Parthenocarpic Fruit Growth Reduces Yield Fluctuation and Blossom-end Rot in Sweet Pepper

The aim of this work was to investigate whether parthenocarpicfruit growth could avoid flushing, i.e. an irregular yield pattern,in sweet pepper. Plants were grown in a greenhouse compartmentfrom April until August. Half of the plants were grown withouta fruit set treatment (control), whereas parthenocarpic fruitswere allowed to develop on the other plants by preventing self-pollinationand applying auxin to the stigma. For node positions 3 to 17,fruit set per node varied between 21 and 55% for control plants[coefficient of variation (CV) = 11%], whereas auxin-treatedplants showed much less variation in fruit set (41–57%;CV = 5%) and average fruit set was higher. In agreement withfruit set, fruit yield was also much more regular in the auxin-treatedplants. Fruit fresh yield varied between 0.2 and 1.0 kg m^-2forcontrol plants (CV = 20%), and between 0.4 and 0.8 kg m^-2forauxin-treated plants (CV = 9%). Results showed that developingseeds in sweet pepper fruits are the main cause of the abortionof new flowers, and irregular fruit set and yield. Parthenocarpicfruit growth resulted in flatter, 30% smaller fruits, becauseof a reduction in fruit growth rate; the duration of fruit growthwas 1 week longer than for fruits from control plants. Parthenocarpicfruits were hardly affected by blossom-end rot (BER) with only1% of fruits being affected compared to 31% in the control.Total dry mass production was the same for treated and controlplants; however, in auxin-treated plants, 50% of the total drymass was allocated to the fruits, compared to 58% in controlplants. Copyright 2001 Annals of Botany Company Abortion, auxin, BER, blossom-end rot, Capsicum annuum L., flushing, fruit set, irregular yield pattern, parthenocarpy, sweet pepper     

Blossom-end rot in relation to growth rate and calcium content in fruits of sweet pepper (Capsicum annuum L.)

The relative importance of growth rate and calcium concentration in sweet pepper fruits (Capsicum annuum L.) for the induction of blossom-end rot (BER) was investigated in (1) four pollination treatments in one cultivar, (2) four cultivars with the same fruit load and (3) three fruit load treatments in four cultivars. For fruits with the same pollination treatment those eventually developing BER had a higher initial fruit growth rate than those not developing BER. Within the same experiment both the growth rate of the young fruit and BER increased with the number of seeds. The Ca concentration of the pericarp in mature fruits was negatively related to both fruit size and BER incidence. Differences in levels of BER between different pollination experiments could not be explained solely by differences in growth rate of the young fruit, but related to different Ca concentrations in the mature fruits. In the spring, but not in the summer, cultivars more susceptible to BER had a larger final size but lower Ca concentration in the young fruit than the resistant ones. By lowering the fruit load in the summer both the final fruit size and the BER incidence increased, but the Ca concentrations of both proximal and distal pericarp in the young fruit of all cultivars were not consistently affected. Despite a correlation between growth rate and low Ca concentration in the fruit, the incidence of BER may only be predicted from separate effects of fruit growth and of Ca concentration of fruit. The data indicated that at a higher growth rate a higher Ca concentration is required to prevent the induction of BER. The usefulness of the total Ca concentration of the fruit for determining the critical Ca concentration in the induction of BER is discussed.Key words: Capiscum annuum L., sweet pepper, blossom-end rot, calcium, growth rate, pollination, fruit load.      

Foraging Behaviour of Wild Bees at Hot Pepper Flowers (Capsicum annuum) and its Possible Influence on Cross Pollination

Native bees are effective pollinators of hot pepper plants,Capsicum annuum. In four gardens in south-central Brazil (Patosde Minas and Brasília) flowers of three cultivars receivedvisits from 16 species of bees in eight genera: Hylaeus(Colletidae),Dialictus, Halictus, Augochlora,Augochloropsis and Ceratalictus(Halictidae),Exomalopsis andBombus (Apidae). No other insects were observedto visit the flowers. Some species of bee occurred in more thanone garden. Individual bees gathered a full pollen load from18 to 47 flowers and visited one to eight plants on a singleforaging trip. In 76 shifts between plants, the bees made nineswitches between cultivars. It is suggested that small nativespecies of bees pollinate the flowers effectively and that theirsmall foraging areas are important in keeping the cultivarsof both hot and sweet peppers genetically distinct where severalcultivars are grown close together. Copyright 2000 Annals ofBotany Company Capsicum annuum, hot pepper, native bees, fruit set, Brazil     

