Responses of resistant and susceptible hybrid clones of Eucalyptus urophylla × Eucalyptus grandis to infection by Ceratocystis fimbriata

Abstract

& Key message A histopathological study using one resistant and one susceptible clone of Eucalyptus urophylla × Eucalyptus grandis hybrid showed that the colonization of Ceratocystis fimbriata was limited by rapid and intense host defense responses such as closure of the vessel pits; formation of tyloses and gels; accumulation of amorphous material, starch, phenolic compounds, and calcium oxalate; and tissue lignification. The defense mechanisms of the resistant clone were not lethal to the pathogen because the fungus was reisolated from the diseased tissue. & Context The use of resistant genotypes of eucalypt is widely used to control Ceratocystis wilt caused by Ceratocystis fimbriata. However, little is known regarding the fungal infection process and the host defense responses. & Aims Thus, the objectives of this study were to compare the histopathological responses of one resistant and one susceptible clone of Eucalyptus urophylla × Eucalyptus grandis to artificial inoculation with C. fimbriata and to identify possible host defense responses against fungal infection. & Methods Fungal colonization was analyzed by light and scanning electron microscopy. The host defense responses to artificial fungal inoculation were evaluated through histochemical analysis and determining of the lignin concentration and lesion lengths, whereas the pathogen viability was confirmed by reisolations. & Results Both tested clones showed similar responses against fungal infection but presented defense responses with different speeds and intensities. Fungal colonization was not restricted in the tissue of plants from the susceptible clone, whereas in the resistant clone, fungal colonization was limited to the xylem vessels and parenchyma around the vessels due to closure of the vessel pits; intense formation of tyloses and gels; accumulation of amorphous material, starch, phenolic compounds, and calcium oxalate; and tissue lignification. However, the fungus was reisolated from the inoculated tissues of both clones.

Growth and pulp production of eucalyptus trees affected by ceratocystis wilt

“…The reduction in growth that we observed was lower than that reported by Mafia et al (2013), which was 87%, likely attributed to the resistance of the clones under study and/or the aggressiveness of the pathogen genotype present in the area. Resistant genotypes manifest more intense and faster defence reactions against ceratocystis wilt than susceptible ones (Silva et al, 2020). However, due to the aggressiveness variability among different C. fimbriata s.l populations, Eucalyptus clones that behave as resistant in a given location may be susceptible to pathogen genotypes from other regions (Oliveira et al, 2015).…”

“…In response to infection by Ceratocystis, eucalyptus trees can interrupt or delay the colonization of the pathogen in the vascular tissues through the formation of tyloses, gels and amorphous compounds inside the vessels, in addition to tissue lignification and accumulation of PR-proteins and phytoalexins (Silva et al, 2020).…”

Aggressiveness and screening for host responses in yerba mate (Ilex paraguariensis) clones to a wilt disease caused by Ceratocystis fimbriata

“…Similar results were found in the kiwi culture, where all the cultivars tested were susceptible to the disease (Pimenta, 2018; Piveta, 2013). Genotypes with resistance to Ceratocystis wilt have been found and used as an efficient control measure in eucalypt (Mafia et al, 2011; Oliveira et al, 2015; Silva et al, 2020; Zauza et al, 2004) and mango (Araujo, Bispo, Cacique, Cruz, et al, 2014; Araujo et al, 2014; Piveta, 2013; Tumura et al, 2012). This shows that despite not having found clones of yerba mate resistant to the disease, continuous work and studies of selection of propagation materials with resistance to this fungus that causes many damages to several cultures in Brazil are necessary.…”

A framework for establishing a rapid ‘Ōhi‘a death resistance program

“…These types of resistance are not exclusive; it is possible for a host to express both MGR and QDR (Vigoroux and Olivier 2004;Sniezko et al 2014Sniezko et al , 2020. A common resistance mechanism in Ceratocystis pathosystems generally involves the occlusion of the pathogen within the xylem by the rapid production of tyloses, phenolic compounds, and other defense compounds, as seen in resistance responses of mango (Mangifera indica L.; Araujo et al 2014a;Araujo et al 2014b) and Eucalyptus urophylla × E. grandis hybrids (Silva et al 2020) to Ceratocystis fimbriata infection. In both cases, resistance is polygenic and thus, QDR (Rosado et al 2010;Arriel et al 2016).…”