Cross-pathogenicity of Rhizoctonia solani strains on pasture legumes in pasture-crop rotations

In Australia, in the past, pasture legumes were rotated mainly with cereals, but increasingly these rotations now involve pasture legumes with a wider range of crops, including legumes. This increasing frequency of the leguminous host in the rotation system may be associated with increased root rots in legumes in the current pasture-crop rotations. The primary aim of this study was to see whether the pathogenicity on pasture legumes of strains of Rhizoctonia solani sourced from lupins and cereals (common crops in rotation with pastures) is associated with increased incidence of root rots in pasture legumes in the disease conducive sandy soils of the Mediterranean regions of southern Australia. The second aim was to determine sources of resistance among newly introduced pasture legumes to R. solani strains originating from rotational crops as this would reduce the impact of disease in the pasture phase. Fifteen pasture legume genotypes were assessed for their resistance/susceptibility to five different zymogram groups (ZG) of the root rot pathogen R. solani under glasshouse conditions. Of the R. solani groups tested, ZG1–5 and ZG1–4 (both known to be pathogenic on cereals and legumes) overall, caused the most severe root disease across the genotypes tested, significantly more than ZG6 (known to be pathogenic on legumes), in turn significantly >ZG4 (known to be pathogenic on legumes) which in turn was >ZG11 (known to be pathogenic on legumes including tropical species). Overall, Ornithopus sativus Brot. cvs Cadiz and Margurita, Trifolium michelianum Savi. cvs Paradana and Frontier and T. purpureum Loisel. cv. Electro showed a significant level of resistance to root rot caused by R. solani ZG11 (root disease scores ≤1.2 on a 1–3 scale where 3 = maximum disease severity) while O. sativus cvs Cadiz and Erica showed a significant level of resistance to root rot caused by R. solani ZG4 (scores ≤1.2). O. compressus L. cvs Charano and Frontier, O. sativus cv. Erica, and T. purpureum cv. Electro showed some useful resistance to root rot caused by R. solani ZG6 (scores ≤1.8). This is the first time that cvs Cadiz, Electro, Frontier, Margurita and Paradana have been recognised for their levels of resistance to root rot caused by R. solani ZG11; and similarly for cvs Cadiz and Erica against ZG4; and for cvs Charano, Erica, and Electro against ZG6. These genotypes with resistance may also serve as useful sources of resistance in pasture legume breeding programs and also could potentially be exploited directly into areas where other rotation crops are affected by these R. solani strains. None of the tested genotypes showed useful resistance to R. solani ZG1–4 (scores ≥2.0) or ZG1–5 (scores ≥2.5). This study demonstrates the relative potential of the various R. solani ZG strains, and particularly ZG1–4, ZG1–5, ZG4 and ZG6 to attack legume pastures and pose a significant threat to non-pasture crop species susceptible to these strains grown in rotation with these pasture legumes. Significantly, the cross-pathogenicity of these strains could result in the continuous build-up of inoculum of these strains that may seriously affect the productivity eventually of legumes in all rotations. In particular, when choosing pasture legumes as rotation crops, caution needs to be exercised so that the cultivars deployed are those with the best resistance to the R. solani ZGs most likely to be prevalent at the location.     

Influence of paternally imprinted genes on development.

The parental origin of chromosomes is critical for normal development in the mouse because some genes are imprinted resulting in a predetermined preferential expression of one of the alleles. Duplication of the paternal (AG: androgenones) or maternal (GG/PG: gynogenones/parthenogenones) genomes will result in an excess or deficiency of gene dosage with corresponding phenotypic effects. Here, we report on the effects of paternally imprinted genes on development following introduction of the AG inner cell mass into normal blastocysts. There was a striking increase in embryonic growth by up to 50%, and a characteristic change in embryonic shape, partly because of the corresponding increase in length of the anterior-posterior axis. These changes, between e12-e15, were proportional to the contribution from AG cells to the embryo. However, a contribution of AG cells in excess of 50% was invariably lethal as development progressed to e15. A limited number of chimeras were capable of full-term development provided there was a relatively low contribution from AG cells. The distribution of AG cells in chimeras was not uniform, especially later in development when there was a disproportionate presence of AG cells in the mesodermally derived tissues. Their contribution was consistently greater in the heart and skeletal muscle, but was considerably lower in the brain. Chimeras detected after birth were either dead or developed severe abnormalities of the skeletal elements, particularly of the ribs which were enlarged, distorted and fused, with greatly increased cartilaginous material with an absence of normal ossification. These phenotypic effects in chimeras are reciprocal to those observed in the presence of GG/PG cells, which resulted in a substantial size reduction approaching 50%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Novel biotransformations of 4-chlorobiphenyl by a Pseudomonas sp

A bacterium, tentatively identified as a representative of the genus Pseudomonas (strain MB86), was isolated from soil contaminated by wood-preservation chemicals by using 4-chlorobenzoate as an enrichment substrate. The pseudomonad was able to grow on 4-chlorobenzoic acid and 4-chlorobiphenyl as sole carbon and energy sources. Spent culture medium from 4-chlorobiphenyl-grown cells contained 4-chlorobenzoic acid, 4'-chloroacetophenone, 2-hydroxy,2-[4'-chlorophenyl] ethane, and 2-oxo,2-[4'-chlorophenyl] ethanol as metabolites. 4'-Chloroacetophenone was produced in large amounts, possibly as a dead-end metabolite.     

Influence of oxygen tension on the respiratory activity of Mycobacterium phlei

Growth of Mycobacterium phlei under low oxygen tension resulted in specific activities two to twenty times lower for formate dehydrogenase, malate dehydrogenase, beta-hydroxybutyrate dehydrogenase, lactate oxidase and NADH dehydrogenase than when cultures were grown under high aeration. An increase in fumarate reductase and succinate dehydrogenase occurred with M. phlei grown under low oxygen tension. Malate: vitamin K dehydrogenase and glucose-6-phosphate dehydrogenase activity were not significantly affected by the oxygen tension used to grow the bacteria, and neither culture contained a lactate dehydrogenase. With growth of M. phlei in conditions of low oxygen tension, cytochrome a was not detected, but cytochrome b was prominent in membranes and cytochrome c was present in the soluble fraction.     

The gene for autosomal dominant polycystic kidney disease lies in a 750-kb CpG-rich region.

PKD1, the locus most commonly affected by mutations that produce autosomal dominant polycystic kidney disease (ADPKD), has previously been localized to chromosome 16p13.3. Since no cytogenetic abnormalities have been found in association with ADPKD, flanking genetic markers have been required to define an interval--the PKD1 region--that contains the PKD1 gene. In this report we demonstrate, through the construction of a long-range restriction map that links the flanking genetic markers GGG1 (D16S84) and 26.6PROX (D16S125), that the PKD1 gene lies within an extremely CpG-rich 750-kb segment of chromosome 16p13.3. Approximately 90% of this region has been cloned in three extensive cosmid/bacteriophage contigs. The cloned DNA is a valuable resource for identifying new closer flanking genetic markers and for isolating candidate genes from the region.