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Stewart's wilt reactions of 98 food-grade, white corn hybrids, 3 yellow dent corn hybrids, and 23 sweet corn hybrids and infection of kernels by E. stewartii were evaluated in 1998, 1999, and 2000. Stewart's wilt symptoms were rated from 1 (no appreciable spread of symptoms) to 9 (dead plants) following inoculation. The mean Stewart's wilt ratings for the food-grade, white corn and yellow dent corn hybrids were 1.9, 2.4, and 2.9 in 1998, 1999, and 2000, respectively. The mean Stewart's wilt ratings for the sweet corn hybrids were 3.8, 4.2, and 4.6 in 1998, 1999, and 2000, respectively. Hybrids with ratings less than 3 were classified as resistant. Hybrids with ratings between 3 and 4.5 were classified as moderate. Hybrids with ratings greater than 4.5 were classified as susceptible. Ears harvested from each row in 1998 and 1999 were assayed for E. stewartii using an enzyme-linked immunosorbent assay (ELISA)-based seed health test. Kernels from 16 hybrids were positive for E. stewartii in 1998. Kernels from 11 hybrids were positive for E. stewartii in 1999. Kernel infection by E. stewartii was affected considerably by the level of host resistance (i.e., reactions of seed parent plants). For hybrids classified as resistant, estimates of kernel infection were 0.024 and 0.0007% in 1998 and 1999, respectively. For hybrids with moderate reactions to Stewart's wilt, estimates of kernel infection were 0.19 and 0.07% in 1998 and 1999, respectively. For hybrids with susceptible reactions to Stewart's wilt, estimates of kernel infection were 11.6 and 7.8% in 1998 and 1999, respectively. Based on high levels of Stewart's wilt resistance in food-grade, white corn hybrids, and low rates of kernel infection by E. stewartii in resistant and moderate hybrids, there is an exceedingly low probability of introducing E. stewartii to areas where it does not occur by transmitting the bacterium in grain of the food-grade, white corn hybrids evaluated in this study. Although all of the kernels harvested in these experiments were produced as grain on open-pollinated F1 hybrids, the rates of kernel infection observed for hybrids with resistant, moderate and susceptible reactions to Stewart's wilt are applicable to seed produced on inbred lines with equivalent Stewart's wilt reactions.

Rates of transmitting Erwinia stewartii from seed to seedlings were estimated from field grow-outs of seedlings grown from seed infected with E. stewartii. Infected seed were produced in 1998, 1999, and 2000 on a Stewart's wilt-susceptible sweet corn hybrid, Jubilee. Seedlings were inoculated repeatedly with pinprick inoculators and suspensions of E. stewartii were injected into ear shanks of the primary ears of each adult plant. Seed from inoculated plants were harvested and bulked. Single kernels were assayed for E. stewartii to estimate the proportion of kernels infected with E. stewartii. Estimates of E. stewartii-infection were 15.6 ± 4.3, 49.4 ± 3.9, and 12.5 ± 2.4% for seed produced in 1998, 1999, and 2000, respectively. Approximately 61,800 seedlings were grown in DeKalb, IL in 1999 and 83,400 and 60,000 seedlings were grown in Plover WI in 2000 and 2001, respectively, from infected seed lots produced the previous year. Approximately 10,000, 12,200, and 29,400 seedlings of susceptible sweet corn hybrids also were grown each year from commercial seed produced in Idaho where Stewart's wilt does not occur. Based on estimates of kernel infection in each seed lot and plant populations in each grow-out trial, about 9,600, 41,200, and 7,500 seedlings were grown from infected kernels in 1999, 2000, and 2001, respectively. Seedlings at the two- to three-leaf stage were examined for symptoms of Stewart's wilt. Infected plants were confirmed by microscopic observations of bacterial ooze and by enzyme-linked immunosorbent assay. When data were combined from all three trials, 59 of approximately 58,300 seedlings grown from infected seed were infected with E. stewartii based on symptoms of Stewart's wilt and E. stewartii-positive leaf tissue samples. Of these 59 seedlings, 22 probably were infected from seed-to-seedling transmission of E. stewartii and 37 probably were the result of natural infection due to the presence of flea beetles in DeKalb in 1999. Twenty-two infected seedlings from 58,300 infected kernels corresponds to a seed-to-seedling transmission rate of 0.038%. This rate of seed-to-seedling transmission of E. stewartii is substantially lower than seed transmission rates reported in the first half of the twentieth century; however, it is similar to seed-to-seedling transmission rates reported from other recent research.

Kleinschmidt, C. E., Clements, M. J., Maragos, C. M., Pataky, J. K., and White, D. G. 2005. Evaluation of food-grade dent corn hybrids for severity of Fusarium ear rot and fumonisin accumulation in grain. Plant Dis. 89:291-297. Fumonisins produced by Fusarium verticillioides (syn = F. moniliforme) and F. proliferatum have been associated with potentially serious toxicoses of animals and humans. Thus, hybrids with low fumonisin accumulation in grain will be valuable for the production of corn-based human food products. We evaluated 68 food-grade dent corn hybrids for severity of Fusarium ear rot and fumonisin accumulation in grain in inoculated trials in Urbana, IL in 2000 and 2001. Our inoculation technique was successful in initiating fumonisin accumulation that allowed discrimination among hybrids. We identified several hybrids that could have acceptable levels (

Resistance to Fusarium ear rot [caused by Fusarium verticillioides (Sacc.) Nirenberg (synonym F. moniliforme Sheldon) (teleomorph: Gibberella moniliformis) and F. proliferatum (Matsushima) Nirenberg (teleomorph: G. intermedia)] and fumonisin contamination is heritable and controlled by at least 11 gene regions in a maize (Zea mays L.) population created by backcrossing the highly resistant donor line, GE440, to the susceptible but commercially successful recurrent parent line, FR1064. The relationship between resistances to Fusarium ear rot and fumonisin contamination and agronomic performance has not been reported. Therefore, the objective of this study was to examine the relationship between disease resistance and agronomic utility in this population by measuring resistances to Fusarium ear rot and fumonisin contamination in BC 1 F 1:2 lines, and yield and agronomic performance in topcrosses of these lines. Fumonisin contamination was not correlated with yield, but two fumonisin quantitative trait loci (QTL) mapped to similar positions as yield QTL. Fusarium ear rot had a small positive correlation with topcross yield (r = 0.29), but QTL for the two traits mapped to distinct genomic positions. Similar results for other traits indicate that QTL can contribute in opposite directions to the overall genetic correlations between traits and that some trait correlations arise in the absence of detectable QTL effects on both traits. In general, no strong relationships were observed between disease resistance traits and agronomic traits, thus selection for increased resistance should not unduly affect agronomic performance.

