Validation and use of a qPCR protocol to quantify the spread of Ralstonia solanacearum in susceptible and resistant eucalypt plants

Abstract

Bacterial wilt caused by Ralstonia solanacearum is a serious disease of eucalypt in humid and high temperature areas worldwide. Spreading of the bacterium in the field or to other nurseries occurs mainly by symptomless infected plant material. The use of pathogen‐free propagating material as well as planting of resistant genotypes are currently the only strategies used for disease control. Therefore, a reliable and sensitive method for detection of low titres of R. solanacearum in infected plant tissue is essential for the success of management programmes. In this work, we adapted an efficient intercalating dye‐based real‐time PCR protocol to detect the bacterium in symptomless eucalypt plants as well as to investigate its movement in eucalypt clones CLR172 and CLR371, which exhibit resistant and susceptible phenotypes, respectively. We found that the bacterium translocates acropetally and basipetally in inoculated but symptomless cuttings of the resistant clone, as in cuttings of the susceptible clone displaying symptoms. Nevertheless, a smaller concentration of bacterial DNA was detected in tissues of the resistant clone. Mature biofilms occluding the xylem vessels were present in the susceptible clone whereas only single cells or small aggregates were observed in the resistant clone. This work contributes to improve our knowledge of the colonization process of R. solanacearum in eucalypt clones with different levels of susceptibility and to understand how the defence mechanisms against bacterial wilt in Eucalyptus work. Our findings could aid in the selection of the most resistant eucalypt clones to be used in wilt disease management programmes.

Sobrevivência e herança da resistência a Erwinia psidii em eucalipto

“…Uma segunda hipótese, seria uma movimentação ativa mediada por estruturas especializadas. Por Ralstonia solanaceraum agente causal da murcha bacteriana do eucalipto, que coloniza vasos do xilema formando biofilme em genótipo susceptível e apresenta movimentação bidirecional no caule através do tecido vascular(Freitas et al 2021).Quando inoculada na parte aérea (gemas axilares) foi possível observar sintomas típicos de infecção por E. psidii como necrose arroxeada na nervura central, cancro no caule, morte do ponteiro apical, perca da dominância e superbrotamento/envassouramento. No entanto, quando inoculada via sistema radicular nenhum sintoma foi observado na parte aérea, o que corrobora com resultados anteriores observados(Montoya-Estrada et al 2019a).…”