Good second wheat performance could be strongly influenced by first wheat variety choice latest findings suggest. Teresa Rush finds out more.
Known winter wheat varieties which under-perform in the second wheat situation would appear to have a negative effect on the following wheat crop if grown in the first wheat situation. Work by plant breeders and scientists has provided an insight into why this might be the case.
According to Ron Granger, Limagrain arable technical manager, there is evidence to suggest poor second wheat varieties allow take-all inoculum to build up in the soil, which can lead to devastating yield loss in the second wheat situation, especially if a poor second wheat variety is selected.
Some wheat varieties classed as ’good’ second wheats on the AHDB Cereals and Oilseeds Recommended List may not in fact be the most suitable for this position but generating good phenotypic data is made difficult by the complexity of take-all disease, Mr Granger adds.
“Take-all infection in the field is very sporadic and consistent evaluation of the data is difficult, but nevertheless, we do have seasons showing high levels of take-all and it is important to acknowledge the diverse differences in varieties,” he says.
Mr Granger believes from a take-all management point of view, first and second wheats need to be considered in pairs.
Trials work carried out by Limagrain in 2008/9, both seasons with high take-all incidence, showed the performance of a second wheat could differ by as much as 4.2 tonnes/hectare were the ‘wrong’ first wheat preceded – representing a significant impact on farm income.
And while some growers may select a variety with high eyespot resistance for a second wheat slot, Mr Granger questions if such varieties would be more useful in the first wheat position?
Evolution is an example of a variety which has performed well in both the first and second wheat situations in Limagrain internal and external independent trials.
Mr Granger says: “Evolution would appear to be more robust in dealing with take-all as it seems to perform better in a second wheat slot than a first wheat. As a first wheat it yields 104% on the AHDB RL 2016/17, but move it into a second wheat slot and its performance jumps 2%.”
Bred by Danish breeder Sejet, the combination of tight regulations around crop inputs in Denmark and the tendency for early generation selection of varieties in a second wheat situation tends to produce wheats with greater root mass to improve nutrient-use efficiency, adds Mr Granger.
Britannia, also from the Limagrain portfolio, is a variety which performs well in the second wheat situation, confirmed by both the AHDB RL and independent data sets. “This may be attributed to its parent Cassius, which was also a very good second wheat, with proven performance on-farm.
“In an early drilling scenario or if eyespot is a known concern, a variety such as Revelation with good eyespot resistance based around the Pch1 Rendezvous resistance should be considered,” says Mr Granger.
Wet and mild conditions over winter and into the spring would indicate take-all could be a problem in crops this season, particularly in the event of a wet summer.
Interestingly, the trials work carried out in 2008/9 suggested a variety with Pch1 (Rendezvous) eyespot resistance grown in the first wheat position had lower take-all build up, with the knock-on effect of higher yields achieved in the second year for all varieties tested.
When choosing a variety for second wheat, take-all is not the only pathogen growers should be considering, says Mr Granger.
“Eyespot, both sharp and common, and fusarium footrot all need to be borne in mind,” he says.
He believes new technologies - such as the CT scanner technology deployed at the University of Nottingham/Biological Sciences Research Council (BBSRC) Wheat Research Centre, at Sutton Bonington, and the work being done by several research institutes on take-all – will allow a better handle to be gained on this complex disease.
“New and evolving technologies will allow researchers and breeders to analyse a variety’s root mass in a non-destructive manner.
“This means breeders may be able to select for more robust varieties against take-all, by choosing varieties with greater root mass development in conjunction with varieties which inhibit lower levels of take-all build up,” he says.
The impact on soil of a first wheat completely overrides any expected impact of a second wheat crop, scientists have found.
Researchers at the John Innes Centre, in Norwich, and Rothamsted Research, in Harpenden, examined the effects of growing high and low ‘take-all building’-susceptible wheat on the make-up of the soil bacterial community associated with the second wheat crop.
They found the variety of wheat grown in ‘year one’ sets the scene in the soil and what goes on in the soil long after harvesting the initial wheat crop and determines the subsequent crop’s root health and yield.
Dr Jake Malone, of the John Innes Centre, says: “We knew plants and microbes in the soil interacted in a multitude of ways, but we didn’t realise just what an impact growing different varieties of the same crop could have on the communities of microbes living in soil.
“We hope to take this further and define exactly how different wheat crops affect these important soil microbes.”
The scientists say these findings point to new guidance for growers to choose carefully the variety of wheat they grow as a first wheat, as this will determine the soil health of the second wheat crop and could have long-lasting effects on yields in subsequent years.
The research, funded by the Biotechnology and BBSRC, used a new approach to analysing microbes in soil, based on the statistical comparison of many bacterial genomes.
The team examined the abundance and the genetic structure of an important soil bacterium, pseudomonas fluorescens. Different strains of this microbe are responsible for boosting plant growth and protecting crops against harmful diseases.
Both the amount of pseudomonas in the soil, and the nature of the strains of this microbe present were strongly influenced by the variety of wheat grown a year earlier. Growing wheat with a high associated level of take-all fungus led to a greater abundance of pseudomonas.
But growing a low take-all building crop resulted in the soil supporting the second wheat crop having lower overall levels of pseudomonas, and selected for bacterial genes for iron scavenging and plant growth manipulation. Unsurprisingly, yield was higher following the low take-all building susceptible variety.
Dr Tim Mauchline, of Rothamsted Research, adds: “The finding the footprint left from the previous year’s crop influences both crop yield and the soil-root microbial community structure in the subsequent year is fascinating, and offers potential as an exciting avenue of research to enhance crop protection.”
The team intends to expand their research to cover a five-year period, to examine how the community of soil microbes develops, and how the presence of the take-all fungus and associated root disease affects the soil microbial community.
Ultimately, this research could lead to new approaches to control root diseases in cropping rotations, by choosing the right varieties to grow at the right time in order to promote healthy soil and minimise the chances of disease outbreak, say the scientists.