Survival ofLeptosphaeria maculansand associated mycobiota on oilseed rape stubble buried in soil

Abstract

Leptosphaeria maculans , the causal agent of phoma stem canker on oilseed rape, is an important pathogen in oilseed rape growing regions of the world, including Australia. Survival of L. maculans and associated mycobiota on oilseed rape stubble buried for 13 months in field soil and in sandy soil was studied under South Australian environmental conditions. Stubble weight decreased significantly by the end of the burial period, more so in field (53·7%) than in sandy soil (22%). Pseudothecia did not develop on stubble buried in field soil and few formed when buried in sandy soil. Moist incubation of stubble following retrieval from both media generated pseudothecia; however, pseudothecial development ceased on stubble that had been buried for 10 and 12 months in field and sandy soil, respectively. In total, 20 and 36 genera of fungi were isolated from stubble before and after burial, respectively. Alternaria spp., L. maculans and Stemphylium botryosum were isolated from 81·7, 70 and 60% of stubble pieces before burial, respectively. Isolation frequency of these species decreased significantly throughout the burial period in both media. Conversely, isolation frequency of Stachybotrys chartarum , Fusarium spp. and Trichoderma spp., having pre-burial frequencies of 26·7, 16·7 and 2·5%, respectively, increased over the burial period regardless of soil type. These findings suggest that inoculum production of L. maculans decreases with the increasing burial duration in field soil over 10 months, before ceasing, and this may be due to associated mycobiota.

Maturation of pseudothecia and discharge of ascospores of Leptosphaeria maculans on oilseed rape stubble

“…Effect of temperature on pseudothecium maturation in continuous wetness Stubble of oilseed rape was obtained from a phoma stem canker disease nursery at Struan, in the southeast of South Australia in January 2004, shortly after harvest, as described by Naseri et al (2008b). The stubble comprised stem and root pieces from a mixture of commercial cultivars and breeding lines with phoma stem canker-resistance rating ranging from 1 to 9, where 1 = greatest susceptibility and 9 = immunity (Potter and Stanley 2002).…”

“…24°C). Pieces of tap root and stem base (ca 20-30 cm in length) with phoma stem cankers (without pseudothecia) were soaked in sterile distilled water (SDW) for 12 h then placed in plastic trays lined with moist, sterile sand, as described by Naseri et al (2008b). Ten replicate stubble pieces were placed in a tray for each temperature treatment.…”

“…Furthermore, although the potential of host resistance to reduce production of pseudothecia and ascospores on stubble has been demonstrated (Marcroft et al 2004), the effects of interrupted wetness and darkness on inoculum production on stubble are little understood. Although burial of stubble in soil reduces production of pseudothecia of L. maculans Kharbanda and Ostashewski 1997;Naseri et al 2008b), the influence of darkness has not been distinguished from other physical, chemical and biological aspects of burial.…”

Managing Crop Disease through Cultural Practices

“…To control blackleg (Leptosphaeria maculans) on canola (oilseed rape), it is recommended that crop debris is buried in the autumn and a non-host crop be direct seeded the following spring to avoid re-exposing the buried residue (Gladders & Musa, 1980;Kolte, 1985). Recent research suggests that inoculum production by L. maculans decreased with increasing duration of stubble burial in the fi eld over 10 months, before stopping completely (Naseri et al, 2008). This effect may be due to the mycobiota associated with the buried stubble and these workers suggest that it might be possible to manipulate the population of saprophytic microbiota present on oilseed rape stubble to facilitate the decline of L. maculans (Naseri et al, 2008).…”

“…Recent research suggests that inoculum production by L. maculans decreased with increasing duration of stubble burial in the fi eld over 10 months, before stopping completely (Naseri et al, 2008). This effect may be due to the mycobiota associated with the buried stubble and these workers suggest that it might be possible to manipulate the population of saprophytic microbiota present on oilseed rape stubble to facilitate the decline of L. maculans (Naseri et al, 2008).…”