Gibberellic acid causes earlier flowering and synchronizes fruit ripening of coffee

The effect of 100 mgl^–1 gibberellic acid (GA₃) on flowering and fruit ripening synchrony, fruit set, fruit fresh weight, and vegetative growth were studied for different size classes of coffee (Coffea arabica L. cv. Guatemalan) flower buds. Flower buds that were > 4 mm, but not developed to the candle stage at the time of GA₃ treatment, reached anthesis 20 days earlier than the controls, and their development was independent of precipitation, unlike the controls. Fruit from buds that were treated with GA₃ at the candle stage showed earlier and more synchronous ripening than the control, although no differences in flowering were found during anthesis. Buds that were smaller than 4 mm at the time of treatment did not respond to GA₃ applications. Treatment with GA₃ did not affect fruit set, fresh weight of fruits, or vegetative shoot growth.     

Fruit Regulates Bud Sprouting and Vegetative Growth in Field-Grown Loquat Trees (Eriobotrya japonica Lindl.): Nutritional and Hormonal Changes

The effects of fruit on bud sprouting and vegetative growth were compared on fruiting and defruited loquat trees from fruit set onward. Carbohydrate and nitrogen content in leaves and bark tissues and hormone concentrations were studied during the fruit development and vegetative growth periods. On defruited trees, a significant proportion of buds sprouted in winter, whereas buds from fruiting trees sprouted only in the spring when fruit reached its final size. Furthermore, when panicles were completely removed in autumn, the buds also sprouted. In addition, fruit directly affected vegetative growth by reducing shoot length. An effect of sink removal (flower or fruit) promoting bud sprouting, regardless of the season, was then demonstrated. Neither soluble sugar concentration nor nitrogen fraction concentration in leaves or bark tissues was related to bud sprouting, but a certain nutritional imbalance was observed during the most active period of fruit development. Moreover, fruit sink activity significantly modified hormone content by increasing indole-3-acetic acid (IAA) and reducing zeatin concentrations, resulting in a higher IAA/zeatin ratio parallel to the lower bud sprouting intensity. Therefore, these changes caused by fruit removal are all related to vegetative growth, but there is no evidence that they are responsible for bud burst.     

Predispersal mortality and fecundity in the grey mangrove (Avicennia marina) in southeastern Australia

Abstract The predispersal mortality of floral buds and fruits in the grey mangrove (Avicennia marina) was examined over a range of populations for 3 years. The average survival of floral buds to anthesis was 34%. Moth larvae (subtribe Phycitina) attack and consume the contents of variable numbers of flower buds, but their activities did not influence bud survival, as experimental exclusion of larvae did not increase the number of buds surviving to anthesis. Fruit mortality is initially high with an average of 21% of floral buds surviving to immature fruit. Subsequent mortality is lower until on average 2.9% of floral buds survive to become viable propagules. Several cohorts of the phycitine moth larvae feed throughout the development of the fruit, and up to 62% of mature fruit show signs of larval attack. Experimental exclusion of moth larvae doubled the survival of fruits. However more than 75% of fruit mortality may be attributed to maternal regulation. Hail storms can also cause fruit mortality. The potential fecundity (number of ovules) of A. marina was measured over a range of age-size classes of trees and the realized fecundity (viable propagules) was estimated from average predispersal mortality. These estimates were subsequently verified in the field. A fecundity schedule was constructed with assumptions on reproductive frequency and reproductive life. The average annual supply of propagules over a lifetime is estimated to be about 247 viable propagules per tree.     

<Emphasis Type="Italic">In vitro</Emphasis> fruiting and seed set of <Emphasis Type="Italic">Capsicum annuum</Emphasis> L. CV. Sweet banana

Summary Plantlets of Capsicum annuum L. ev. Sweet Banana regenerated via somatic embryogenesis from immature zygotic embryos were capable of producing flower, fruit, and seed when cultured in small tissue culture containers. In vitro floral buds were first formed on plantlets that grew on plantlet development medium [agar-gelled Murashige and Skoog (MS) basal medium containing 1 mgl⁻¹ (5.3 μM) α-naphthaleneacetic acid (NAA)] in a growth room at 22°C and continuous illumination. However, floral buds rarely developed further into mature flowers. This problem was overcome using the vented autoclavable plant tissue culture containers. In vitro fruit formation and ripening was observed when liquid half-strength MS basal medium supplemented with 5 μg ml⁻¹ silver thiosulfate, 1 mg l⁻¹ (5.3 μM) NAA, and 3% sucrose was added to the surface of the plantlet development medium. Hand-pollination improved fruit set. Further research in needed to determine why the pepper seeds formed in vitro failed to germinate.     

