Abstract
Fruit size declines in strawberries (Fragaria × ananassa Duch.) as the season progresses in many subtropical areas, possibly due to inadequate leaf area, over-cropping, or high temperatures. An experiment was conducted to investigate the importance of these factors on fruit growth in ‘Festival’ in Queensland, Australia. Groups of plants were defoliated to remove half of the mature leaves on each plant, thinned to remove all the inflorescences on each plant, or defoliated and thinned. Control plants were left intact. Defoliation, thinning, or defoliation + thinning decreased yield (total and/or marketable) by 15% to 24% compared with the control. Defoliation, or defoliation + thinning decreased average fruit weight (total and/or marketable fruit) by 1 to 2 g compared with the control, whereas thinning had the opposite effect. The incidence of small fruit increased towards the end of the season. There were strong relationships between fruit weight and average daily mean temperature in the seven weeks before harvest (R2s greater than 0.80). Fruit weight decreased from 24 g to 8 g as the temperature increased from 16 °C to 20 °C. This response was not affected by defoliation or thinning. The strong effect of temperature on fruit size indicates a problem for production in the future in the absence of heat-tolerant cultivars.
Highlights
One of the major issues affecting strawberry cultivation in the subtropics is the production of small fruit [1,2,3,4]
This paper reports on a study to investigate the importance of leaf area, over-cropping, and high temperatures on fruit growth of strawberries in Queensland
Defoliation, and defoliation + thinning decreased fruit weight by 1 or 2 g compared with the control, whereas thinning had the reverse effect
Summary
One of the major issues affecting strawberry cultivation in the subtropics is the production of small fruit [1,2,3,4]. In Queensland, Australia, the incidence of small fruit increases as the season progresses, with more than half the fruit smaller than 12 g in October. A high incidence of small fruit reduces marketable yields and increases the costs of harvesting. A study in Italy showed that for each one gram decrease in average fruit fresh weight, the cost of harvesting was increased by about €500/ha [5]. Small fruit at the end of the season could be due to inadequate leaf area, over-cropping, or high temperatures [4,6]. The berry is an aggregate fruit originating from the receptacle tissue, and has a number of ovaries, which develop into one-seeded fruit or achenes. The achenes are composed of a seed and ovary tissue and originate at the base of each pistil [10]. The number of achenes reflects the number of pistils in the developing flower, and typically decreases with the ranking of the Agriculture 2019, 9, 127; doi:10.3390/agriculture9060127 www.mdpi.com/journal/agriculture
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