B.W.W. Grout

Opportunities to learn scientific thinking in joint doctoral supervision

Research into doctoral supervision has increased rapidly over the last decades, yet our understanding of how doctoral students learn scientific thinking from supervision is limited. Most studies are based on interviews with little work being reported that is based on observation of actual supervision. While joint supervision has become widely used, its learning dynamics remains under-researched and this paper aims to address these gaps in research by exploring learning opportunities in doctoral supervision with two supervisors. The study explores how the tensions in scientific discussion between supervisors can become learning opportunities. We combine two different theoretical perspectives, using participation and positioning theory as a sociocultural perspective and variation theory as an individual constructivist perspective on learning. Based on our analysis of a complex episode we suggest that multiple supervisors can add value to supervision through authentic practice of scientific argumentation.

An assessment of Osmia rufa (syn. bicornis) as a pollinator of the sour cherry (Prunus cerasus) cv. Stevnsbaer in eastern Denmark

Summary The sour cherry (Prunus cerasus) cv. Stevnsbaer is self-fertile but it is recommended that bees are placed in the orchards during flowering. The solitary bee Osmia rufa can be managed, and has previously been suggested as an alternative pollinator to Apis mellifera, so consequently, this study investigates the activity and food preferences of this species during flowering of sour cherry (P. cerasus cv. Stevnsbaer). Female O. rufa provisioned a mean of 2.96 ± 1.44 cells each with 6.24 ± 1.46 pollen types during the receptive period of flowering. In all 17 different pollen types were collected of which the most dominant were Salix(41.4% ± 9.34%) and Acer (33.24% ± 8.81%), followed by Betula (8.16% ± 5.08%), P. cerasus (8.16% ± 1.79%) and Fagus (3.56% ± 1.96%). P. cerasus was present in all samples. Nine pollen types were from anemophilous plants and represented 87.94% of the pollen collected. The remaining 8 pollen types were from entomophilous plants. Based on the results it is estimated that a mean of 220,000 O. rufa cocoons would be needed per hectare if the species were to be an effective, supplementary pollinator of P. cerasus cv. Stevnsbaer. Practical, economic and environmental considerations suggest that the use of O. rufa as an alternative pollinator to A. mellifera in this instance is not realistic.

Effectiveness of managed populations of wild and honey bees as supplemental pollinators of sour cherry (Prunus cerasus L.) under different climatic conditions

Managed populations of Apis mellifera, Bombus terrestris and Osmia have been investigated rufa as sour cherry pollinators in two flowering seasons with different weather patterns. Flight activity of the three bee species during the pollination-receptive period of the cultivar ‘Stevnsbaer’ was recorded. Also, using insect-proof cages constructed around ‘Stevnsbaer’ trees, fruit set and yield were recorded and compared with self-pollination in the absence of insects and open pollination. When floral development and seasonal conditions are suitable, there is a potential role for introduced Osmia rufa and B. terrestris to add to the pollination activity of conventionally employed A. mellifera. However, in a season with a less favourable weather history, and despite comparable activity of the three species during the pollen-receptive period, introduced bees had only a limited effect on fruit set and yield and could not raise yield above that of freely pollinated branches. The contribution of appropriately dense populations of introduced bees in the orchard, given favourable weather conditions, is clear, but maintenance of populations of introduced, wild bees, compared with honey bees may well be impractical due to cost. Known ecological risks associated with species introduction also need to be considered. Consequently, if wild bee populations are to be used to secure the potential benefits of increased fruit set and yield, then positive habitat management will be necessary to sustain the required populations.

Gas exchange measurement as a non-destructive viability assay for frozen-thawed, winter-dormant apple buds

Low temperature studies with winter-dormant buds are severely limited by the lack of a rapid,non-destructive assay for their viability. Investigations involving the winter harvest of ecodormant buds of woody subjects, including cryopreservation, are restricted if viability cannot be assessed until dormancy is broken. If post-treatment grafting indicates low survival of the harvested population then further collection and study has to be delayed until the next winter season. This study trials the use of a portable gas exchange system able to discriminate between live and dead buds rapidly, with the assay confirmed as non-destructive by subsequent micropropagation. Active respiration was recorded for 85% of a winter-dormant Malus domestica buds population that showed 91% viability when grafted (n = 45). Lethally stressed material gave no false positive results. When micropropagated after respiratory measurement, a population viability of 76% was recorded. There was a significant, positive correlation between respiration and fresh weight for buds of mass >10 mg, from a population with a mean fresh weight of 17 mg.