SEED TRANSMISSION OF LIGHT LEAF SPOT (Pyrenopeziza brassica) IN WINTER OILSEED RAPE
K.G. Sutherland, E.J. Booth and K.C.Walker
SAC, Craibstone Estate, Bucksburn, Aberdeen, AB21 9YA
Light leaf spot (Pyrenopeziza brassicae) is one of the most important diseases of winter oilseed rape in the UK, incurring yield losses of £48 million/annum. Growers in Scotland routinely spray crops in the autumn and spring for light leaf spot control. Preliminary studies at SAC Aberdeen indicated that disease control in the growing oilseed rape crop can effect the levels of light leaf spot in the daughter crop grown from that seed, suggesting that light leaf spot may be seed-borne. However, these effects have not been quantified accurately nor the results translated into a form (e.g. yield penalty) whereby a grower home-saving seed can take this into account. Seed transmission of light leaf spot could have major implications on where certified seed is sourced and on autumn spray decisions. The aim of this study was to determine if light leaf spot is transmitted in the seed and if treatments applied to the crop influence disease in the daughter crop. Three fully replicated field experiments were carried out in Aberdeen during the seasons 2000 – 2003, plot sizes 40 m2. Varieties used included the conventional varieties Apex, Bristol and Lipton and the restored hybrid variety Pronto and the varietal association Synergy. Seeds from different parental sources were used, including home-saved seed from a parental crop that had received a fungicide treatment, home-saved seed from a parental crop that had no fungicide treatment and certified seed. In Years 2 and 3 seed harvested from field experiments that had received fungicide (+/-) and sulphur as a nutrient (+/-) was also included. Experiments received standard fertiliser and pesticide inputs for the region with the exception of fungicide, which was not applied. Disease assessments were carried out at 4-8 week intervals during the season, either after incubation in the laboratory or in the field. Yields were determined to 91% dry matter. Epidemics of light leaf spot were severe in all three years, with 60-100% of plants in all varieties showing light leaf spot infection on leaves. Parental seed source, fungicide treatment to the parent crop and application of sulphur fertiliser to the parent crop did not affect the levels of light leaf spot shown in the daughter crop nor did they affect yield of 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 compared with crops grown from certified seed. Experiments were carried out in small plots with a plentiful supply of pollen from adjacent plots and result should only be used as an indication of the potential for home-saving the varieties, particularly Pronto and Synergy, and do not reflect what may occur in whole field crops. It should also be noted that the British Society of Plant Breeders indicate that growers are not permitted to home-save seed from hybrids.
Relationship of partial disease resistance components detected in detached leaf and seed germination assays using Microdochium nivale
R.A. Browne and B.M. Cooke
Department of Environmental Resource Management, Agriculture and Food Science Building, University College Dublin, Belfield, Dublin 4, Ireland; e-mail: firstname.lastname@example.org
Microdochium nivale is well documented as a casual agent in seedling blight, snow mould, rot foot rot and Fusarium head blight (FHB) in wheat. Significant correlations between FHB resistance and a detached leaf assay have been reported using M. nivale among Irish and UK commercial cultivars. This suggests resistances detected in the leaf assay and FHB resistance, in part, share a common genetic background. However, Miedaner [Plant Breeding 1997, 116: 201-220] summarizing data from a number of studies suggested strong interactions between plant growth stages, host genotypes and plant organs, respectively. The objective of the research reported here was to evaluate resistance expressed in the germinating seed to M. nivale among commercial wheat cultivars and its relationship to resistances detected in the detached leaf assay. Results indicate that resistances detected in the germination assay were independent of the components of PDR detected in the detached leaf assay. It is likely that the resistances detected in the germination assay primarily reflect those found in the grain rather than in the developing shoot and root organs, as inhibition of seed germination rather than a reduction in subsequent growth of the seedling was evaluated in this work. The relationship between the germination assay and diseases caused by fungal species implicated in the FHB complex including seedling blight, foot rot and snow mould is unclear. However it could be hypothesised that the germination assay would relate most closely to seedling blight where failure of seedling emergence is characteristic.
A novel method for producing mycelium-free conidial suspensions from cultures of Microdochium nivale
R.A. Browne and B.M. Cooke
Department of Environmental Resource Management, University College Dublin, Belfield, Dublin 4, Ireland (E-mail email@example.com)
A novel method to improve the sporulation in culture of Microdochium nivale, (a member of the Fusarium disease complex in wheat and causal agent of pink snow mould, stem rot and seedling blight), and to produce mycelium-free pathogenic conidial suspensions for plant inoculations was developed using cellophane-covered potato dextrose agar (CPDA). Cellophane membranes were cut to a 6 cm diam from uncoated non-moisture proof cellophane cellulose film type PT300, autoclaved in distilled water to remove plasticisers and to sterilise the cellophane, and each placed flat on the agar surface in separate 7 cm Petri dishes. Inverted plugs of mycelium taken from the edge of a growing colony were placed in the centre of the cellophane-covered PDA plates and incubated at 20 C on coolplates for 7 days under a diurnal cycle of near-ultraviolet