Fruit characteristics, seed production and pollen tube growth in the wild chilli pepper Capsicum flexuosum

Fruits formed after different pollination regimes (flowers hand pollinated, unpollinated, and open pollinated) and the seeds obtained were characterized in the wild chilli pepper Capsicum flexuosum Sendtn. Pollen tube development in vivo and ovary growth were also analyzed. Seedless fruits and empty seeds were abundant among the fruits from hand pollinated and open pollinated flowers, while no more than one seed with embryo was found in a low percentage of fruits from such pollination treatments. Parthenocarpic fruits were formed from unpollinated flowers. Pollen tube growth was arrested in the upper third of the style for almost all pollen tubes except for a single one that may continue elongating occasionally. The ovary size increased continuously after pollination, even without fertilization. The sum of the evidence registered may help to explain the low number of seeds with embryo harvested, the abundance of seedless fruits formed from pollinated flowers (possibly parthenocarpic), and the high rate of parthenocarpic fruits formed from unpollinated flowers.     

Physiological and morphological changes during early and later stages of fruit growth in Capsicum annuum

Fruit‐set involves a series of physiological and morphological changes that are well described for tomato and Arabidopsis, but largely unknown for sweet pepper (Capsicum annuum). The aim of this paper is to investigate whether mechanisms of fruit‐set observed in Arabidopsis and tomato are also applicable to C. annuum. To do this, we accurately timed the physiological and morphological changes in a post‐pollinated and un‐pollinated ovary. A vascular connection between ovule and replum was observed in fertilized ovaries that undergo fruit development, and this connection was absent in unfertilized ovaries that abort. This indicates that vascular connection between ovule and replum is an early indicator for successful fruit development after pollination and fertilization. Evaluation of histological changes in the carpel of a fertilized and unfertilized ovary indicated that increase in cell number and cell diameter both contribute to early fruit growth. Cell division contributes more during early fruit growth while cell expansion contributes more at later stages of fruit growth in C. annuum. The simultaneous occurrence of a peak in auxin concentration and a strong increase in cell diameter in the carpel of seeded fruits suggest that indole‐3‐acetic acid stimulates a major increase in cell diameter at later stages of fruit growth. The series of physiological and morphological events observed during fruit‐set in C. annuum are similar to what has been reported for tomato and Arabidopsis. This indicates that tomato and Arabidopsis are suitable model plants to understand details of fruit‐set mechanisms in C. annuum.     

The Effect of Fruit Load, Defoliation and Night Temperature on the Morphology of Pepper Flowers and on Fruit Shape

The shape and regularity of bell pepper (Capsicum annuumL.)fruit are known to be determined at a very early stage of flowerdevelopment. Small, flattened fruit which are commonly parthenocarpicdevelop under low-temperatures (below 16 °C) from flowerswith enlarged ovaries. In such flowers self-pollination is notefficient because of the large distance between the stigma andstamens. Flower deformation of this kind is common during thewinter season. In the present study it was found that deformationsof flowers, similar to those found under low temperatures, wereinduced in 15 d by complete removal of fruit from plants growingunder night-time temperatures of 18 °C. Only flowers whichwere at the pre-anthesis stage at the time of fruit removalwere deformed by this treatment. Removal of leaves from thelower part of the plant (source leaves) partially reduced theeffect of fruit removal on the shape of the flowers and on subsequentfruit morphology. Fruit removal induced significant increasesin the concentrations of starch and reducing sugars, but notsucrose, in the flower buds. Likewise, flower buds of plantswhich grew under a night-time temperature of 12 °C containedmore carbohydrate than those which grew at 18 °C. Theseresults suggest that flower morphology in pepper is at leastpartly controlled by source-sink relationships. Assimilateswhich are normally transferred to developing fruit may be transported,upon fruit removal, to the flower buds which subsequently swell.A similar increase in assimilate translocation to flower budsmay occur under low temperatures, subsequently causing deformationof fruit.Copyright 1999 Annals of Botany Company Pepper, (Capsicum annuumL), flower shape, low temperatures, source-sink relationship, fruit shape, seeds, reducing sugars, sucrose, starch.     