Reproductive trade-offs in genetically distinct clones ofVaccinium macrocarpon,the American cranberry

Patterns of resource allocation to growth, current reproduction, and potential future reproduction were quantified in six genetically distinct cultivars ofVaccinium macrocarpon. For all cultivars (genotypes), vegetative size is positively correlated with some measures of current reproduction (fruit and flower number) but negatively correlated with others (seed number per fruit, seed weight per fruit). Vegetative growth in the current year is significantly related to the production of reproductive terminal buds, a measure of the potential for reproduction in the following year. Stems with low levels of current reproduction — lower flower number, fruit number, and seed weight — were more likely to form reproductive terminal buds than stems with higher levels of current reproduction. Individual genotypes differed significantly for vegetative size, fruit number, fruit weight, seed number, and seed weight, as well as for the frequency of fruiting stems and reproductive terminal buds produced. Genotypes were segregated in principal component space, indicating overall differences between them in allocation to the suite of variables measured. These results indicate the possibility of fitness differences among cultivars due to genetically determined allocation strategy, which has implications for fitness differences among genotypes within natural populations.     

Gene note. Mdh3 encoding a Phalaenopsis 039-like homeodomain protein expressed in ovules of Malus domestica

A cDNA clone, Mdh3, was isolated from young fruit of Malus domestica Borkh. The Mdh3 gene is closely related to the Phalaenopsis 039 homeobox gene, which is involved in ovule development in orchids. Mdh3 mRNA was expressed in young apple leaves, flower buds and young fruit. In situ hybridization of flower buds showed that Mdh3 mRNA accumulated in the ovules, suggesting that Mdh3 may be involved in apple ovule development.     

Effect of modified endogenous ethylene production on sex expression, bisexual flower development and fruit production in melon (Cucumis melo L.)

Members of the Cucurbitaceae family display a range of sexual phenotypes including various combinations of male, female, or bisexual flowers. Ethylene appears to be a key hormone regulating the sex determination process. Application of ethylene, or inhibition of ethylene action, increases or decreases the number of pistil-bearing buds, respectively. Elevated levels of ethylene production and expression of genes for ethylene biosynthesis, have been correlated with pistillate flower production. In this study, we sought to determine the effect of modified endogenous ethylene production on sex expression by constitutively expressing ACS (1-aminocyclopropane-1-carboxylate synthase), the first committed enzyme for ethylene biosynthesis, in transgenic melons (Cucumis melo L.). Most melon genotypes are andromonoecious, where an initial phase of male flowers is followed by a mixture of bisexual and male flowers. ACS melon plants showed increased ethylene production by leaves and flower buds, and increased femaleness as measured by earlier and increased number of bisexual buds. ACS melons also had earlier and increased number of bisexual buds that matured to anthesis, suggesting that ethylene is important not only for sex determination, but also for development of the bisexual bud to maturity. Field studies showed that ACS melons had earlier mature bisexual flowers, earlier fruit set, and increased number of fruit set on closely spaced nodes on the main stem. These results provide a direct demonstration of the importance of endogenous ethylene production for female reproductive processes in melon.     

