Flower Abscission Research Articles

Handroanthus impetiginosus (BIGNONIACEAE) AS AN IMPORTANT FLORAL RESOURCE FOR SYNANTHROPIC BIRDS IN THE BRAZILIAN SEMIARID

Handroanthus impetiginosus (Bignoniaceae) is commonly used in urban afforestation in the Brazilian semiarid, and it attracts native urban fauna during the dry season, when the plants are flowering. We conducted focal observations on nine flowering H. impetiginosus in an urban area at Brazilian semiarid to record the bird species that used flowers as a food resource and their behavior. We recorded four species of visiting birds at the H. impetiginosus flowers: Eupetomena macroura , Chlorostilbon lucidus , Icterus pyrrhopterus and Tangara sayaca . Of these, E. macroura and C. lucidus were observed on illegitimate visits, not contributing to the pollination, and E. macroura was the most aggressive species. Icterus pyrrhopterus and T. sayaca feeding on parts of the flowers or flower buds, generally promoting the flower abscission to access the nectar. The presence of H. impetiginosus can support generalist nectarivorous bird species, as E. macroura , C. lucidus and I. pyrrhopterus , and bees, as Xylocopa spp. in urban areas, which may contribute to the pollination of other native plant species in reforestation projects in this semiarid region.

Spatio-temporal IAA gradient is determined by interactions with ET and governs flower abscission

The abscission zone (AZ) is a specialized tissue that usually develops at the base of an organ and is highly sensitive to phytohormones, e.g., abscisic acid (ABA), ethylene (ET), and gibberellins (GAs). A current model of organ abscission assumes that the formation of an auxin gradient around the AZ area determines the time of shedding; however, that thesis is supported by studies that are primarily concerned with auxin transporters. To better understand the events underlying the progression of abscission, we focused for the first time on indole-3-acetic acid (IAA) distribution following AZ activation. We performed a series of immunolocalization studies in proximal and distal regions of floral AZ cells in yellow lupine, which is an agriculturally important legume. The examined phytohormone was abundant in natural active AZ cells, as well as above and below parts of this structure. A similar gradient of IAA was observed during the early steps of abscission, which was induced artificially by flower removal. Surprisingly, IAA was not detected in inactive AZ cells. This paper is also a consequence of our comprehensive studies concerning the phytohormonal regulation of flower abscission in yellow lupine. We present new data on interactions between IAA and ET, previously pointed out as a strong modulator of flower separation. The detailed analysis shows that disruption of the natural auxin gradient around the AZ area through the application of synthetic IAA had a positive effect on ET biosynthesis genes. We proved that these changes are accompanied by an accumulation of the ET precursor. On the other hand, exposure to ET significantly affected IAA localization in the whole AZ area in a time-dependent manner. Our results provide insight into the existence of a spatio-temporal sequential pattern of the IAA gradient related to the abscission process; this pattern is maintained by interactions with ET. We present new valuable evidence for the existence of conservative mechanisms that regulate generative organ separation and can help to improve the yield of agronomically significant species in the future.

Heat tolerance in garden roses

Roses generally experience a decrease in flower productivity and size in response to summer temperatures greater than 30°C that is common throughout the southern states of the USA. In College Station, Texas, the August mean and mean maximum summer temperatures can be 32 and 40°C, respectively. Under these extreme heat stress conditions, a large rose germplasm collection was evaluated for flowering intensity that takes into account both flower number and flower size. Of the 234 accessions evaluated, most showed moderate flowering during August and about 6% consistently had over 50% flower intensity in August. Experiments done in the growth chamber with potted roses containing young flower buds indicated that a 3-h heat shock (44°C) treatment resulted in decreased flower size and increased flower abscission. Consequently, this approach was used to assess the heat tolerance of 18 rose cultivars in this collection. The results indicated that field ratings of heat tolerance based on flower productivity were negatively correlated to flower abscission and leaf necrosis (r=-0.55* and r=-0.64**) and not correlated with leaf MTS (cell membrane thermostability) of the potted rose plants subjected to the heat shock treatment.

