In Brazil, more efficient methods are a necessity for evaluating blast severity on spikes in the breeding programs of rye, triticale, wheat, and barley. The objective of this work was to determine the feasibility of assessing blast severity based on the analysis of digital images of symptomatic rye and triticale spikes. Triticale and rye genotypes were grown to anthesis in pots and were then inoculated with a mixture of Magnaporthe oryzae isolates. Blast severity on the spikes was evaluated visually and after that the spikes were detached and photographed. Blast severity was determined using the program ImageJ to analyze the obtained images. Two methods of image analysis were used: selection of symptomatic areas using a mouse cursor (SCU) and selection of symptomatic areas using image segmentation (SIS). The SCU method was considered the standard reference method for determining the true value of blast severity on spikes. An analysis of variance did not determine any difference among the evaluation methods. The coefficient of determination (R2) obtained from a linear regression analysis between the variables SIS and SCU was 0.615. The obtained data indicate that the evaluation of blast severity on spikes based on image segmentation is feasible and reliable. 1. Introduction Blast disease, caused by Magnaporthe oryzae B. Couch (anamorph. Pyricularia oryzae Cavara), is a major constraint to food production in the world, affecting crops of high agricultural importance, such as rice. Since the mid-1980s, blast has also constituted one of the most serious problems for wheat crops in South America, especially in Brazil, Bolivia, and Paraguay. In Brazil, among the crops known as “winter cereals,” the problem transcends wheat fields, affecting triticale and rye. Despite being relatively minor crops in terms of occupied area, these crops suffer significantly from blast. The first observation of the disease in rye fields was in 1995, in Paraná State [1]. It was observed in triticale in the same year, in experiments conducted at Embrapa Cerrados, Planaltina, DF [2]. In general, blast is as difficult to control in these two crops as it is in wheat. The adoption of management practices such as crop rotation, balanced fertilization, and fungicide application on the aerial parts of the plants is not enough to prevent blast damage, especially in seasons of severe epidemics. A contributing factor to the significant blast damage that is observed in Brazilian fields is the susceptibility of available rye and triticale cultivars. This situation demonstrates that the
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