Effects of added sulphur on fungicide control of light leaf spot
About this project
Growers in Scotland have recently voiced concerns that triazole fungicides, the main products available for control of light leaf spot, are not giving as good control of the disease now as compared with a few years ago. This has implications for growers throughout the UK . Other methods of controlling light leaf spot or ways of enhancing fungicide efficacy need to be identified. Preliminary investigations have shown that light leaf spot may be transmitted via the seed but further studies are required to confirm this. The aim of this project was to determine if application of sulphur fertiliser could induce disease resistance in oilseed rape plants so aiding the efficacy of fungicides and also to determine if light leaf spot was transmitted within the seed and the implications this would have for home-saving seed.
Identical factorial field experiments were set up in Aberdeen and Inverness to investigate the influence of variety, fungicide and sulphur on light leaf spot (Pyrenopeziza brasssicae ) in oilseed rape. The sites differed in sulphur availability. Two varieties of different disease resistance were tested using both fungicide and no fungicide at two different sulphur and nitrogen levels. Application of sulphur to the soil did not delay the start of or reduce light leaf spot infection; it increased yield but was not cost-effective. Fungicide reduced disease at the low sulphur, low disease site but not at the high sulphur, high disease site. High nitrogen levels had no effect on disease, but increased yield. There were some interactions of fungicide, sulphur and nitrogen on yield but not on control of light leaf spot.
Sulphur fertiliser increased both the sulphur content of young leaves in spring and the leaf content of the amino acid cysteine and its breakdown products. Sulphur also increased the glucosinolate content of leaves at the lower sulphur status site and the glucosinolate content of seeds at both sites. Increased sulphur nutrition tended to increase all of the compounds associated with sulphur-induced resistance (SIR) but disease resistance in the field was not affected. In these experiments enhanced sulphur nutrition could not be used to improve the efficacy of fungicides.
Three field experiments were carried out in Aberdeen to investigate seed transmission of light leaf spot and the potential for home-saving seed. Five varieties were used (Apex, Bristol Lipton, Pronto, Synergy), with seed from different parental sources, including home-saved seed from parental crops that had received a fungicide treatment or had no fungicide treatment and certified seed. Experimental plots did not receive fungicide. The source of the parent seed had no influence on the levels of light leaf spot shown in the daughter crop. Application of fungicide or sulphur fertiliser to the parent crop had no influence on levels of light leaf spot in the daughter crop. It is concluded from this work that light leaf spot is not transmitted in the seed or, if it is, is of no importance for disease development in the daughter crop. All varieties tested could be grown from home-saved seed with no penalties in yield or agronomic characteristics compared with crops grown from certified seed. Breakdown of the heterosis effect was not apparent from home-saving seed of the restored hybrid Pronto and variety association Synergy, when grown in small plots.
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