Resource allocation

Few studies of carbohydrate allocation or reallocation in pineapple during reproductive development were found. During vegetative growth, the dominant carbohydrate sinks are the young leaves and the roots, and there is an allometry between the leaves and the stem (Malezieux, 1988). There is little increase in stem length or diameter once flowering has been initiated, but experi ments conducted in Côte d'Ivoire and Hawaii show that stem growth rate, on a dry-weight basis, and starch accumulation increase rapidly after flower initiation (see Fig. 5.11; H.Y. Young, 1965, personal communication; Malézieux, 1993; E. Malézieux, 1993, unpublished results). In Hawaii, starch in the stem, on a dry-weight basis, increased from about 15% 9 months after planting to over 60% midway through the fruit development period some 10 months later. Leaf starch on the same basis increased from less than 2.0% to about 8.0% during this same time period. While the change in starch concentration in leaves is relatively small, when multiplied by the large amount of leaf weight present, it represents a large storage reserve.

A surplus of starch in the plant during early reproductive development probably results from a lack of new sinks during this phase, as no new leaves are initiated and the fruit does not yet represent a significant sink for carbon. About 100 days after forcing in Hawaii and sooner in Côte d'Ivoire, where temperatures are warmer and fruit growth is more rapid, there is a decrease in stem dry matter (see Fig. 5.11) and probably in stem starch, or both, indicating mobilization of starch from the stem to help meet fruit carbon demand. In Hawaii, leaf starch is apparently also mobilized to meet the increasing demand from the rapidly developing fruit. The intensity and importance of reallocation of assimilates from the stem and leaves to the fruit may depend on climate (irradiance, drought) during fruit filling and on carbon balance between source (assimilates produced) and sinks. Reallocation was greater for large than for small plants in Côte d'Ivoire (Malézieux, 1993), presumably because, with a higher dry-matter content and possibly higher starch, there was more substrate to reallocate.

Data from Australia, Côte d'Ivoire and Hawaii clearly show that the developing fruit is a stronger sink than are the suckers. When flower induction occurs, apical dominance over axillary buds is broken and destructive sampling soon after induction shows a few to several axillary buds beginning to grow. However, in the warmer tropics, sucker development is typically delayed, i.e. no visible suckers form, until after the fruit has matured. In all regions where pineapple is grown, sucker development may also be delayed where plants are small and in fields with high plant population densities. In subtropical areas, such as Australia and Hawaii, the situation is more complicated. In these cooler climates, the date of forcing typically determines the size of the fruit. Forced induction in the winter months - November until at least January in Hawaii and June to August in Australia -tends to produce smaller fruit on a plant of a given size than does forcing during warm summer months, when irradiance is high. These somewhat smaller fruit develop and mature during the warm spring and summer months when temperatures are warm and irradiance is high. Because photosynthetic leaf area is large relative to the size of the developing fruit, we speculate that photo-synthetic capacity exceeds carbohydrate demand by the developing fruit, so there is surplus carbohydrate available for sucker growth. Thus, suckers initiated at forcing develop along with the fruit. In southern Queensland, Australia, suckers on plants from which fruit is harvested in summer can become large enough to shade the fruit. The converse of this situation occurs when forcing occurs in January-February in Australia and in the midsummer months in Hawaii.

Fruits initiated during this time are large relative to plant size, presumably because high rates of photosynthesis provide the energy required to initiate large numbers of fruitlets. These relatively large fruit mature and ripen during cool weather, when irradiance is near a minimum. Sucker development on such plants is delayed, presumably because the leaves do not have sufficient photosynthetic capacity to support both the developing fruit and sucker growth. In Australia, the time after initiation at which suckers between 5 and 40 g weight were first seen in a time-of-planting trial depended on the month in which forcing occurred. Forcing in January resulted in the longest interval before suckers appeared (295 days), while plants forced in September and October produced suckers in the shortest time, about 100 days (Sinclair, 1992a).

Defoliation experiments clearly show the importance of leaf area and weight to the developing fruit, slips and suckers. A. Hepton (personal communication) showed that the weight of fruit, slips and suckers all increased linearly the closer to harvest plants were defoliated (Fig. 8.5). It is clear that anything that decreases carbon assimilation by leaves, such as reduced irradiance or decreased effective leaf area, will reduce yield and the size and number of shoots available for propagation.

Date of defoliation

Fig. 8.5. Effect of date of leaf defoliation on mean fruit, slip and sucker mass at the date of fruit harvest. For fruit, y = 636.4 + 12.57x, R2 = 0.98; for slips, y = 141.2 + 5.11x, R2 = 0.92; for suckers, y = 106.5 + 3.42x, R2 = 0.76; n = 9 for all. (Data from A. Hepton, personal communication.)

Date of defoliation

Fig. 8.5. Effect of date of leaf defoliation on mean fruit, slip and sucker mass at the date of fruit harvest. For fruit, y = 636.4 + 12.57x, R2 = 0.98; for slips, y = 141.2 + 5.11x, R2 = 0.92; for suckers, y = 106.5 + 3.42x, R2 = 0.76; n = 9 for all. (Data from A. Hepton, personal communication.)

Was this article helpful?

0 0
Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

Get My Free Ebook


Post a comment