Fruit Development

Bract, calyx and ovary tissues have become fused within and between fruitlets during development to form the collective fruit

© CAB International 2003. The Pineapple: Botany, Production and Uses (eds D.P. Bartholomew, R.E. Paull and K.G. Rohrbach)

(Okimoto, 1948). Due to the fused nature of the tissue within a single fruitlet, the flesh of the fruit is not sterile but contains fungi, yeasts and bacteria (Rohrbach and Apt, 1986) though the population of microorganisms declines with fruit development (C.-C. Chen and R.E. Paull, unpublished results). No floral abscission occurs, so the withered style, stamens and petals can be found on a mature fruitlet. The large bract subtending each fruit-let is fleshy and widened at its base and bends over the flattened calyx surface, covering half of the fruitlet. Cell division is completed prior to anthesis and all further development is the result of cell enlargement (Okimoto, 1948). Fruit-development studies (Sideris and Krauss, 1938) have shown that fruit weight and its components (core, fruitlets, the collective flesh, fruit shell) increase in a continuous sigmoid fashion (Fig. 10.1A) once the inflorescence has been initiated (Gortner et al., 1967). More recent data have confirmed the results of the earlier study (Singleton, 1965; Teisson, 1973). Fruit mass increases about 20-fold from the time of flowering until maturation (Singleton, 1965; Teisson and Pineau, 1982). The number of fruitlets comprising a fruit varies widely with plant condition and environmental conditions. A typical 'Smooth Cayenne' fruit has about 150 fruitlets, which produce a mature fruit weighing about 2.2 kg (Tay, 1977). Fruit dry-matter content can vary with the conditions prevailing during fruit development. While the crown probably has

Fig. 10.1. Pineapple fruit growth and development (A) and changes in flesh starch, alcohol soluble carbohydrate (Alc. Sol. CHO) and protein (B) (after A. Hepton, 1995, personal communication).

no direct effect on the growth of the fruit (Senanayake and Gunasena, 1975; Chen, 1999), crown growth increases for about 30-45 days after fruit growth has commenced. Crown removal early in fruiting does not always lead to greater fruit weight. Crown size can be reduced by the plant growth regulator chloroflurenol when applied at the flowering stage (Dalldorf, 1981; Py et al, 1987); naphthalene acetic acid (NAA) and 2-(3-chlorophenoxy)-propionic acid (3-CPA) have also been used to reduce crown size (Bartholomew and Criley, 1983). Preliminary work also suggests that the crown may play a role in fruit translucency development (Paull and Reyes, 1996). Translucency is when the flesh has a water-soaked appearance.

Crown size is an aesthetic character of economic concern for packing and is generally part of the grading standard (Table 10.1). There does not appear to be a relation throughout the year between crown, fruit size and stem starch; the crown photoassimilates seem to be derived from its own photosynthesis (see Hepton, Chapter 6, this volume).

Under short day lengths and cool night temperatures, natural induction of inflorescence development occurs (see Malezieux et al., Chapter 5, and Hepton, Chapter 6, this volume). This precocious flowering disrupts harvest scheduling, increases the number of passes necessary to harvest a field and, if small plants are induced, leads to smaller fruit. Applying plant growth regulators is a possible approach to limiting environmental induction (see Bartholomew et al., Chapter 8, this volume), or transgenic plants with reduced environmental sensitivity may be produced.

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