Soft fruit is one of the most buoyant sectors of UK commercial horticulture and production of strawberries has been expanding rapidly to meet rising consumer demand. Average year on year growth in supermarket sales of berries has been c.20% over the last 6 years and strawberries account for 78% of this market with a retail sales value of £372M in 2006 (data from Taylor Nelson Sofres). UK growers supply 85% of the market from May to October and they are innovative and progressive, having achieved large improvements in productivity in recent years by adopting new cultivars and new technologies such as portable tunnels and harvesting rigs. Currently 80% of UK strawberry production for supermarkets is under polythene tunnels, although this may decrease slightly in future due to changes in planning regulations. The dominant strawberry cultivar is Elsanta, accounting for around 65% of total production, but the heavy reliance on this one cultivar leads to problems of overproduction in the second or third week of June, when supply exceeds demand and consequently a lot of fruit is wasted. There are also other problems with Elsanta – it is susceptible to all the common diseases of strawberry, and hence has a heavy requirement for chemical pesticides; it typically produces only 75% class 1 fruit, so there is significant waste; the plant habit is too leafy to be ideal for intensive production under polythene tunnels. These problems are all relevant to Defra research priorities in the programme ‘Food chain meeting consumer needs’ – there is scope to reduce the environmental footprint of strawberry production by reducing fruit wastage, improving plant productivity to reduce the area of polythene tunnels, reducing pesticide inputs and improving the consistency of strawberry fruit quality over the long production season.
East Malling Research has a successful strawberry breeding programme that has released 17 cultivars since 1984. Sales of EMR cultivars are currently over 20 million plants per annum. Cultivar development is funded by industry, who contribute c. £275K per annum for breeding at EMR and trials on commercial farms, while underpinning strategic research has been funded by Defra (HH3201SSF, 2001-2006: Genetic improvement of strawberry for sustainable production in the UK). The programme has close links with retailers, particularly the major supermarkets, and this has ensured that new cultivars have fruit quality that matches their specifications. This project will develop resources for further underpinning research to develop improved strategies and identify germplasm for use in the EMR programme. This will then result in the development of cultivars that will help to reduce the environmental impact of strawberry production, in line with Defra’s priorities.
The project has four independent objectives:
Florence is an important UK cultivar for production in July. It has good all round disease resistance and is the best cultivar for organic production. Until recently it was widely grown in the UK but it is no longer favoured by the major retailers due to a dark colour and susceptibility to bruising if harvested in hot weather. In Defra project HH3201SSF 11 somaclonal variants of Florence were identified with potentially beneficial changes in fruit colour and/or firmness. Further research is now needed to determine if these changes are stable and whether or not they are accompanied by deleterious changes to other characteristics. Plants will be propagated to establish field production trials and also to test susceptibility to Verticillium wilt and powdery mildew, in order to detect any changes in the level of resistance.
Cold stored plants of Elsanta are often planted in spring for programmed production 60 days after planting. Currently Elsanta is the only cultivar well adapted to this system but EMR has identified lines that have higher yield and a longer season. To exploit this material in the breeding programme it is necessary to understand the mechanisms contributing to better 60 day performance, so that a breeding strategy can be developed. Twelve selected lines will be compared to Elsanta in a 60 day trial and, in parallel, plants will be dissected to determine how many flowers were initiated in autumn. This will allow us to determine if the most desirable phenotypes (with >2 inflorescences per crown and an extended season) are initiating flowers only in autumn or also in spring. The best breeding lines will be identified and used in a systematic crossing programme.
Following recent releases of cultivars with improved fruit quality, everbearing strawberries are now widely grown in the UK for production from August to October. However, all the available cultivars are closely related and they are intolerant to periods of high temperatures (>28C) during the summer, which result in a reduction in yield, berry size and fruit quality. To investigate the breeding potential of germplasm unrelated to modern everbearers, six old everbearing cultivars and two accessions of the North American wild strawberry (Fragaria virginiana) will be tested for their responses to high temperatures. If any of these lines are more tolerant of high temperatures then they will have potential for use as parents in a cultivar development programme. Crosses will be made to enable the inheritance of heat tolerance to be studied.
Around 80% of UK strawberries are now produced under plastic tunnels but the cultivars in use were bred for outdoor production and are thus not ideally suited to this system. More compact plants with a better ratio of fruit to leaf are required to increase productivity per hectare and reduce waste. Five compact genotypes from the EMR programme will be used as parents in a systematic crossing programme designed to study the inheritance of the important plant characteristics.