Simulation of fruit-set and trophic competition and optimization of yield advantages in six Capsicum cultivars using functional-structural plant modelling

Abstract

Background and aims: Many indeterminate plants can have wide fluctuations in the pattern of fruit-set and harvest. Fruit-set in these types of plants depends largely on the balance between source (assimilate supply) and sink strength (assimilate demand) within the plant. This study aims to evaluate the ability of functional-structural plant models to simulate different fruit-set patterns among Capsicum cultivars through source-sink relationships.

Methods: A greenhouse experiment of six Capsicum cultivars characterized with different fruit weight and fruit-set was conducted. Fruit-set patterns and potential fruit sink strength were determined through measurement. Source and sink strength of other organs were determined via the GREENLAB model, with a description of plant organ weight and dimensions according to plant topological structure established from the measured data as inputs. Parameter optimization was determined using a generalized least squares method for the entire growth cycle.

Key results and conclusions: Fruit sink strength differed among cultivars. Vegetative sink strength was generally lower for large-fruited cultivars than for small-fruited ones. The larger the size of the fruit, the larger variation there was in fruit-set and fruit yield. Large-fruited cultivars need a higher source-sink ratio for fruit-set, which means higher demand for assimilates. Temporal heterogeneity of fruit-set affected both number and yield of fruit. The simulation study showed that reducing heterogeneity of fruit-set was obtained by different approaches: for example, increasing source strength; decreasing vegetative sink strength, source-sink ratio for fruit-set and flower appearance rate; and harvesting individual fruits earlier before full ripeness. Simulation results showed that, when we increased source strength or decreased vegetative sink strength, fruit-set and fruit weight increased. However, no significant differences were found between large-fruited and small-fruited groups of cultivars regarding the effects of source and vegetative sink strength on fruit-set and fruit weight. When the source-sink ratio at fruit-set decreased, the number of fruit retained on the plant increased competition for assimilates with vegetative organs. Therefore, total plant and vegetative dry weights decreased, especially for large-fruited cultivars. Optimization study showed that temporal heterogeneity of fruit-set and ripening was predicted to be reduced when fruits were harvested earlier. Furthermore, there was a 20 % increase in the number of extra fruit set.

Fig. 1.

Description of the topological structure of Capsicum plants with three physiological ages. PA1, PA2 and PA3 are for lower stem, two main branches and secondary branches on the two main branches.

Fig. 2.

Weekly number of fruit set (A) and weekly number of fruit harvest (B) for the six Capsicum cultivars. Error bars indicate s.e. (n = 12).

Fig. 3.

Biomass of shoot (vegetative + fruit), vegetative organs and fruits for measured (symbols) and simulated (lines) plants for the six Capsicum cultivars.

Fig. 4.

A comparison between measured and simulated harvested individual fruit dry weight from 12 observed plants for each Capsicum cultivar. The number of simulated fruits ranged from 74 to 142 for sweet pepper and 311 to 439 for hot pepper.

Fig. 5.

Measured and simulated individual fruit weights and their corresponding position on one sampled plant for ‘Funky’, ‘Nazar’ and ‘Medina’. The named fruit rank refers to Fig. 1.

Fig. 6.

Individual fruit growth rates for ‘Funky’, ‘Nazar’ and ‘Medina’ and their corresponding potential growth curves. The named fruit rank refers to Fig. 1.

Fig. 7.

Simulation of three-dimensional architecture for small-fruited cultivar ‘Medina’ and large-fruited cultivar ‘Funky’ 210 d after sowing. Ripped fruit, growing fruit and dead leaves are characterized with red, green and yellow, respectively. Top: sweet pepper, ‘Funky’; bottom: hot pepper, ‘Medina’. (A, D) Each node bears a fruit; (B, E) every three nodes bear one fruit; (C, F) every five nodes bear one fruit.