Pinewood nematode population growth in relation to pine phloem chemical composition

Abstract

The pinewood nematode, Bursaphelenchus xylophilus, native to North America (NA), is now a major invasive pine pest in Eurasia. Pine species differ greatly in their susceptibility to B. xylophilus, and differences in susceptibility might be related to differences in phytochemistry. This study addressed two major questions: (i) which plant chemical profiles (including compounds that act as plant defences and those important for nutrition) favour pinewood nematode development; and (ii) are NA and Portuguese pinewood nematodes different in their capacity to subsist on plant tissues? For this, B. xylophilus isolates from NA and Portugal were tested on pine phloem and xylem of different pine species. It was found that unaltered pine phloem can sustain the population growth of B. xylophilus, but only in a few cases, and this was clearly related to distinct chemical profiles in some pine species. No evidence was found of evolutionary divergence between B. xylophilus populations in Portugal and NA. The pine species with phloem on which pinewood nematodes could grow tended to have low levels of total phenols, condensed tannins, flavonoids and lignin. Evidence was also found that nutrients such as N may be important.

Resistencia de Pinus pinaster Ait. al marchitamiento del pino causado por Bursaphelenchus xylophilus (Steiner & Burher), Nickle

“…Niveles de significación: *** p < 0,001; ** p < 0,01; * p < 0,05; a p < 0,10 rece relacionarse con una mayor tolerancia; mientras que altos niveles de compuestos liposolubles y bajos niveles de manganeso con una menor tolerancia a NMP. La mayor parte de los estudios relacionan el mayor contenido de polifenoles y taninos condensados con una mayor resistencia o tolerancia (Nunes da Silva et al, 2015;Pimentel et al, 2016Pimentel et al, , 2017; sin embargo, un estudio muestra una mayor migración de nematodos en ramas con un mayor contenido en polifenoles totales (Zas et al, 2015). Otro de los caracteres que parece tener relación con la susceptibilidad es el contenido en resina, la cual constituye la principal defensa de las coníferas frente a agresiones externas, ya sean causadas por patógenos o por factores abióticos (Phillips and Croteau, 1999).…”

A Phytochemical Perspective on Plant Defense Against Nematodes

“…xylophilus was cultured on the phloem sap of eight pine species, its growth rate was negatively correlated to the concentration of condensed tannins in the sap of each species (Pimentel et al, 2017). However, negative correlations were also observed between nematode growth rate and total flavonoid concentration as well as total phenolic compound concentration.…”

“…However, negative correlations were also observed between nematode growth rate and total flavonoid concentration as well as total phenolic compound concentration. This makes it difficult to assess the relative contribution of condensed tannins, flavonoids, and other phenolic metabolites to the inhibitory effect on B. xylophilus (Pimentel et al, 2017).…”

Sublethal infection of different pine species by the pinewood nematode

“…xylophilus is that its life cycle includes a pathogenic phytophagous phase and a saprophytic mycetophagous phase, which sets it apart from most other plant‐parasitic nematodes (Espada et al ., 2016). The passage through both stages is not required for the pathogen to complete the life cycle (Pimentel et al ., 2017b). Theoretically, B .…”

“…xylophilus is widespread and common in a wide climatic range of native pine forests of North America that are not obviously affected with PWD (Wingfield et al ., 1984; Giblin‐Davis et al ., 2003; Pimentel et al ., 2014). It could be hypothesized that invasive populations of pinewood nematode in Eurasia are more virulent than North American populations because they have been selected for increased capacity to feed directly on plant tissues due to the abundance of susceptible hosts (see Pimentel et al ., 2017b).…”