This is the final report of a 48 month project (RD-2004-3099) which started in March 2006. It was a Sustainable Arable LINK project funded by a contract for £392,077 from BBSRC with in-kind contributions from HGCA, Du Pont UK, Masstock Arable, KWS UK and Scottish Agronomy.
Controlled environment (CE) and field experiments were done to investigate effects of fungicide on growth of L. maculans and L. biglobosa in relation to development of phoma leaf spots and phoma stem canker on oilseed rape. In CE experiments, for plants inoculated with L. maculans, fungicide treatment decreased lesion size and amount of L. maculans DNA in leaves; for plants inoculated with L. biglobosa, fungicide did not affect lesion size or amount of pathogen DNA. In field experiments in 2006/07 and 2007/08, fungicide treatment decreased phoma leaf spot incidence in autumn and stem canker severity at harvest, and increased yield. Fungicide treatment decreased stem canker severity more on cv. Courage, with a good yield response, than on cv. Canberra. In 2006/07, fungicide decreased the amount of L. maculans DNA more than that of L. biglobosa in stem tissues (measured by quantitative PCR). There was a linear relationship between the amount of L. maculans DNA in stems and the stem canker severity score at harvest, but there was no clear relationship between the amount of L. biglobosa DNA in stems and the stem canker severity score. These results suggest that effects of fungicides on interactions between L. maculans and L. biglobosa might affect severity of phoma stem canker and yield response.
Herbicide-resistant weeds pose a significant threat to the sustainability of global grain production. Of all weeds in Australian farming systems, wild radish (Raphanus raphanistrum L.) is one of the most economically damaging, aggressively competing for water, nutrients and light. As a result of herbicide over-reliance, wild radish populations in the Western Australian (WA) grainbelt have evolved multiple resistances to inhibitors of acetolactate synthase (ALS), phytoene desaturase (PDS), photosynthetic electron transport (PSII) and synthetic auxin herbicides. However, following 40 years of over-reliance on glyphosate, this PhD study is the first to report glyphosate resistance in wild radish. Two wild radish populations from fallow fields near Mingenew and Carnamah in the WA grainbelt exhibited a heritable, 3.2 (WARR37) and 4.5 (WARR38) fold resistance (LD50) to glyphosate. Both populations also had multiple resistances to ALS inhibitors, PDS inhibitors and synthetic auxin herbicides, which is expected to intensify the selection for glyphosate resistance in these populations. The inspection of 24,000 ha of the first commercial transgenic glyphosate-resistant (GR) canola plantings in the WA grainbelt (2010–2011) found large wild radish populations treated solely with glyphosate, which often resulted in less than complete control. Glyphosate resistance in wild radish however was rare, with only one additional GR population identified. This survey also identified glyphosate resistance in eight annual ryegrass (Lolium rigidum L.) populations. However no glyphosate resistance was identified in barley grass species (Hordeum sp.), brome grass species (Bromus sp.), wild oat species (Avena sp.), capeweed (Arctotheca calendula L.) and mallow (Malvia parviflora L.). The less than complete control of wild radish in the first GR canola crops grown in the WA grainbelt was of concern, as four generations of glyphosate selection at rates that do not provide full control, resulted in modest increases in glyphosate resistance (2.4-fold). Additionally this selection also resulted in weak cross resistance to the ALS-inhibiting herbicides imazamox (4.7fold) and metosulam (3.7-fold). The biochemical basis of this weak resistance remains to be investigated. In response to the growing number of dicot species that have evolved glyphosate resistance in the Americas, synthetic auxin tolerance has been incorporated into transgenic herbicideresistant crops. This study highlights that the sustainability of 2,4-D amine use on wild radish is contingent on consistently achieving high levels of control. Following four generations of lowdose 2,4-D amine selection, 2,4-D resistance increased 9.6-fold (LD50). Alarmingly along with 2,4-
Pests and particularly diseases cause serious loss of yield and quality in winter oilseed rape estimated to exceed £80 million/annum in some years. These losses have occurred despite an annual expenditure of about £3.5 million for insecticides and £12 million on fungicides. Decision-making is difficult because there is complex spatial and temporal variation in pest and disease problems and improved guidance is required. The main objective of this project was to test new disease models developed in the first phase of this project and deliver a decision support system for both pest and disease control in oilseed rape.
The regional light leaf spot forecast is well-established and reliable and indicates an increased risk of this disease in spring 2006. A new regional forecast for stem canker incidence preharvest has been developed and made available on the Internet. It was successful in 2004/05 and offers strategic guidance on risk provided weather factors are within the range used to develop the model. A four-stage crop-specific stem canker risk assessment method was developed that predicts the onset of phoma leaf spotting using post-harvest weather data and thermal time relationships for canker development and canker severity. Yield loss can then be calculated from canker severity and the economic impact of stem canker predicted.
There is some flexibility in the timing of fungicide sprays to control stem canker. Delays of 2 to 3 weeks beyond a 10-20% plants affected threshold did not adversely affect yield. Stem canker severity and yield of different cultivars showed large variation between years and sites and smaller, but significant, variation in responses to fungicide. When phoma leaf spot appears in late autumn, it is only when plants are small that stem canker is likely to cause yield loss. In commercial crops, there were consistent trends for higher yields to be associated with higher fungicide inputs. Light leaf spot was very difficult to control with fungicides in the Aberdeen area where use of resistant cultivars is essential. The most effective disease control was obtained using a combination of resistant cultivars and fungicides. In some years, responses to fungicides were not cost-effective and targeting their use to high-risk situations is necessary to give the best margins over input costs.
Close contact was maintained with potential users during the project and they influenced priorities and design features. The components of PASSWORD decision support system were tested and provide guidance for the management of invertebrate pests, phoma stem canker and light leaf spot. The system will be available to ArableDS for use in autumn 2006.
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