Commercial propagation of pineapple is not through seeds but by vegetative propagation. Except for A. macrodontes, Ananas sp. does not produce underground stolons. Pineapple seeds lack dormancy, have a very tough seed coat and a hard, flinty endosperm. Without treatment germination is slow and very irregular. Commercially, seeds are desired only in breeding programs and are usually the result of hand pollination. Although pineapple can be grown from seed, fertility in commercially grown cultivars of pineapple is very low and consequently seed production is very rare. Seeds retain germination capacity for about six months at tropical ambient temperature. The seeds are hard and slow to germinate. Treatment with sulfuric acid achieves germination in 10 days, but higher rates of germination (75 - 90%) and more vigorous growth of seedlings results from planting untreated seeds under intermittent mist. The seedlings are planted when 15 - 18 months old and will bear fruit 16 - 30 months later.
Vegetative propagation is the dominant form of reproduction by the use of vegetative shoots including the crown, slips and suckers. There are four general types: slips that arise from the stalk below the fruit, suckers that originate at the axils or leaves, crowns that grow from the top of the fruits, and ratoons that come out from the under-ground portions of the stems. Crowns are the green leafy tops of the fruit. Slips are small shoots that develop on the upper part of the fruit stalk (peduncle) below the fruit and may have small fruit structures (knobs) at the base. Suckers are the large vigorous shoots that develop from axillary buds on the lower stem and called aerial suckers when they are away from the ground or called ground suckers when emerge beneath the ground. Ground or aerial suckers that emerge close to the ground are very vigorous and are often retained for the ratoon crop. Although slips and suckers are preferred, crowns are the main planting material preferred by home gardeners. Vegetatively propagated plants fruit in 15 - 22 months.
Healthy, disease-free planting materials from bona fide cultivars are important for the production of high yield, uniform and good quality pineapples. Where the source of planting material is limited as in the case of newly released cultivars, planting materials are usually propagated using the rapid quartering technique, stem sectioning, leaf bud cutting or tissue culture. Sometimes growth regulators called morphactin containing chloroflurenol are used to induce proliferation of small slips. It induces axillary bud growth after apical dominance has been broken with ethephon application. Planting materials can be increased ten-fold with morphactin induction. Very rapid multiplication of pineapple plants has been reported to be possible through tissue culture. About 5,000 plantlets from a single crown and 100,000 plantlets from a single shoot can be obtained in 12 months. Dormant lateral buds excised from crown leaves when cultured on Murashige and Skoog basal media containing NAA, IBA and kinetin, produce multiple shoots or plantlets. Plantlets can be rooted in MS salts and vitamins, 0.3% Phytagel and 1 mg/l napthalene acetic acid (NAA). After four weeks of root initiation, rooted plantlets can be transferred to peat pots and hardened for 8 weeks before planting into the nursery. It will take another 3 months before nursery plantlets can be field-planted. Even though the tissue culture technique is very efficient for rapid multiplication, it has some shortfalls. Mass propagation by this technique produces quite high variability (soma-clonal variation) among the progenies especially in traits like leaf spine. First-generation tissue culture plants showed less vigor in field performance and bear significantly smaller fruits.
For established cultivars, standard planting materials are usually used without resorting to rapid propagation techniques. The conventional planting materials are taken from the vigorous aerial and ground suckers, large slips and occasionally crowns. The suckers are usually harvested monthly within a period of 2 - 5 months after the fruit is picked. Suckers must be uniform in size, with a height of at least 45 cm. The suckers after harvest are left to dry for a few days. The leaves are then trimmed and the suckers dipped in pesticides before planting in the field. The source of planting materials affects the time from planting to fruit maturation. For suckers which are usually the largest propagules, it takes about 14 - 17 months to maturation while for slips it is 15 - 20 months. The crowns which are usually the smallest propagules will take 18 - 24 months from planting to harvesting.
In Queensland, closely stored upside down tops and slips from the summer crop of 'Smooth Cayenne' are used for planting in the fall. Some growers salvage the crowns from the largest grades of fruits going through the processing factory to be assured of high quality planting material.
