Resistance of Brazilian wheat cultivars to blast under controlled condition

Abstract

The first report of wheat blast in the world was in Brazil, in 1986. Since then, a great effort has been made towards the development of wheat cultivars resistant to this disease, which is caused by the fungus Pyricularia oryzae Triticum (PoT). The objective of this research was to (i) evaluate the resistance of wheat genotypes to blast and (ii) verify the correlation between disease severity on wheat spikes and sporulation rate of PoT on spike rachises. Plants of 40 cultivars grown in pots, at the flowering stage (stage 65 on the Zadoks scale), were inoculated with a suspension of conidia of a PoT isolate representative of the main variant of the fungus reported in Brazil. Severity of blast on the spikes at 5 and 7 days after inoculation (dai) and the rate of sporulation of the fungus on the rachis (conidia per g of rachis) were evaluated. Eighty percent of the cultivars that were classified in the group with the lowest sporulation rate were also classified in the group with the highest resistance at 7 dai. However, the correlation coefficients of the analysis established between the cultivar severity at 5 and 7 dai averages and the PoT sporulation rate averages were not significant (r=0.2464 and r=0.2047, respectively). Results obtained represent the updated characterization to blast of wheat cultivars in Brazil and constitute an important exploratory framework for the evaluation of the reaction of wheat genotypes based on the sporulation rate of PoT on their tissues.

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

“…Severity considers both the diseased and healthy tissues, while I summarize only the presence or absence of symptoms on a sample, regardless of the severity (Bock et al, 2021. Therefore, S can vary considerably for a specific value of I, especially for I greater than 30% in blast epidemics, as established in a previous study (dos Santos et al, 2022). Also, When evaluating the reaction of several cultivars to wheat head blast, the authors of one study observed that the cultivars with the greatest I did not always present the greatest yield losses (Dianese et al, 2021).…”

“…In some studies on the relationship between disease and yield, the resistance of the cultivar is an important source of variation in the intensity of the blast in the experiment either under natural epidemics or artificial ones. The cultivars utilized in other works show a broader classification of blast reaction (Coelho et al, 2016;Gomes et al, 2017;Maciel et al, 2022). However, in the trials conducted to generate our data, the main source of variation in wheat head blast intensity was due to varying planting dates, a fact that may have reduced any possible influence of the varietal resistance of the three cultivars evaluated in our study.…”

“…the latter being the product of the I and DHS (dos Santos et al, 2022). The relatively small value of the correlation coefficient for DHS-Y relationship may be due to the fact that DHS only takes into account the diseased heads, and not all heads as in S.…”