Susceptibility and Response of Pines to Sirex noctilio

Abstract

Sirex noctilio uses an unusual, two-component approach to kill pine trees and provide a source of nutrition for its developing larvae. A substantial amount of research was undertaken in the 1960s and 1970s to examine the mechanisms by which these two components -a mucus produced in the woodwasp acid -(venom) gland, and a pathogenic fungus, Amylostereum areolatum , both of which are introduced into trees during oviposition -contribute to the death of trees. This chapter reviews the effects that the woodwasp mucus was shown to have when introduced to trees in the absence of the fungus, including resinosis, premature senescence and abscission of needles, and collapse of parenchymal cells with consequent loss of photosynthate translocation, as well as changes in respiration, and reduced growth rates. The effects seen in trees that were artifi cially inoculated with A. areolatum, including increased ethylene production and the induction of polyphenol biosynthesis, are also reviewed. Also discussed are the roles played by tree health and environmental stresses in determining overall susceptibility of host trees to attack by S. noctilio . These past observations are placed within the context of our current understanding of plant defense responses to attack by insects and pathogens, and a number of promising areas for future research are highlighted. (Madden 1974 ) . During oviposition, S. noctilio inoculates the host tree with a symbiotic fungal pathogen, Amylostereum areolatum (Fr.) Boidon , that not only kills the tree, but is also the primary food source for developing wasp larvae (Talbot 1977 , Chap. 2 ). Along with the fungus, the wasp also injects a socalled 'mucus' that affects tree responses and assists the fungus in establishing a productive infection (Coutts 1969b, c ) . Thus, we must dissect the recognition and response mechanisms of all three organisms if we are to fully understand the infection process. IntroductionSirex noctilio is not typically considered a signifi cant threat to trees in its native range where the forest species have evolved in concert with this pest, and attacks are usually limited to suppressed and dying trees (Borchert et al. 2007a ;Ciesla 2003 ;Gauld et al. 1990 ) . Woodwasps in the Siricidae family, including Sirex spp., are successful on conifers generally, but S. noctilio shows a marked preference for pines and is the only Siricid in its native range that attacks living trees (Spradbery and Kirk 1981 ) . In its native range (Europe, Turkey, and North Africa) primary host species include Turkish ( Pinus brutia Ten.), Canary Island ( P. canariensis Smith), Aleppo ( P. halapensis Mill.), Austrian ( P. nigra Arn.), maritime ( P. pinaster Ait.), stone ( P. pinea L.), and Scots pines ( P. sylvestris L.) (Spradbery and Kirk 1978 ) . However, where Sirex populations have become established in the Southern Hemisphere, they have proven a devastating problem for commercial pine plantations (Chaps. 13 -18 ). These commercial forests are frequently planted with North American specie...

Noctilisin, a Venom Glycopeptide of <I>Sirex noctilio</I> (Hymenoptera: Siricidae), Causes Needle Wilt and Defense Gene Responses in Pines

“…The activity contained in each fraction was measured by dosing individual shoot tips from sensitive Pinus radiata D. Don plants maintained in a growth chamber with a 50- μ l aliquot of the water suspension followed by 24-h incubation. Procedures for RNA extraction, cDNA synthesis, and qRT-PCR quantitation were described previously (Bordeaux et al 2012). Briefly, 5 μ l of 0.5 μ M primer pair, 5 μ l of 0.5 μ M cDNA template, and 10 μ l of SybrGreen 2× Supermix (Bio-Rad, Hercules, CA) were mixed, and the 20 μ l reactions were run on an iCycler thermal cycler (Bio-Rad, Hercules, CA) using the following program: 95°C for 3 min, 40 cycles at 95°C for 30 s, 65°C for 45 s, and 78°C for 20 s, followed by 95°C for 1 min, and 55°C for 1 min.…”

“…One of the most notable of these was the wilting of needles when venom-alone was applied to cut stems or bore holes in the tree trunk. A heat-stable, water-soluble fraction from S. noctilio venom was subsequently shown to induce the same responses (Wong and Crowden 1976, Bordeaux and Dean 2012). However, venom alone was not lethal to treated trees, and mortality was only seen when trees were inoculated with both the venom and the fungus (Coutts 1969a).…”

“…Xylem mobility of a factor causing needle wilt suggested a small, water-soluble molecule, and stability to boiling temperatures or autoclaving was taken as evidence against the factor being an enzyme or large polypeptide (Coutts 1970, Wong and Crowden 1976). However, sensitivity to protease digestion (Bordeaux et al 2012) suggested that the active factor might be a bio-active peptide, particularly as many such molecules have been found in other hymenopteran venoms (Vetter et al 2011). Quantitative real-time–polymerase chain reaction (qRT-PCR) assays that measured induction of pine pathogenesis-related protein (PR4) and thaumatin-like protein (TLP) gene expression in response to the heat-stable activity (Bordeaux et al 2012) were used to follow the wilt-inducing factor during venom fractionation.…”

“…However, sensitivity to protease digestion (Bordeaux et al 2012) suggested that the active factor might be a bio-active peptide, particularly as many such molecules have been found in other hymenopteran venoms (Vetter et al 2011). Quantitative real-time–polymerase chain reaction (qRT-PCR) assays that measured induction of pine pathogenesis-related protein (PR4) and thaumatin-like protein (TLP) gene expression in response to the heat-stable activity (Bordeaux et al 2012) were used to follow the wilt-inducing factor during venom fractionation. Purification and characterization of the active factor are described here.…”

SirexWoodwasp: A Model for Evolving Management Paradigms of Invasive Forest Pests

“…noctilio is a secondary pest that attacks only stressed or dying trees (4,12,68,106). Managing stress is thus important in efforts to manage Sirex (20,31,71).…”