Morphoanatomy and histochemistry analyses of cassava roots do not discriminate resistant from susceptible genotypes to soft root rot

• Published in: Acta amazonica Vol. 47; no. 1
• Main Authors: Silva, Jonny Lucio Sousa, Moura, Elisa Ferreira, Ilkiu-Borges, Fernanda, Galvao, Jessivaldo Rodrigues, de Farias-Neto, Joao Tome, da Silva, Gisele Barata, Rego, Marcela Cristiane Ferreira, Cunha, Roberto Lisboa
• Format: Journal Article
• Language: Portuguese
• Published: 01-03-2017
• Subjects: Sudan
• ISSN: 0044-5967; 1809-4392
• DOI: 10.1590/1809-4392201600513

Cassava is an important culture in Brazil and in the North of the country, and soft root rot has affected root production. The aim of this work was to identify root morphoanatomic and histochemical characters associated with root rot resistance. In areas with no occurrence of the disease, nine cassava genotypes were tested, four of which were resistant, and five were susceptible to root rot. Root harvest was carried out twelve months after sowing, and thickness of suber, suber and cortex, and secondary xylem were measured. Moreover, texture, suber cell layers, lignin content, and lignin monomers content of the portion suber and cortex were analyzed. Also, histochemical tests and scanning electron microscopy (SEM) analyses of the roots were performed. Results were subjected to analysis of variance, and means were compared by the Scott-Knott test (p [< or =]0.05). The characters thickness of suber and cortex at proximal and medium portions, thickness of secondary xylem at medium and apical portions, number of cell layers of suber, thickness of suber, and root texture showed differences among genotypes; however, the characters could not be associated with resistance or susceptibility. There were no differences for: vessel elements, lignin and lignin monomers, and for the histochemical tests with Sudan IV and Lugol. Images of SEM showed differences among genotypes, which could not be associated with resistance or susceptibility. Thus, the characters evaluated cannot be used in selection for cassava resistance to soft root rot in genetic breeding programs.Original Abstract: A mandioca e uma cultura importante no Brasil e no Norte do pais, e a podridao mole da raiz tem afetado a producao. O objetivo deste trabalho foi identificar caracteres morfoanatomicos e histoquimicos da raiz associados a resistencia a podridao da raiz. Em areas sem ocorrencia da doenca, nove genotipos de mandioca foram testados, quatro resistentes e cinco suscetiveis. A colheita da raiz foi realizada doze meses apos o plantio e medidas de espessura do suber, suber e cortex e xilema secundario foram realizadas. Alem disso, foram analisados a textura, as camadas de celula do suber, o conteudo de lignina e os monomeros de lignina da porcao suber e cortex. Ainda, testes histoquimicos e microscopia eletronica de varredura (MEV) das raizes foram realizados. Os resultados foram submetidos a analise de variancia e as medias foram comparadas pelo teste de Scott-Knott (p[< or =]0.05). Os caracteres: espessura de suber e cortex nas porcoes mediana e proximal, espessura do xilema secundario nas porcoes mediana e apical, numero de camadas de celulas do suber, espessura do suber e textura da raiz apresentaram diferencas entre os genotipos, mas nao associadas a resistencia ou suscetibilidade. Nao houve diferencas para: elementos de vaso, lignina e monomeros de lignina para os testes histoquimicos com Sudan IV e Lugol. Imagens de MEV apresentaram diferencas entre os genotipos, mas nao associadas a resistencia ou suscetibilidade. Assim, os caracteres avaliados nao podem ser usados na selecao de mandioca com resistencia a podridao mole da raiz em programa de melhoramento genetico.