Abstracts of Selected Papers Relating to Plant-Parasitic Nematodes

Smiley, R.W., K. Merrifield, L.-M. Patterson, R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2004. Nematodes in dryland field crops in the semiarid Pacific Northwest USA.  Journal of Nematology 36:54-68.

ABSTRACT   

Soils and roots of field crops in low-rainfall regions of the Pacific Northwest were surveyed for populations of plant-parasitic and non-plant-parasitic nematodes. Lesion nematodes (Pratylenchus species) were recovered from 123 of 130 non-irrigated and 18 of 18 irrigated fields. Pratylenchus neglectus was more prevalent than P. thornei but mixed populations were common. Population densities in soil were affected by crop frequency and rotation but not by tillage or soil type (P<0.05). Many fields (25%) cropped more frequently than 2 of 4 years had potentially damaging populations of lesion nematodes. Pratylenchus neglectus density in winter wheat roots was inversely correlated with grain yield (R2 = 0.64, P = 0.002), providing the first field-derived evidence that Pratylenchus is economically important in Pacific Northwest dryland field crops. Stunt nematodes (Tylenchorhynchus clarus and Geocenamus brevidens) were detected in 35% of fields and were occasionally present in high numbers. Few fields were infested with pin (Paratylenchus species) and root-knot (Meloidogyne naasi and M. chitwoodi) nematodes. Nematodes detected previously, but not during this survey included cereal cyst (Heterodera avenae), dagger (Xiphinema species), and root-gall (Subanguina radicicola) nematodes.

Smiley, R.W., R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2005. Pratylenchus thornei associated with reduced wheat yield in Oregon. Journal of Nematology 37:45-54.

ABSTRACT   

Pratylenchus thornei reaches high population densities in non-irrigated annual cropping systems in low-rainfall regions of the Pacific Northwest. Two spring wheat varieties with different levels of tolerance and susceptibility to P. thornei were treated or not treated with aldicarb in three experiments. Grain yield was inversely correlated (P< 0.05) with pre-plant populations of P. thornei in soil and with P. thornei density in mature roots. As population of P. thornei increased, yield of the moderately tolerant/moderately susceptible variety Krichauff was generally more stable than for the intolerant/susceptible variety Machete. The reproductive factor (Pf/Pi) was generally lower (P < 0.05) for Krichauff than Machete. Aldicarb improved wheat yield (P < 0.05) in highly infested fields by an average of 67% for Krichauff and 113% for Machete. Aldicarb increased (P < 0.05) numbers of headed tillers, plant height, and grain test weight and kernel weight, and reduced (P < 0.05) the density of P. thornei in mature wheat roots, variability in height of heads, and leaf canopy temperature. Aldicarb did not improve yield in a soil with a low population of P. thornei. This is the first report that P. thornei causes economic damage to wheat in the Pacific Northwest.

Smiley, R.W., R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2005. Suppression of wheat growth and yield by Pratylenchus neglectus in the Pacific Northwest. Plant Disease 89: 958-968.

ABSTRACT   

Many wheat fields planted annually in the Pacific Northwest are infested by high numbers of the lesion nematode, Pratylenchus neglectus. Spring wheat cultivars varying in tolerance and resistance to P. neglectus were treated or not treated with aldicarb to examine relationships between the nematode and growth and yield of annual direct-seeded (no-till) wheat. Increasing initial density of P. neglectus in soil was more strongly associated with declining growth and yield of intolerant (Machete and Spear) than moderately tolerant (Frame and Krichauff) cultivars. Yield suppression by P. neglectus was generally 8 to 36% for intolerant cultivars, but reached 71% in soil also harboring Heterodera avenae, Rhizoctonia solani AG-8, and Gaeumannomyces graminis var. graminis. Intolerant cultivars had lower yields than Krichauff in rainfed but not irrigated experiments. Density of P. neglectus in mature roots was lower for moderately resistant Krichauff than susceptible Machete and Spear in two experiments. Aldicarb improved yields in irrigated but not rainfed experiments, and generally increased plant height and reduced variability in tiller height, canopy temperature, and density of P. neglectus in roots. This is the first report of damage to wheat by P. neglectus in the Pacific Northwest. Breeding wheat for tolerance and resistance is suggested.

