No abstract

No abstract

SUMMARYIncidence and severity of the take‐all disease in spring wheat and spring barley caused by Gaeumannomyces graminis (syn. Ophiobolus graminis) were studied during seven years of monoculture.The fungus apparently survived for much longer periods in the soil under non‐susceptible break‐crops than previously recorded. The incidence and severity of infection increased progressively with each successive cereal crop from initially low levels to a maximum within 3–7 years, which was followed by a progressive but limited decline in the disease. Spring wheat was more susceptible to take‐all than spring barley and the development of take‐all decline (TAD) was recorded earlier in the sequences of wheat than of barley crops. Nitrogen did not influence the disease until the point of maximum incidence and severity, when it caused a reduction in disease levels in addition to that associated with TAD. Factors influencing the time of onset and the rate of development of take‐all and of TAD are discussed and possible explanations for TAD are suggested.

Abstract. Although Arctic marine ecosystems are changing rapidly, year-round monitoring is currently very limited and presents multiple challenges unique to this region. The Chukchi Ecosystem Observatory (CEO) described here uses new sensor technologies to meet needs for continuous, high-resolution, and year-round observations across all levels of the ecosystem in the biologically productive and seasonally ice-covered Chukchi Sea off the northwest coast of Alaska. This mooring array records a broad suite of variables that facilitate observations, yielding better understanding of physical, chemical, and biological couplings, phenologies, and the overall state of this Arctic shelf marine ecosystem. While cold temperatures and 8 months of sea ice cover present challenging conditions for the operation of the CEO, this extreme environment also serves as a rigorous test bed for innovative ecosystem monitoring strategies. Here, we present data from the 2015–2016 CEO deployments that provide new perspectives on the seasonal evolution of sea ice, water column structure, and physical properties, annual cycles in nitrate, dissolved oxygen, phytoplankton blooms, and export, zooplankton abundance and vertical migration, the occurrence of Arctic cod, and vocalizations of marine mammals such as bearded seals. These integrated ecosystem observations are being combined with ship-based observations and modeling to produce a time series that documents biological community responses to changing seasonal sea ice and water temperatures while establishing a scientific basis for ecosystem management.

The effects of take-all, nitrogen and cropping sequence on grain yield were compared for spring barley and spring wheat grown in extended monoculture. Initial crops showed least take-all and maximum yields. Yields fell to a minimum more rapidly in wheat than in barley while the take-all intensity increased to a maximum ; take-all decline occurred and yields improved from the 4th and 5th years respectively. Without nitrogen, yields were at their lowest level ; application of nitrogen increased yields considerably with responses in proportion to the rate applied. At optimum rates, yield losses were 33 96 for wheat and 11 96 for barley with maximum disease intensity but only 9 % and 3 k respectively with take-all decline. Potential maximum yields in the absence of take-all were calculated to be greater with barley than with wheat. introduction A detailed description has been published (SHIPTON, 1972) of the development of the take-all disease of cereals (caused by Gaeumunnomyces graminis [Sacc.] Arx & (Xivier var. kitici J. Walker) and the onset of take-all decline (TAD) on spring-sown wheat grown in monoculture in trials in the south of England.In view of the considerable possibilities for the commercial exploitation of TAD there is need for information on factors influencing the yield of cereals grown continuously under a range of conditions. This paper describes further the relationship of the yields of grain harvested over a 7 year period (1963)(1964)(1965)(1966)(1967)(1968)(1969) with take-all and applied nitrogen (N). Materlals and MethodsFull experimental details of the phased introduction of 6 cropping sequences (A-F) in the spring barley and spring wheat trials (site A) and of the continuous spring barley trial (site B) at Winchester, Hampshire, have been given in an earlier paper (SHIPTON, 1972) which describes the assessment of take-all and presents data on the incidence and severity of take-all, with particular reference to the development of TAD. These results are summarized in tables 1-3.Yields of grain at maturity were calculated from the amount of grain obtained by combine-harvester from an area 60 f t (18.3 m) x 8 f t 2 in. (2.5 m) equivalent to 0.011 acre (0.0044 ha), and corrected to 85 96 dry matter content.