Regulation of defence responses in avocado roots infected with Phytophthora cinnamomi (Rands)

Abstract

Phytophthora cinnamomi occurs worldwide and has a host range in excess of 1,000 plant species. Avocados (Persea americana Mill) have been described as highly susceptible to this soilborne pathogen. Here, the regulation of defence responses in avocado root seedlings inoculated with P. cinnamomi mycelia is described. A burst of reactive oxygen species (ROS) was observed 4 days after inoculation. The higher physiological concentration of H 2 O 2 induced by P. cinnamomi on avocado roots had no effect on in vitro growth of the oomycete. Total phenols and epicathecin content showed a significant decrease, but lignin and pyocianidins exhibited no changes after inoculation. Also, increased nitric oxide (NO) production was observed 72 h after treatment. We studied the effects of one NO donor [sodium nitroprusside (SNP)], and one NO scavenger [2-to 4-carboxyphenyl-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide (CPTIO)] to determine the role of NO during root colonisation by P. cinnamomi mycelia.Pretreatment of the roots with CPTIO, but not with SNP, inhibited root colonisation suggesting an important role for NO production during the avocado-P. cinnamomi interaction. Our data suggest that although defence responses are activated in avocado roots in response to P. cinnamomi infection, these are not sufficient to avoid pathogen invasion.

Induction of defence responses by cinnamomins against Phytophthora cinnamomi in Quercus suber and Quercus ilex subs. rotundifolia

“…In this study, POD activity was found to be higher in infected plants in comparison with the healthy ones. Similar results were observed on POD activity in avocado roots infected with P. cinnamomi (García-Pineda et al 2010). In cork oak roots the increase in enzyme activity start to be significant from 24 hpi when compared with controls, coincident with one peak of H2O2 production.…”

“…The production of ROS in these interactions can debilitate the host tissue at early stages of infection and, consequently enhance growth and development of the pathogen. In fact, P. cinnamomi is a hemi-biotroph pathogen that can also colonize dead tissue and could therefore benefit from such a host defence response and higher ROS accumulation as demonstrated in the interaction of avocado roots and P. cinnamomi ( García-Pineda et al 2010). In addition, other studies have shown that higher ROS accumulation results in greater susceptibility to necrotrophic fungi infection, whereas a reduced ROS level confers higher disease resistance (van Kan 2006).…”

Hydrogen peroxide scavenging mechanisms are components of Medicago truncatula partial resistance to Aphanomyces euteiches

“…The concentration 300 μM was found by García-Pineda et al (2010) in avocado roots inoculated with the oomycete Phytophthora cinnamomi at 4 dpi. In order to know the limit of tolerance of A. euteiches to H 2 O 2 , the concentration of 20 mM was tested, which was reported to partially inhibit the in vitro growth of P. cinnamomi (García-Pineda et al 2010) and totally inhibit the in vitro growth of the fungal pathogen Botrytis cinerea (Schouten et al 2002). Plates were inoculated with plugs of agar containing 15-day old mycelium of A. euteiches with the mycelium facing down and incubated at 24°C in darkness.…”

Interaction of Extracellular Proteinases of Phytophthora cinnamomi with Proteinase Inhibitors Produced by Avocado Root

“…In a previous work, we characterized the symptoms in avocado plants infected with P. cinnamomi [14] and based on these symptoms, plant responses were assayed up to 4 days after infection. An increase in inhibitory activity was observed in root tissue after 4 days of infection (35%) (Figure 1).…”

“…Avocado inhibitor had no effect on in vitro growth of the oomycete, suggesting that the inhibition of root colonization could be due to its interaction with pathogen proteinases. [14]. A burst of reactive oxygen species (ROS) was observed.…”