Understanding the Castanea spp. – Phytophthora cinnamomi pathosystem: a histopathological approach
Castanea sativa, the European chestnut, is an important forest species of great economic value. However, it is declining due to its susceptibility to Phytophthora cinnamomi, while C. crenata, the Japanese chestnut, demonstrates resistance to this aggressive pathogen that causes root rot, also known as ink disease. To face this problem, in 2006 a breeding program was initiated in Portugal based on the introgression of resistance genes from the Asian species into the European chestnut, through controlled crosses. Hybrid segregating progenies obtained were phenotyped through inoculation with the pathogen (Santos et al., 2015). Hybrids showing different levels of susceptibility to P. cinnamomi, together with the contrasting phenotypes regarding disease resistance (C. crenata; C. sativa), will be used to understand the cellular and molecular modifications induced by the pathogen. The initial steps of this study aim to clarify the pattern of infection and histological changes induced by P. cinnamomi in the susceptible (C. sativa) and resistant (C. crenata) chestnut species. The experimental procedure consisted of the inoculation of the roots of six-month-old plantlets (obtained by in vitro culture) with a P. cinnamomi zoospore suspension. Inoculated and healthy roots were collected at four time points after inoculation (3.5, 24, 48 and 72 hours after inoculation - hai) and prepared for light microscopic observations. Zoospore encystment, germination and root penetration were observed at 3.5 hai in both susceptible and resistant chestnut genotypes. The cortex of C. sativa roots were colonized by hyphae at 24 hai, proposing thin roots as a possible entry point. At more advanced stages of the infection process, the collapse of cortex cells became evident. Also, the hyphae reached the vascular system, demonstrating the high P. cinnamomi virulence. The next steps of this study will include the interspecific hybrid genotypes selected from the on-going breeding program and the histopathology results will be used to select the key time-points to collect root samples after inoculation for transcriptome analysis, in order to identify candidate genes linked with the resistance to the pathogen. This work was funded by Fundação para a Ciência e Tecnologia through the PhD grant SFRH/BD/115424/2016. References: Santos, C., Machado, H., Correia, I., Gomes, F., Gomes-Laranjo, J., and Costa, R. (2015). Phenotyping Castanea hybrids for Phytophthora cinnamomi resistance. Plant Pathology 64, 901–910.
Patrícia Fernandes won an ISHS student award for the best oral presentation at the VI International Chestnut Symposium in Turkey in October 2017.
Patrícia Fernandes, Instituto Nacional de Investigação Agrária e Veterinária I.P., Avenida da República, 2780-159 Oeiras, Portugal; Centro de Investigação das Ferrugens do Cafeeiro, Instituto Superior de Agronomia, Universidade de Lisboa, Quinta do Marquês, 2784-505 Oeiras, Portugal; Linking Landscape, Environment, Agriculture and Food (LEAF), Instituto Superior de Agronomia, Universidade de Lisboa, 1349-017 Lisboa, Portugal; PhD student at Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Avenida da República, 2780-157 Oeiras, Portugal, e-mail: firstname.lastname@example.org
The full article is available in Chronica Horticulturae