The role of autotoxins from root residues of the previous crop in the replant disease of asparagus     

W. J. Blok  G. J. Bollen 《European journal of plant pathology / European Foundation for Plant Pathology》1993,99(3):29-40

Replant disease is a common phenomenon in asparagus growing in the Netherlands. It is distinct from the decline phenomenon reported from many other asparagus producing area’s. The involvement of autotoxins from root residues of former asparagus crops was evaluated. Residues of aspar agus roots decompose extremely slowly. At two locations, each with fields where asparagus production was terminated 1 and 10 years before, biomass of root residues was 4180 and 11060 kg dw ha^?1 after 1 year and 420 and 1140 kg dw ha^?1 after 10 years.Although 10-year-old residues were for the greater part decomposed, crude aqueous extracts inhibited root growth of asparagus seedlings significantly and even more of garden cress. In root observation boxes with field soil mixed with non-sterilized or sterilized asparagus root fragments, growth of secondary roots was inhibited. Non-sterilized strawberry roots did not inhibit root growth, suggesting that effects of organic matter were not involved. In a pot experiment, sterilized asparagus root fragments inhibited root growth when added at a rate of 20 g1^?1, but not a 2 g1^?1 Addition of non-sterilized root fragments strongly inhibited root growth at both levels. This was probably due to simultaneous infection byFusarium oxysporum present in these residues. When an asparagus field is replanted, the amount of root residues left behind in soil after termination of the crop in the previous season is about 2 g dw 1^?1, that corresponds to approx. 11000 kg dw ha^?1. This level is too low for considering direct growth inhibition by autotoxins as a major factor. Their possible indirect effects are briefly discussed.  相似文献   

The energy density of water and ice nucleation     

Wilen L 《Science (New York, N.Y.)》1993,259(5100):1469

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A 2000-year tree ring record of annual temperatures in the sierra nevada mountains     

Scuderi LA 《Science (New York, N.Y.)》1993,259(5100):1433-1436

Tree ring data have been used to reconstruct the mean late-season (June through January) temperature at a timberline site in the Sierra Nevada, California, for each of the past 2000 years. Long-term trends in the temperature reconstruction are indicative of a 125-year periodicity that may be linked to solar activity as reflected in radiocarbon and auroral records. The results indicate that both the warm intervals during the Medieval Warm Epoch ( approximately A.D. 800 to 1200) and the cold intervals during the Little Ice Age ( approximately A.D. 1200 to 1900) are closely associated with the 125-year period. Significant changes in the phase of the 125-year temperature variation occur at the onset and termination of the most recent radiocarbon triplet and may indicate chaotic solar behavior.  相似文献   

Mesostructure silicate names     

Stucky G 《Science (New York, N.Y.)》1993,262(5134):640

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Converting weapons to fuel     

Prussin SG  Glassey CR  Melese G 《Science (New York, N.Y.)》1993,260(5108):607

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The biological history of a seaway     

Vermeij GJ 《Science (New York, N.Y.)》1993,260(5114):1603-1604

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E-mail withdrawal prompts spasm     

Taubes G 《Science (New York, N.Y.)》1993,262(5131):173-174

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Elderly migration and development in small communities   总被引：1，自引：0，他引：1  

Rowles GD  Watkins JF 《Growth and change》1993,24(4):509-538

"This paper develops a conceptual model of the process of community change [in the United States] in response to elderly inmigration. Analysis of intra-regional variation in elderly migration patterns in Appalachia, and synthesis of an emergent literature on the benefits and costs of attracting elderly migrants, serve as a backdrop for case studies, based on field observations and interviews, of three contrasting Appalachian communities at different stages of development as retirement destinations."  相似文献   

Mourning the plight of the condor     

Taubes G 《Science (New York, N.Y.)》1993,259(5101):1531

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Measurement of endogenous amino acid losses in poultry     

P. Siriwan  W. L. Bryden  Y. Mollah  E. F. Annison 《British poultry science》1993,34(5):939-949

1. Ileal endogenous amino acid losses were determined in broiler chickens and in cannulated cross‐bred layer strain cockerels using either a nitrogen‐free diet, regression analysis or a 48 h fast.

2. Endogenous amino acid flows to the ileum in fasted cockerels were significantly lower than those obtained both by feeding the nitrogen‐free diet, and from regression analysis in either broilers or cockerels. Regression analysis gave the highest flows.

3. The apparent digestibility coefficients of amino acids in a diet containing 200 g/kg crude protein were lower in broilers (0.84) than in cockerels (0.88). When corrected, by regression analysis, for the contribution of endogenous amino acids, the true digestibility coefficients became 0.90 and 0.92 respectively.  相似文献