Survival of Tilletia indica Teliospores in Different Soils.

To determine the potential for Tilletia indica, cause of Karnal bunt of wheat, to survive and become established in new areas, a teliospore longevity study was initiated in Kansas, Maryland, Georgia, and Arizona. Soil from each location was infested with T. indica teliospores and placed in polyester mesh bags. The bags were placed within soil from the same location within polyvinyl chloride pipes. Pipes were buried in the respective plots such that the bags were at 5-, 10-, and 25-cm depths. Each pipe was open at the ends to allow interaction with the outside environment, however fitted with screens preventing possibility of teliospore escape. In the Karnal bunt-quarantine area of Arizona, bags of infested soil also were placed outside the pipes. Teliospore-infested soil from each location was maintained dry in a laboratory. During the first 2 years, viability declined more rapidly in pipes than outside pipes, and more rapidly in fields in Kansas and Maryland than in Georgia or Arizona. After 2 years, viability declined nearly equally. In the laboratory over 3 years, viability decreased significantly more rapidly in dry soil from Kansas or Maryland than in dry soil from Georgia or Arizona, while pure teliospores remained unchanged. We hypothesized that soils, irrespective of weather, affect teliospore longevity.

Identity and conservation of mating type genes in geographically diverse isolates of Phaeosphaeria nodorum.

Mating type idiomorphs (MAT1-1 and MAT1-2) were identified from the heterothallic loculoascomycete Phaeosphaeria nodorum (wheat biotype) using DNA from a pair of isolates from Poland and Georgia, USA that are known to mate. MAT predicted proteins of P. nodorum are similar in sequence and in phylogenetic relationship to those described for other loculoascomycetes such as Cochliobolus spp., Alternaria alternata, and Didymella zeae-maydis. The organization of the MAT locus of the P. nodorum differs from these species in that its idiomorph begins within an adjacent upstream conserved ORF of unknown function. MAT-specific primers were used to identify isolates of both mating types in field populations, demonstrating that an absence of either mating type is not the reason that the teleomorph has not been found in New York. Portions of MAT1-1 and MAT1-2 were sequenced from geographically diverse isolates, including those from regions where the teleomorph has been reported. MAT was highly conserved and no significant differences in sequence were found.

The isolation and identification of several trichothecene mycotoxins from Fusarium heterosporum.

An isolate of Fusarium heterosporum Nees ex Fr. that parasitizes the honeydew and immature sclerotia of Claviceps paspali was shown to be highly toxigenic to day-old chickens. The major toxicity of culture extracts of the fungus was due to the presence of several trichothecene mycotoxins. Six trichothecenes were isolated and chemically identified by spectroscopic methods as T-2 toxin (1), HT-2 toxin (2), T-2 tetraol (6), 3alpha,4beta,dihydroxy-15-acetoxy-8alpha-(3-hydroxy-3-methylbutyryloxy)-12,13-epoxytrichothec-9-ene (3), 3alpha,4beta,15-trihydroxy-8alpha-(3-hydroxy-3-methylbutyryloxy)-12,13-epoxytri chothec-9-ene (5), and 3alpha,4beta,8alpha-trihydroxy-15-acetoxy-12,13-epoxytrichothec-9-ene (4). The acute toxicities of the trichothecenes were compared to the effects of T-2 toxin in day-old chickens and on the back skins of rabbits. The comparative inhibitory effects of the trichothecene mycotoxins in the Triticum coleoptile bioassays were also determined.

Effect of irradiance upon the population of Pseudomonas coronafaciens in leaves and symptom expression of halo blight of rye.

The toxin-induced chlorosis caused by Pseudomonas coronafaciens is influenced by irradiance. Three levels of irradiance caused differences in symptom expression but did not affect the rate of increase or final population of viable cells of P. coronafaciens in rye leaves. Distinct and faint halo blight symptoms appeared in 3--4 days in full light (1425 microW cm-2), and 58% shade (598 microW cm-2) respectively. No symptoms or only faint symptoms appeared after 7 days at 86% shade (202 microW cm-2). When plants kept in 58 and 86% shade were moved to full light 5 days after inoculation, lesion size and chlorosis increased rapidly during the next 2 days. On the 7th day after inoculation, the size of lesions from the 58 and 86% shade treatments exceeded those in full light by 2.5 and 5 times, respectively. A chlorosis index based on lesion size and chlorophyll loss within lesions also reflected this trend although chlorophyll loss was greater in lesions in full light for 7 days. Conditions of low irradiance such as that caused by overcast weather and (or) a dense leaf canopy followed by bright sunshine can cause greater losses from halo blight than a continuous period of high irradiance. Sympton expression may be masked by low irradiance but increase of inoculum is not impaired. Although increased light enhances chlorosis, toxin diffusion or production may be reduced.