Abstract
A new distribution map is provided for Cronartium ribicola J.C. Fischer. Hosts: Pinus and Ribes. Information is given on the geographical distribution in ASIA, China (Shensi), India (N.W.), Iran, Japan, Korea, Nepal, Pakistan, Taiwan, USSR (Siberia), EUROPE, Austria, Belgium, Great Britain and Northern Ireland, Czechoslovakia, Denmark, Finland, France, Germany, Hungary, Irish Republic, Italy, Netherlands, Norway, Poland, Romania, Spain, Sweden, Switzerland, USSR (Tranzschel; Kuprevich & Tranzschel loc. cit.), (Ukraine), Yugoslavia, NORTH AMERICA, Canada, USA.
White pine seedlings were treated with triadimefon two weeks prior to natural inoculation with Cronartium ribicola and were observed for two growth seasons. During the second growth season in the greenhouse the incidence of blister rust symptoms was 70.8% for the untreated controls, whereas only 3.8% of the treated seedlings showed symptoms of blister rust. Triadimefon offers effective protection against white pine blister rust infection and would enable the production of bare root seedlings in areas prone to blister rust infection.
SUMMARYThe commonly held view that the kinetoplastida, and in particular trypanosomes, are asexual is largely derived from the principle that an organism is asexual until proved sexual. If the basis for this view is examined in detail, it largely arises from the lack of morphologically distinguishable gametes, the difficulties encountered in visualizing chromosomes and a few experiments, using drug-resistant stocks, in which no recombination between stocks could be demonstrated. While it is clear that these organisms are able to reproduce asexually, the existence of a sexual cycle was, until recently, an entirely open question. The early work strongly suggests that any sexual process (in the species examined extensively at the morphological level) does not involve classical well-differentiated gametes and so must involve fusion of morphologically very similar cells. These findings taken together with the inability to visualize chromosomes and thereby identify meiosis, mean that classical methods are unable to detect any sexual process even if it did occur. This review examines the evidence provided by the experimental approaches which have been applied recently to the question of kinetoplastid sexuality. These approaches include isoenzyme studies and the analysis of possible genetic exchange by the use of selective markers (e.g. drug resistance). The results which these techniques have produced make it clear that the kinetoplastid protozoans cannot be regarded as a totally asexual group of organisms.
SUMMARYThe genetic basis of slow growth rate and aberrations in the ciliary pattern was studied in the multi-left-marginal variant ofParaurostyla weissei. The 3:1 segregation in F2 sibling crosses and 1:1 segregation in test crosses indicate that the aberrant phenotype is controlled by a recessive allele at a single gene locus termedmlm. The phenotypic change from wild type tomlmtakes place about 5–8 cell cycles after conjugation. The study established that total conjugation inP. weisseiis a true sexual process in which meiosis, fertilization and Mendelian segregation occur.
The ribosomal gene repeat in Cronartium ribicola J.C. Fisch is highly variable among spore samples from British Columbia, Canada. Both restriction site variation and length variation occur. Length heterogeneity results from differences in the number of subrepeats in the intergenic spacer (IGS). The number of IGS size classes in haploid cultures is limited but is very large and highly variable in aeciospores from single cankers. The proportions of different size classes vary among cankers on different trees, and among subsamples taken around the periphery of large old cankers. The results are consistent with the fungus having a haploid infective mycelium that produces functional pycnia that result in localized dikaryotic areas following fusion between flexuous hyphae and pycnia. Restriction site variation appears lower than has been reported in range-wide samples of endemic fungal species, consistent with the hypothesis that introduction of C. ribicola to western North America was limited and does not represent the full genetic range of the species. No particular restriction site variants or IGS size classes characterize samples from particular geographic areas. No evidence for geographic races of the fungus was obtained. Keywords: rusts, rust races, ribosomal DNA, intergenic spacer, population structure, RFLP.
Lack of genetic markers has hindered the study of the mating system of Cronartium ribicola, an exotic forest pathogen Meeting natural and cultivated white pines throughout North America. Isozymes, randomly amplified polymorphic DNA (RAPDs), and restriction length polymorphisms (RFLPs) were used to study the mating system of this rust. Heterozygosity (outcrossing) in diploid telia was demonstrated by analysis of cultures derived from the meiotic products (basidiospores) of individual telia. Families of basidiospores cultured from single telia were used to test for Mendelian segregation and for conformance of loci to Hardy–Weinberg equilibrium. A total of 18 polymorphic loci were identified with the three marker systems. All except for three RAPD loci showed Mendelian segregation in the single-telium families. To quantify the level of outcrossing, gene and genotype frequencies were calculated for families from a single population. Up to 24 families were surveyed with isozymes, 14 with RAPDs, and 18 with RFLPs. Except for one isozyme locus (MPI) in one sample, all 14 loci tested with these families were in Hardy–Weinberg equilibrium, indicating random mating. Further studies, with a different sample from the same population, showed all three isozyme loci to be in Hardy–Weinberg equilibrium. The three marker systems were consistent as to the amount of variation detected. Resistance selection and breeding programs must consider the implications of genetic recombination that outcrossing affords the rust. Keywords: isozymes, RAPDs, RFLPs, Hardy–Weinberg equilibrium, white pine blister rust.
Cultured tissues from Pseudotsuga menziesii (Mirb.) Franco were successfully inoculated with Cronartium ribicola J. C. Fisch. ex Rabenh. Typical intracellular haustoria were formed 60 days after inoculation. Invaded nonhost tissues were necrotic within 90 days, and dead within 120 days. Tissue cultures of either Pinus monticola Dougl. or P. menziesii had an attractant effect on nearby rust mycelium.
Use of triadimefon to control white pine blister rust