Plant Density‐Dependent Variation in Density, Frequency, and Size of Watermelon Fruits

Quantitative analyses of the continuous response of components of the biomass of fruits of watermelon [ Citrullus lanatus (Thunb.) Matsum & Nakai] to variation in plant density could provide insight into the mechanisms underlying effects of plant density on marketable yield. Per unit area, the linear response of fruit biomass to plant density recently has been shown to explain the linear response of marketable yield. In the current study we quantify plant density‐dependent variation in the size, density (no. per unit area), and frequency (no. per plant) of watermelon fruits. In single‐row plots, at least 3.7 m apart, plant density varied from 0.4 to 4.1 plants m 2 (1000–9000 plants ha −1 ). In each experiment, the linear effect of plant density explained more than 80% of the variation in fruit density. Fruit density increased at linear rates of 0.6 to 1.1 thousand fruits ha −1 per thousand plants ha −1 . The plant density‐dependent response of the size of fruits varied considerably among experiments but the frequency of fruits responded consistently. In four experiments, there was no evidence of an effect of plant density on fruit size but in three experiments, fruit size decreased at a curvilinear rate of approximately 2.0 (kg −1 fruit −1 per thousand plants −1 ha −1 )(plants ha −1 ) 2 . Frequency of fruits decreased with plant density at curvilinear rates of 0.8 to 2.8 (fruits plan −1 per thousand plants ha −1 )(plants −1 ha −1 ) 2 . The response of size of fruits and frequency of fruits, respectively, probably measured an environment‐dependent and an environment‐independent effect of intraspecific competition.