Workers in Johore, Malaysia, report, without specifying cultivar, that large crowns give highest yield and more slips, followed by small crowns, big slips, small slips, large and small suckers in descending order.
With the 'Red Spanish' in Puerto Rico, the utilization of large slips for planting in the first quarter of the year, medium slips during the next six months, and small slips in the final quarter, provides fruits of the maximum size over an extended period of harvest. South African experiments with 'Smooth Cayenne' have shown medium-size slips to be the best planting material. Next in order of yield were large crowns, medium-size suckers, medium-size crowns and large suckers. However, medium and large suckers fruited earlier. Trimming of basal leaves increased yields. Storage of slips until optimum planting time prevents premature bloom and diminished fruit size.
The 'Red Spanish' reaches shipping-green stage (one week before coloring begins) in Puerto Rico 150 days after natural blooming.
In South Africa the 'Queen' is grown mainly from stumps, secondly from suckers. The stumps which have fruited are detached from the mother plant as soon as possible to avoid their developing suckers of their own. In comparison with suckers, the stumps are consistently heavier in yield after the 4th crop. When suckers are used, those of medium size, approximately 18 in (45 cm) long, planted shallow and upright, yield best.
In the past, growers preferred plants that supplied abundant basal slips for planting, not recognizing the fact that such plants gave smaller fruits than those without slips or suckers. Also, breeders aim toward elimination of slips to facilitate harvesting. Because of the increased demand for planting material, a new method of mass propagation received wide attention in 1960. During the harvest, plants that have borne single-crowned, superior fruits without basal slips are selected and marked. Following harvest, these plants are cut close to the ground, the leaves are stripped off and the stems-usually (30-60 cm) long and 3 to 4 in (7.5-10cm) thick-are sliced lengthwise into 4 triangular strips. The strips are disinfected and placed 4 in (10 cm) apart, with exterior side upward, in beds of sterilized soil, semi-shaded and sprinkler-irrigated. Shoots emerge in 3 to 5 weeks and are large enough to transplant to the nursery in 6 to 8 weeks. 'Smooth Cayenne' yields an average of 3 shoots/slice whilst 'Red Spanish' and 'Natal Queen', 4 shoots/slice.
This use of the stem is a major improvement over the former practice of allowing it to develop suckers high up after the fruit is harvested. If such suckers bear fruit in situ they are not strong enough to support it and collapse. They are better removed for planting, but repeated removal of suckers weakens the mother plant.
In Sri Lanka, the shortage of planting material inspired experiments at first utilizing stem cross-sections 2.5cm thick-15 to 24 from each stem. These sprouted in 4 weeks but plant growth was slow and fruiting was delayed for 30 months. Most of the cuttings developed a single sprout, some as many as 5, others, none at all. Accordingly, this technique was abandoned in favor of a system developed for purposes of reproducing a selected strain in Hawaii. Stems are cut into segments bearing 3 to 5 whorls of leaves. The leaves are trimmed to 10-12.5 cm and the disinfected cuttings set upright in beds until each gives rise to one strong plantlet which is then transferred to the nursery.
The butts, or bases, of mother plants, with leaves intact, are laid end to end in furrows in nurseries and covered with 5-7.5cm of soil. Sprouting occurs in 6 to 8 weeks. The butts give an average of 6 suckers each, though some have put forth up to 25. A 0.4 ha nursery of 25,000 butts, therefore, yields between 100,000 and 200,000 suckers.
The Pineapple Research Institute in Hawaii has also employed axillary buds at the base of crowns. Each crown segment may develop 20 plantlets. This method has been adopted in Sri Lanka for perpetuating superior strains but not for commercial cultivation because the resulting plants require 24 months or more to fruit.
In India, because of low production of slips and suckers in 'Smooth Cayenne', crown cuttings (15-16 per crown) have been adopted for propagation with 95% success, and this method is considered more economical than the utilization of butts.
Vegetative propagation does not assure facsimile reproduction of pineapple cultivars, as many mutations and distinct clones have occurred in spite of it.