Fusarium verticillioides (Sacc.) Nirenberg (synonym F. moniliforme Sheldon) (teleomorph: Gibberella moniliformis) and F. proliferatum (Matsushima) Nirenberg (teleomorph: G. intermedia) are fungal pathogens of maize (Zea mays L.) that cause ear rot and contaminate grain with fumonisins, mycotoxins that can harm animals and humans. The objective of this study was to identify quantitative trait loci (QTL) for resistance to Fusarium ear rot and fumonisin contaminationintwomaizepopulations,comprisedof213BC1F1:2familiesfrom the first backcross of GE440 to FR1064 (GEFR) and 143 recombinant inbred lines from the cross of NC300 to B104 (NCB). QTL mapping was used to study the genetic relationships between resistances to ear rot and fumonisin contamination and to investigate consistency of QTL acrosspopulations.IntheGEFRpopulation,sevenQTLexplained47% of the phenotypic variation for mean ear rot resistance and nine QTL with one epistatic interaction explained 67% of the variation for mean fumonisin concentration. In the NCB population, five QTL explained 31% of the phenotypic variation for mean ear rot resistance and six QTL and three epistatic interactions explained 81% of the phenotypic variation for mean fumonisin concentration. Eight QTL in the GEFR population and five QTL in the NCB population affected both disease traits. At least three ear rot and two fumonisin contamination resistance QTL mapped to similar positions in the two populations. Two QTL,localized tochromosomes fourand five, appearedtobe consistent for both traits across both populations.

Fusarium verticillioides (Sacc.) Nirenberg (synonym F. moniliforme Sheldon) (teleomorph: Gibberella moniliformis )a ndF. proliferatum (Matsushima)Nirenberg (teleomorph:G. intermedia) are fungalpathogens of maize (Zea mays L.) that cause ear rot and contaminate grain with fumonisins, a family of mycotoxins that adversely affect animal and human health. The objective of this study was to estimate heritabilities of and genotypic and phenotypic correlations between fumonisin concentration, ear rot, and flowering time in two maize populations. In the (GE440 3 FR1064) 3 FR1064 backcross population, the genotypic and phenotypic correlations between ear rot and fumonisin concentration were0.96and0.40,respectively.Heritabilityestimatedonanentrymean basis was 0.75 for fumonisin concentration and 0.47 for ear rot resistance. In the NC300 3 B104 recombinant inbred line population, the genotypic and phenotypic correlations between ear rot and fumonisin concentration were 0.87 and 0.64, respectively. Heritability estimated on an entry mean basis was 0.86 for fumonisin concentration and 0.80 for ear rot resistance. Correlations between fumonisin concentration and silking date were not significant in either population, and correlations between ear rot resistance and silking date were small (less than 0.30) in both populations. Moderate to high heritabilities and strong genetic correlations between ear rot and fumonisin concentration suggest that selection for reduced ear rot should frequently identify lines with reduced fumonisin concentration. Ear rot can be screened visually and so is less costly and less time-consuming to evaluate than laboratory assays for fumonisin concentration.

Our objective was to determine the value of corn (Zea mays) inbred Oh516 as a source of resistance to Aspergillus ear rot and aflatoxin accumulation in grain. Types and magnitudes of gene action associated with resistance were determined with generation means analysis. Molecular markers associated with resistance were identified from BCP1S1families developed from the cross of the susceptible inbred B73 and Oh516. In 2001 and 2002, B73 (P1), Oh516 (P2), and the F1, F2, F3, BCP1, BCP2, and BCP1S1generations were evaluated for aflatoxin concentration in grain, percent bright greenish yellow fluorescence (BGYF), and severity of Aspergillus ear rot following inoculation in Urbana, IL. BCP1S1families testcrossed with LH185 also were evaluated at three locations in 2002. Molecular marker-quantitative trait loci (QTL) associations with all traits were determined with single factor analysis of variance. Dominance gene action was associated with aflatoxin concentration in grain and percent BGYF. QTL associated with aflatoxin accumulation in grain were identified on chromosomes 2, 3, and 7 (bins 2.01 to 2.03, 2.08, 3.08, and 7.06). Alleles from inbred Oh516 on chromosomes 2, 3, and 7 should improve resistance of commercially used, B73-type inbreds.

Two sets of experiments were done to examine whether seed-treatment chemicals affected the ability of an enzyme-linked immunosorbent assay (ELISA)-based seed health test to detect Erwinia stewartii. The chemicals evaluated included Actellic, Apron, Captan, Cruiser, Gaucho, Maxim, Poncho, Thiram, and Vitavax in 11 seed-treatment combinations. In one experiment, seed-treatment chemicals were evaluated quantitatively in a critical region of ELISA absorbance values near 0.5 using maize seed that were spiked with uniform quantities of a liquid suspension of E. stewartii. The number of bacteria in each sample was estimated from ELISA absorbance values using standard curves. Log CFU of E. stewartii per sample were not significantly different among the untreated control and the 11 seed treatments compared with Tukey's Studentized Range Test (P = 0.05). Means of log CFU/ml for all treatments were tightly clustered around 5.70 which corresponded to an absorbance value of 0.440 and a bacterial population of about 500,000 CFU/ml. In a second set of experiments, seed treatment chemicals were evaluated based on qualitative decisions that resulted from the ELISA-based seed health test of seed lots of Jubilee and A632 infected with E. stewartii. The number of negative samples was not substantially greater than expected based on binomial probabilities except for samples of Captan/Vitavax-treated A632, which we considered to be a type I error. The mean absorbance values of positive samples ranged from 1.42 to 1.72 for A632 and from 1.51 to 1.91 for Jubilee and did not differ significantly among the seed treatments. There was no consistent evidence from these experiments that fungicide or insecticide seed treatments interfered with the sensitivity of the ELISA or altered low (e.g., 0.5) or high (e.g. 1.4 to 1.9) absorbance values. The ability of the ELISA-based seed health test to detect E. stewartii in maize seed was not affected by these seed treatments.

Researchers at the University of Illinois seek to identify sources of genetic resistance that contribute alleles for low aflatoxin and low fumonisin accumulation in grain and low severity of Aspergillus and Fusarium ear rots to commercial corn (Zea mays L.) inbreds. Studies of resistance to aflatoxin accumulation in grain and Aspergillus ear rot began in 1988 with experiments designed to address fundamental needs of a new breeding program. Through the 1990s, diverse inbred lines, test crosses, and segregating populations were developed and evaluated for resistance in numerous environments. Concerns of industry inspired researchers to initiate an accelerated program for resistance to fumonisin accumulation in grain and Fusarium ear rot in the late 1990s. Present research in both programs is directed with the latest molecular marker technology, and is focused on incorporating novel genes for resistance from diverse sources into elite inbred lines that impart high yield to hybrid performance. With continued ...

