Effect of Soil Temperature and pH on Resistance of Soybean to Heterodera glycines

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is a major pest of soybean, Glycine max L. Merr. Soybean cultivars resistant to SCN are commonly grown in nematode-infested fields. The objective of this study was to examine the stability of SCN resistance in soybean genotypes at different soil temperatures and pH levels. Reactions of five SCN-resistant genotypes, Peking, Plant Introduction (PI) 88788, Custer, Bedford, and Forrest, to SCN races 3, 5, and 14 were studied at 20, 26, and 32 C, and at soil pH''s 5.5, 6.5, and 7.5. Soybean cultivar Essex was included as a susceptible check. Temperature, SCN race, soybean genotype, and their interactions significantly affected SCN reproduction. The effect of temperature on reproduction was quadratic with the three races producing significantly greater numbers of cysts at 26 C; however, reproduction on resistant genotypes remained at a low level. Higher numbers of females matured at the soil pH levels of 6.5 and 7.5 than at pH 5.5. Across the ranges of temperature and soil pH studied, resistance to SCN in the soybean genotypes remained stable.     

Parasitism of Hoplolaimus galeatus on Diploid and Polyploid St. Augustine grasses

''Floratam'' and ''FX-313'' St. Augusfinegrasses (Stenotaphrum secundatum) were compared in a time-course experiment for host suitability and susceptibility to the lance nematode, Hoplolaimus galeatus. Nematode densities were determined in the soil and acid-fuchsin stained roots 42, 84, 126, 168, and 210 days after pots containing 230 cm³ of autoclaved native Margate fine sand/pot were infested with 104 ± 9 nematodes and maintained at 25 ± 2 C in the laboratory. ''FX-313'' was a more suitable host for H. galeatus. Numbers of H. galeatus reached a maximum at 210 days after inoculation, with 5,550 and 4,120 nematodes (adults plus juveniles)/pot for ''FX-313'' and ''Floratam,'' respectively. Root and shoot dry weights of both grasses were not affected by H. galeatus throughout the experiment. Three polyploid, 2n = 30 to 32 (''Floratam,'' ''FX-10,'' and ''Bitterblue'') and three diploid, 2n = 18 (''FX-313,'' ''Florida Common,'' and ''Seville'') S. secundatum genotypes were inoculated with H. galeatus (99 ± 9/pot) and compared with uninoculated controls 210 days after inoculation. St. Augustinegrass genotypes differed as hosts of H. galeatus. ''FX-313'' and ''Florida Common'' represented the high and low extremes, respectively, for nematode reproduction (9,750 and 5,490 nematodes/pot or 4,239 and 2,387 nematodes/100 cm³ of soil). However, differences in root and shoot growth were not detected 210 days after inoculation with H. galeatus.     

Disinfection Alternatives for Control of Ditylenchus dipsaci in Garlic Seed Cloves

Hot-water dips with and without the additives abamectin and sodium hypochlorite were evaluated for control of Ditylenchus dipsaci infection of garlic seed cloves. All treatments were compared to hot water-formalin clove dip disinfection and to nontreated infected controls for garlic emergence, midseason infection, bulb damage, and yield at harvest in field plots in 12 experiments. Hot-water treatments without additives only partially controlled D. dipsaci when a warming presoak dip (38 C) of 30, 45, or 60 minutes'' duration was followed by a hot-water dip (49 C) of 15-30 minutes'' duration. Exposure to 49 C for 30 minutes caused slight retardation of garlic emergence, although normal stand was established. Abamectin at 10-20 ppm as the 20-minute hot dip (49 C) or as a 20-minute cool dip (18 C) following a 20-minute hot-water dip and sodium hypochlorite at 1.052-1.313% aqueous solution as the 20-minute hot dip were highly effective in controlling D. dipsaci and were noninjurious to garlic seed cloves. None of these treatments was as effective as a hot water-formalin dip and were noneradicative, but showed high efficacy on heavily infected seed cloves relative to nontreated controls. Abamectin was most effective as a cool dip. These abamectin cool-dip (following hot-water dip) and sodium hypochlorite hot-dip treatments can be considered as effective alternatives to replace formalin as a dip additive for control of clove-borne D. dipsaci. Sodium hypochlorite was less effective as the cool dip, and at concentrations of 1.75-2.63% was phytotoxic to garlic.     

