Suitability of Southern Pines, Other Selected Crops, and Nutsedge to a Longidorus sp. Associated with Stunting of Loblolly Pine Seedlings

Fraedrich, S. W., Cram. M. M.. and Handoo. Z. A. 2003. Suitabiliiy of southern pines. other selected crops. and nutsedge to a O~?~qicloru.s sp. associated with stunting of loblolly pine seedlings. Plant Dis. X7: 1129-l 132. An undescribed needle nematode (Longirlonrs sp.) has been associated with severely stunted loblolly pine seedlings at a south Georgia nursery. Containers with selected crop and weed species were infested with 100 or 200 adults and juveniles of the Lor~gido/~r.s individuals to evaluate host suitability. Nematode populations increased in containers with slash, lohlolly. and longleaf pine seedlings. The Lr~n~ido/~r.s sp. significantly reduced the dry root weights of slash (P = 0.00X) and lohlolly (P = 0.047) but not longleaf (P = 0.095) pine compared with controls. Populations of Ir,qirlonr.s decreased on nutsedge and small grains, including wheat, rye, oat, sorghum, and millet; and, in most experiments, populations decreased to levels found in fallow containers. Populations decreased on tomato and cabbage but increased slightly on red oak. The periodic removal of fields f’rom pine production to grow cover crops consisting of small grains or to maintain fallow fields may be an important practice for management of-this Lrtn~irlonrs sp. Areas of stunted and chlorotic loblolly pine (Pir7u.s foedo L.) seedlings have been periodically observed at the Flint River Nursery (Byromville, CA). An undescribed needle nematode (Longidorus sp.) has been associated with the problem and, in a controlled study, the nematode was found to damage root systems of loblolly pine (6). Root systems of seedlings affected by the disease arc greatly reduced in size and lack lateral and feeder roots, resulting in seedlings that are severely stunted. Scedling damage usually is confined to small patches when initially observed; however, in 2001, seedlings were noticeably affected by the disease over large areas of one field, rendering much of the production unharvestable. The Flint River Nursery was established in 1987 on agricultural fields that reportedly were used for the production of cabbage and other crops. The nursery currently produces a large variety of forest tree seedlings to support Georgia’s rcforestation programs. Loblolly, longleaf (p pu/u.sfris Mill.). and slash (I? clliottii Engelm. var. elliotrii) pine seedlings constitute a major portion of the yearly Publication no. D-2003-0626-02R This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2003. production. Hardwood seedlings also are produced and include numerous species of oak (QUUCUS spp.). The nursery uses a variety of small grains as cover crops when fields are not in production. Certain weed species, most notably purple and yellow nutsedge (C~~prvus ro~rtrzd~s L . a n d C . esdmtus L., respectively), can be problems in production fields if not controlled by fumigation or presowing herbicide applications. The field with the nematode problem also has been used in recent years to produce oak and other hardwood seedlings. Management of plant-parasitic nematode populations can be achieved with the rotation of host and nonhost crops if the species of nematode has a narrow host range (13). The host range of the Lore@ clonrs sp. associated with damage to loblolly pine seedlings presently is not known. This study was undertaken to determine it slash and longleaf pines arc also suitable hosts ihr the Lorl,gidonts sp., and if their root systems are susceptible to damage. We also evaluated the host suitability of small grains that typically are used as cove1 crops at the nursery, as well as oak, cabbage, tomato, and yellow and purple nutsedge. MATERIALS AND METHODS Pine species. Host suitability and susceptibility to damage by the Lorqic/or~r.s sp. was determined for slash, longleaf, and loblolly pine in two experiments. The experiments were conducted in growth chambers. In each experiment, [email protected] and noninfested treatments were established for each pine species. There were four containers (replications) for each pine species and treatment combination. Containers were 7 cm high by 10 cm wide, and the soil used in containers was a loamy sand (86% sand, 9% silt, 5% clay; pH 5.6, 1.X?% organic matter) from the Flint River nursery. Soil was microwaved in 2,000-g batches for 8 min and approximately 650 g was added to each container. Seeds were placed in 30% hydrogen peroxide for up to 60 min (I) and rinsed three times with sterile distilled water. Loblolly pine seeds then were stratified for 30 to 60 days prior to germination: slash and longleaf pine seeds were not stratified. Seeds were germinated under sterile conditions at 25°C on germination paper in clear containers (17.5 by 12.5 by 6 cm). Five germinated seeds were transplanted to containers with microwave-treated soil. The Longidoms sp. was produced on loblolly pine seedlings grown in containers at 22°C for 14 to 26 weeks, and extracted from soil using the procedure of Flegg (4) with modifications by Fraedrich and