Heat Tolerance and Aging of the Anhydrobiotic Seed Gall Nematode with SEM Observations.

The seed gall nematode, Anguina agrostis, feeds and reproduces within the developing ovaries of bentgrass seeds and overwinters in seed galls as anhydrobiotic juveniles. These dormant juveniles can survive within the seed gall for many years. In this dehydrated state, they are more tolerant to extreme environmental conditions than are their hydrated counterparts. Nematodes in seed galls were exposed to various high temperatures (80 to 160°C) for time intervals of 5 to 30 min. Survival decreased as time and temperature increased. Remarkably, these nematodes survived exposure to 155°C for 5 min, higher than that recorded for any other metazoan. In contrast, seed galls that had been stored at room temperature and humidity for 5 yr also survived exposure to extreme temperatures; however, their survival rates were not as high as those for freshly collected galls. Juveniles within the seed gall were coiled and grouped together conforming to the shape of the seed gall. The gross morphology of the cuticle of the juveniles was very smooth and relatively undistorted by the shrinkage from the loss water from their body tissues. Wherever the nematodes were cut with a razor blade, a small amount of their contents oozed out of the opening and coalesced with that of other nearby specimens and appeared gel-like. Elucidation of the mechanisms that enable these nematodes to remain viable after exposure to extreme heat remains a mystery. Understanding the changes that occur in these nematodes as they rehydrate and return to life from an ametabolic state may have major impacts on the life sciences, including insights into the answer of the age-old question: "What is life?"

First Report of Cephalosporium gramineum, Causal Agent of Cephalosporium Stripe of Wheat, in a Commercial Winter Wheat Field in Virginia.

Cephalosporium stripe (CS) (2) was identified in a commercial field of winter wheat (Triticum aestivum) near Riner, Montgomery County, Virginia in May 2006. Nearly 15% of the field was severely affected. Broad, yellow-brown stripes were observed on the leaf blades of affected plants, and many plants were stunted and had ripened prematurely. Symptomatic plants were associated with low acidic (pH 5.2), wet spots of the field. Leaves and nodes of affected plants were surface disinfested for 1 min in 5% sodium hypochlorite, plated on corn meal agar (CMA), and incubated at 20°C for 5 days. Cephalosporium gramineum was isolated from numerous plants. Cultures of the fungus produced hyaline conidiophores approximately 5 µm long and unicellular conidia 3 to 7 µm long. Aqueous suspensions of mycelia and conidia were prepared from pure cultures. Several spring wheat cultivars were wounded by severing the root mass and were inoculated when the fifth stem node was detectable (35 on Zadoks scale). Noninoculated plants were wounded as controls. Plants were kept in the greenhouse at temperatures of 22 to 27°C. After 14 days, inoculated plants produced symptoms of CS, and the fungus was reisolated from the leaves of these plants. No symptoms were observed on noninoculated control plants. Though CS had been observed in Virginia in research nurseries (1), to our knowledge, this is the first confirmed report of the disease in a commercial wheat field in Virginia. References: (1) J. B. Jones et al. Plant Dis. 64:325, 1980. (2) C. M. Stiles and T. D. Murray. Phytopathology 86:177, 1996.

First Report of Bentgrass Seed Gall Nematode, Anguina agrostis, in Virginia and Minnesota.

