wheat head blast (WHB), caused by the fungus Pyricularia oryzae Triticum pathotype, is one of the most damaging diseases of wheat. In Brazil, the disease has limited the expansion of wheat in the tropical regions of the Cerrado biome. In this study, wheat yield (Y) and visual estimates of WHB incidence (I) and severity (S) (assessed 25 to 30 days after flowering) were measured in a single location in the Cerrado (Minas Gerais state) where field experiments were conducted during seven sequential years (2013 to 2019) using three cultivars and 12 planting dates each year. Pearson correlation (r) analysis, used to study the association between each of the three disease variables (I, DHS = diseased-head severity and S) and Y, under a meta-analytic framework, showed the strongest association between incidence and yield (r I-Y = -0.92) and severity and yield (r S-Y = -0.90). The functional relationship between WHB intensity (I or S) and Y was studied based on the fit of a random coefficients model to I or S and the log-transformed Y data. The population average estimated intercept and slope for the I or S and log-Y relationships were 7.798 log units (2,435.7 kg/ha) and -0.020 for the I-Y and 7.721 log units (2,373.4 kg/ha) and -0.030 for the S-Y relationship. The relative yield loss when I or S reaches 10% was predicted at 18.4% and 26.1% yield loss, respectively. This study provides a basis for understanding and predicting yield losses due to wheat blast based on the visual assessment of two disease measures at a single time during the epidemics.

Weather-based logistic regression models for predicting wheat head blast epidemics

“…In the second source, field experiments were set up to examine the impact of wheat head blast on wheat yields at a single location (Patos de Minas, MG, Brazil) from 2013 to 2019. The latter experiments were originally planned to investigate the effect of planting date on disease intensity and their data were used and made available in a previous study on yield loss due to wheat head blast (Dos Santos et al 2022a). In addition, three Brazilian spring wheat cultivars, all susceptible to wheat head blast, namely BRS 264, BRS 404, and MGS Brilhante, were utilized.…”

“…Incidence variable was binarized as either outbreak when incidence was equal or greater than 20% incidence or non-outbreak otherwise. The 20% threshold was defined based on our previous yield loss studies (Dos Santos et al 2022a) and the median value of its distribution. Out of the 143 epidemics, 65 were classified as a non-outbreak and 78 were classified as outbreak (Table 1).…”

“…In the Brazilian Cerrado, where the disease is more common, yield losses due to wheat head blast have been reported to range from 62.8 to 80.1% (Coelho et al, 2016). Further experiments in that region have shown that when the incidence (percent of heads diseased) or severity (percent of the wheat head area affected) reached 25%, relative losses in the yield were estimated at 39.8% and 52.8% respectively (Dos Santos et al 2022a).…”

PyriculariaPopulations are Mostly Host-Specialized with Limited Reciprocal Cross-Infection Between Wheat and Endemic Grasses in Minas Gerais, Brazil

“…In fact, leaf blast sporadically occurs in Brazilian wheat fields when warm and wet weather during the early season might favor infection and inoculum build-up on young leaves (Cruz et al 2015). The first detailed report of yield losses due to wheat blast was estimated at around 27% in Brazil (Goulart et al 1990), but greater losses, nearing 100%, have also been reported (Coelho et al 2016;Dianese et al 2021;Santos et al 2022;Goulart and Paiva, 2000;Trindade et al 2006). In the first major epidemics in Bangladesh, in 2016, the disease caused losses in more than 15,000 ha, which resulted in complete destruction of some affected fields (Islam et al 2016;Malaker et al 2016).…”

Weather-based logistic regression models for predicting the risk of wheat blast epidemics

“…In such conditions, and if control measures (e.g. fungicide sprays) are not utilized, the disease can severely reduce crop yield by more than 80% (Coelho et al, 2016;Dos Santos et al, 2022a).…”