AHDB research has shown the duration of seed filling is precisely determined by growing day degrees (GDD) – so effectively the warmer the temperatures the quicker seed filling will shut down, while in cool conditions the period can be significantly extended.
At an average temperature of 25degC, seed filling could be over in less than 35 days, while at an average temperature of 17degC it could go on for 55 days, reports Syngenta OSR field technical manager Georgina Wood.
Discussing the effects of the cold, slow start to spring growth with iOSR growers, she says: “Oilseed rape seed fill is likely to start later this year – when temperatures can be expected to be hotter. In a short, intense seed fill period you need the maximum photosynthetic activity of the green leaf to feed the seed fill period and maximise oil yield.”
The temperature differential could prove particularly pertinent for growers in the north of England and Scotland, where average GDD temperatures can be three to five degrees lower than the south and eastern counties.
She says: “They have real potential to continue pushing yield for longer with effective canopy management and more important now is green leaf retention. Including an Amistar application at the later flowering timing, to protect against disease and enhance physiological plant greening, will maintain energy capture for longer.
“Managing the effects of summer drought is now outside growers’ control, but they can still influence the negative effects of disease and early desiccation, which have been identified as the key factors which cut short the green leaf period.”
The importance of green leaf for energy production during seed fill cannot be over emphasised, she adds. While the seed is only a small part of the overall crop biomass – typically accounting for less than a third of dry matter at harvest – the energy-rich oil it holds equals well over half of the plant’s overall content and ultimately, that is what we are looking to harvest.
“One of the physical limitations of the oilseed rape plant is that it is very poor at reallocating its energy reserves. Unlike wheat, which can remobilise up to half of its biomass reserves into filling grain, the oil content of OSR is 90% generated by photosynthetic energy capture after flowering.
“If the plant doesn’t have the green leaf area exposed to the sun, it will never reach its potential,” she advises. Growers generally attribute OSR yield losses from crop lodging to problems with combining, whereas in fact most of the lost performance could be due to the lodged crop shading itself and preventing light from reaching the lower green leaf.
Earlier season canopy management, through initial seed rates, autumn management and spring PGR use, would have all had a significant contribution in creating the plant structure to make the best use of available sunlight – as well as developing a deep root structure to minimise the impact of summer drought.
Studies by AHDB have shown half of all OSR crops could be compromised by insufficient rooting depth below 40cm.
Ms Wood advocates: “Getting the deep soil structure right before planting this autumn will help plants right through to next summer.”
However, she also urges growers to consider clubroot as a cause of poor rooting. While the soil-borne pathogen can cause the characteristic malformation and knurling of roots – often leading to premature plant death – at low levels of infection it could still be having an adverse effect on rooting depth.
“Good establishment conditions and nutrition can help to mask the effects of clubroot, however, there will be an underlying cost in plant health and its ability to take up moisture and nutrients,” she warns.
“There are now some very good clubroot-resistant varieties, with little or no yield penalty over conventional genetics, which growers in susceptible areas or with a known problem should be looking to utilise.”
While clubroot has historically been considered a major pathogen in Scotland, where brassicas have been more frequently grown in the rotation and soil conditions have suited it, the problem has been increasingly seen in northern and eastern counties associated with warmer and wetter winters. The clubroot-resistant variety SY Alibaba, for example, has resistance to both the P1 and P3 clubroot pathotypes. Yields in trials have been comparable with leading conventional varieties, such as Windozz and Alizze, she reports, as well as showing good phoma resistance and robust LLS scores.
Soil pathogens could be one of the key factors holding back the yield potential of oilseed rape. iOSR growers will be at the forefront of investigating in-field effects of Rhizoctonia solani, and the potential of new seed treatment developments to mitigate its impact on rooting and crop establishment.
Research at Nottingham University has revealed specific strains of the soilborne pathogen can eat away at the developing root. While cereal plants can, if they survive, put out compensatory roots, for the oilseed rape plant which depends primarily on a singular tap-root, the consequences are more serious.
“R. solani is an overlooked pathogen and its effect on OSR has been ignored,” according to Sutton Bonnington-based researcher Dr Rumiana Ray. Soil sampling studies had shown that, where oilseed rape had been grown prior to a cereal crop, the levels of the AG2-1 strain was far greater – by up to four times compared to after a wheat crop.
The Nottingham School of Biosciences’ team considered the OSR was selecting for that strain, but looked to investigate what its effects were actually having on the crop. Putting together the industry funded ICAROS project, in conjunction with Syngenta, AHDB and BBSRC, along with other Agri-Tech funding partners, they have used epidemiology and field trials to evaluate varietal differences and novel seed treatments.
Dr Ray’s work, including x-ray analysis of root system architecture, demonstrated that while the OSR seed can germinate and seedlings emerge in the Rhizoctonia infected soils, after six days the root had gone. She believes crop losses attributed to slugs and pests, could in fact be the effects of Rhizoctonia.
In inoculated trials, using levels of pathogen comparable to that measured in the field, the Nottingham University team has seen a yield response of about three tonnes/hectare from a novel Syngenta three-way seed treatment in development. Notably in the trial they had seen the effects of the pathogen led to a delayed flowering, which the seed treatment had effectively negated. The team is also looking at the potential for varietal resistance or tolerance to the presence of the Rhizoctonia pathogen, which could have an effect on the development of the growing crop, or the residual level of pathogen left in the soil.