Parâmetros genéticos e seleção de acessos de mandioca para diferentes características agronômicas e índice de antracnose e bacteriose

Abstract

Anthracnose and bacteriosis are diseases of great importance to cassava cultivation in Brazil, being one of the main causes of production losses. There are few options of methods to control these diseases, and the use of resistant cultivars is the best alternative to reduce losses. Therefore, the objective of this work was to select materials resistant to anthracnose and bacteriosis for different agronomic characteristics, estimate the genetic parameters of these materials and verify the anthracnose and bacteriosis index. The experiment was carried out in the 2017/2018 harvest, in the municipality of Dourados, Mato Grosso do Sul. To this were used 36 cassava clones donated by Embrapa Cassava e Fruticultura. The characteristics evaluated were size, plant height (AP), total root production (PTR), shoot production (PPA), dry matter production (DMS), anthracnose index (Ant), bacteriosis index and index of survival (Surv.). The heritability in the broad sense, the phenotypic and genetic correlations between the traits and the gain with selection were estimated. There was a difference between the clones regarding the evaluated agronomic characteristics. Most of the phenotypic expression of the variables AP, PTR, PPA and MS was a function of genetic variance. The characteristic size was strongly influenced by environmental conditions in its phenotypic expressions. Heritability was high for PTR, PPA, MS and AP. According to the variation index, it was verified that the characteristics AP, Ant, MS, PTR and PPA favored the genetic improvement of the accessions. The genetic and phenotypic correlations were dependent on the analyzed characteristics. PTR was the characteristic that obtained the most selection gain compared to the others. Based on the results obtained, we concluded that the clones 2011-34- 45 and BGM-0717 stand out for commercialization, as they have high root production and lower incidence of anthracnose. Clone BGM-0080, although intermediate in root production, also showed good performance. For mechanized planting, clone BGM-0717 stands out in terms of size; 2011-34-45, with high aerial part production; and the BGM-0080, with adequate size, high production of aerial parts and dry matter. For the selection of cassava clones, in relation to agronomic characteristics and resistance to anthracnose and bacteriosis, we concluded that the genetic coefficient exerts greater influence on most of the evaluated agronomic characteristics, except for size, and heritability is expressive in the height characteristics of plant, anthracnose index, dry matter production, total root yield and shoot yield. Therefore, these characteristics must be considered when selecting materials for cultivation.