Selective fruit filling in relation to pollen load size in Alstroemeria aurea (Alstroemeriaceae)

 We conducted an experiment in a natural population of Alstroemeria aurea, a clonal perennial, to determine (1) if reproduction was resource limited, and (2) if fruits would be selectively filled based on differences in pollination intensity when pollen loads were adequate for full seed set. Under these conditions, differences in pollination intensity are unlikely to affect seed number, but could affect seed quality, providing an interesting test of the gametophytic competition hypothesis. To test for resource limitation, percent fruit maturation, number of seeds per fruit and average seed weight were compared to paired controls for ramets in which all but one fruit was removed. To test the effect of pollination intensity on selective resource allocation, three types of pollination treatments were performed: (1) all flowers of the single inflorescence received a low pollen load, (2) all flowers received a high pollen load, (3) alternate flowers of the inflorescence received either a high or a low pollen load. We determined the percentage of fruit that reached maturity, counted the number of seeds and ovules and calculated the average seed weight for all capsules in each treatment. Resources appeared to limit reproduction in this population since seed number and weight were significantly higher than in controls when competing capsules were removed. At the whole ramet level, a four fold difference in pollen loads had no significant effect on any of the parameters measured. However, when pollination intensity varied within an inflorescence, the number of seeds per fruit increased by about 10% in flowers that received the higher pollen load. We observed the same trend in each of 2 years, but the increase was significant in only 1 year. The differences, although not great, were only slightly smaller than when all competing fruits were removed, and were consistent with selective resource allocation based on pollination intensity independent of seed set. Received: 28 September 1997 / Accepted: 30 April 1998     

Effects of Cross-pollination and Flower Removal on Fruit Set in Macadamia

Macadamia racemes were cross-pollinated and had flowers removedto determine whether manipulation of initial fruit set wouldaffect final fruit set or yield. Examination of flowers collected7 d after pollination indicated that the cross-pollination treatmentgenerally induced a small (13-19%) but significant increasein the number of pollen grains per stigma. All flowers possessedsome pollen grains, but in all cases cross-pollination approximatelydoubled the percentage of flowers with a pollen tube at thebase of the style (42-68% of flowers on cross-pollinated racemescompared with 21-35% of flowers on control racemes). Fruit setafter 14 d was always improved by cross-pollination, and thistranslated into increased final fruit numbers on two out offour occasions. In these two cases, kernel weights were increasedby 24 and 31% in the cross-pollinated treatments. This indicatesa possible xenic (paternal parent) effect in macadamia. Flowerremoval resulted in retention of a greater percentage of flowersas fruits, so that only severe reductions in flower number decreasedfinal fruit numbers. Improved efficiency of cross-pollinationin macadamia may increase both nut numbers and nut size.Copyright1994, 1999 Academic Press Macadamia integrifolia Maiden and Betche, Macadamia tetraphylla L. A. S. Johnson, Proteaceae, macadamia, pollination, pollen tube growth, flower number, fruit drop, fruit set, xenia     

Pollination intensity and potential seed set in Passiflora vitifolia

Summary Initial seed set and fruit set were pollen-limited in a Costa Rican population of Passiflora vitifolia, a self-incompatible species with 200–350 ovules per flower. Pollination intensity was measured by counting the number of allogamous pollen grains on stigmas of the large one-day flowers. Hand-pollinations demonstrated that 25–50 pollen grains are required for fruit set, and >450 are needed for maximum seed set, with a pollen:seed ratio of about 1.6:1.0. Hummingbirds (Phaethornis superciliosus) delivered sufficient allogamous pollen for maximum seed set to only 28% of the flowers examined. Naturally pollinated flowers yielded fewer fruits and fewer seeds per fruit than those pollinated by hand. Most pollen transferred by humming-birds was self-incompatible; emasculated flowers yielded higher seed set than flowers with intact anthers. Visitation rates did not provide a good index of effective pollination.There were significant differences in ovule number, maximum seed set, and maximum per cent seed set among individual vines. More than half of an individual's flowers failed to set fruit, whether pollinated by birds or by hand. In this population, maximum reproductive potential may be limited by maternal resources for fruit development, but seed set varies with pollination intensity. Pollen-limited seed set may be a disadvantage of self-incompatibility, especially in species with many-seeded fruits.     

