Effect of Watering Regime on Disease Development in Pinus sylvestris Seedlings Inoculated with Bursaphelenchus vallesianus and B. mucronatus

Abstract

Several Bursaphelenchus spp. have been detected in declining pine trees in Europe during intensive monitoring for the pine wood nematode B. xylophilus. We investigated the pathogenicity of B. vallesianus and B. mucronatus, isolated from declining Scots pine (Pinus sylvestris) forests in Valais (Switzerland), in relation to drought stress. Four isolates of B. vallesianus and two isolates of B. mucronatus were inoculated into 3-year-old P. sylvestris trees, which were subjected to different watering treatments (50, 100, 150, and 250 ml of water per pot, biweekly). Disease symptoms, plant mortality, nematode population density, and nematode distribution in dead plants were assessed. Both Bursaphelenchus spp. proved highly pathogenic to the seedlings and watering treatment affected disease development in the inoculated pine trees. With decreasing water supply, we observed faster disease progress and higher pine mortality for both Bursaphelenchus spp. The overall mortality 70 days after inoculation was 60, 92, 95, and 100% for B. vallesianus and 40, 95, 100, and 100% for B. mucronatus in the 250-, 150-, 100-, and 50-ml watering treatments, respectively. Both nematode species multiplied in the inoculated plants; however, B. mucronatus had higher population densities than B. vallesianus in all watering treatments (on average, 33,159 versus 14,702 nematodes/dead plant compared with the initial inoculum density of 6,000 nematodes/plant). The highest nematode density was found in the lower part of the stem. About 7 to 16% of the nematodes were extracted from the roots. This study demonstrated that B. vallesianus has a pathogenicity potential comparable with that of B. mucronatus and provided experimental evidence that drought stress can result in increased symptoms caused by either Bursaphelenchus sp.

Comparative molecular analysis ofBursaphelenchus vallesianus, a wood‐inhabiting nematode isolated from declining pine trees in theCzechRepublic

“…More recently, a pathogenic potential of B. vallesianus was also observed in greenhouse conditions, where 2-year-old seedlings of three different pine species, Pinus nigra, P. brutia and P. pinea, were experimentally inoculated (Dayi & Akbulut, 2012). These findings supported the theory that overall mechanisms causing PWD are shared by all pathogenic Bursaphelenchus species, including B. vallesianus (Polomski & Rigling, 2010). Therefore, further investigations on B. vallesianus are needed to get broader insights into its biology, possible pathogenicity and evolutionary history, and thus to better understand its role in PWD development.…”

“…In contrast, involvement of a few other Bursaphelenchus species, for example B. mucronatus and B. sexdentati, in PWD development remains unclear. However, recent controlled experimental inoculations in greenhouse conditions showed that these species also possess a pathogenic potential (Polomski & Rigling, 2010;Dayi & Akbulut, 2012). Therefore, because of the detection of B. xylophilus in Europe, strategic programmes have been applied to monitor the distribution of Bursaphelenchus spp.…”

“…Involvement of B. vallesianus in PWD is poorly understood. However, recent bioassays showed that experimental inoculation of 3-yearold P. sylvestris trees led to similar, if not identical, external and internal symptoms that are caused by B. xylophilus (Polomski & Rigling, 2010). More recently, a pathogenic potential of B. vallesianus was also observed in greenhouse conditions, where 2-year-old seedlings of three different pine species, Pinus nigra, P. brutia and P. pinea, were experimentally inoculated (Dayi & Akbulut, 2012).…”

Comparison of pathogenic potential of Bursaphelenchus species on conifer seedlings between greenhouse and outdoor conditions

“…mucronatus, B. sexdentati, B. leoni Baujard, B . h e l l e n i c u s S k a r m o u t s o s , B r a a s c h a n d Michalopoulou, B. vallesianus were also tested by using different tree species (Caroppo et al 2000;Polomski & Rigling 2010;Skarmoutsos & MichalopoulosSkarmoutsos 2000;Tomminen 1993). In these studies, the most pathogenic species reported was B. xylophilus followed by B. mucronatus.…”

“…The mean number of reisolated nematodes from seedlings kept under greenhouse conditions was higher than that under outdoor conditions. Due to similarities between B. xylophilus and B. mucronatus in terms of morphology and biology, there are several reports indicating pathogenic potential of B. mucronatus with different ranges of mortality (Akbulut et al 2007b;Caroppo et al 2000;Kulinich et al 1994;Polomski & Rigling 2010). Caroppo et al (2000) used four different Bursaphelenchus species and their different isolates in a pathogenicity study.…”