Predicting Fruit Development and Yield

It is possible to predict the rate of plant growth, fruit development and yield in relation to environmental factors and cultural practices by simulating plant development (leaf appearance and fruit phenology), carbon assimilation and allocation to various plant parts using integrated modelling techniques. ALOHA-Pineapple (Zhang and Bartholomew, 1993; Zhang et al., 1997) is a pineapple crop model that simulates pineapple growth, development and yield on a daily time-step basis in different environments. A flow chart of the major factors incorporated into the model that affect pineapple growth, development and yield are summarized in Fig. 5.17. The model was calibrated and validated using data from Australia, Côte d'Ivoire and Hawaii and takes into account temperature, irradiance and plant-soil water relations. Nutrition effects, such as nitrogen, remain to be introduced into the model. The model was developed using the structure and format of the CERES-maize model (Jones and Kiniry, 1986) and works under the IBSNAT-DSSAT shell (Anon., 1994).

Fruit growth of 'Smooth Cayenne' has been studied fairly intensively and it is a highly predictable process up to the time the developing fruit becomes visible. Development progresses with increasing thermal time from forcing until about the time the 1 cm open-heart stage is reached (Fleisch and Bartholomew, 1987; Malézieux et al, 1994;

Zhang et al., 1997). Thermal time is calculated as the sum of daily mean air temperature minus a basal temperature below which it is assumed that no development occurs. For modelling purposes, the basal temperature was set at 10°C (Malezieux et al., 1994). After the inflorescence emerges, and especially after anthesis begins, fruit development is more difficult to predict. It is assumed that this is due to the absorption of solar radiation during the day, which can significantly elevate fruit temperature above air temperature (Bartholomew and Malezieux, 1994). For the period from flowering to fruit maturation, fruit growth and maturation were best predicted by fruit thermal time calculated from estimates of fruit rather than air temperature (Malezieux et al., 1994). Direct absorption of solar radiation raises fruit temperature well above air temperature (Bartholomew and Malezieux, 1994) and apparently hastens the development rate up to some optimum temperature. Above that optimum, fruit development can be delayed (Malezieux et al., 1994). While it is clear that solar irradiance elevates fruit temperature, the relationship between irradi-ance and fruit temperature, and especially average fruit temperature, has not been adequately characterized. It also seems likely that fruit temperature declines somewhat with increasing wind speed, but no data were found on the subject.

Detailed data on the effects of nutrition on rate of development were not found, but Py (1955) reported that fruit development took longer where N was high without K than was the case for a balanced fertilizer.

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