EFFECTS OF ENVIRONMENTAL STRESS ON COMPONENTS OF REPRODUCTION IN CLARKIA UNGUICULATA

The effects of stress on reproduction in Clarkia unguiculata were investigated by monitoring flower number, seed number and seed wt after subjecting plants to drought and heavy fruit loads, and by monitoring seed number after pollinating overage flowers. Fewer main-stem flowers were produced in drought stressed plants than in non-stressed plants. Drought stress did not affect overall seed numbers and seed wt in 1981, but did significantly affect seed number and wt in different flower age classes. Overall seed numbers were not affected by drought stress in 1982, but seed wt was significantly lower in plants with stressed ovules. Fewer flowers but more seeds per pollination were produced by plants in which all or ½ the flowers were pollinated than by plants in which ¼ or 1/6 of the flowers were pollinated. Seed wts were lowest in plants with a full fruit load and in fruits produced late in the growth cycle. Seed number was variable but high following pollination of flowers with 1–7 day old stigmas, and much lower in flowers with older stigmas.     

Comparison of two cacao (Theobroma cacao L.) clones for the effect of pollination intensity on fruit set and seed content

We compared the influence of pollination intensity (PI) on fruit set and seed number per pod in two cacao (Theobroma cacao L.) clones, IFC5 (Forastero Lower-Amazon Amelonado), which is self-compatible and known to produce a high number of seeds per pod under open pollination, and SCA6 (Forastero Upper-Amazon), which is self-incompatible and known to produce a low number of seeds per pod under open pollination. With both clones, PI had a positive effect on fruit set, with the maximum rate requiring more than 150 pollen grains per pod. One-half of the maximum rate of fruit set was reached with 39 pollen grains per pod for SCA6, and 78 for IFC5. With SCA6, a significant positive effect of PI on seed number per pod was also observed, with maximum seed number requiring more than 200 pollen grains per pod. In contrast, seed numbers with IFC5 were approximately equal over the PI range 100–800 pollen grains per pod. Patterns of seed number per pod were compared after: (1) open insect pollination, (2) low-intensity hand pollination and (3) high-intensity hand pollination. The patterns obtained with IFC5 under open pollination showed a peak of 40–50 seeds per pod, whereas the distribution patterns were more even with SCA6. The pattern of seed number under open pollination was similar to that obtained with high-intensity hand pollination for IFC5, and with low-intensity hand pollination for SCA6. We concluded that the high number of seeds per pod observed with IFC5 under natural insect pollination may be explained by a high number of compatible self-pollen grains on the stigma and by a severe drop of low-pollinated flowers eliminating potential lowfilled fruits. With SCA6, however, the number of compatible pollen grains deposited on the stigma was probably low under open pollination, and the flowers required lower pollen quantities to set fruit, which resulted in a high frequency of low seed numbers per fruit. This difference in the capacity to set low-seeded fruits might be considered as an adaptive trait related to the mode of reproduction.     

Enhancement of fruit quality in Capsicum annum through pollination by Hypotrigona gribodoi in Kakamega,Western Kenya

A study was carried out in Kakamega forest, in the western region of Kenya, to evaluate the effectiveness of the stingless bee Hypotrigona gribodoi (Magretti, 1884) on the pollination of green pepper. Three treatments were applied and consisted of self‐pollination, pollination by feral pollinators in the open field and pollination by H. gribodoi in a net cage. The differences in fruit yield and seed quality were compared among treatments. Flowers pollinated by H. gribodoi produced the heaviest fruits with the highest seed numbers followed by feral pollinators and lastly self‐pollinated flowers. Moreover, seeds were significantly bigger in size in fruits resulting from flowers pollinated by H. gribodoi compared to fruits obtained from self‐pollinated flowers or flowers pollinated by feral insects. We, therefore, conclude that H. gribodoi is an efficient pollinator of green pepper in the tropical region of East Africa.     