On August 24, 2003, during a foray for grasses infected with fungi, redtop creeping bentgrass (Agrostis stolonifera L.) was collected on Butt Mountain Lookout near an abandoned fire tower with coordinates 80°37'40.3″ W and 37°22'14.0″N at an altitude of 1,284 m overlooking the New River between the towns of Pembroke and Ripplemead, VA. Seed heads with very elongated glumes, lemmas, and paleas were very common, and the incidence rate was nearly 95% on the basis of symptomatic plants in the immediate area surrounding the tower comprising more than 5 ha of a grassy meadow. Close examination revealed the occurrence of elongated, blackish galls replacing the ovaries and containing Anguina agrostis (Steinbuch, 1799) Filipjev, 1936. Nematode cultures were established and maintained on red top creeping bentgrass (A. stolonifera) in a greenhouse. Identification was based on morphology and measurements of juveniles L = 407 + 22 (376-418) µ, stylet L = 18.5 + 1.7 (17.0-21.3) µ males L = 351 + 17 (339-367) µm; and females L = 455 + 33. Examination of specimens collected previously by C. Roane revealed that another population of Anguina agrostis was also found on August 9, 1990 parasitizing the same host growing along Echo Trail near Big Lake Lodge Rd. in St. Louis County, MN. The infestation at the Virginia site may have been from sowing infested seeds at the disturbed construction site for the fire lookout tower and other buildings. However, the occurrence at the Minnesota site is less likely to be anthropogenic. Voucher specimens from both locations were placed in the Virginia Tech Nematode Collection, and voucher cultures are maintained in the Virginia Tech Nematode Culture Collection.

Inheritance and allelism tests of Raiden soybean for resistance to soybean mosaic virus.

The gene symbol Rsv2 was previously assigned to the gene in the soybean [Glycine max (L.) Merr.] line OX670 for resistance to soybean mosaic virus (SMV). The Rsv2 gene was reported to be derived from the Raiden soybean (PI 360844) and to be independent of Rsv1. Accumulated data from our genetic experiments were in disagreement with this conclusion. In this study, Raiden and L88-8431, a Williams BC5 isoline with SMV resistance derived from Raiden, were crossed with two SMV-susceptible cultivars to investigate the mode of inheritance of SMV resistance in Raiden. They were also crossed with five resistant cultivars to examine the allelomorphic relationships of the Raiden gene with other reported genes at the Rsv1 locus. F1 plants, F2 populations, and F2-derived F3 (F2:3) lines were tested with SMV strains G1 or G7 in the greenhouse or in the field. The individual plant reactions were classified as resistant (R, symptomless), necrotic (N, systemic necrosis), or susceptible (S, mosaic). The F2 populations from R x S crosses segregated in a ratio of 3 (R + N):1 S and the F2:3 lines from Lee 68 (S) x Raiden (R) exhibited a segregation pattern of 1 (all R):2 segregating:1 (all S). The F2 populations and F2:3 progenies from all R x R crosses did not show any segregation for susceptibility. These results demonstrate that the resistance to SMV in Raiden and L88-8431 is controlled by a single dominant gene and the gene is allelic to Rsv1. The heterozygous plants from R x S and R x N crosses exhibited systemic necrosis when inoculated with SMV G7, indicating a partial dominance nature of the resistance gene. Raiden and L88-8431 are both resistant to SMV G1-G4 and G7, but necrotic to G5, G6, and G7A. Since the resistance gene in Raiden is clearly an allele at the Rsv1 locus and it exhibits a unique reaction to the SMV strain groups, assignment of a new gene symbol, Rsv1-r, to replace Rsv2 would seem appropriate. Further research is ongoing to investigate the possible existence of the Rsv2 locus in OX670 and its relatives.

Identification and population dynamics of bacteria in symptomatic oat leaves.

Bacteria isolated from symptomatic oat leaves included pseudomonads,Erwinia herbicola, and others.Pseudomonas coronafaciens was isolated predominantly from leaves with halo blight symptoms or necrotic spots. Leaves with red leaf symptoms yielded many types of bacteria, including saprophytic pseudomonads,P. syringae, E. herbicola, Bacillus sp.,Micrococcus sp.,Corynebacterium sp., a yeast, and other unidentified species. Only isolates ofP. coronafaciens were pathogenic on the plant hosts tested. The bacteria associated with red leaf symptoms exist as saprophytes and/or epiphytes on leaves with those symptoms. It is concluded that bacteria do not contribute to red leaf symptom development in oats, but symptomatic leaves provide an environment for their growth.