Long-term population dynamics of Aphelenchoides besseyi on Oryza sativa in a paddy field, and changes in the pathological and ecological traits of the two populations

Summary An Oryza sativa cultivar inoculated with the white tip nematode, Aphelenchoides besseyi, was cultivated over 18 years to investigate the population dynamics of the nematode and the change in the virulence of nematodes and tolerance/resistance of plants. The mean number of living nematodes per seed (S) showed two peaks, each of which was followed by a 3-year decrease in the S value, during the initial 10 years. The annual reproduction curve between in year and in year t had a peak in a range of of <1.1. The incidence of white tip disease increased with increasing mean number of living nematodes seed−1 in the previous year, whereas the proportion of seeds with living nematodes increased with increasing mean number of living nematodes seed−1 in the current year. Inoculation tests of the nematode cohorts on the seedling cohorts derived from seeds harvested in the same or different years indicated that the initial 6-year interaction between the rice and nematode populations caused the nematodes to increase the incidence of white tip disease and to decrease the degree of seed swelling and the proportion of heavy seeds. On the other hand, the interaction caused the rice plants to prevent the incidence of disease from increasing and the degree of seed swelling and the proportion of heavy seeds from decreasing.

Tone Reproduction Curve: rendering intents and their realization in halftone printing

Approaches to determining the Tone Reproduction Curve (TRC) which provides the reliable transfer of visual information in typical conditions of the halftone gray scale compression in relation to dynamic range of a graphic original or input image file are overviewed. The issues of such curve realization are also analyzed with taking into account the specifics of multiple stages of illustrative printing technology.

Exploitation of Multiple Stocks by a Common Fishery

A complete analytical solution is presented for the problem of finding the common rate of exploitation that maximizes total sustained yield from a mixture of stocks when each stock follows a Ricker reproduction curve. A computer program is described which solves this problem for up to 20 stocks varying in both reproductive potentials and absolute sizes. Some aspects of the management of Pacific salmon and fishing strategies are discussed in relation to the question of obtaining maximum yields when harvesting mixtures of stocks under various constraints.

Spawning Stock Size and Resultant Production for Skeena Sockeye

For age 4 and 5 Skeena sockeye, plots of total production of adults from individual brood years against number of parent spawners gave a reproduction curve with an almost linear ascending limb and a very precipitous descending limb. Maximum reproduction (2.4 million sockeye) was achieved at spawning levels of slightly over 0.9 million; the maximum sustained yield (1.4 million) was provided by spawnings of 0.9 million. The stock is very sensitive both to small changes in fishing intensity, and to random variations in survival caused by density-independent environmental fluctuations. Therefore the attainment of high sustained yields by application of a constant optimum exploitation rate is not practical. Regulation to provide the optimum number of spawners each year would more likely provide the highest average yield. Observed fluctuations in commercial catches over the past 50-odd years can be accounted for by changes in annual rates of exploitation. Still higher yields might be attained if individual components of the composite stock studied could be managed separately.