Inheritance of anthracnose resistance (Colletotrichum scovillei) in ripe and unripe Capsicum annuum fruits

Anthracnose, caused by Colletotrichum spp., is one of the most common diseases affecting sweet pepper and chilli pepper production worldwide, especially in tropical and subtropical zones. This disease results in severe fruit damage both pre- and postharvest. The development of resistant cultivars is the most effective strategy for disease control, which requires knowing the genetic basis of resistance. In this study, we analysed the inheritance of resistance of Capsicum annuum to Colletotrichum scovillei at two fruit development stages. The ripe and unripe fruits were inoculated by conidia suspension, and anthracnose severity was evaluated for 8 days using a score scale. It was found that the inheritance of resistance has independent expression in ripe and unripe fruits. In both cases, two main genes are responsible for resistance with polygenic effects. Genetic control, with a quantitative aspect, is more affected by dominance than the additive effects, in both fruit development stages of C. annuum.     

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.     

The Relationship between Sucrose Supply, Sucrose-cleaving Enzymes and Flower Abortion in Pepper

Abortion of pepper flowers depends on the light intensity perceivedby the plant and on the amounts of sucrose taken up by the flower(Aloni B, Karni L, Zaidman Z, Schaffer AA. 1996.Annals of Botany78: 163–168). We hypothesize that changes in the activityof sucrose-cleaving enzymes within the flower ovary might beresponsible for the changes in flower abortion under differentlight conditions. In the present study we report that the activityof sucrose synthase, but not of cytosolic acid invertase, increasesin flowers of pepper plants which were exposed, for 2 d, toincreasing photosynthetically active radiation (PAR) in therange of 85–400 µmol m^-2s^-1at midday. Sucrose synthaseactivity increased in parallel with the increasing concentrationsof starch in the flower ovary. Feeding flower explants, preparedfrom 3-d-predarkened plants, with 100 mM sucrose for 24 h, causeda 23% increase in reducing sugars and a 2.5-fold increase instarch concentration, compared with explants fed with buffer.Likewise, feeding explants of pepper flowers with sucrose, glucose,fructose and also mannitol increased the sucrose synthase activityin the ovaries. Concomitantly, sucrose, glucose and fructose,but not mannitol, reduced the abortion of flower explants. Itis suggested that sucrose entry into the flower increases theflower sink activity by inhibiting abscission and inducing metabolicchanges, thus enhancing flower set. Pepper; Capsicum annuum L.; abscission; light; pepper flowers; sucrose; glucose; fructose; starch; acid invertase; sucrose synthase     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18°C). With a temperatureregime of 35°C day, 25°C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35°C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acidinvertase, heat stress, reproductive organs, sink leaves. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves.     

Application of N-(9-Acridinyl)maleimide as a Fluorescent Detection Reagent of Cysteine and Related Thiols and Disulfide Compounds on Thin-layer Chromatogram

Fluctuations of pungent principles of hot pepper fruits (capsaicinoid), chlorophylls, carotenoid, and fresh fruit weight in Capsicum annuum var. annuum cv. Karayatsubusa at different growth stages after flowering were examined. Capsaicinoid was first detected 20 days after flowering, and reached maximal level around 40 days after flowering, then later decreased gradually. The capsaicinoid composition did not show any appreciable change throughout the stages after flowering. CAP and DC were the major components in all of the stages examined. By using radioisotopic technique, it was found that the main formation and accumulation sites of capsaicinoid are in the placenta of the fruits.     

Comparative efficiency of Nannotrigona perilampoides, Bombus impatiens (Hymenoptera: Apoidea), and mechanical vibration on fruit production of enclosed habanero pepper

The native bee Nannotrigona perilampoides Cresson (Apidae: Meliponini) has been evaluated with promising results in greenhouse pollination of Solanaceae in Mexico. However, no comparison has been done with imported bumble bees (Apidae: Bombini), which are the most common bees used for greenhouse pollination. We compared the foraging activity and fruit production of habanero pepper. Capsicum chinense Jacquin, by using N. perilampoides and Bombus impatiens Cresson in pollination cages. Both bee species collected pollen on a similar number of flowers per unit time, but N. perilampoides visited significantly more flowers per trip, lasted longer on each flower, and spent more time per foraging trip. Ambient temperature and light intensity significantly affected the foraging activity of N. perilampoides. Light intensity was the only environmental variable that affected B. impatiens. Except for the fruit set, there were not significant differences in the quality of fruit produced by both bee species; however, N. perilampoides and B. impatiens performed better than mechanical vibration for all the variables measured. The abortion of fruit caused the low fruit set produced by B. impatiens, and we speculate it might be due to an excessive visitation rate. Pollination efficiency per visit (Spear's pollination efficiency index) was similar for both bee species in spite of the significantly lower amount of pollen removed by N. perilampoides. We suggested that the highest number of flowers visited per foraging trip coupled with adequate amounts of pollen transported, and transferred between flowers, could explain the performance of N. perilampoides as a good pollinator of habanero pepper. Our experiments confirm that N. perilampoides could be used as an alternative pollinator to Bombus in hot pepper under tropical climates.     

