One stop mycology

Seasonal variation in abundance of spores of arbuscular mycorrhizal fungi was examined for four growing seasons on burned and unburned sand prairies in Illinois. The three leading mycorrhizal species were an undescribed species of Glomus, Scutettospora heterogama, and Sclerocystis rubiformis, in order of decreasing abundance. Mycorrhizal spore abundance for all species generally showed similar seasonal patterns on burned and unburned sites during the sampling period, i.e., minimal in the middle of the growing season and maximal near the end of the season. Individual species, however, exhibited different seasonal patterns of sporulation or sporulation strategies. Burning caused a 2-year depression in spore abundance for Glomus species and Scutellospora heterogama, and a 3-year long depression in spore abundance for Sclerocystis rubiformis. The seasonal patterns observed were more discernible in root zone than in randomly collected soil. Spore abundances were always significantly lower on burned sites than on unburned sites early in the growing season. The results of this study, and studies conducted parallel to this one, suggest that the greater decline in spore abundance in burned sites than in unburned sites early in the growing season may be indirectly due to greater root growth, and (or) related changes in host physiology, in response to fire. Key words: mycorrhizae, fire, sand prairie, grassland, sporulation, inoculum, fungi.

Seasonal dynamics of dominant species of arbuscular mycorrhizae in burned and unburned sand prairies

Dhillion¹,

Anderson²

1993

Copper and nickel pollution: frequency of endophytic fungi in Scots pine shoots and endophyte growth in vitro

Ranta¹,

Neuvonen²,

Kääriäinen³

et al. 1994

The frequency of endophytic microfungi was measured from current-year shoots of Scots pine trees growing in Harjavalta, a heavily polluted area in western Finland. The copper (Cu) and (Ni) concentrations in bark plus phloem and needles of the same trees were measured. The frequency of isolates of endophytic taxa were either negatively (Hormonema sp. 2 and Sterile sp. 1) or positively (Hormonema sp. 1, BL132) correlated with the Cu and Ni concentration of bark plus phloem. Isolates of the most common endophytic taxa and the pathogenic Gremmeniella abietina from Harjavalta were grown in vitro in different levels of Cu (0.6 – 126 μg/mL) and Ni (0.3 – 50 μg/mL) separately and in combination. This experiment included also isolates of G. abietina and Hormonema sp. 1 from the northern (unpolluted) area. The concentrations of Cu and Ni that reduced the linear growth to 50% of control were estimated. The endophyte taxa with positively correlated frequency with increasing concentration of Cu and Ni in the shoots were able to withstand elevated levels of Cu and Ni in vitro. Compared with most of the other fungi, G. abietina isolates were particularly sensitive to addition of Ni. No evidence for intraspecific adaptation of G. abietina and Hormonema sp. 1 to Cu and Ni was found. Key words: endophyte, Gremmeniella, heavy metal, Hormonema, Scots pine.

Generation and utilization of chemical-resistant mutants in Pyrenophora tritici-repentis, the causal agent of tan spot of wheat

McCallum¹,

Bernier²,

Lamari³

1994

Tan spot, caused by the fungal pathogen Pyrenophora tritici-repentis, is a major leaf spot disease of wheat worldwide. To facilitate genetic analysis of this homothallic fungus, mutants resistant to the fungicide iprodione or hygromycin B were created through ultraviolet light mutagenesis and used in sexual crosses. Conidia from two isolates of P. tritici-repentis, sensitive to both chemicals (iprodione-S hygromycin-S), were exposed to ultraviolet light to obtain four mutants resistant to iprodione but sensitive to hygromycin B (iprodione-R hygromycin-S) and three mutants resistant to hygromycin B but sensitive to iprodione (iprodione-S hygromycin-R). The mutants were paired in all combinations, and the markers allowed crossed progeny to be distinguished from selfed progeny. Crossed ascospore progeny from pairings between iprodione-R hygromycin-S isolates and iprodione-S hygromycin-R isolates and between iprodione-R hygromycin-R isolates and iprodione-S hygromycin-S segregated 1:1 for resistance–sensitivity to both iprodione and hygromycin B. These results indicate that one locus controls iprodione resistance and a second independent locus controls hygromycin B resistance. This study should facilitate further genetic research on the tan spot fungus by providing a simple marker system. Key words: genetics, inheritance, Drechslera, yellow spot, leaf spot.