Cram (6). Nematodes were hand picked, and 100 individuals in experiment 1 or 200 individuals in experiment 2 were added to each container in the LorzRitk,rcl.s-inCestet1 treatment. Containers were placed in a growth chamber at 22°C with a 14-h photoperiod for 19 weeks in experiment 1 and 26 weeks in experiment 2. At the end of the experiments, nematodes were extracted from soil as previously described and populations of the Lon~idoms sp. were determined for each container. Roots or seedlings were removed at the root collar and dried for 4X h at XO”C, after which root dry weights were determined. The nematode reproduction factor (Rf = final population of all juveniles and adults divided by the initial population) was calculated as a measure of host suitability among the different plant treatments tested (1 1 ). Plant species with Rf values less than 1 were considered to be nonhosts or poor hosts for the Lort~idoru.r sp., and those species with RF values greater than 1 were considered to bc hosts. Statistical comparisons of the final Lor~gidoru~s populations among pine species in infested containers were conducted by an analysis of variance (ANOVA) using PROC GLM in SAS (The SAS System fat Windows, version 8.01 ; SAS Institute, Inc., Gary, NC), and Tukey’s honest significant difference (HSD) test was used Plant Disease / September 2003 1129 for mean separation. Seedling root dry weights were compared between infested and noninfested treatments within pine species by a I test (PROC TTEST, The SAS System for Windows). Nutsedge, small grains, and other selected crops. The suitability of other selected crops and weeds to the Lq~i&~r-~l.s sp. was determined in a series of four experiments. The number of hosts that could he tested within each experiment was limited by our abilities to produce, extract, and handle the Longidorus sp. In experiment I, host suitability was evaluated for yellow nutsedge and ctrltivars of wheat (Tri~icxm aesrivunz L. ‘Saluda’), rye (S~~cr/~ wretrle L. ‘Wrens Albruzzi’), and grain sorghum (.Sr~rglzl*m hicolor L. ‘Richardson 9300’). Experiment 2 was a repeat of experiment 1, with the exception that purple nutsedge was tested in place of yellow nutsedge. Northern red oak (Querms r&w L.), tomato (Lycopersicon emdmrwn Mill. ‘Rutgers’), cabbage (Rrmsicu olerucetr L. ‘Copenhagen Market Early’), and oat (Avenc7 snfivrr I,. ‘FLA 501 ‘) were evauated in experiment 3. In experiment 4, brown top millet (Panicurn rmnosun~ L. ‘DW-01’) and Sorghum-Sudan (S. hicolor ‘SC Ultra’) were evaluated. A Lon~idoru.sinfested loblolly pine treatment and a Longirlorms-infested fallow treatment were included in all experiments with the exception of experiment 3, for which a Loqi&Jrus-infested fallow treatment was not included. A noninfested loblolly pine treatment also was included in all experiments to monitor possible cross-contamination among treatments. There were four containers (replications) for each treatment in each experiment. Containers, soil, and production and extraction of the Longitr’orus sp. were as previously described. III all experiments, 100 adults and juveniles of t h e Longidorm s p . were added to containers in the infested treatments. Seeds of all species except northern red oak were germinated under sterile conditions and transplanted to containers. Loblolly pine seeds were treated, stratified, and germinated as previously described. Oak acorns were germinated in a potting medium consisting of sphagnum peat moss, vermiculite, and perlite (MIX #2; Fafard, Agawam, MA) before transplanting to containers with nursery soil. Nutsedge tubers were obtained from the Flint Rivet Nursery, washed to remove soil, and sprouted in microwave-treated soil. Plants in the threeto four-leaf stage were transplanted to containers. Five seedlings or plants were established in containers for most species, but only three seedlings were established in containers for oak because of their rapid growth and greater size. Containers were placed in a growth chamber at 22°C with a 14-h photoperiod for 12 to 14 weeks. At the end of the experiments, Longidorrrs populations were determined in containers of each treatment. The determination of Rf values and basic assessments of host suitability were determined as discussed previously for pine species. Additional conclusions regarding the suitability of individual plant species were based on statistical comparisons of final Longidorus populations among treatments within experiments. Statistical comparisons were conducted on the final Lnngifi0ru.s populations for all treatments (except noninfested loblolly pine) within each experiment by an ANOVA using the PROC GLM procedure of SAS (The SAS System for Windows), and mean separation was performed by Tukey’s HSD test. Nematode counts were transformed with the log,& + 1) transformation (IS) prior to analysis, but only nontransformed values are presented in text and tables. Table I. Initial and final Lm,qi~IOm\ populations, reproductive factor (Rf) values. and root dry weights of southern pine species I9 weeks (experiment 1) or 26 weeks (exprrimcnt 2) after infestation with Lo~gicl0rrr.s sp.?