Relative Susceptibilities of Five Pine Species to Three Populations of the Pinewood Nematode

piece of sterile, absorbent cotton conDwinell, L. D. 1985. Relative susceptibilities of five pine species to three populations of the taining 4,000 nematodes was attached pinewood nematode. Plant Disease 69:440-442. with Parafilm over the wound. About 21 seedlings (seven in each of three flats) Seedlings of eastern white, loblolly, pond, slash, and Virginia pines were inoculated in a greenhouse were inoculated with each nematode at the rate of 4,000 nematodes per tree with three populations of the pinewood nematode population. Equal numbers of wounded (Bursaphelenchus xylophilus) from declining Virginia pines. Twelve weeks after inoculation, pine but uninoculated seedlings served as mortality and susceptibility rank were highest for slash pine, moderate for eastern white, loblolly, controls. The study began in and pond pines, and lowest for Virginia pine, which was highly resistant. Mortality was also cntr The and bed I significantly related to differences in virulence of nematode populations. There was a highly Dcmer 1983uand significant correlation between percent mortality and mean number of nematodes recovered from after inoculation. recently killed seedlings. The greatest number was recovered from slash pine, and successively fewer Seedlings were examined weekly, and were recovered from eastern white, loblolly, pond, and Virginia pines, recently killed seedlings were sampled for nematodes by extracting from a 25-mm Additional key words: Pinus elliottii var. elliottii, P. serotina, P. strobus, P. taeda, P. virginiana section of the stem directly below the inoculation point and another at the base of the seedling. Sections were incubated in 5 ml of water in separate test tubes for Although the impact of the pinewood Furthermore, disease occurrences in seed 24 hr. Extracted nematodes in a l-ml nematode, Bursaphelenchus xylophilus orchards may signal future problems in aliquot were counted and expressed as (Steiner & Buhrer) Nickle (= B. lignicolus pine plantations and natural forest stands the number per gram of fresh wood Mamiya & Kiyohara), on pine forests in as they become more intensively weight. At the conclusion of the study, Japan has been well documented (11), the managed. remaining seedlings were also sampled role of the nematode in mortality of pines This study wasundertaken to determine for nematodes. in the United States is still being defined the relative susceptibilities of seedlings of (14). As Malek and Appleby (10) recently five pine species to the pinewood RESULTS noted, two very different systems nematode, the pathogenic variation of The pinewood nematode caused involving B. xylophilus may be operating three nematode populations, and the significant mortality of seedlings in four in the United States. Where native pines population dynamics of the nematode in of the five pine species tested. Data for the are grown under minimal environmental inoculated pine seedlings. A preliminary three nematode populations were pooled stress, the nematode may be a secondary report has been presented (3). to calculate the percent mortality vs. time invader transmitted during oviposition