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- Author or Editor: Thomas L. Davenport x
Individual avocado (Persea americana Mill.) flowers are perfect, opening two times to display two distinct reproductive stages on consecutive days. Stage 1 focuses on presentation of pistils and Stage 2 on presentation of pollen. The Stage 1 opening offers the greatest opportunity for outcrossing due to the absence of available pollen in that stage. Stage 2 flowers, however, are self-pollinated within flowers in direct proportion to the number of white stigmas present at the time of pollen dispersal. The potential success of these self-pollination events was examined in orchard trees of seven commercial Florida cultivars: Booth 7, Brooks Late, Choquette, Monroe, Simmonds, Tonnage, and Tower 2 and compared with hand-pollinations from complementary cultivars (cross pollination) and from flowers of the same cultivar (close pollination). The furthest advancement of pollen tubes down styles and into the ovaries on their way to the egg apparatus was noted in hundreds of individual flowers 24 and 48 h after pollen deposition on receptive white stigmas of the Stage 2 flowers. Virtually none of the seven cultivars exhibited pollen tubes reaching the egg apparatus by 24 h after deposition. By 48 h, however, pollen tubes had reached the egg apparatus in 25% to 85% of the pollinated flowers, depending upon cultivar. Pollen source was inconsequential. The results demonstrate the success of self-pollination in avocados. It is especially important for cultivars growing in humid climates, which display a high proportion of receptive white stigmas in Stage 2.
Pruning is an unavoidable necessity of virtually all arboreal fruit crops. In the tropics and subtropics, pruning of mango (Mangifera indica L.) is particularly important due to its tendency for frequent flushes, especially in humid tropics. Commercial orchards must maintain control of both tree size and orchard productivity in order to remain productive. Tip, formation, and severe pruning can be used in a variety of circumstances to produce predictable and useful results for a variety of purposes. For example, tip pruning can be used to encourage frequent flushing and branching of young trees to bring them into commercial production years earlier than if left alone. It can also stimulate timely flushes of lateral stems in an annual program to maintain tree size and prepare trees for synchronous flowering. Formation pruning shapes trees in an overgrown orchard to receive the maximum amount of light for high productivity and sets them up for annual pruning in a flowering management program. Severe pruning coupled with subsequent tip pruning of huge, nonproductive trees facilitates rapid restoration of orchard production. Each of these types of pruning can be used to get mango trees into production quickly and thereafter maintain maximum annual production while maintaining their desired size.
The reproductive phenology of temperate tree fruit species, such as apple and peach, will be briefly introduced and compared to the reproductive phenologies of several tropical and subtropical tree fruit species. Conceptual models of citrus and mango flowering will be described which help to understand the physiological mechanisms of flowering and vegetative flushes in trees growing in subtropical and tropical environments. Possible roles for auxin and cytokinins in shoot initiation and for gibberellins and a putative florigenic promoter in induction will be discussed as they relate to the physiology of flowering and vegetative flushes of tropical species. Successful application of these conceptual flowering models in controlling flowering of citrus, mango, lychee, and longan through the use of growth regulators and other horticultural management techniques will be described.
Abstract
The percentage of stigmas bearing pollen were determined in flowers of avocado (Persea americana Mill.). Stigmas were harvested at the end of the first and second floral openings (functionally female and male, respectively) in several cultivars located at several locations in southern Florida. Generally, <2% of the flowers were pollinated during the first opening of all observed cultivars. Due to the synchronously dichogamous flowering behavior of avocado, the source of this pollen was likely from interplanted complimentary cultivars (cross-pollination). Up to 15 times as many flowers received pollen during the second opening in some cultivars. The most likely source of this pollen was from within the same flowers. These preliminary observations suggest that self-pollination within avocado flowers during the second opening may be an important mechanism of avocado reproduction in the humid tropics.
The reproductive phenologies of temperate fruit tree species are briefly introduced and compared to the reproductive phenologies of three tropical and subtropical fruit tree species. The impact of leaf and fruit development and the phytohormones they may produce on the reproductive or vegetative fate of bourse buds in apple spurs serves as the model to discuss temperate fruit flowering. In contrast, conceptual models of citrus (Citrus L.), mango (Mangifera indica L.), and lychee (Litchi chinensis Sonn.) flowering are described which propose physiological mechanisms for both flowering and vegetative flushing in trees grown in subtropical and tropical environments. Possible roles for auxin and cytokinins in shoot initiation and for gibberellins and a putative florigenic promoter in induction are discussed as they relate to the physiology of flowering and vegetative flushing of tropical species. Successful application of these conceptual flowering models through the use of growth regulators and other horticultural management techniques to control flowering of citrus, mango, and lychee is described.
Abstract
Gibberellin (GA3) applied to ‘Tahiti’ lime (Citrus latifolia Tan.) markedly inhibited flowering, producing morphologically typical vegetative growth. Butanedioic acid mono-(2,2-dimethylhydrazide) (daminozide) slightly inhibited production of flowering shoots. Neither treatment consistently affected the number of new shoots.
Floral induction of mango is determined by interaction of a short-lived, florigenic promoter that is up-regulated in leaves during exposure to cool temperatures and an age-dependent vegetative promoter at the time that initiation of shoot growth occurs. Research conducted during the past flowering season demonstrated that 1/4 of a leaf per stem was sufficient to stimulate flowering in 100% of the tested stems. Three or more leaves on a donor stem of an isolated branch also bearing five defoliated stems induced flowering on all six stems. One leaf on the donor stem was sufficient to induce flowering in all of the donor stems and most of the five defoliated stems, and 1/2 leaf on the donor stem stimulated flowering in that stem and in less than 1/2 of the defoliated stems. Stems that did not flower initiated vegetative shoots instead. Flowering occurred on those stems that were inserted into main branches in the same phylotaxic position as the leaf. Evidence suggests that leaves are capable of producing far greater amounts of florigenic promoter during floral inductive conditions than needed for induction of buds and that the promoter can move great distances in phloem aligned in the same phylotaxic position as the source leaf.
Flowering and fruit set characteristics were examined in the popular commercial cultivar Magaoa in an effort to elucidate the reproductive phenology of mamey sapote, Calocarpum sapota (Jacq.) Merr. [syn. Pouteria sapota (Jacq.) H.E. Moore and Stearn]. Flowers opened during the night with anthesis beginning around sunset. The length of floral opening varied according to season, ranging from 6 days in winter to a single day in summer. Bursts of new flowers generally appeared in cycles of about 7 days in declining numbers of flowers per burst until all the floral buds of a particular floral bud flush had flowered. Floral buds flowered randomly along a branch with only a few flowers open at any one time. Flower position around the branch was a factor in fruit set. Flowers and small fruitlets encircled horizontal branches in great numbers, but immature fruit most often developed from flowers located on the upper branch quadrant. The lower quadrant contained the fewest immature fruit. As fruit matured, however, more upper quadrant fruit abscised until by harvest, most mature fruit were found on the lower quadrant. The observations provide new insights into the reproductive phenology of mamey sapote.
Abstract
Avocado (Persea americana Mill., cv. Simmonds) flowers and fruitlets were histologically examined to characterize the development of disfiguring bumps and ridges, as well as to investigate possible causes of the disorder. The outer cell layers of the ovary are damaged by a small, surface-feeding insect during and soon after anthesis. Bumps and ridges form as a result of cell proliferation in the pericarp directly beneath the wounds. Circumstantial evidence suggests that two species of flower thrips (Frankliniella) are the possible causal agents.