The tale (or phenology) of two wild blueberries in Canada

Fournier and colleagues from the Université du Québec à Chicoutimi, Université du Québec en Outaouais and the Canadian government have been investigating plant allometry and phenology in blueberries. Understanding allometry, how plants change their characteristics as they grow, and phenology, the timing of those changes could help improve fruit yield.

Several blueberry species belong to the genus Vaccinium (family Ericaceae) and are categorised into different groups, for example, Vaccinium corymbosum (highbush), Vaccinium ashei (rabbiteye), Vaccinium angustifolium (lowbush) and Vaccinium myrtillus (bilberry or European blueberry). The ‘lowbush’ and ‘highbush’ categories are based on plant growth and climate preference. Whilst the highbush, cultivated varieties prefer warmer, Mediterranean climates, the lowland, wild varieties are suitable for colder areas. 

The team delicately tracked leaf and flower development of two wild blueberry species and discovered how the number of branches, buds and flowers, can predict fruit yield. In order to optimise fruit production, it is important for scientists to understand how plants partition biomass differentially for vegetative parts (e.g. leaves) and reproductive parts (e.g. fruits). The scientists found that a particular species is not only high yielding but the delayed leaf and flower bud phenology protected buds from early spring frosts.

Fournier and colleagues established two field trials with two lowbush species, V. angustifolium and V. myrtillus, in Normandin Quebec in the fall of 2017. The sites were at a research station called Bleuetière d’Enseignement et de Recherche (French) where over 50 beehives ensured flower pollination. Commercial wild blueberry production consists of a two-year crop cycle, a pruning and harvest year. The researchers recorded the growth of 580-600 V. angustifolium and 160-180 V. myrtillus plants per year per site.

Every 3-4 days the scientists counted the number of leaf buds, flower buds, flowers, leaves, branching, number of fruits and measured plant height, branch length, leaf surface area, leaf and fruit biomass. The scientists calculated average dates for plant phenology, used generalised multinominal logistic models to compare the phenology of two species and structural equation models to assess the direct and indirect effects of allometric traits on fruit numbers and biomass.

Fournier and colleagues found phenological differences between the two species only during the harvesting year and not the pruning year. There were eight days between the probability of flower opening of the two species which limits cross-pollination. Leaf buds opened five days prior to flower buds in V. angustifolium and two days before flower buds in V. myrtilloides. V. angustifolium had a greater flower bud number and biomass per fruit than V. myrtilloides.

The researchers explain, “delayed phenology can increase reproductive biomass indirectly by protecting flower buds from spring frost and favour reproductive success due to improved pollination”. They conclude “thus, allometric traits, determined by specific plant architecture and phenology, influence the production of fruit, and V. myrtilloides represents a promising species due to its delayed phenology, slightly greater vegetative biomass, and greater number of flowers relative to V. angustifolium”.

Canada is the world’s second-largest producer and exporter of cultivated and wild blueberries. Early frost days can seriously injure flowers and fruit production and therefore, selecting blueberry species with delayed flowering can protect producers from losses.

“These findings are of great importance because a plant architecture having more vegetative and reproductive structures is going to present a sink competition in those structures that reduced carbon allocation, and a delayed leaf and flower bud phenology protected buds from early spring frosts. Vaccinium myrtilloides has an architecture that promotes both greater fruit production, in terms of number, and a delayed phenology. This study provides new perspectives on how to improve the reproductive output of Vaccinium by enhancing both vegetative biomass and plant architecture,” conclude the authors.

Whilst not reported in the current publication by Fournier and colleagues, the effect of different pruning methods  (mechanical or mechanical combined with thermal pruning), fungicide application (with or without) and fertilisation (mineral, organic and without) were also tested during the field trials. Do keep an eye out for their next publication and you could try growing blueberries yourself!