Our objectives were to determine if the corn (Zea mays) inbred MI82 has alleles for resistance to Aspergillus ear rot (caused by Aspergillus flavus) and aflatoxin accumulation in grain that can be transferred to commercially used inbreds, and to determine the types and magnitudes of gene action, heritabilities, and gain from selection for low levels of bright greenish-yellow fluorescence (BGYF), aflatoxin, and ear rot with MI82. Also, we hoped to determine if selection against BGYF would substantially reduce the concentration of aflatoxin in grain. Primary ears and ground grain from inbred MI82 (P1), the susceptible inbred B73 (P2), and the F1, F2, F3, BCP1S1, and BCP2S1generations developed from these inbreds were evaluated for BGYF, concentration of aflatoxin in grain, and severity of Aspergillus ear rot in 2000 and 2001. Dominance was the most important gene action associated with low levels of BGYF and a low concentration of aflatoxin in grain. Heritabilities for low levels of BGYF (83.5%), aflatoxin (74.1%), and ear rot (62.8%) were high. Correlation coefficients between aflatoxin and BGYF were high in both years (r = 0.75 and 0.79 for 2000 and 2001, respectively). Unlike aflatoxin, BGYF was not affected by the year in which plants were grown. Selection for low levels of BGYF prior to selection based on aflatoxin concentration is as effective as selection for either factor alone. MI82 has value in programs designed to improve the resistance of commercially used corn inbreds.

Fusarium ear rot of corn (Zea mays L.) is associated with feeding damage from the European corn borer (ECB), Ostrinia nubilalis Hubner, and the corn earworm (CEW), Helicoverpa zea Boddie. Specific transformation events encoding for Cry1Ab protein from Bacillus thuringiensis Berliner (Bt) may reduce Fusarium ear rot and fumonisin concentration in grain by minimizing damage from certain insects. The objective of this study was to determine if effects from Cry1Ab protein in kernels and silks on fumonisin concentration in grain vary depending on the genotype of the hybrid or the predominant insect species. Four Bt corn hybrids and their corresponding nontransgenic, near-isogenic hybrids were compared for ear rot severity and fumonisin concentration in grain in four environments. Treatments included inoculation with F. verticillioides (Sacc.) Nirenb. (Syn = F. moniliforme J. Sheld.) and F. proliferatum (Matsushima) Nirenb., infestation with ECB larvae, infestation with CEW larvae, and controls. Cry1Ab protein from the Mon810 transformation event was associated with reduced ear rot severity when hybrids were not inoculated with Fusarium spp., regardless of whether hybrids were infested or not infested with insects. Cry1Ab protein was associated with reduced fumonisin concentration in grain when ECB was the predominant insect, but not when CEW was the predominant insect. Cry1Ab protein was not associated with reduced fumonisin concentration in grain for the most resistant hybrid pair in this study. Results suggest that Bt hybrids can reduce fumonisin concentration in grain during seasons when ECB is favored, but not during seasons when CEW is favored. Hybrid genotype was an important factor in reducing fumonisin concentration in grain.

Aflatoxin B(1) formed by Aspergillus flavus Fr:Link has been associated with animal disease and liver cancer in humans. We performed genetic studies in progenies derived from maize inbred Tex6, associated with relatively low levels of aflatoxin production, crossed with the historically important inbred B73. (Tex6 x B73) x B73 BC(1)S(1) and Tex6 x B73 F(2:3) mapping populations were produced and evaluated in 1996 and 1997 in Champaign, Ill. Ears were inoculated 20 to 24 days after midsilk using a pinboard method and a mixture of conidia of A. flavus Link:Fr. isolates. Aflatoxin B(1) levels in harvested ears were determined using an indirect competitive ELISA. Molecular markers were assayed on the populations and used to generate maps. Molecular marker - QTL associations for lower levels of aflatoxin production were determined using multiple regression (MR) and composite interval analysis with multiple regression (CIM MR). MR revealed sets of markers associated with lower aflatoxin production in 1996 and 1997, and CIM MR detected a smaller subset of loci significant in 1997. QTLs for lower aflatoxin were attributed to both Tex6 and B73 parental sources. Environment strongly influenced the detection of QTLs for lower aflatoxin production in different years. There were very few chromosome regions associated with QTLs in more than 1 year or population with MR analysis, and none with CIM MR analysis. In 1997, QTLs for lower aflatoxin were detected with CIM MR in bins 5.01-2 and 5.04-5 in the BC(1)S(1) population, and in bins 3.05-6, 4.07-8 and 10.05-10.07 in the F(2:3) population. These QTL associations appear the most promising for further study.

High-oil corn (Zea mays L.) grain is a valuable component of feed for monogastric livestock. One method of increasing the concentration of oil in corn grain is the TopCross method. With TopCross, ears of a cytoplasmic male-sterile, normal-oil hybrid are pollinated by a male-fertile, high-oil synthetic hybrid. The concentration of oil in the resulting grain is increased because of xenia effects. Kernels of high-oil corn typically have a larger germ and a smaller endosperm than kernels of comparable normal hybrids. The growth of Aspergillus flavus Link:Fr within germ tissue has been reported to be more extensive than that on the whole corn kernel; therefore, the severity of Aspergillus ear rot could be more extensive and aflatoxin concentrations could be higher in high-oil grain produced by TopCross than in grain with a lower concentration of oil. The objective of this study was to compare Aspergillus ear rot severity levels and aflatoxin concentrations in the grains of hybrids crossed with high-oil or normal-oil pollinators. Fifteen hybrids were evaluated in 1998 and 1999 in Urbana, Ill. Primary ears were inoculated with A. flavus and evaluated for susceptibility to Aspergillus ear rot and aflatoxin production in grain. Concentrations of aflatoxin and oil in corn kernels were significantly higher for high-oil hybrids than for normal-oil hybrids; however, ear rot severity was unaffected by the type of pollinator. These results suggest that grain from high-oil hybrids is at greater risk for aflatoxin contamination during some growing seasons.

Fumonisins have been associated with potentially serious toxicoses of animals and humans. Prior to initiating a corn (Zea mays) breeding program for resistance to these mycotoxins, an efficient inoculation technique must be developed. Four inoculation techniques were evaluated on 14 commercial corn hybrids in Urbana, IL in 1999 and 2000. The techniques were: injection of inoculum through the ear husk leaves at R2 (blister); silks sprayed with inoculum at R2 and covered with a shoot bag until harvest; silks sprayed with inoculum at R2, covered with a shoot bag, reinoculated 1 week thereafter, and covered with a shoot bag until harvest; and insertion of six Fusarium-colonized toothpicks into the silk channel at R2. Only injection of inoculum through the husk leaves significantly increased the concentration of fumonisin in grain and severity of Fusarium ear rot compared with a control. This technique effectively differentiated hybrids previously identified as resistant or susceptible to Fusarium ear rot. The rank order of hybrids inoculated with this technique did not significantly change in the 2 years of this study. This technique is suitable for efficiently evaluating a large number of corn genotypes for resistance to Fusarium ear rot and fumonisin concentration.