Growth and Dormancy Cycles in Citrus Bud Cultures and Their Hormonal Control

An in vitro bud culture method was devised in order to better understand the control mechanism of Citrus bud development. This technique offers a new approach to the study of hormonal control of growth, dormancy and flowering cycles in perennial plants. Buds were excised from orchard trees throughout the year, cultured on defined media for prolonged periods, and their vegetative growth responses to various growth hormones were determined. The buds proceeded with their vegetative development in vitro and achieved sprouting on a basal medium. The various growth regulators affected both the time required for sprouting (TRS) and the type of growth. In summer buds, IAA delayed sprouting, while GA enhanced it and caused shoot elongation. Cytokinins specifically induced the formation of numerous adventitious buds, whereas ABA completely inhibited sprouting; this inhibition, however, was reversible. A marked decrease in total protein and in the rate of its synthesis was evident during the first 20 days of sprouting induction and early bud growth. The annual growth rhythm was determined in spring buds sampled and cultured throughout the year, and an innate dormancy of citrus buds was revealed. Both the dormancy and the sprouting periods of buds in vitro corresponded to the natural periods occurring under field conditions. The effect of exogenous IAA, GA and cytokinins on the TRS varied at different periods along the season, suggesting the concept of “critical levels” in the endogenous balance of hormones.     

Between-year variation in flowering and fruit set in frost-prone and frost-sheltered populations of dioecious Rubus chamaemorus

Summary The flowering and fruiting patterns of the dioecious perennial herb Rubus chamaemorus L. were studied in frost-prone (open) and frost-sheltered (Shaded) habitats in northern Sweden over 6 years. The number of ramets with flower buds, the proportion of flower buds that opened, and fruit set varied markedly between years. In the frost-prone populations, the occurrence or absence of detrimental frosts during the development of flowers and fruit could explain much of the variation, both in the proportion of flower buds that developed into flowers, and in fruit set. In the frost-sheltered populations, most female flowers that did not develop into fruit aborted without any signs of physical damage and before any ovules had begun to enlarge. Flower mortality caused by herbivores feeding on reproductive parts was commonly low, but reached values higher than 10% in one of the shaded populations. Hand-pollination increased the proportion of ovules producing seeds in the mature fruits by about 20%, and in one year also increased fruit set significantly in one population. Fruit-producing female ramets had a higher mortality and a lower probability of flowering in the subsequent year than male ramets and non-fruiting female ramets. In R. chamaemorus, the conditions for fruit maturation are highly unpredictable at the time of flower initiation. It is suggested that the apparent over-initiation of flower buds is advantageous, as it allows the plant to attain a high reproductive success in years favourable for flowering and fruit development.     

The timing of sprays for the protection of terminal buds on apple shoots from powdery mildew

Post-blossom sprays of fungicides, repeated at 10-day intervals until leader (syn. extension) shoots had stopped producing new leaves, provided the best protection of terminal buds against Podosphaera leucotricha on the apple cv. Lane's Prince Albert. Spraying was most effective in early summer, although many of these buds were not invaded until later, when the rate of shoot growth declined; applications from July to September did not compensate for the enhanced infection which followed interruptions of the post-blossom programme between late May and early July. This early period was critical because most leaf infections occurred then, and because this phase of the epidemic on foliage determined the eventual intensity of mildew on terminal leaves, and hence the inoculum available for infecting terminal buds. Also, many lateral shoots ceased growth early and their apices were directly protected by sprays applied in June. Applications after early June were too late to protect newly formed fruit buds on spur branches.     

Eriophyoid mite damage in Vitis vinifera (grapevine) in Australia: Calepitrimerus vitis and Colomerus vitis (Acari: Eriophyidae) as the common cause of the widespread ‘Restricted Spring Growth’ syndrome