Smiley, R.W., J.A. Gourlie, R.G. Whittaker, S.A. Easley, and K.K. Kidwell. 2004. Economic impact of Hessian fly (Diptera: Cecidomyiidae) on spring wheat in Oregon and additive yield losses with Fusarium crown rot and lesion nematode. Journal of Economic Entomology 97:397-408.

ABSTRACT   

Damage caused by Hessian fly, Mayetiola destructor (Say), was quantified in spring wheat, Triticum aestivum L., trials near Pendleton and Moro, OR, during 2001 and 2002. Five field experiments were established to examine genetic resistance to Fusarium crown rot, Fusarium pseudograminearum (O'Donnell & Aoki), and economic damage by lesion nematodes, Pratylenchus neglectus ((Rensch, 1924) Filipjev Schuurmanns & Stekhoven, 1941) and P. thornei (Sher & Allen, 1941). Hessian fly became the dominant factor affecting grain yield in four experiments. Genotypes carrying the H3-resistance gene had grain yields 66% and 68% higher than susceptible genotypes in cultivar trials during 2001 and 2002, respectively. Yield reductions were detected when Hessian fly infestation rates exceeded 50% plants during 2001 and 15% plants (8% tillers) during 2002. In two trials during 2001, in-furrow application of aldicarb (Temik) at planting improved yields of four Hessian fly-susceptible cultivars by 72% and 144% (up to 1,959 kg/ha) and yields of one Hessian fly-resistant cultivar by 2% and 3%. Resistant cultivars and aldicarb improved grain quality as much as two market grades during 2001. The value of increased grain production with Hessian fly-resistant cultivars in four field experiments ranged from $112 to $252/ha, excluding price incentives for improved market quality. Yield reduction due to combined damage from Hessian fly and either Fusarium crown rot or lesion nematode was additive. This report seams to be the first quantitative yield loss estimate for Hessian fly in spring wheat in the semiarid environment of the inland Pacific Northwest.

Smiley, R.W., R.E. Ingham, W. Uddin, and G.H. Cook. 1994. Crop sequences for winter wheat in soil infested with cereal cyst nematode and fungal pathogens. Plant Disease 78:1142-1149.

ABSTRACT   

In the Pacific Northwest, Heterodera avenae is spreading to soils infested with root-infecting fungal pathogens of wheat. A poorly drained, silty clay loam infested with multiple pathogens was used to examine productivity of winter wheat in 11 crop sequences. Breaks between wheat crops included summer fallow or crops of pea, barley, rape, alfalfa, or Kentucky bluegrass. In the fifth year, winter wheat was planted in all sequences, after half of each plot was treated with aldicarb. Yield of annual winter wheat was always 40-60% less than wheat alternated with fallow or any other crop, except alfalfa contaminated with grass weeds. Wheat yielded equally following 1- or 2-yr breaks from wheat. Effective breaks included summer fallow, pea, and weed-free alfalfa. H. avenae was the most important individual constraint to yield. Combined damage from H. avenae and Gaeumannomyces graminis var. tritici caused highest overall yield loss, whereas H. avenae and Pythium spp. had the greatest negative effect on number of roots. During the fifth year, where aldicarb was applied, root damage by H. avenae decreased but damage by Rhizoctonia solani and Pythium spp. increased, resulting in no yield improvement.

Smiley, R.W., R.G. Whittaker, J.A. Gourlie, S.A. Easley, and R.E. Ingham. 2005. Plant-parasitic nematodes associated with reduced wheat yield in Oregon: Heterodera avenae. Journal of Nematology 37:297-307.

ABSTRACT   

Heterodera avenae is widely distributed in the western USA. Wheat in Oregon and Washington is grown mostly in non-irrigated winter wheat/summer fallow rotations in low rainfall regions. Economic and social pressures have motivated growers to pursue a transition from winter wheat/summer fallow rotation to no-till annual spring cereals. Some irrigated fields are also planted annually to cereals. The impact of H. avenae on spring wheat yield in Oregon had been observed but not quantified. Spring wheat was planted with or without aldicarb to examine relationships between H. avenae and yield under dryland and irrigated conditions in moderately infested fields in eastern Oregon. Spring wheat yields were negatively correlated (P < 0.05) with initial densities of H. avenae. Aldicarb application improved spring wheat yield by as much as 24%. The yield of irrigated annual winter wheat was also negatively correlated with initial density of H. avenae. Infective juvenile stages of H. avenae reached a peak density during mid-spring. Additional research is necessary to develop management strategies for cereal cyst nematode in the western United States.

