East Malling strawberry trials focus on 60-day yield

Strawberry growers are discovering significant differences in yield potential, says Brian Lovelidge.

Big differences in the 60-day yield potential of varieties produced by the East Malling Research (EMR) Strawberry Breeding Club-funded programme are being found.

Identifying varieties that are better suited to the system than Elsanta at an early stage is very important, because most June bearers start life as 60-day plants to help achieve good continuity of fruit production throughout the season.

For the past 20 years or so Elsanta has set the standard for 60-day production and that is one reason why it dominates the June-bearer market. But improved knowledge of how to identify new selections best suited to the system and the inheritance of the trait means that Elsanta's supremacy is now being strongly challenged.

"Some selections that do very well in their initial trials have no adaptation at all for 60-day production," said Dr David Simpson, who runs the breeding programme. "Elegance, the newest EMR June-bearer front runner, has much better 60-day potential than Elsanta and we hope that some of this season's new selections will be as good because they have a similar pedigree."

At an East Malling Research/East Malling Research Association strawberry walk at EMR on 29 June, Simpson explained that around 100 varieties will be whittled down to the best six to ten this year. These will go into small grower trials run by marketing group and grower co-operative club members for two years to "narrow them down" to one or two front runners that will then be trialled on a larger scale.

"The whole process takes five years then club members decide which varieties will be worth releasing," he said. "The advantage of our varieties is that they are available to all UK growers."

Elegance, which was part way through its trials programme when the club was formed in April 2008, has very good 60-day potential, outyielding Elsanta by as much as 40 per cent, said Simpson.

It has the added benefit of very good all-round fruit quality, producing attractive, uniform, firm, large berries with good colour and skin strength. The variety also has a consistently high class-I gradeout, usually around 90 per cent compared with 75 per cent to 85 per cent for Elsanta. Its maincrop season is slightly later than Elsanta's.

Simpson pointed out that the breeding programme aims to produce everbearers and early-, mid- and late-season June bearers to provide continuity of production for the whole marketing season with 60-day crops filling the gap between the main and everbearer seasons. For commercial success new varieties require good fruit quality and size, disease resistance and presentation for ease of picking.

On the day of the walk about 75 per cent of the Elsanta, used for comparison purposes in the trials, had been picked; some of the early selection had finished and the later ones were somewhat less forward than Elsanta.

The best 10 selections in the current trial were available for visitors to taste and comment on. Simpson said that, so far, EM1764 has done consistently well in tastings and has good grower attributes although it is too early to know its 60-day potential. It is more or less matched for eating quality by EM2008. Both selections' class-I gradeout is 95 per cent compared with 75 per cent, 83 per cent and 84 per cent for Elsanta (in three plots).

"EM1764 is an early selection and so it's getting to the end of its season now," said Simpson. "It has a lot of very good characteristics including very uniform berry shape, very good shelf life and a Brix (sweetness) reading one or two points higher than Elsanta's."

In the EMR part of the proceedings visitors heard about a HortLINK project using pheromones to improve the control of the European tarnished plant bug, arguably the worst strawberry pest.

Dr Michelle Fountain explained that this pest, a species of capsid, over-winters in the crop as adults, the females starting egg laying in early spring. It is really difficult to find until later in the summer, "so you need to know what's going on in your crop" for control purposes early in the season.

EMR researchers have found that the females release three types of pheromone. Depending on their ratio they are used for defence or alarm purposes or to attract males. The Natural Resources Institute's Professor David Hall came up with the idea of impregnating cigarette filters with the three chemicals for use in traps placed in the crop to monitor the number of males. The trap is thought to be the first in the world for capsids.

"We discovered what time of day the females produce the pheromone combination to attract the males and by doing so we homed in on the ratio of the three chemicals," said Fountain. "This season we were trapping overwintered males as early as March and using this sort of information we aim to established an optimum spray timing threshold."

This will help to reduce the number of sprays required to control the pest. However, EMR research team leader Professor Jerry Cross reckoned that only broad spectrum insecticides such as chlorpyrifos and pyrethroids such as bifenthrin are really effective against the bug and said the pyrethroids have distinct disadvantages.

"They disrupt the biological control of the insecticide-resistant western flower thrips and tarsonemid mite, both potentially bad strawberry pests, and so we need to find alternative ways of managing the bug," he maintained.

Cross said that in another HortLINK project numerous means have been developed over the past three years to minimise or eliminate residues on strawberries of pesticides used for controlling the major pests and diseases. In the next two years these measures will be brought together in an integrated programme for commercial use.

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