Leaf and shoot distortions and retarded shoot growth in Vitis vinifera L. prevalent in Australian vineyards in early spring, were investigated in replicated field experiments over 3 yrs. Leaf distortion and retarded shoot growth were identified as damage due to feeding of extremely high populations of over-wintered deutogynes of Calepitrimerus vitis (Nalepa) (grape rust mite). This damage was hitherto known in Australia as Restricted Spring Growth (RSG), a syndrome comprising several growth abnormality symptoms, none with a clearly identified cause or a successful treatment. A successful treatment against C. vitis was used to selectively eliminate RSG, while C. vitis numbers were recorded using a validated trapping technique; intercepting deutogynes migrating from winter shelters in the wooden vine structure, to emerging green tissues. Severe leaf distortion was associated with >400 C. vitis deutogynes per spur, while >1000 per spur had the added effect of severely retarding shoot growth. A 43.0–47.2% shoot length reduction was recorded for Cabernet Sauvignon, 27.1–32.8% for Sauvignon Blanc, when 4–6 leaves were separated. Symptoms were most prominent up to 8–9 separated leaves, however 24.7–30.4% shoot length reduction was still evident at flowering, and 12.8% circa fruit set. C. vitis effect on vine fruitfulness, and yield parameters at fruit set, were also studied. Once successfully treated to prevent C. vitis damage, poor bud burst remained evident in some vineyards. Surveys of unburst buds from such vineyards revealed presence of Colomerus vitis (Pagenstecher) (grape bud mite). When Col. vitis numbers in unburst buds reached 100–500 per bud, apical meristems of primary, and commonly also secondary buds were dead, preventing bud burst. The remaining living scale tissue was distinctly scarred. Bud and associated shoot damage were documented. Retarded shoot growth and leaf distortion, previously attributed to RSG, are misdiagnosed C. vitis spring feeding damage. Clustered high infestations of Col. vitis can cause bud-axis necrosis, bud burst failure, shoots with short basal internodes, and short, thin, zigzagged shoots with absent fruit clusters; all previously considered RSG.This revised version was published online in May 2005 with a corrected cover date.     

Changes in Photosynthesis and Fruit Characteristics in Olive in Response to Assimilate Availability

The source level in the olive cultivar Leccino was varied by girdling at different stages of fruit growth. Afterwards, the effects on gas exchange, fruit growth, and ripening and blooming were studied. Girdling during fruit growth did not significantly influence net photosynthetic rate (P _N) except in the last phase of fruit growth when the P _N was reduced. In the girdled branch, P _N began to decrease at the onset of starch accumulation because fruit growth ceased. In mid-November stomatal conductance (g _s) and transpiration rate (E) were also reduced by girdling, whereas sub-stomatal CO₂ concentration (C _i) increased in leaves from the girdled branches. The total chlorophyll content (Chl) tended to decrease in parallel with the reduced P _N. Girdling did not substantially influence the leaf and shoot water contents. The large availability of assimilates seems to cause an earlier fruit ripening. In general, girdling increased fruit dry mass. Healing before the time when the majority of pulp growth occurs reduced the effect of girdling. June girdling increased the pit dry mass. Girdling at the beginning of August and September, compared to the control, increased the pulp dry mass, but the pit dry mass did not differ with respect to the control. The percentage of oil in the fruit, on a dry mass basis, increased with August and September girdlings, but the percentage of oil in the pulp did not change. Girdling reduced shoot growth, but the internode length was unchanged. Girdling slightly stimulated differentiation of flower buds.     

Dispersal of Acalitus essigi to blackberry (Rubus fruticosus agg.) fruit

The eriophyoid mite, Acalitus essigi (Hassan), is hypothesised to be responsible for redberry disease of blackberry (Rubus fruticosus L. agg.) fruit. Infested fruit ripen unevenly with affected drupelets becoming hard, inedible and bright red, whereas unaffected drupelets ripen evenly. As a first step toward possible control of this disease, the method and timing of dispersal of A. essigi onto developing blackberry fruit was examined. No mites were found on unopened flower buds or open flowers. However, infestation of fruit was found to commence during the green stage of fruit development and significantly increase during the red fruit stage. Although redberry symptoms were not observed, experimental exclusion of A. essigi to prevent the mite moving up the pedicel of open flowers by a sticky barrier significantly reduced A. essigi populations within the resultant fruit by over five fold that of control fruit. Although very low levels of aerial dispersal onto fruit cannot be discounted it was concluded that non-aerial or crawling dispersal via the fruit pedicel was the dominant method of blackberry fruit infestation.     