Dry Matter Assimilation and Partitioning in Pepper Cultivars Differing in Susceptibility to Stress-induced Bud and Flower Abscission

Stress-induced abscission of buds and flowers is a constraintto the production of peppers (Capsicum annuum L.). Susceptibilityof pepper cultivars to stress-induced abscission may be relatedto assimilate levels and partitioning. Growth analysis experimentswere conducted in the field to determine whether cultivars differingin susceptibility to stress-induced abscission showed correspondingdifferences in growth rates and dry matter partitioning whensubjected to low light stress. With the stress susceptible cultivar'Shamrock', reduction in net assimilation rate (NAR) and relativegrowth rate (RGR) was greater under low light stress than withthe more tolerant cultivar 'Ace'. Compared to 'Ace', 'Shamrock'partitioned a smaller proportion of dry matter into reproductiveorgans and a larger proportion into expanded leaves. Cultivarsdid not differ in the amount of dry matter partitioned to youngleaves or in the extent to which accumulation of dry matterby young leaves was reduced by low light stress. Other experimentsconducted in growth chambers and greenhouse examined the effectof removal of leaves less than 3 cm long on high temperatureand low light stress-induced bud and flower abscission. Forboth 'Ace' and 'Shamrock', abscission was not altered by removalof these leaves. Preferential partitioning of assimilate toyoung leaves does not appear to be involved in stress-inducedabscission in these pepper cultivars.Copyright 1994, 1999 AcademicPress Pepper (Capsicum annuum L.), abscission, low light stress, high temperature stress, assimilate partitioning, assimilation/growth rate, growth analysis, defoliation     

Pollination and Resource Constraints on Fruit Set and Fruit Size ofPersoonia rigida(Proteaceae)

Flower and immature fruit abscission can be caused by proximatefactors preventing the development of all flowers into maturefruits. Two potential limiting factors, pollen supply and carbohydrateavailability, were assessed as relative constraints on accumulationof fruit dry matter inPersoonia rigida(Proteaceae). Naturalpollen transfer was highly efficient, and no evidence of self-incompatibilitywas found. Levels of fruit set (67.4% following open-pollinationand 50.4–58.8% following hand-pollinations) may be thehighest recorded for a species of Proteaceae with hermaphroditicflowers. Fruit abscission occurred principally in a single phasefrom 4–10 weeks post-anthesis, with a peak during theeighth week post-anthesis, and this early abscission was theresult of fertilization failure in some flowers. Manipulationof carbohydrate availability by girdling and/or defoliationof branches provided evidence that carbohydrate supply affectedfruit set only when supply was very low. Fruit abscission dueto very low carbohydrate availability on defoliated brancheswas evident during the early abscission phase but was more pronouncedduring the second half of the fruit development period (>17weeks post-anthesis), coinciding with the period of greatestdry matter demand by the fruits. Minimal fruit abscission occurredduring this later period on leaf-bearing branches. Increasesin carbohydrate supply had no effect on fruit set, but fruitsize was highly sensitive to carbohydrate availability. Subtendingand adjacent leaves were identified as major contributors tothe carbohydrate supply of fruits, although some carbohydratecould be obtained from beyond the fruiting branch. Despite thehigh levels of natural fruit set, both pollen supply and resourceavailability were indicated as potential constraints on accumulationof fruit dry matter inP. rigida.Copyright 1999 Annals of BotanyCompany. Persoonia rigidaR.Br., Proteaceae, pollination, carbohydrates, fruit set, fruit size, abscission, girdling.