Colisepticaemia is a major health and economic concern for the mink industry, yet little information is available about the Escherichia coli that cause this disease. In this study, 40 E. coli, isolated from mink clinically diagnosed with colisepticaemia that had been submitted to the North Dakota State University Veterinary Diagnostic Laboratory, were randomly selected for characterization. These isolates were serotyped and screened for resistance to 18 antimicrobials, possession of transmissible R plasmids, and the presence of several virulence traits or genes using bioassays or the polymerase chain reaction. Several serotypes were identified that have previously been associated with septicaemia in other animal species. The majority of the isolates exhibited multiple antimicrobial resistance phenotypes. Common resistance phenotypes observed included those to tetracycline, sulfamethoxazole, streptomycin, ampicillin and kanamycin. Several of the isolates that could be studied by conjugation contained transmissible R plasmids coding for multiple antimicrobial resistance phenotypes. About half of the isolates produced colicin; all produced enterobactin: and all but one-quarter produced aerobactin. None of the isolates tested produced enterohaemolysin, and one-fifth were considered to be beta haemolytic. About half appeared to contain the gene encoding cytotoxic necrotizing factor-1; three contained the gene encoding EAE, but none appeared to contain the genes coding for LT, Sta/b, SLT-I/II or CNF-II toxins or K99 antigen. Approximately one-third of the isolates elaborated capsule. The results show that the E. coli isolates implicated in mink colisepticaemia possess similar virulence traits and antimicrobial resistance phenotypes to those associated with diarrhoeal diseases in food animals.

A 2-yr field and laboratory study investigated insect resistance of the maize, Zea mays L., inbred Tex6, which has previously demonstrated resistance to Aspergillus ear rot and aflatoxin production, relative to susceptible inbred B73. Field studies indicated significantly greater resistance to insect feeding of V4-V8 growth stage Tex6 plants compared with B73 plants in both years, primarily to flea beetles (Chaetonema spp.). Field studies of natural (1999) and artificial (2000) infestations of corn earworms, Helicoverpa zea (Boddie), indicated much lower levels of kernel damage at milk stage (approximately three-fold) and smaller surviving larvae (approximately three-fold) in Tex6 compared with B73 ears. At harvest similar trends in reduction of numbers of damaged kernels per ear, as well as incidence and numbers of kernels per ear symptomatically infected by Fusarium spp. were noted. Laboratory studies indicated little difference in mortality or survivor weight of caterpillars or sap beetle adults caged with milk stage kernels of the two inbreds. However, assays with silks indicated significantly greater mortality of H. zea in both 1999 and 2000, and European corn borer, Ostrinia nubilalis (Hubner) in 1999 (only year tested) when fed Tex6 silks compared with B73 silks. Pollinated Tex6 silks were generally darker colored and more toxic than unpollinated silks. Thus, it is possible that commercially usable inbreds with resistance to insects, which also contribute to the mycotoxin problem through vectoring and damage, could be produced using Tex6 as a source.

Unacceptable levels of contamination by aflatoxin, a carcinogenic toxin, produced by Aspergillus flavus Link:Fr can halt the sale and shipment of maize (Zea mays L.) grain. Our objectives were to: (i) determine the relative resistance to A. flavus and aflatoxin accumulation in F 1 hybrids produced by crossing promising resistant maize inbreds, regardless of heterotic pattern; (ii) investigate the genetic basis of resistance for this subset of inbreds through diallel analysis; and (iii) determine which inbreds are the most promising sources of resistance for molecular marker mapping and breeding programs. Two historically important inbreds and six inbreds tentatively associated with reduced ear rot and inhibition of aflatoxin production were crossed in all combinations. The resulting F 1 hybrids were evaluated for two years. Ears were inoculated 20 to 24 d after midsilk by a pinboard method and a mixture of conidia of Aspergillus flavus Link:Fr. isolates. Individual ears from each plot were rated by scoring the percent visible rot in the inoculated area. Aflatoxin B 1 levels in harvested ears were determined by an indirect competitive ELISA. The highest level of resistance for ear rot and aflatoxin accumulation was detected for resistant inbred x resistant inbred F 1 hybrids, but they were not significantly different from many resistant inbred x historically important inbred F 1 hybrids. Diallel analysis indicated general combining ability (GCA) effects for ear rot and aflatoxin levels were highly significant among hybrids overall, and for the inbreds Tex6 and Oh516. The results indicate that Tex6 and Oh516 are promising resistance sources for molecular marker mapping and breeding programs in diverse genetic backgrounds.

A guideline on the responsible and prudent use of antimicrobials in animal husbandry has been developed by the Ad hoc Group of experts on antimicrobial resistance, created by the Office International des Epizooties. The objectives of responsible use are to maintain antibiotic efficacy, to avoid the dissemination of resistant bacteria or resistance determinants and to avoid the exposure of humans to resistance through food. The guideline attributes a central role to the competent authorities responsible for granting marketing authorizations for antimicrobial substances. Requirements before and after granting of marketing authorizations are defined. Important aspects include the control of the pharmaceutical product quality and the therapeutic efficacy, the assessment of the selection pressure, the protection of the environment, specific and non-specific antimicrobial resistance surveillance. The guideline is also addressed to the veterinary pharmaceutical industry, veterinary practitioners, dispensing pharmacists and farmers. The respective roles and responsibilities of these groups are defined.

A guideline on the harmonisation of national antimicrobial resistance monitoring and surveillance programmes in animals and animal-derived foods has been developed by the Ad hoc Group of experts on antimicrobial resistance of the Office International des Epizooties. The objective of the guideline is to allow the generation of comparable data from various national surveillance and monitoring systems in order to compare the situations in different regions or countries and to consolidate results at the national, regional and international level. Definitions of surveillance and monitoring are provided. National systems should be able to detect the emergence of resistance, and to determine the prevalence of resistant bacteria. The resulting data should be used in the assessment of risks to public health and should contribute to the establishment of a risk management policy. Specific factors identified for harmonisation include the animal species, food commodities, sampling plans, bacterial species, antimicrobials to be tested, laboratory methods, data reporting, database structure and the structure of reports.