The Morphogenesis of Apple Buds: IV. The Effect of Fruit

The course of development of spur buds on fruiting trees of‘biennial’ and ‘regular’ apple varietieswas followed throughout the season by dissection of successivesamples of buds and the effect on bud development of de-fruitingtrees at two different times in the season was recorded. In the biennially fruiting variety Miller's Seedling, the patternof bud development on fruiting trees was very similar to thatin buds on non-fruiting trees which failed to form flowers followingdefoliation, as were the number and sizes of leaves precedingthe bud in each instance. The failure to form flowers was associatedwith the occurrence of an 18-day plastochrone in buds, and itwas concluded that on fruiting trees it was not due to a competitiveeffect of the fruit for nutrients. This long plastochrone was not found in buds of de-blossomedtrees of Miller's Seedling, and in trees de-fruited later inthe season the buds immediately broke into a new flush of growthand at the same time the plastochrone was shortened. These resultssuggest that the long plastochrone was due to the inhibitoryeffect of fruit on the older primordia of the bud, an effectwhich did not occur until after the resting buds had begun toform. A phase with an 18-day plastochrone was also found inbuds of another biennial variety, Laxton's Superb, but not inthose of the regularly fruiting variety Sunset. Developing fruitlets of biennial varieties caused bud-scalesto form sooner and hastened their rate of development, possiblydue to changes induced in the levels of a gibberellin-like apexfactor in the buds. The rate of increase in number of bud-scalesin the bud appeared to depend upon the extent to which the budwas affected by the primary leaves of the flower cluster andthose of other clusters.     

Rapid in vitro propagation of Aloe barbadensis Mill

Axillary bud development and adventitious bud formation was obtained with decapitated shoot explants of Aloe barbadensis Mill. Maximal bud growth and rooting of shoots was obtained on a modified medium of Murashige and Skoog supplemented with 5 M IBA. More adventitious and axillary buds developed on nutrient media supplemented with IBA than with NAA. Axillary buds but not adventitious buds developed with IAA in the medium. Morphogenesis was inhibited by 2,4-D. Kinetin, benzyladenine and thidiazuron were toxic to the explants and did not stimulate the development of axillary of adventitious buds. The optimal temperature for bud growth and development was 25°C. Axillary bud growth and the formation of adventitious buds was slowed down at 10°C and totally inhibited by 30°C. The optimal sucrose concentration was 3% with the inhibition of bud growth and development by higher sucrose levels.     

COMPARATIVE EFFECTS OF GIBBERELLIN AND INDOLE COMPOUNDS ON THE INDUCTION OF PARTHENOCARPY IN SEXUALLY INCOMPATIBLE PERESKIA ACULEATA

Sachar , R. C. (U. Delhi, India.) Comparative effects of gibberellin and indole compounds on the induction of parthenocarpy in sexually incompatible Pereskia aculeata. Amer. Jour. Bot. 49(9): 913–917. Illus. 1962.—The effects of indoleacetic acid (IAA), indolebutyric acid (IBA), gibberellin (G) and gibberellic acid (GA) were studied on the fruit growth of the sexually incompatible Pereskia. Under natural conditions, this plant did not produce any fruits and seeds, and the flowers abscised a week after anthesis. IAA (50–500 ppm) delayed the formation of an abscission layer by another 2 weeks, but it was ineffective in inducing parthenocarpy. IBA (50–500 ppm) induced fruit-set in only 15% of the flowers. Best response was achieved by G (100–500 ppm), or GA (100–500 ppm), which gave 100% fruit-set. The effect of GA in inducing parthenocarpy was not inhibited when used in conjunction with IAA. Maximum size of the fruits was obtained with 2 sprayings of GA, and subsequent sprays were of no consequence. Further, fruit size was the largest when GA or G was sprayed at anthesis, or on old flower buds, but it was much less when the chemicals were sprayed on young flower buds. There was no stimulation of the growth of ovules; instead, a translucent mucilaginous placental tissue developed within the cavity of the fruit wall. Attempts were made to culture ovules and the placental tissue on artificial nutrient medium, but without success.     

