Histology of Quercus ilex roots during infection by Phytophthora cinnamomi

Abstract

Key message The speed of infection of Quercus ilex by Phytophthora cinnamomi is influenced by the method of inoculation used, and structural changes in the host do not differ depending on whether primary or secondary roots are infected. Abstract This study aimed to elucidate the infection process of the invasive pathogen Phytophthora cinnamomi on primary and secondary roots of 2-month-old Quercus ilex seedlings. To test if different methods of inoculation lead to different changes in the host caused by the pathogen, the root system of plants was either immersed into a suspension of P. cinnamomi zoospores, or placed in direct contact with agar plugs colonized by P. cinnamomi mycelium. Histology of root sections obtained every 24 h for 10 days revealed similar changes in the structure of cells and tissues of the host irrespective of the inoculation method used. However, the immersion method resulted in a delay in the colonization of the host, different aerial symptoms, and the formation of different reproductive structures of the pathogen. Emerging secondary and tertiary roots and sites where secondary or tertiary roots were about to emerge were identified as main entry points. Hyphae in the xylem tissues were more frequently found in secondary than in primary roots, but in both types of roots the phloem was the most important pathway of colonization. For the first time in the interaction between Q. ilex and P. cinnamomi, transmission electron microscopy was used to describe degradation of the host cell walls, pit penetration and extrahaustorial matrix. Haustoria development during intracellular growth and hyphal aggregations (stromata) caused no damage to the host cell walls indicating hemibiotrophic parasitism.

Regulation by biotic stress of tannins biosynthesis in Quercus ilex: Crosstalk between defoliation and Phytophthora cinnamomi infection

“…mRNA expression from genes for tannin biosynthesis was analyzed by qPCR on nucleic acids isolated after treatments by P. cinnamomi infection and/or defoliation of Q. ilex . Sampling was performed 4 days post infection, corresponding to a late stage during the biotrophic growth of the oomycete (Redondo et al ), whereas gene expression was studied in leaves, the tissue where interactions between herbivory and P. cinnamomi infection are expected to take place. Leaves of Q. ilex accumulated detectable amounts of ANR , ANS , LAR1 , SDH1 and SDH2 (but not LAR2 ) transcripts (Fig.…”

“…*P < 0.05 and **P < 0.01. treatments by P. cinnamomi infection and/or defoliation of Q. ilex. Sampling was performed 4 days post infection, corresponding to a late stage during the biotrophic growth of the oomycete (Redondo et al 2015), whereas Fig. 4.…”

Early survival of Quercus ilex subspecies from different populations after infections and co‐infections by multiple Phytophthora species

“…Causes of differential survival of seedlings depending on the Phytophthora species have not been described in Q. ilex . Variation in seedling mortality may have resulted from variation in growth of Phytophthora hyphae in host tissue (Redondo et al ., ), root necrosis, lack of water absorption capacity of infected plants following root destruction (Sghaier‐Hammami et al ., ), hormonal changes triggering a generalized dysfunction in plant water relations, or involvement of toxic metabolites (Jung et al ., ; Osswald et al ., ). In the present study, the longest tap roots and highest necrosis lengths were observed in seedlings growing in P. gonapodyides ‐infested soils.…”

“…Because seed weight affects early‐life traits of plants such as growth and resistance to pathogens (Solla et al ., ; Vivas et al ., ), this study included a morphological approach using seed weight and seed asymmetry as covariates of plant mortality. Moreover, because fine roots are important elements of plant health (Redondo et al ., ), and species of the genus Phytophthora are among the organisms that most seriously damage roots, plant performance was assessed.…”

Phytophthora cinnamomi

“…Although previously considered to be a necrotrophic pathogen, recent observations of putative P. cinnamomi haustoria within cortical and vascular tissues in a number of host plants, including Lupinus augustifolius (Fig. 5A), have suggested that P. cinnamomi can grow as a hemibiotroph (Crone et al, 2013b;Redondo et al, 2015). In Arabidopsis, the extrahaustorial membrane surrounding haustoria of the Oomycete, Hyaloperonospora arabidopsidis, contains the plasmodesmata-located protein1 (PDL1) (Caillaud et al, 2014).…”