This study determined the types and magnitude of gene action, estimated heritabilities, and predicted gain from selection for resistance to Aspergillus ear rot and aflatoxin production in the cross of resistant corn inbred CI2 to susceptible inbred B73 in 1998 and 1999. The warm, dry summer of 1998 favored aflatoxin production, whereas the conditions of 1999 did not. Resistance to ear rot was mainly controlled by additive gene action. Aflatoxin values were analyzed by individual years (environments) because of the highly significant generation × environment interaction. Resistance to aflatoxin production was mainly controlled by epistasis in 1998 and by additive gene action in 1999. Heritabilities for ear rot and aflatoxin production were higher in the F3generation than in the BCP1-selfed generation. In 1998, Spearman's correlation coefficients between Aspergillus ear rot ratings and aflatoxin values for the F3and the BCP1-selfed families were not significant (P > 0.05). In 1999, both were highly significant (P < 0.01), but low at 0.41 and 0.17 for the F3and BCP1-selfed generations, respectively. We found that CI2 is not an acceptable source of resistance due to lower heritabilities and disease resistance compared to other sources of resistance.

A possible use of nonelite germplasm is as a source of alleles for disease resistance. Our objective was to determine the value of tropical and temperate maize (Zea mays L.) germplasm accessions as sources of alleles to improve disease resistance of the Corn Belt hybrid FR1064 x LH185. A group of tropical populations and hybrids from the Germplasm Enhancement of Maize Project (GEM) crossed to either Mol7 or B73 (temperate inbreds), was studied. In addition, a group of temperate accessions was evaluated. Reaction to southern corn leaf blight (SCLB) [Bipolaris maydis (Nisikado & Miyake) Shoemaker = Helminthosporium maydis Nisikado & Miyake], northern corn leaf spot (NCLS) [Bipolaris zeicola (G. L. Stout) Shoemaker = Helminthosporium carbonum Ullstrup Races 2 and 3], gray leaf spot (GLS) (Cercospora zeae-maydis Tehon & E.Y. Daniels), northern corn leaf blight (NCLB) [Exserohilum turcicum (Pass.) K. J. Leonard & E. G. Suggs = Helminthosporium turcicum Pass., Races 1, 1, 2, 23N and three unidentified races] and common rust (Puccinia sorghi Schwein) was studied using Dudley's method for identifying populations with favorable alleles. All accessions had favorable dominant alleles for resistance not present in FR1064 x LH185 for common rust, GLS, and SCLB. Four accessions had a number of favorable alleles for resistance not significantly different from the best accession for all five diseases. Crosses of the accessions containing Mol7 to FR1064 and LH185 were less susceptible to SCLB, NCLB, and rust than crosses of accessions containing B73. At least seven of the best 10 populations were tropical x Mo17 crosses for SCLB, NCLB, and rust when populations were ranked for presence of favorable alleles for resistance not present in either LH185 or FR1064. Net value statistics for tropical x B73 and tropical x Mol7 accessions differed in indicating whether backcrossing or selfing from the F 1 is more desirable. Therefore, if tropical populations are crossed to Corn Belt inbreds to increase adaptation, comparisons among tropical populations should only be made when all populations being compared have been crossed to the same Corn Belt inbred.

Thirty-seven of 53 diarrhoeic calves hospitalised for intravenous fluid therapy were classified as very severely acidotic (total carbon dioxide less than 8 mmol/litre) by using a Harleco apparatus. All the calves were given intravenously 10 to 20 litres of electrolyte solution which contained 144 mmol/litre sodium, 4 mmol/litre potassium, 113 mmol/litre chloride and 35 mmol/litre bicarbonate, and in addition the 37 very severely acidotic calves received 400 ml of 1M sodium bicarbonate in the first 5 litres of fluid administered. Sixteen of the 37 very severely acidotic calves had a distended right flank, suggesting the presence of a dilated fluid-filled viscus. Neither their history nor other clinical signs were useful predictors of the distension. The distended calves had significantly higher plasma concentrations of sodium and chloride, and significantly lower plasma creatinine concentrations than the calves which were not distended. Treatment was successful in all the 21 non-distended calves but four of the distended calves died despite treatment. The resolution of the distension in the successfully treated calves, coincided with a significant increase in plasma bicarbonate concentration and the passage of large amounts of malodorous mucoid faeces.

Changes occurring in stored solin/flax cultivars over 6 mo at temperatures ranging from 10 to 35 °C and moisture contents of 8.0, 9.5, 11.0 and 12.5% were observed. The cultivars were NorLin, McGregor, FP1001 (high linolenic acid), LinolaTM 947 (solin) and LinolaTM 989 (solin). Oil composition in all cultivars changed only slightly over 6 mo with a significant increase in palmitic acid. Doubling of free fatty acid levels was considered an indicator of quality deterioration. The deterioration occurred in 6 mo at 8% MC and 20 °C in FP1001 and in NorLin, McGregor, and LinolaTM 947 at 25 °C; LinolaTM 989 could be stored at 30 °C. LinolaTM 989 could be safely stored at moderately higher temperatures at a given moisture level than LinolaTM 947. Visible mold with corresponding germination loss was usually associated with Aspergillus glaucus group infection. Stored-product insects that could survive and develop on the solin/flax were the red flour beetle, Tribolium castaneum (Herbst), the confused flour beetle, T. confusum J. du Val, the sawtoothed grain beetle, Oryzaephilus surinamensis (L.) and the merchant grain beetle, O. mercator (Fauvel).In general, LinolaTM 947 and FP1001 were slightly more difficult to store than the other cultivars but there was no consistent difference between solin and flaxseed. Key words: Flaxseed, solin, storage, quality

Thirty-eight, one- to two-week-old calves with experimentally induced Escherichia coli diarrhoea were randomly assigned to three treatment groups. Two groups of 15 calves were treated intramuscularly once daily for three days with either danofloxacin mesylate at 1.25 mg/kg bodyweight, or with baquiloprim/sulphadimidine as a positive control (10 mg of combined active ingredient/kg); eight calves were treated with 0.9 per cent sodium chloride solution as a negative control (1 ml/20 kg). Faecal consistency, demeanour, hydration status, appetite and bodyweight were monitored before, during, and for four days after treatment by an investigator unaware of the animals9 treatment. Before treatment, the clinical, biochemical, and faecal indices were similar among the groups. By 24 hours after treatment began, the proportion of observations of faeces recorded as of normal consistency was highest in the danofloxacin-treated group (26 of 60), compared with 16 of 60 in the baquiloprim/sulphadimidine treated groups and four of 32 in the control group. The proportion of calves with a normal demeanour was highest in the danofloxacintreated group at all the evaluations and these calves gained significantly (P

Corn grain (19.8% moisture, wet basis) was treated with P-7 Grain Preservative (15% propionic acid, 85% inert ingredients, Nayfa Industries, Dallas, Tex.), at rates of 0.0, 0.1, 0.2, and 0.3%, on a wet basis, immediately after harvest as it was augered into modified grain bins. The grain was low temperature dried using ambient air. Samples were taken every two weeks for 42 weeks and the incidence of fungi was determined by plating on malt salt agar. Samples for the determination of percent damaged kernels (DKT) were taken at weeks two, four, six, and then every six weeks until week 42. Treatment with P- 7 was associated with a reduction in incidence of Penicillium spp. and Aspergillus spp. for the first half of the experiment but not for the second half. In the second half of the experiment, treatment with P-7 was associated with an increase in incidence of Penicillium spp. Based on percent damaged kernels, there was no economic benefit to P-7 application in this experiment.