Role of indoleacetic Acid and abscisic Acid in the correlative control by fruits of axillary bud development and leaf senescence

When fully filled pods of bean plants were deseeded, the rate of axillary bud growth and the chlorophyll content of leaves were increased. Application of 0.1% indoleacetic acid (IAA) in lanolin on the deseeded pods caused abscission of axillary buds, inhibited growth of the remaining buds, and decreased leaf chlorophyll content. The response of bud development to fruit-applied IAA was concentration dependent between 0.001 and 0.1% IAA (representing from 2 to 200 micrograms IAA per fruit) resulting in greater growth inhibition at higher IAA concentrations.     

Flower developmental stage and organ sensitivity of bell pepper (Capsicum annuum L.) to elevated temperature

High temperatures adversely affect crop productivity of several plant species including bell pepper (Capsicum annuum L. var. annuum). The objectives of this study were: (1) to determine whether flower ontogeny is adversely affected by high temperature during different phases of development, including pre‐ and post‐pollination events; (2) to determine the duration of high temperature exposure necessary to cause reduction in fruit set; and (3) to determine whether injury to the pistil or stamen during development is responsible for reduced fruit set during high temperature. We determined that flower buds at <2·5 mm in length, corresponding to microspore mother cell meiosis to tetrad dissolution, and flowers that reached anthesis during the high temperature exposure had reduced fruit set when exposed to 33 °C for 48 or 120 h. Flower buds at <2·5 mm in length also had reduced pollen viability when exposed to 33 °C for 120 h. Morphological examination demonstrated that meiocytes initiated tetrad formation, but after dissolution the microspores remained small and clumped without a thick exine. High temperature exposure at a late‐development, pre‐anthesis stage did not affect pistil or stamen viability, but high post‐pollination temperatures inhibited fruit set, suggesting that fertilization is sensitive to high temperature stress.     

Effect of strictly plant-related factors on the response ofHevea brasiliensis andTheobroma Cacao nodal explants culturedIn vitro

Summary Nodal cuttings (primary nodal explants) were used to initiate microcutting cultures ofHevea brasiliensis andTheobroma cacao. The physiological stage of growth reached by the branches from which the explants were taken had a considerable influence on culture initiation and response. In both species, the buds of the nodal explants taken from dormant branches (stages 11, 12 and 13 inTheobroma; stage D inHevea) revealed greater opening abilityin vitro and shoot elongation than buds taken from branches in a phase of active meristem growth inTheobroma (stages F1 and F2) or during a foliar growth phase inHevea (stage C). InHevea, the branch growth phase effect persisted into the multiplication phase when shoots developedin vitro were used as the source of secondary nodal explants. However, it disappeared during subcultures of primary nodal explants. In both species, the position of the nodes on the branch with respect to the apex also had an effect on culture initiation. The buds of nodes furthest from the apex were more likely to develop into shoots. InHevea, the position of secondary nodal explants obtained from the primary shoot was seen to vary in effect depending on growth regulator applications during primary culture. These results are analyzed in terms of variations in the balance between endogenous growth promoters/inhibitors in the buds, depending on morphogenic stages and the bud position on the branch.     

The relationship between xylem differentiation and dormancy evolution in apricot flower buds (Prunus armeniaca L.): the influence of environmental conditions in two Mediterranean areas

Environmental and climatic conditions affect the flower bud growth, flowering and yield performance of fruit species. Temperature and water availability appear to be important factors for temperate fruit trees in mild climates. The aim of this research was to study the involvement of temperature regime on biological processes, such as xylem differentiation and dormancy evolution, in apricot flower buds (Prunus armeniaca L.). Over 3 consecutive years, biological and anatomical investigations were carried out in Tuscany (Italy) and Murcia (Spain) on two cultivars characterized by a different chilling requirement (CR): Currot, a traditional Spanish cultivar with a very low CR, and Stark Early Orange (SEO), a North American cultivar with a very high CR. Currot had a regular bearing, and was characterized by a synchronism between endodormancy release and xylem differentiation. On the other hand, SEO showed an irregular flower bud growth leading to flowering and fruit-set failure, even with a high level of chilling accumulation. No relationship was found in SEO between xylem development and flower bud growth reactivation. The de-synchronism between these processes could determine the poor adaptability to different environmental areas of SEO cultivar, and its very high CR is not the main hypothesised cause of the altered flower bud development.