A review of productivity in strawberry: do the plants need larger canopies, more flowers, or higher CO₂ assimilation for higher yields?

ABSTRACT

Productivity in strawberry (Fragaria ×ananassa Duch.) is dependent on the production of new crowns, leaves and inflorescences, with fruit growth dependent on CO₂ assimilation in the leaves. The yields of new cultivars peaked in the 1970s and 1980s in many locations, possibly because of the focus of breeding on fruit quality and other plant traits and the loss of diversity across commercial breeding populations. It is not known if higher yields are related to higher plant growth or higher CO₂ assimilation in the leaves. This review assessed whether cultivars need larger canopies, more flowers, or higher CO₂ assimilation for higher yields. There were moderate to strong relationships between plant growth or yield, and net CO₂ assimilation per leaf area (P < 0.05; R² = 0.42 to 0.84) or the stability of net CO₂ assimilation (P = 0.052, R² = 0.48) across cultivars and environments. Carbon dioxide enrichment increased mean (± SE) net CO₂ assimilation by 88 ± 40% compared with plants at ambient and increased yield by 112 ± 73%. There was a linear decrease in yield as light levels decreased below full sun (P < 0.001, R² = 0.66), and linear decreases in yield the longer two cultivars were grown under 20% full sun (P = 0.002, R² = 0.84; P < 0.001, R² = 0.86). Daily gross primary productivity (GPP, mol CO₂ per m²) estimated by measuring the changes in the concentration of CO₂ above a crop was still increasing when the PAR (photosynthetic active radiation) was above 2,000 µmol per m² per s (rectangular hyperbola models, R²s = 0.44 or 0.72). There were linear decreases in yield as the number of leaves (P < 0.05, R² = 0.70 to 0.90), crowns (P < 0.001, R² = 0.82) or flowers (P < 0.05, R² = 0.51) were removed from plants. There were moderate to strong phenotypic correlations (R_P > 0.50, N = 47 studies) and weak correlations (R_P < 0.50, N = 69 studies) between yield and vegetative growth and flowering. Estimate of broad- and narrow-sense heritability for canopy growth and yield are low to moderate (H² and h² = 0.15 to 0.40). Cultivars produce high yields in different ways, suggesting that breeders consider the relationship between yield and plant architecture when developing cultivars. Initial experiments should include data on the number of leaves, crowns and inflorescences per plant. Subsequent experiments should include data on leaf area index (LAI) and/or LAD (leaf area density) using image analysis technology. More research is required to determine the value of measuring net CO₂ assimilation per leaf area, with current technology time-consuming and the results variable. The use of image analyses to characterise the canopy will assist the development of high-yielding cultivars. Genome-wide association (GWA) and genomic prediction (GP) will also accelerate the identification of high-yielding populations and individuals.

KEYWORDS:

• Canopy growth
• crowns
• cultivars
• flowers
• fruit
• inflorescences
• leaves
• leaf area index
• leaf area density
• net CO₂ assimilation
• plant vigour
• yields

Acknowledgments

The Queensland Government funded the research through the Department of Agriculture and Fisheries. Special thanks to Pat Abbott and Zalee Bates from the DAF library for supplying much of the literature.

Disclosure statement

No potential conflict of interest was reported by the author.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/14620316.2022.2077240