Survival of Teliospores of Tilletia indica in Soil.

This study was conducted to assess survival of Tilletia indica teliospores in a location in the northern United States. Soils differing in texture and other characteristics were collected from four locations, equilibrated to -0.3 MPa, and infested with teliospores of T. indica to give a density of 103 teliospores per gram of dry soil. Samples (22 g) of the infested soil were placed in 20-µm mesh polyester bags, which were sealed and placed at 2-, 10-, and 25-cm depths in polyvinyl chloride tubes containing the same field soil as the infested bags. Tubes were buried vertically in the ground at Bozeman, MT, in October 1997. Soil samples were assayed for recovery and germination of T. indica teliospores 1 day and 8, 20, and 32 months after incorporation of teliospores into soil. The rates of teliospores recovered from soil samples were 90.2, 18.7, 16.1, and 13.3% after 1 day and 8, 20, and 32 months after incorporation of teliospores into soil, respectively, and was significantly (P < 0.01) affected by soil source. The percentage of teliospore recovery from soil was the greatest in loam soil and lowest from a silt loam soil. The rate of teliospores recovered from soil was not significantly affected by depth of burial and the soil source-depth interaction during the 32-month period. The percentage of germination of teliospores was significantly (P < 0.01) affected by soil source and depth of burial over the 32-month period. The mean percentage of teliospore germination at 1 day, and 8, 20, and 32 months after incorporation into soils was 51.3, 15.1, 16.4, and 16.5%, respectively. In another experiment, samples of silty clay loam soil with 5 × 103 teliospores of T. indica per gram of soil were stored at different temperatures in the laboratory. After 37 months of incubation at 22, 4, -5, and -18°C, the rates of teliospore recovered from soil were 1.6, 2.0, 5.7, and 11.3%, respectively. The percentage of spore germination from soil samples was highest at -5°C. Microscopy studies revealed that disintegration of teliospores begin after breakdown of the sheath-covering teliospore. The results of this study showed that teliospores of T. indica can survive in Montana for more than 32 months and remain viable.

One foot in the furrow: implications to one's career in plant pathology.

Most of us want to be successful in what we do-either financially or programmatically. For me, being a good, well-respected plant pathologist is what motivated me throughout my professional career. After being trained as a plant pathologist at the University of California-Davis, an institution that prides itself in solving problems, I spent the majority of my career in population-sparse Montana-"the last best place." And best place it has been for me as I became involved in researching a number of plant disease problems and solving a few. J.C. Walker's philosophy of keeping "one foot in the furrow" has stood by me, and I encourage young plant pathologists to adopt it as well to ensure a productive and satisfying life in agricultural science.

A Method for Extraction and Enumeration of Teliospores of Tilletia indica, T. controversa, and T. barclayana in Soil.

A sucrose-centrifugation method was developed to extract teliospores of Tilletia indica, T. con-troversa, and T. barclayana from soil. Six soil types were artificially infested with teliospores of each of the three fungi separately to produce 102, 103, 104, or 105 teliospores per 10 g. Each 10 g of infested soil was suspended in 200 ml of water with one drop of Tween 20 and shaken for 30 s. The soil suspension was first passed through a 117-µm sieve and then through a 53-µm mesh filter, and the filtrate was collected. The filtrate was then passed through a 20-µm mesh filter, and materials caught on the mesh were washed into two 50-ml centrifuge tubes and spun for 3 min (1,200 × g). The pellet was suspended in 1.6 M sucrose solution and centrifuged for 40 s (200 × g). The supernatant was passed through a 20-µm mesh filter. The materials caught on the 20-µm mesh were collected, and the number of teliospores was determined. This procedure was initially used to extract teliospores of T. indica in soil. For extraction of teliospores of T. contro-versa and T. barclayana, 1.0 M and 1.3 M sucrose solutions, respectively, were used, and the 20-µm mesh was replaced with a 13-µm mesh filter. Teliospores of T. indica, T. controversa, T. barclayana, and T. indica-like fungus on rye grass were successfully extracted from naturally infested soils. The relationships between number of teliospores recovered from the soil and number of teliospores incorporated into the soil were Y= -0.60 + 1.28(X) - 0.04(X2),Y = -1.25 + 1.56(X) - 0.07(X 2), and Y = -0.71 + 1.33( X) - 0.04(X2) for T. indica, T. controversa, and T. barclayana, respectively, where Y = log10 of the number of teliospores recovered from soil and X = log10 of the actual number of teliospores in soil.

DWARF BUNT: politics, identification, and biology.

Dwarf bunt is a disease of wheat caused by the smut fungus Tilletia controversa Kuhn. Winter wheat (Triticum aestivum L.) is the primary host of economic significance. Although the total acreage affected by dwarf bunt is small relative to total wheat production worldwide, the disease has assumed attention disproportionate to its economic impact because it has become a matter of contention in world trade in cereals. This review describes the political and economic issues underlying the study and identification of T. controversa.

Identification and characterization of rhizosphere-competent bacteria of wheat.

To obtain rhizosphere-competent bacteria which could subsequently be modified for the development of biological control agents, bacteria were isolated from the rhizosphere and rhizoplane of wheat and barley plants by standard techniques. Of these isolates, 60 were selected for field testing as spring wheat seed inoculants in 1985. Isolates were marked genetically for resistance to antibiotics via selection of spontaneous mutants to detect and monitor isolates in the field. Forty-three days after planting, the average log(10) CFU/mg (dry weight) of roots and rhizosphere soil for the mutant isolates sampled ranged from 0 to 3.4. Twenty mutant isolates were retested in 1986. A total of 4 isolates were not detected, but the other 16 had an average root colonization value of log(10) 2.1 CFU and a range of log(10) 0.9 CFU to log(10) 3.2 CFU when sampled 32 days after planting. The average colonization value dropped to log(10) 1.1 CFU 51 days later. Some isolates detected previously were not detected in the second sampling; others had root colonization values similar to those obtained in the first sampling. Mutant isolates of rhizosphere bacteria included Bacillus pumilus, Bacillus subtilis, Pseudomonas fluorescens, Streptomyces spp., Xanthomonas maltophilia, and a saprophytic coryneform. Mixtures of isolates from different genera and species were compatible on seeds and roots.

Mode of action of oxathiin systemic fungicides. V. Effect on electron transport system of Ustilago maydis and Saccharomyces cerevisiae.

The systemic fungicide carboxin (5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide) at 100 mum inhibited succinate cytochrome c reductase in mitochondria from Ustilago maydis and Saccharomyces cerevisiae. It did not have any effect on reduced nicotinamide adenine dinucleotide (NADH) cytochrome c reductase. Succinate coenzyme Q reductase was also inhibited, but NADH coenzyme Q reductase was not. When dichlorophenolindophenol (DCIP) was used as the terminal acceptor of electrons from the oxidation of succinate, carboxin was very effective in inhibiting succinate-DCIP reductase. Carboxin was inhibitory to succinic dehydrogenase assayed with phenazine methosulfate plus DCIP when intact mitochondria were used as the enzyme source but not when solubilized enzyme was used. The main site of action of carboxin, therefore, appears to lie between succinate and coenzyme Q. The dioxide analogue of carboxin was also effective in inhibiting succinate-cytochrome c reductase, succinate-coenzyme Q reductase, or succinate-DCIP reductase, whereas the monoxide analogue was less effective in inhibiting these enzymes.