Morphometrics of Infective Juveniles of Steinernema spp. and Heterorhabditis bacteriophora (Nemata: Rhabditida)

Selected morphometrics of Heterorhabditis bacteriophora and seven species of Steinernema from in vivo culture were compared in relation to time of harvest. In addition, five Steinernema species were reared in vitro and their morphometrics were compared with those from in vivo culture. With in vivo culture, there was generally a negative linear relationship between body length of infective juveniles (IJ) and time of harvest. The distance from the anterior end to the excretory pore (EP) and the tail length (T) of IJ also varied with time of harvest. The E percentage (= EP/T x 100) was the least variable. Body lengths of IJ reared in vitro were much less than those of IJ reared in vivo. The study suggests that IJ harvested from in vivo culture within 1 week of emergence from cadavers are best for species identification. Infective juveniles from in vitro culture should not be used for species identification.     

Effects of a Mutant Strain and a Wild Type Strain of Verticillium lecanii on Heterodera glycines Populations in the Greenhouse

A wild type strain ofVerticillium lecanii and a mutant strain with increased tolerance to the fungicide benomyl were evaluated in greenhouse experiments for effects on Heterodera glycines populations. Nematodes were applied at 300 eggs and juveniles per 4,550-cm³ pot (two soybean plants in 4,990 g loamy sand per pot) and at both 300 and 10,000 eggs and juveniles per 1,720-cm³ pot (one soybean plant in 2,060 g sand per pot). With 300 nematodes added per pot, both V. lecanii strains significantly reduced nematode populations in loamy sand (fungus applied at 0.02% dry weight per dry weight loamy sand) and sand (0.006% and 0.06% fungus application rates). The mutant strain applied at 0.002% to sand also significantly reduced cyst numbers. When 10,000 nematodes were added per pot, only the mutant strain at 0.06% significantly decreased population. Various media were tested for isolation of the fungus strains from prills, loamy sand, and sand, but the fungi were recovered from few of the greenhouse pots.     

A Nondestructive Method of Determining Bursaphelenchus xylophilus Infestation of Monochamus spp. Vectors

Pine wilt is caused by the nematode Bursaphelenchus xylophilus, which is transported to host trees in the trachea of Monochamus spp. (Coleoptera: Cerambycidae). The study of the relationship between the nematode and its beetle vectors has been hampered by the inability to estimate nematode presence or density within live beetles. This report describes a rapid method for estimating nematode load within live M. carolinensis and M. alternatus by visual examination of the atrium of the first abdominal spiracle. Visual estimates of nematode numbers correlated highly with actual nematode numbers. This method is a timesaving technique for determining relative numbers of B. xylophilus in pine wilt research.     

Nitric oxide is involved in heat-induced HSP70 accumulation

Heat shock potentiated the nitric oxide production (EPR assay) in the liver, kidney, heart, spleen, intestine, and brain. The heat shock-induced sharp transient increase in the rate of nitric oxide production preceded the accumulation of heat shock proteins (HSP70) (Western blot analysis) as measured in the heart and liver. In all organs the nitric oxide formation was completely blocked by the NO-synthase inhibitor (L-NNA). L-NNA also markedly attenuated the heat shock-induced accumulation of HSP70. The results suggests that nitric oxide is involved in the heat shock-induced activation of HSP70 synthesis.     

A modeling study of anaerobic biofilm systems: II. Reactor modeling

A rigorous steady-state model of anaerobic biofilm reactors taking into account acid-base and gas-phase equilibria in the reactor in conjunction with detailed chemical equilibria and mass transfer in acetate-utilizing methanogenic biofilms is presented. The performances of ideal completely stirred tank reactors (CSTRs) and plug-flow reactors, as well as reactors with nonideal hydraulic conditions, are simulated. Decreasing the surface loading rate increases the acetate removal efficiency, while decreasing the influent pH and increasing the buffering capacity improves the removal efficiency only if the bulk pH of the reactor shifts toward more optimal values between 6.8 to 7.0. The reactor can have negative or positive removal efficiencies depending on the start-up conditions. The respiration coefficient plays a critical role in determining the minimum influent pH required for reactor recovery after failure. Having multiple CSTRs-in-series generally increases the overall removal efficiency for the influent conditions investigated. Monitoring of the influent feed quality is critical for plug-flow reactors, becasue failure of the initial sections of the reactor may cause a cascading effect that may lead to a rapid reactor failure. (c) 1995 John Wiley & Sons, Inc.