PhD Studentship (1) : The genetics of flowering in raspberry and blackberry (Rubus) – what makes a primocane?

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The genetics of flowering in raspberry and blackberry (Rubus) – what makes a primocane? Suzanne Litthauer, Timo Hytonen (NIAB EMR); Jim Dunwell (University of Reading)

Alteration in flowering habit has been one of the most significant innovations in many soft fruit crops, extending the season and allowing the most consistent volumes of supply. Raspberries and blackberries can be divided into two different groups according to their fruiting habits; primocane cultivars bear fruits in their first-year shoots whereas floricane ones flower and fruit in the second year after the canes have gone through dormancy. Crop scheduling and manipulation of fruiting season to ensure continuity of supply with the same or very similar varieties are becoming key for profitable production worldwide but interventions are based solely on empirical experience.

Despite the importance of fruiting type and the earliness of fruiting, the genetic control of these traits is poorly understood. Identifying the genes and precise mechanisms controlling initiation of flowering, growth rate and inflorescence development is a key to the advancement of breeding for improved primocane and floricane cultivars best suited to modern production systems.

The aim of this PhD project is to understand the genetic control of primocane vs. floricane fruiting habit and earliness of fruiting in both raspberry types in the first instance and investigate the correspondence of these traits in blackberry. To map QTLs controlling these traits the student will utilize existing breeding populations available in the East Malling Rubus Breeding Consortium. Detailed characterization of fruiting habits will be carried out throughout the breeding program and the most suitable families will be genotyped for mapping using SNP markers. In doing so, this project will contribute to the development of molecular tools in Rubus which currently lags behind strawberry in availability of genomic resources.

Based on QTL mapping data, genetic markers will be developed to facilitate marker assisted breeding targeting different fruiting habits. To understand the control of flowering in more detail, the expression of selected candidate genes will be studied in cultivars with contrasting flowering habits. Moreover, based on our strong expertise in genetic transformation, a gene-editing protocol will be developed for raspberries, and the function of at least two candidate genes will be tested using gene-edited lines as a proof of concept.

Location: Kent
Closing date: 17 Jun 2022
Reference number: CTP_FCR-2022_1

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PhD Studentship (2): What factors control variation in floral initiation in strawberry?

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What factors control variation in floral initiation in strawberry? Dan Sargent, Prof Timo Hytonen (NIAB EMR); Jim Dunwell (University of Reading) The research on the control of meristem fates lacked sufficient attention at the molecular level, despite its large importance in the horticultural industry. As with all rosaceous perennials (apart from everbearing strawberries and primocane raspberries), floral initiation happens in short days at the end of summer, followed by an obligatory dormancy/chilling period, after which flowers emerge.

It is well known that there is large, genetically determined variation in yield in strawberry that is largely determined by the production of flowering shoots from axillary meristems during the floral initiation process. While we have identified major players controlling floral initiation and the production of flowering shoots in the model strawberry, Fragaria vesca, comparative molecular studies should be done between lines of the octoploid strawberry to improve yield.

Based on the current knowledge in the model strawberry, this student will carry out detailed physiological studies combined with molecular analyses of candidate genes in the octoploid strawberry lines with contrasting number of flowering shoots. To test the gene functions in octoploid strawberry, two candidate genes will be manipulated using gene editing technology, and the edited lines will be tested in a controlled climate. Understanding the key molecular processes that underpin floral initiation will facilitate the selection of high yielding lines and optimisation of the propagation processes which in turn will deliver plant material to growers that has higher yield potential. This is necessary, since yield is still a primary limiting factor to enhanced profitability for growers especially in programmed cropping systems.

Location: Kent
Closing date: 17 Jun 2022
Reference number: CTP_FCR-2022_2

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PhD Studentship (3): Interaction between light intensity and rootzone water deficit stress to improve strawberry nutrient content

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Exploring the interaction between light intensity and rootzone water deficit stress as a means of improving berry phytonutrient content and Class 1 strawberry yields in TCEA systems. Mark Else (NIAB EMR), Paul Hadley and Carrie Twitchen (University of Reading)

Total environment-controlled agriculture (TCEA) systems offer great potential for a consistent supply of high quality and phytonutritious strawberries, provided that initial plant quality is high and growing conditions are fully optimised. However, this is often not the case. Although diurnal temperatures, photoperiods, light intensities, and wavelengths can all be controlled precisely, the optimum growing conditions for proprietary strawberry varieties are not known, and so Class 1 yields are significantly lower than anticipated in many TCEA systems. High relative humidifies often arise due to the constant high evaporative demand and imprecise irrigation scheduling, and so the energy costs associated with maintaining RH in the optimum range are often high.

Our previous work at East Malling showed that regulated deficit and transient deficit irrigation techniques could be used to improve resource use efficiency (light, water, fertiliser) and improve berry phytonutrient content whilst maintaining good commercial yields. The effect of a deficit-induced burst of ethylene production on antioxidant accumulation in non-climacteric strawberry fruit was also explored, and the work suggested that an interaction between light intensity and rootzone water deficits was more likely to raise berry phytonutrient content than either treatment alone.

This PhD programme will investigate the role of hydraulic and chemical signals in the regulation of strawberry responses to targeted rootzone water deficits, and this knowledge will be used to inform, develop, and test new growing protocols for TCEA systems that incorporate beneficial stresses to improve resource use efficiency, marketable yields, and berry quality.   The lighting environment (intensity, wavelength, photoperiod) will be manipulated to maximise photosynthesis throughout the light period in TCEA systems, and to accommodate the diurnal decline in photosynthetic efficiency measured in strawberry. Sensor technologies will be deployed to monitor and control the growing environment, and to measure root, leaf, and fruit responses to applied treatments in real-time. Outputs from this plant environmental science-based CTP PhD study will include innovative growing protocols for proprietary strawberry varieties, and the resulting blueprints will help to inform commercial strawberry production in TCEA systems.

Location: Kent
Closing date: 17 Jun 2022
Reference number: CTP_FCR-2022_3

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