Potential adaptation zones for temperate pasture species as constrained by climate: a knowledge-based logical modelling approach

Potential adaptation zones were modelled for major temperate pasture species using climate data and knowledge-based logical rules. A GIs database was constructed using a 0.025 degree digital elevation model and the Australian Climate Surfaces to create layers of monthly mean climate data for Australia. Soil pH maps for New South Wales, Victoria, and south-eastern South Australia were digitised and added to the database. Simple models using logical operators were constructed using estimates of temperature and aridity thresholds for the main temperate pasture species. The logical models were executed using primary and derived climate layers to create raster maps of potential adaptation zones for pasture species in eastern and south-western Australia. Areas of adaptation on freehold/leasehold land were expressed relative to a potential temperate pasture adaptation zone described by the lower (arid) limit of annual legume adaptation in temperate Australia and the northern limit of lucerne adaptation. Potential adaptation within this area ranged from 66% for lucerne down to <20% for perennial ryegrass in eastern Australia, and 93% for subterranean clover down to zero for perennial ryegrass in south-western Australia. Utility of the species adaptation zones could be enhanced using soil pH maps: a zone for serradella in NSW was refined by restricting adaptation to areas of climatic suitability with low soil pH. Maps for lucerne and Mount Barker subterranean clover showed good agreement with validation data for NSW. The zones may be readily adjusted by simple changes to parameter values in the algorithms. This knowledge-based approach has potential as an aid to targeting resources for plant improvement or to provide advice for more efficient utilisation of existing commercial pasture plants.

Fish, n-3 fatty acids and human colorectal and breast cancer mortality

Although there is a strong positive association between total fat consumption and colorectal and breast cancer risk, there is evidence that n-3 fatty acids, mainly found in fish oil, are protective. If this is so, we would expect to be able to detect an inverse correlation between fish consumption and colorectal cancer and breast cancer mortality. Mortality data for breast and colorectal cancer in 24 European countries were correlated with current fish and fish oil consumption and with consumption 10 and 23 years previously. In males there was an inverse correlation between colorectal cancer mortality and current intake of fish (P = 0.036), a weaker correlation with fish consumption 10 years earlier (P = 0.042) and none with consumption 23 years earlier (P = 0.12). The data were not statistically significant in females. There was no correlation at all between breast cancer mortality and fish or fish oil consumption at any time. It is concluded that fish consumption is associated with protection against the later promotional stages of colorectal carcinogenesis, but not with the early initiation stages. The results are discussed in terms of the role of prostaglandins in colorectal carcinogenesis.

Diet and chemoprevention of colorectal cancer

There is copious evidence of the importance of diet in the causation of colorectal cancer. This comes from studies of populations, case-control studies, and prospective or cohort studies. The evidence from epidemiology is now beginning to treach a clear concensus that the disease is associated with high intakes of fat and meat and low intakes of cereal fibre, fruit and vegetables. There are various ways in which these observations are being applied to colorectal cancer prevention. These include dietary advice to populations and specific advice given to individuals at high risk of the disease.

The association between typhoid carriage, typhoid infection and subsequent cancer at a number of sites

It has been demonstrated that bacteria can produce the very potent carcinogens (N-nitroso compounds), from nitrite and suitable amines. It has been hypothesized that this can happen whenever a body site which is normally sterile becomes colonized by bacteria. If this is so then such chronic infections should result in an increased incidence of local cancers and also of cancers at some distant sites. To test this we studied the risk of cancer at various sites in a cohort of chronic carriers of Salmonella typhi/paratyphi. We have observed a greatly increased risk of cancers of the biliary tract and also of cancers of the colorectum, pancreas, lung and all sites. The results are discussed in terms of the hypothesis being tested.

Seedling vigour and rhizome development in Trifolium ambiguum M. Bieb. (Caucasian clover) as affected by density of companion grasses, fertility, drought and defoliation in the first year

Trifolium ambiguum was grown from seed in a mixture with Festuca arundinacea and Phalaris aquatica at four grass densities under high fertility, and at two intermediate grass densities under low fertility, with frequent or infrequent defoliation imposed from week 15 to week 31, in large pots for 1 year. Selective defoliation of the clover at week 35, and 3-4 weeks drought were imposed on high and low fertility treatments in the post-cutting period. The impact of these treatments was assessed by destructive harvest of shoots, roots and rhizomes. Plant densities of T. ambiguum and grasses were unaffected by the treatments; however, rhizome numbers were reduced by increasing density of grasses, by frequent defoliation, and at high fertility compared with low fertility where grass vigour was very poor. Selective defoliation of T. ambiguum and short-term drought temporarily reduced the contribution of T. ambiguum to harvested herbage, but had no permanent effect on growth rate. Final root and rhizome biomass of T. ambiguum was reduced by increasing density of grass, by frequent defoliation and at high fertility where grass competition was vigorous. We conclude that early growth of T. ambiguum, in particular root and rhizome development, may be better where the density of companion grasses is low, or grass vigour is low due to low fertility, provided soil P and S are not limiting for clover growth. Defoliation in the presence of vigorous grass competition reduces root and rhizome development and may not be effective in minimizing competition. Options for inclusion of T. ambiguum in mixed swards are discussed.