Alteration of physiological parameters of Austrocedrus chilensis by the pathogen Phytophthora austrocedrae

Abstract

The effect of the pathogen Phytophthora austrocedrae on tree physiology of Austrocedrus chilensis in Patagonia was studied in a 4‐week study. In the first week, stem‐inoculated saplings showed a significant decrease in photosynthesis (A) without alteration of stomatal conductance (gs) or stem‐specific hydraulic conductivity (Ks). From the second week on, progressive decreases in A, gs and Ks were observed, concomitantly with development of significant stem lesions. Water use efficiency (WUE) increased in the second week and declined progressively from the third week. Hyphae and resinous materials were observed in tracheids and rays below lesions. Necrosis of parenchyma ray cells and blockage of tracheids torus were observed. Healthy xylem showed no resinous materials or tracheid blockage, but abundant starch in rays, which was absent in altered xylem. The culture filtrate (CF) of the pathogen was shown to induce changes in extracellular pH and conductivity, and increased necrosis in tissues of leaves and stem challenged with CF in vitro. Similar results were obtained in leaf tissues of the inoculated saplings in vivo. CF injection into xylem of saplings induced a decline in A and disturbance of leaf tissue integrity, without altering gs, WUE or Ks. The decrease of A correlated with changes in tissue integrity. A possible mechanism of A. chilensis decline induced by P. austrocedrae is discussed.

Sex-related difference in susceptibility to cypress mortality in Austrocedrus chilensis from Northwestern Patagonia (Argentina)

“…Conside ring that growth has relatively low priority for resource allocation within trees (Waring and Pitman 1985) data su ggest that trees affected by extreme drought events were those of the higher vigor. In other words these results do not support a contrary sequential hypothesis, namely that P. austrocedrae infected and weakened trees before drought events (Vélez et al 2012). In addition, only the 44 % of the symptomatic trees from matched-pairs showed lesions of P. austrocedrae at root collar (El Mujtar 2009) and both sexes were similarly affected (9 females, 9 males and 4 trees without reproductive structures).…”

Phytophthora austrocedrae emerges as a serious threat to juniper (Juniperus communis) in Britain

“…Lesions found on live infected J. communis were a bright orange‐brown (cinnamon) colour whereas on recently killed trees all phloem was dull brown and desiccated in appearance, making it difficult to identify a lesion margin. On A. chilensis , hyphae of P. austrocedrae also invade the xylem ray parenchyma and fibre tracheids below phloem lesions, blocking water transport and thus contributing to foliage decline (Vélez et al ., ). Xylem infection of J. communis was not investigated in this study but should be examined in a more detailed analysis of individual infected trees in which the roots are excavated further to confirm the origin and extent of infection relative to crown symptoms.…”

“…Following an in‐depth study of the impact of P. austrocedrae on the physiological status of A. chilensis , Vélez et al . () suspected the involvement of effectors such as elicitins and toxins secreted by the pathogen ahead of the infection front. Whether such a mechanism is responsible for the yellowing of otherwise healthy phloem in infected J. communis needs to be clarified.…”

Changes in leaf gas exchange and chlorophyll a fluorescence on soybean plants supplied with silicon and infected by Cercospora sojina

“…Some studies reported that lower A values on plants infected by pathogens are intrinsically linked to their lifestyle (Alves et al., ; Bassanezi et al., ; Berger et al., ; Luque, Cohen, Savé, Biel, & Álvarez, ; Resende et al., ; Vélez, Silva, Troncoso, & Greslebin, ). In the present study, the negative effect of C. sojina infection on A values from plants from cultivar Conquista was governed chiefly by a reduction in the g s values.…”