The inheritance of resistance to aflatoxin production in corn (Zea mays) caused by the fungus Aspergillus flavus was studied following inoculation in progeny derived from the cross between the susceptible inbred B73 and the resistant inbred LB31. In 1993, the susceptible parent B73 (P1), resistant parent LB31 (P2), F1, F3, and BCP1-selfed generations were evaluated. In 1994, the study was expanded to include the F2, BCP1, and BCP2generations. Aflatoxin concentrations were higher in 1993 than 1994. Generation mean analysis showed that additive and dominant gene action were important for resistance to aflatoxin production. Potence ratios indicated dominance for resistance in both years. In 1993, aflatoxin values of the F1generation were significantly lower than the calculated mid-parent values, indicating dominant gene action favoring resistance. In 1994, values of the F1generation were not significantly lower than the calculated midparent value. The frequency distributions of aflatoxin values for families of the F3and BCP1-selfed generations were skewed toward the resistant parent, also indicating dominance. Heritability based on a progeny mean basis of F3families representing the additive variance plus one-fourth of the dominance variance was estimated at 66% over both years combined. Based on these results, selection for resistance to aflatoxin production in progeny derived from the cross between B73 and LB31 should be effective.

The number of potential annual generations of the rusty grain beetle,Cryptolestes ferrugineus, was simulated in wheat stored in granaries for all crop districts in the prairie provinces of Canada each year from 1952 to 1990 using a population dynamic model driven by ecological variables. Granary size was assumed to be 6 m in diameter. Historical data for temperatures at harvest and times when storage began were used in the simulation model. A second model, which predicted the rate of temperature change at the centre of a 6-m-diameter bulk of wheat, determined environmental parameters for the population dynamic model. (Grain moisture content was assumed constant at 14.5% wet mass basis.) The combined model shows that the initial storage temperature is the most important factor responsible for predicting the number of generations and levels of infestation ofC. ferrugineus. This finding was largely validated by historical grain storage and infestation data. For various years initial grain temperature ranged from 17.7 to 37.4 °C and harvest dates were between 1 August and 20 October. The number of generations annually in simulations based on field conditions ranged from 0.35 to 6.77 with a mean of 3.29. Three or more generations result in a severe infestation and every year at least three simulated generations were completed in some crop districts. In one year, at least three generations were completed in every crop district. Harvest temperature and date permit prediction of crop districts that will potentially have the largest populations of C.ferrugineus so that early monitoring of wheat for infestations can be targeted to areas most at risk.

Future maize (Zea mays L.) productivity Increases require breeding materials with high grain yield potential and multiple disease resistance. As part of an integrated program to develop breeding populations with high grain yield potential and multiple disease resistance, two maize synthetics were reciprocally recurrently selected for yield and mass selected for multiple disease resistance. The objective of this study was to determine selection response of two maize synthetics to six cycles of tandem selection for multiple leaf diseases (MLD) and multiple stalk rots (MSR). Plants were inoculated each cycle and evaluated for MLD including their causal agents; northern corn leaf blight, (NCLB) [Exserohilum turcicum (Pass.) Leonard and Suggs, Races 0 and 1], southern corn leaf blight (SCLB) [Bipolaris maydis (Nisik) Shoem.], northern corn leaf spot (NCLS) [Bipolaris zeicola (Stout) Shoem. Races 1, 2, and 3], anthracnose leaf blight [Colletrotri-chum graminicola (CES) G. W. Wils.], and eyespot (Kabatiella zeae Narita and Hurasyka). Following anthesis, plants were inoculated and evaluated for resistance to MSR including their causal agents; diplodia stalk rot (DSR) [Stenicarpella maydis (BERK) Sutton = syn. Diploidia maydis (BERK)], anthracnose stalk rot (ASR) (Colletotrichum gramini-cola), gibberella stalk rot (GSR) [Gibberella zeae (Shw.) Petch.], and fusarium stalk rot [Fusarium moniloforme, Shield]. In 1993 and 1994, selection cycles 0, 2, 4, and 6 of synthetics RSSSC, RBS10, and their cycle crosses were evaluated. Selection response to MLD, NCLB, SCLB, NCLS, gray leaf spot (GLS; Cercospora zeae-maydis Tehon and Daniels), MSR, DSR, GSR, and ASR were measured in separate experiments. Decreases in leaf blight severity from C 0 to C 6 in RSSSC was 29% for MLD, 23% for NCLB, 33% for SCLB, 28% for NCLS, and 21% for GLS. Decreases for RBS10 were 34% for MLD, 33% for NCLB, 37% for SCLB, 49% for NCLS, and 16% for GLS. Cycle crosses were usually intermediate in values for leaf bright reductions. For stalk rots, the reduction in percentage internode area discolored from C 0 to C 6 for RSSSC was 44% for MSR, 42% for DSR, 39% for GSR, and 18% for ASR. Reductions for RBS10 were 63% for MSR, 67% for DSR, 64% for GSR, and 63% for ASR. Selection for multiple disease resistance along with a reciprocal recurrent program for yield resulted in significant improvement in resistance to multiple and individual diseases in RSSSC, RBS10, and their crosses.

Novel thermal death models were developed with certain assumptions, and these models were validated by using actual heat treatment data collected under laboratory conditions at constant temperatures over time and in commercial food-processing facilities where temperatures were dynamically changing over time. The predicted mortalities of both young larvae and adults of the red flour beetle, Tribolium castaneum (Herbst), were within 92-99% of actual measured insect mortalities. There was good concordance between predicted and observed mortalities of young larvae and adults of T. castaneum exposed to constant temperatures in laboratory growth chambers and at variable temperatures during structural heat treatments of commercial food-processing facilities. The models developed in this study can be used to determine effectiveness of structural heat treatments in killing young larvae and adults of T. castaneum and for characterizing insect thermotolerance.

The occurrence of microfloral components on medicated and non-medicated swine and chicken feed pellets and crumbles, produced in a Manitoba feed mill between June 1991 and October 1992, was determined. Addition of medicates to feeds generally decreased bacterial incidence and increased that of Eurotium spp. fungi. The effect was less pronounced when copper sulphate was added to medicated swine feeds.

Corn grain (23.6% moisture) was treated immediately after harvest with DMX-7 Mold Inhibitor (48% propionic acid) at rates of 0, 0.05, 0.1, and 0.2% DMX-7. After treatment, the grain was augered into modified grain bins and dried using ambient air. The incidence of storage fungi was determined following plating of kernels on malt salt agar. DMX-7 Mold Inhibitor reduced the incidence of Penicillium spp. and at some grain sampling levels Aspergillus spp. when compared to the untreated. In general, the control of storage fungi resulted in fewer damaged kernels as determined by a licensed federal grain inspector, however, the difference was only significant on some sampling dates.

