Effects of Temperature and Wetness Duration on Infection of Oilseed Rape Leaves by Ascospores of Leptosphaeria maculans (Stem Canker)
- 110 Downloads
In controlled environment experiments, ascospores of Leptosphaeria maculans (stem canker) infected oilseed rape (cv. Nickel) leaves and caused phoma leaf spots at temperatures from 8°C to 24°C and leaf wetness durations from 8 h to 72 h. The conditions that produced the greatest numbers of leaf spot lesions were a leaf wetness duration of 48 h at 20°C; numbers of lesions decreased with decreasing leaf wetness duration and increasing or decreasing temperature. At 20°C with 48 h of leaf wetness, it was estimated that one out of four spores infected leaves to cause a lesion whereas with 8 h of leaf wetness only one out of 300 spores caused a lesion. As temperature increased from 8°C to 20°C, the time from inoculation to the appearance of the first lesions (a measure of the incubation period) decreased from 15 to 5 days but leaf wetness duration affected the length of the incubation period only at sub-optimal temperatures. Analyses suggested that, within the optimal ranges, there was little effect of temperature or wetness duration on incubation period expressed as degree-days; the time until appearance of 50% of the lesions was ca. 145 degree-days. A linear regression of % leaves with lesions (Pl) (square-root transformed) on % plants with lesions (Pp) accounted for 93% of the variance: √Pl=1.31+0.061Pp. This relationship was also investigated in winter oilseed rape field experiments in unsprayed plots from October to April in 1995/96 (cv. Envol), 1996/97 (cv. Envol), 1997/98 (cvs Bristol and Capitol) and 1998/99 (cvs Apex, Bristol and Capitol) seasons. The linear regression of % leaves with lesions (square-root transformed) on % plants with lesions accounted for 90% of the variance and had a similar slope to the controlled environment relationship: √Pl=0.81+0.051Pp. These results were used to examine relationships between the development of phoma leaf spot on plants in winter oilseed rape crops, the incubation period of L. maculans and the occurrence of infection criteria (temperature, rainfall) in the autumns of 1996, 1997 and 1998.
Unable to display preview. Download preview PDF.
- Badawy HMA, Hoppe HH and Koch E (1991) Differential reactions between the genus Brassica and aggressive single spore isolates of Leptosphaeria maculans. Journal of Phytopathology 131: 109-119Google Scholar
- Fitt BDL, Gladders P, Turner JA, Sutherland KG, Welham SJ and Davies JML (1997) Prospects for developing a forecasting scheme to optimise use of fungicides for disease control on winter oilseed rape in the UK. Aspects of Applied Biology 48: 135-142Google Scholar
- Figueroa L, Fitt BDL, Welham SJ, Shaw MW and McCartney HA (1995) Early development of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in relation to temperature and leaf wetness. Plant Pathology 44: 641-654Google Scholar
- Gladders P and Musa TM (1980) Observations on the epidemiology of Leptosphaeria maculans stem canker in winter oilseed rape. Plant Pathology 29: 28-37Google Scholar
- Gladders P and Symonds BV (1995) Occurrence of canker (Leptosphaeria maculans) in winter oilseed rape in Eastern England 1977–1993. International Organisation for Biological Control Bulletin 18: 1-11Google Scholar
- Gladders P, Symonds BV, Hardwick NV and Sansford CE (1998) Opportunities to control canker (Leptosphaeria maculans) in winter oilseed rape by improved spray timing. International Organisation for Biological Control Bulletin 21: 111-120Google Scholar
- Hammond KE and Lewis BG (1986) The timing and sequence of events leading to stem canker disease in populations of Brassica napus var. oleifera in the field. Plant Pathology 35: 551-564Google Scholar
- Hammond KE and Lewis BG (1987) The establishment of systemic infection on leaves of oilseed rape by Leptosphaeria maculans. Plant Pathology 36: 135-147Google Scholar
- Hammond KE, Lewis BG and Musa TM (1985) A systemic pathway in the infection of oilseed rape plants by Leptosphaeria maculans. Plant Pathology 34: 557-565Google Scholar
- Payne RW, Lane PW, Digby PGN, Harding SA, Leech PK, Morgan GW, Todd AD, Thompson R, Wilson GT, Welham SJ and White RP (1993) Genstat 5 Release 3 Reference Manual. Clarendon Press, OxfordGoogle Scholar
- Rotem J (1994) The Genus Alternaria; Biology, Epidemiology and Pathogenicity. APS Press, St. PaulGoogle Scholar
- Welham SJ (1992) Procedure GLMM. pp. 154-158. In: Genstat 5 Procedure Library Manual. Payne RW and Arnold GM (eds). Numerical Algorithms Group, OxfordGoogle Scholar