Take-all in autumn-sown wheat, barley, triticale and rye grown with high and low inputs

Winter cultivars of wheat, barley, triticale and rye were grown under two contrasting husbandry systems (low and high inputs) at two locations (Woburn and Rothamsted) known to be infested with the take-all fungus. The sandy loam at Woburn is less fertile than the silty clay loam at Rothamsted. Root infection in these crops was assessed in spring and summer.
Rye was least infected by the take-all fungus, wheat the most infected and barley and triticale had intermediate levels of infection. Barley yields were less affected by take-all than those of wheat or triticale, because barley was at a later growth stage by the time severe infection occurred. Yields of wheat and barley responded most to the high-input husbandry on the less fertile soil at Woburn. On the basis of quantity of grain, triticale would appear to be a good substitute for wheat on the less fertile soil when inputs are low, but not where they are high. At Rothamsted, yields of wheat and triticale were similar in both input systems. There was no strong support, at either site, for the contention that triticale could be a useful substitute for barley where low or high inputs are used. A total of 177 isolates of Gaeumannomyces graminis var. tritici (the causal fungus of take-all) were obtained from infected roots in these experiments and tested for their pathogenicity on wheat and rye seedlings. These tests revealed a range of pathotypes with varying pathogenicities to wheat and rye, but pathogenicities were not correlated with the host plant from which the fungi were isolated.     

A model to explain the formation of catarina scallop, Argopecten circularis (Sowerby, 1835), beds, in Magdalena Bay, Mexico

Abstract. During the years of 1989 and 1990, the yield of the commercial fishery for the catarina scallop, Argopecten circularis (Sowerby, 1835), in Magdalena Bay, was 750 million organisms (5186t of muscles), which were gathered by diving at 12–30m depth. This production is the largest registered to date and accounted for 53% of the total Mexican scallop production since 1981. The formation of large beds in that area is a sporadic phenomenon which needs to be studied. In the present paper, a model to explain the formation of such beds is drawn, in which the bentho-pelagic red crab, Pleuroncodes planipes (Stimpson, 1860), plays a role as primary substrate for the recruitment of the spat and simultaneously is the active transporter of juveniles into the Bay during the winter months of cold years. Apparently exploitable beds are formed only when temperatures of 16°C or lower, are registered deep inside the Bay for at least 2 months. Relating these findings with short and long-term temperature fluctuations, it seems possible to predict future exploitable stocks in the area.