Smiley, R.W., G.P. Yan, and Z.A. Handoo. 2008. First record of the cyst nematode Heterodera filipjevi on wheat in Oregon. Plant Disease 92: (in press).

FULL REPORT

Plant and soil samples from an irrigated winter wheat (Triticum aestivum) field near Imbler (Union County), OR, were evaluated for root diseases during April 2007. The field exhibited patches with up to 90% plant mortality. Previous crops were winter wheat (2004), chickpea (Cicer arietinum, 2005) and spring wheat (cv. ‘Jefferson’, 2006). Stubble was baled and removed and the field was cultivated before replanting to winter wheat cv. ‘Chukar’ in October. Patches of stunted seedlings (3-5 leaf stage) appeared in March 2007. Stunted seedlings exhibited chlorotic or necrotic lower leaves, healthy younger leaves, few or no tillers, rotting of lower culms and crowns, and light brown roots with little or no branching. Signs and symptoms of fungal pathogens (Pythium spp., Gaeumannomyces graminis var. tritici, Rhizoctonia solani AG-8 and Typhula incarnata) were present on affected plants. Most small grain fields in Union County are infested with Heterodera avenae (4) but none of the roots, on either healthy or stunted plants, exhibited the bushy branching pattern typical of sites where H. avenae females penetrate and encyst. Extraction of motile nematodes (Whitehead tray method) from soil revealed high populations of Pratylenchus neglectus (6,560/kg of soil), Tylenchorhynchus spp. (2,369/kg) and a species initially thought to be H. avenae (3,098 juveniles/kg). Cysts were also extracted. During PCR-RFLP identification (1) of H. avenae collected in Oregon, Washington and Idaho, four restriction enzymes applied to amplified DNA of cysts from the Imbler field consistently revealed a pattern identical to that of a H. filipjevi DNA standard and distinct from patterns of H. avenae, H. schachtii, and H. latipons. DNA standards were obtained from Roger Rivoal, INRA, Rennes, France. Morphological evidence confirmed that the specimens were H. filipjevi , a member of the ‘H. avenae Group’ of cereal cyst nematodes (2,3). Measurements of second-stage juveniles (n = 15) included length of body (range = 530-570 μm, mean = 549, st. dev. = 13.0), stylet (22.5-24.5, 23.2, 0.6) with anchor-shaped basal knobs, tail (52.5-62.5, 57.4, 2.7), and hyaline tail terminal (30-38, 33.5, 2.6). The lateral field had four lines of which the inner two were more distinct. Shapes of the tail, tail terminus, and stylet knobs were also consistent with H. filipjevi. Cysts (n = 10) were lemon-shaped, light brown in color. The cyst wall had a zigzag pattern. The vulval cone was bifenestrate with horseshoe-shaped semifenestra. The cysts were characterized by body length including neck (range = 718-940 μm, mean = 809.7, st. dev. = 61.8), body width (395-619, 504, 71.2), L/w ratio = (1.1-2.2, 1.4, 0.3), neck length (75-140, 103.2, 22.1) and width (50-95, 71.4, 10.9), fenestra length (50-65 μm, 56.5, 6.6) and width (27-40, 29.0, 3.8), heavy underbridge (60-80, 69, 8.5), vulval slit (7.5-8.5, 7.8, 0.4), and many bullae. Cysts hatched much more readily and at lower temperatures than populations of H. avenae, as has been described for H. filipjevi. Detection of H. filipjevi in Oregon represents a new record for the occurrence of this species in the U.S.A. and for North America. The pathotype and resistance genes for incorporation into wheat, barley and oat are being identified.

References: (1) Bekal, S. et al., Genome 40:479. 1997. (2) Handoo, Z.A., J. Nematol. 34:250, 2002. (3) Holgado, R. et al., J. Nemat. Morph. Syst. 7:77-84, 2004. (4) Smiley, R.W. et al., J. Nematol. 37:297, 2005.

Smiley, R.W., R.G. Whittaker, J.A. Gourlie, and S.A. Easley. 2006. Geocenamus brevidens associated with reduced yield of no-till annual spring wheat in Oregon. Plant Disease 90:885-890.

ABSTRACT