The life span of the rusty grain beetle, Cryptolestes ferrugineus, was determined at 30 degrees C, 75% relative humidity (RH) for virgin and mated adults of a malathion-resistant strain (BC6RR), a malathion-susceptible strain (SS), the F1 progeny of a cross between resistant females and susceptible males (RS), and an outbred strain (GV). The BC6RR strain was derived from the SS strain by incorporating the malathion resistance gene into the susceptible genome with six backcrosses and recovery of heterozygous resistant F1 adults between crosses. The mean life span of virgin, malathion-resistant adults (BC6RR and RS) was 37 weeks; the mean life span of virgin, susceptible adults (SS and GV) was 32 weeks. Resistant virgin adults lived significantly longer (15-16%) than susceptible virgin adults, and mated resistant adults lived significantly longer (3-20%) than mated susceptible adults (p < .05). Since C. ferrugineus has a relatively long reproductive period and females with the longest life spans produce the most offspring, life span can be considered an important component of fitness in this insect. The malathion resistance gene did not reduce fitness, and this gene or genes closely linked to it may be responsible for increasing life span in C. ferrugineus.

We examined 27 hepatectomy specimens to assess the frequency of foam cell endovasculitis and bile duct loss in chronic rejection. Arterial lesions, defined as total occlusion by subintimal foam cells and/or fibromuscular proliferation, were found mainly in hilar and septal arteries, whereas bile duct loss, defined as the absence of bile ducts in more than 50% of portal tracts, affected mainly small tracts. Both were found in 20 livers (74%). In two livers (7%) there was significant bile duct loss but no arterial lesions, whilst in five cases (19%) there were occlusive arterial lesions but no bile duct loss. Small arteries were involved in only 10% of the cases. These results indicate that in one-third of the cases arterial and bile duct lesions develop independently of each other, suggesting different pathogenetic pathways. In addition, liver biopsy may not be pathognomonic since small arteries are involved in only 10% of cases and bile duct loss may not be extensive. In such cases the diagnosis of chronic rejection should only be made in the presence of progressive clinical deterioration.

Acanthamoeba is a small, free-living amoeba which is characterized by a feeding and replicating trophozoite and dormant cyst stage. The resistance of acanthamoeba cysts to extremes of temperature, disinfection and desiccation accounts for the ubiquitous distribution of the organism in our environmen

This investigation involved the use of a fungicide, iprodione (trade name ROVRAL® 4F, Rhone-Poulenc Ag Company), to retard mold growth in shelled corn while it was being dried with unheated ambient air at lower-than-normal airflow rates. The lowest airflow of about half of normal recommended airflow resulted in savings for drying of 50% and electrical demand reduction of 75%, compared with drying with normal airflow. In conducting this research, corn of approximately 24% moisture was loaded into five different drying bins. Each of the bins was divided vertically down the center, with one half of the corn being treated with a fungicide and the other half left untreated. Mold damage levels in the treated corn were appreciably lower than in the untreated corn in all the bins, averaging 7.2% mold damage for treated corn and 10.9% for untreated corn. The drying cost (including energy, fungicide, and estimated typical damage discounts) was lower for treated corn in two of the five bins.

Wheat treated with chlorpyrifos-methyl [O,O-dimethyl O-[(3,5,6-trichloro-2-pyridyl) phosphorothioate] and stored for 28 months at 20 degrees C contained about 70% of the applied insecticide as nonextractable (bound) residue mainly in the form of parent compound. The stored wheat containing bound chlorpyrifos-methyl was fed to rats. The bound residue in wheat was released and metabolized predominantly by hydrolysis, as indicated by the presence of a major metabolite, 3,5,6-trichloro-2-pyridinol, in urine and feces. The major route of elimination was via urine, which contained 3,5,6-trichloro-2-pyridinol and O-methyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate. The acetone-extractable portion of feces contained both chlorpyrifos-methyl and 3,5,6-trichloro-2-pyridinol, whereas the nonextractable portion of feces contained only chlorpyrifos-methyl. The results show that bound residues of chlorpyrifos-methyl in stored wheat, which cannot be extracted by methods commonly used in residue analysis of grain, are highly bioavailable.

1. The role played by the endothelium-derived relaxing factor (EDRF), nitric oxide (NO) in the regulation of blood flow to the skeletal muscle vasculature of the dog skinned hindlimb has been determined by examining the effects of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) upon (i) basal iliac artery blood flow, (ii) vasodilator responses to endothelium-dependent and -independent agonists and (iii) reactive hyperaemic responses to arterial occlusion. 2. L-NAME (0.1-3 mg min-1) infused directly into the iliac artery dose-dependently reduced basal iliac artery blood flow by a maximum of 48.6 +/- 6.9% (n = 4) and also increased mean systemic arterial blood pressure by 25.6 +/- 5.0 mmHg (n = 4) (at 3 mg min-1 L-NAME). 3. Over the same dose range, L-NAME also inhibited the peak vasodilator responses to intra-arterially administered, submaximal bolus doses of the endothelium-dependent agonists, bradykinin (3-300 ng) and acetylcholine (30-300 ng) by approximately 40%. In contrast, peak vasodilator responses to the endothelium-independent agonists, sodium azide (3-30 micrograms) and adenosine (0.3-1 mg), and peak reactive hyperaemic responses to arterial occlusion (60 s) were largely unaffected by L-NAME. 4. The dose-related effects of L-NAME on basal iliac artery blood flow, mean systemic arterial blood pressure and endothelium-dependent vasodilator responses were significantly attenuated by pretreatment with L-arginine (100 mg min-1) followed by co-infusion of L-arginine (100 mg min-1) with L-NAME. 5. In conclusion, these data suggest that NO plays some role in regulating basal blood flow and in mediating the vasodilator responses to the endothelium-dependent agonists bradykinin and acetylcholine in the skeletal muscle vasculature of the dog hindlimb. The substantial component (~60%) of the peak vasodilator responses to bradykinin and acetylcholine, unaffected by L-NAME, may be independent of NO, or be mediated by an alternative EDRF-dependent but L-NAME-insensitive mechanism.

