Abstract
Among the most produced cereals worldwide, sorghum (Sorghum bicolor (L.) Moench), presents low productivity in Brazil, mainly due to the occurrence of diseases, with a prominence of sooty stripe, caused by the fungus Ramulispora sorghi, until then considered a secondary disease, has increased its incidence and severity, especially in conditions of high humidity and temperature. The most efficient means of control is the use of resistant cultivars, in this sense, studies on the genetic variability of the fungus through molecular markers are of great importance for the breeding programs of sorghum. The objective of this work was to evaluate the genetic variability in isolates of Ramulispora sorghi belonging to the mycoteca of the Laboratory of Genetic Resources & Biotechnology of the Universidade do Estado de Mato Grosso, campus of Cáceres, via molecular markers of the ISSR type. The results indicate the existence of genetic variability among the isolates of R. sorghi. The Polymorphic Information Content (PIC) showed that the primers were classified as medium informational with an average value of 0.27. 71 polymorphic fragments were formed considering the 40 isolates of R. sorghi, which presented the value of k = 2, represent the differentiation of the isolates into two distinct clusters. The genetic dissimilarity measures were estimated by the Coefficient of Nei and Li, where the combination between the isolates B107/16 (15) and B103/15 (16) obtained the smallest magnitude (0,12) and the combinations between isolates B111/16 (2) and S114/15 (33), S316/15 (3) and S114/15 (33), B115/16 (4) and S114/15 (33), B118/16 (6) and S114/15 (33) were more dissimilar (1,00). The “UPGMA” method provided a breakdown of the 40 isolates into 4 distinct groups. The Cophenetic Correlaction Coefficient (CCC) presented significant value with r = 0,84. The Tocher’s optimization method allowed the 40 isolates to be distributed in 10 different groups. These results provide relevant information on the genetic variability among the 40 isolates of R. sorghi analyzed. In addition, they indicate that fungus have a wide genetic diversity, and have been recurring in different regions of Brazil and the world, and thus, larger studies become essential for more effective control measures.
Highlights
The sorghum (Sorghum bicolor (L.) Moench) occupies a prominent position as to its importance among the most consumed/produced cereals in the world, together with wheat, maize, rice and barley (FAO, 2019; Nida et al, 2019)
The results obtained through the genetic analysis of the isolates of R. sorghi showed the existence of genetic variability in the collected isolates
The values obtained by the analysis of the Polimorphic Information Content (PIC) showed that the primers used in the study revealed the existence of genetic variability among the isolates, classified as medium information with an average value of 0.27
Summary
The sorghum (Sorghum bicolor (L.) Moench) occupies a prominent position as to its importance among the most consumed/produced cereals in the world, together with wheat, maize, rice and barley (FAO, 2019; Nida et al, 2019). Brazilian productivity is still considered low, mainly due to occurrences of diseases, among them the sooty stripe of sorghum, caused by the fungus Ramulispora sorghi (Ellis & Everh.) Olive and Lefebvre (1946) (Ribas et al, 2008; Cota et al, 2013; CONAB, 2019). The sooty stripe is a disease whose etiological agent is the fungus Ramulispora sorghi that causes necrotic foliar lesions, promoting the reduction of the photosynthetic area and, reducing the productive capacity of the plant (Williams et al, 1978; Bandyopadhyay, 2000; Ferreira et al, 2007; Brady et al, 2011; Little et al, 2018). In the Brazilian scenario, the occurrence of the sooty stripe of sorghum has increased mainly in succession crops to summer crops and where high temperature and humidity conditions are present during the crop cycle (Ferreira et al, 2007). Susceptible cultivars may present low productivity due to the appearance of the fungus R. sorghi (Little et al, 2018)
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