Spring 2016 shows value of plant disease resistance

KWS UK’s oilseed rape breeder Carl Gibbard has recently completed a tour of variety trials across Great Britain. His findings reveal a worryingly high level of disease and pest pressure.

Above: Regional Light Leaf Spot risk forecast - Rothamsted Research website, 2015/16 season - forecast updated 10 March 2016

A recent tour of oilseed rape crops in England and Scotland highlights the two most significant challenges that both growers and breeders face: light leaf spot and cabbage stem flea beetle.

Cabbage stem flea beetle is not a new threat, but its impact in the past two seasons has been profound. Where crops have suffered attack, the damage is severe and often resulting in serious stunting. At first sight last autumn many crops, including those in our own trials, appeared to be coping well with the pressure. It wasn’t until mid-March that the true extent of the damage became clear when crops failed to develop as we would typically expect.

We investigated and were regularly finding 30 or more flea beetle larvae per plant. This is supported by recent findings from CropMonitor which reported a large increase in larvae per plant in the north and the south east. It’s possible to bring the crop through the adult attack, but the real damage is sustained when the larvae become active and begin eating through the petioles.

We will take these crops to harvest, but we expect a lot of side branching and crops will not look at their best. One consequence is likely to be an extended flowering period, but we fully anticipate a yield impact of some level.

From what I have seen so far it is my belief that the varieties that demonstrate strong autumn vigour and produce a big, leafy canopy are those that can best survive an attack. This is one of the reasons I am highly encouraged by one of our NL1 candidates, MH10FH080.† It is one of the most vigorous varieties I have ever seen and is worthy of a closer look next year.

Unfortunately, breeding can only achieve so much. Unless the EU decides to lift its moratorium on neonicotinoid seed dressings we will have to learn to live with the pest. This season will give us an understanding of how we might best achieve this, but we still have much to learn.

Light leaf spot and Phoma

Above: left - LLS infection, right - Phoma infection

Conditions this winter were highly favourable to disease and consequently nearly all crops in the north and east are suffering from light leaf spot (LLS). It is clear that plant resistance will become a significant consideration in variety choice, but the disease scores only tell part of the story.

In the interests of protecting crops against shifts in pathogen types, it is wise to select those varieties with multi-gene resistance, otherwise termed ‘qualitative resistance’. We simply don’t regard single gene resistance to be sustainable and it is KWS policy to stack resistance genes for durability.†††

Those of you planning to visit crop trials this season should take a close look at Flamingo, our candidate for 2017, which is demonstrating the benefits of our policy on stacking genes to great effect.

Lastly, our crop assessments have identified a lot of†phoma†in crops this spring. This is perhaps not surprising since disease pressure has been at its highest in four seasons. Consequently, growers should prepare for a high incidence of stem canker later in the season. Just as with LLS, plant resistance will be an increasingly important part of how we manage this threat. Later season trials will provide the best visual display of plant resistance, but both Barbados, our high-yielding conventional, and Flamingo are comparatively clean and in good shape.