Minimum inhibitory concentrations of 13 beta-lactam antibiotics (ampicillin, amoxycillin, amoxycillin/clavulanate, imipenem, cefazolin, cefadroxil, cefaclor, cefuroxime, cefotaxime, cefepime, cefpirome, cefpodoxime and cefixime), were determined for 76 strains of beta-lactamase negative Haemophilus influenzae, isolated over a five year period (1985-1990) that gave reduced zones to cefuroxime on disc testing when compared to the control strain H. influenzae NCTC 11931. MIC90 values for all antibiotics (except imipenem) were approximately ten times higher than the MIC90 values for a susceptible control group. Increased resistance was not associated with any particular biotype, although three biotype III strains were highly resistant to imipenem. More than 50% of strains with reduced susceptibility to beta-lactam antibiotics were isolated from patients with chronic respiratory disease. Published data on the sputum concentration of each antibiotic were compared to the MIC90 values obtained for the susceptible and resistant strains.

Three-hundred and twelve episodes of fever in 234 neutropenic patients with haematological malignancies were treated empirically with either imipenem or a combination of piperacillin and gentamicin. There were no significant differences in the percentages of patients responding to therapy at either 72 h (59% and 56% of assessable episodes in the imipenem and combination groups respectively) or at the end of treatment (55% and 53% of assessable episodes in the imipenem and combination groups respectively). Patients in the piperacillin plus gentamicin group experienced significantly more renal tubular damage whereas those who received imipenem suffered more nausea or vomiting. We conclude that imipenem monotherapy represents an acceptable alternative to piperacillin plus gentamicin as empirical therapy of the febrile neutropenic patient.

An adult Chinese red panda ( Ailurus fulgens styani) transported by airplane from Florida to a North Dakota zoo died 1 week after arrival. Grossly, an interscapular abscess, subcutaneous inflammation, lymphadenitis, and pulmonary abscesses were observed. Microscopic findings included necrotizing inflammation in liver, lung, lymph node, and spleen. Chromobacterium violaceum was cultured from the interscapular abscess, liver, lung, and spleen and was injected into Swiss Webster mice. These mice died 18 hours postinoculation, and C. violaceum was cultured from liver, lung, and spleen. Chromobacterium violaceum is a sporadically reported but highly virulent pathogenic bacterium of both animals and humans typically found as a soil and water inhabitant of tropical and subtropical regions.

Flaxseed (Linum usitatissimum L. 'McGregor') stored at 10, 20, 30, 40, and 50 °C and 35, 50, 60, and 70% relative humidity (RH) for up to 12 mo deteriorated in quality in −1 dry seed (0.51% free fatty acids in oil) rarely increased more than 1.5-fold over 12 mo at 10 or 20 °C and up to 10% MC, or at 30 °C and 7 to 8% MC. Using FAV as a storage quality-loss criterion, flaxseed at 8–9% MC could be stored for 6 mo at 30 °C, 1–2 mo at 40 °C, or a few weeks at 50 °C with less than a 1.5-fold increase. A twofold increase in FAV was correlated to a discoloured or charred appearance of seeds and a rapid loss in seed germination. Seed germination did not decrease during 12 mo at 10 or 20 °C and 70% RH, or at 30 °C and 60% RH. The fungi Aspergillus glaucus group, A. candidus Link, and Penicillium spp. infected seed at some temperatures and relative humidities with low frequency by 6 mo, and A. flavus Link also occurred at 12 mo. Visible microflora were absent after 6 mo on seed at 40 and 50 °C. The beetles Oryzaephilus mercator (Fauvel), O. surinamensis L., Tribolium castaneum (Herbst), and T. confusum J. duVal survived and produced some larvae on both whole and ground flaxseed in 2 mo. McGregor was slightly more suitable for insect reproduction than NorMan or NorLin. Five other insect species could not survive. Extensive infestation of flaxseed by stored-product insects is unlikely. Key words: Flaxseed, storage, free fatty acids, germination, microflora, insects

Restriction endonuclease digestion of Acanthamoeba whole-cell DNA was used to study the relationship between 33 morphologically identical strains from keratitis cases (30 strains), contact lens storage containers (2 strains), and soil (1 strain). Samples digested with BglII, EcoRI, or HindIII and separated by agarose gel electrophoresis contained detectable mitochondrial DNA restriction fragment length polymorphisms (RFLPs). By comparing RFLPs, the strains could be assigned to seven multiple-strain and three single-strain groups. The largest of these contained nine strains, eight of which were isolated in keratitis cases in various locations worldwide and may indicate a group particularly associated with keratitis. Restriction endonuclease analysis of whole-cell DNA is proposed as a valuable technique for detecting mitochondrial DNA RFLPs in the differentiation of morphologically identical Acanthamoeba strains and may therefore be useful in resolving the complex taxonomy of the genus, which has hitherto been founded on subjective morphological criteria.

Three populations derived from crosses of selected resistant inbreds (061, B37HtN, and DS:74:1071) with susceptible inbred FR1141 and a population derived from a cross of B37 × B37HtN were evaluated for gray leaf spot severity in 1992 and 1993 at Urbana, IL, and Andrews, NC. Populations included the susceptible parent (P1), the resistant parent (P2), F1 and F2 generations, backcrosses BCP1 and BCP2, and, when space and seed were available, one or more of the F3, BCP1S1, and BCP2S1 generations. Plants at Urbana were inoculated, and naturally occurring disease was relied upon at Andrews. Individual plants were rated by visually estimating the percent leaf area blighted (necrotic). Generation mean analysis of data combined over years or locations indicated that a simple additive-dominance model was able to explain the inheritance of resistance for all populations. Dominance effects were detected in all population evaluated. For the FR1141 × 061 and FR1141 × B37HtN populations, dominance was significant at early ratings, but not at late ratings. Results from generation mean analysis for individual years, locations, and rating were variable.

The inheritance of resistance to Aspergillus ear rot and aflatoxin production in corn (Zea mays L.) caused by Aspergillus flavus was studied in progeny derived from crosses between the resistant corn inbred cv. Tex6 and susceptible inbred cvs. B73 and Mo17. From 1994 to 1996, plant generations included were the P1(susceptible B73 or Mo17), P2(resistant Tex6), F1, F2, F3, BCP1, BCP1-selfed, and BCP2. The BCP2-selfed generation was added in 1995 and 1996 for the B73 × Tex6 cross. Primary ears were pinboard inoculated and evaluated for Aspergillus ear rot severity. F1means deviated from the midparent value toward resistance for aflatoxin production and toward susceptibility for ear rot in both crosses. Analyses of generation means indicate that additive gene action was most important in the resistance to both ear rot and aflatoxin production in the B73 × Tex6 cross. Mo17 was somewhat resistant to both traits, so resistance from Tex6 was not well defined in this cross. Broad-sense heritabilities for ear rot and aflatoxin production were 58 and 63% for Mo17 × Tex6, and 66 and 65% for B73 × Tex6. Narrow-sense heritabilities for ear rot and aflatoxin production were 39 and 45% for B73 × Tex6. It is estimated that one cycle of selection for resistance within B73 × Tex6 F3families would reduce the percentage of ear rot severity by 8.5% and aflatoxin concentration by 19 ng/g.