Efficacy of Double Nickel LC (Bacillus amyloliquefaciens D747 Strain) for Management of White Mold in Snap and Dry Bean

White mold caused by Sclerotinia sclerotiorum is a serious disease affecting snap and dry bean production. Management is reliant upon fungicides to protect flowers from infection by ascospores. The inability to use conventional fungicides in organic production represents a substantial hurdle, although products approved by the National Organic Program (NOP) offer a substitute for disease management. In many cases, copper-based products are central to disease management programs in organic production, but the potential for crop loss from premature flower abscission in snap and dry bean owing to phytotoxicity when applied at high temperatures and for other undesirable environmental outcomes has driven interest in biopesticides registered by the NOP as alternatives. Five small-plot, replicated field trials (three in snap bean and two in light red kidney bean) were conducted across three years (2016 to 2018) to evaluate the efficacy of the biopesticide Double Nickel LC (Bacillus amyloliquefaciens D747 strain) for the management of white mold. Trials were inoculated with S. sclerotiorum ascospores to ensure uniform disease potential. The incidence of white mold in plots receiving two applications of Double Nickel LC (2.34 liters/ha) was not significantly different from the conventional fungicide standards. No significant difference in white mold incidence was found between 2.34 and 4.68 liters/ha of Double Nickel LC in either crop. Responses in pod yield components from improved white mold management in either crop were variable. The potential of Double Nickel LC for use in organic production of snap and light red kidney bean for management of white mold is discussed.

Removal of flowers or inflorescences affects ‘Barnea’ olive fruitlet post-anthesis abscission

ABSTRACT A typical olive (Olea europaea L.) inflorescence consists of about 20 flowers. However, in many cultivars, only one fruit develops. This is due to massive abscission of flowers and fruitlets, which occurs during the first month after anthesis. In this study, we used the olive cultivar 'Barnea' to characterize the abscission mechanism and to try to increase fruit set by increasing the number of developed fruit per inflorescence. Removing the lateral flowers 3 weeks before anthesis increased fruit set by more than 50%. Removing all inflorescences but one from a branch increased the number of developed fruits from 0.93 to 2.8 during 2017 and from 0.91 to 3.34 fruits per inflorescence in 2018. Sugar quantification in the pistil revealed that starch level is high on the day of anthesis and low 25 days later in abscised as well as in developed fruit. Soluble carbohydrates are low on the day of anthesis, low in abscised flowers/fruitlets 25 days after anthesis and high in developed fruit. Screening the natural variation found in the Israeli germplasm collection revealed that in most cultivars less than one fruit per inflorescence has developed. However, there are unique cultivars with a higher fruit set.

Flower-Inhabiting Sap Beetles (Coleoptera: Nitidulidae: Carpophilinae) in Guatemala

We report three species of Nitops Murray (Nitidulidae: Carpophilinae) sampled from fallen and freshly withered flowers of the columnar cactus Stenocereus pruinosus (Otto) Buxb. (Cactaceae) in a subtropical dry forest in Guatemala. Our observations suggest that adults of these species oviposit inside the flowers during or prior to the blooming period, and the larvae feed on floral tissues. Larval feeding likely occurs without damaging floral ovaries due to flower abscission.

Natural fruitlet abscission as related to apple tree carbon balance estimated with the MaluSim model

Apple trees produce many more flower clusters than needed for a full crop, but natural early season flower and fruitlet abscission drastically reduce the final fruit number. Natural fruit abscission varies significantly year to year. There have been attempts to try to model apple fruit abscission in the past. However, due to the great complexity of a perennial crop system in a dynamic environment with significant plant manipulations, regulatory processes and controlling environmental variables have been difficult to elucidate. In 1995, a field trial was planted at the New York State Agricultural Experiment Station in Geneva, New York with 3 apple cultivars (‘Delicious’, ‘Gala’, and ‘McIntosh’). Beginning in 2000 and for 18 years thereafter, we recorded the natural whole-season fruit abscission of untreated trees that received no chemical or hand thinning. We also estimated early season patterns of carbohydrate supply-to-demand each year with a carbon balance model. These data were used to correlate tree carbon balance status and other environmental variables with natural fruit abscission responses. In general terms, natural set, defined as final fruit/flower cluster, of ‘Gala’ averaged ˜1 fruit for each flower cluster (fruit set = 0.9), whereas fewer fruits were set on ‘Delicious’ and ‘McIntosh’ (fruit set = 0.7 and 0.6, respectively). Fruit set of ‘Gala’ was less variable than of ‘Delicious’ or ‘McIntosh’, and there was a clear pattern for decreasing fruit set when the number of initial flower clusters per tree increased. Fruit weight was less dependent on fruit number for ‘Delicious’ and ‘McIntosh’ than for ‘Gala’. Multiple regression models indicated that number of flower clusters per tree and average carbohydrate balance between 0–60 degree days (DD) after bloom and 300–360 DD after bloom were the main significant variables that explained 60–80% of the variability in natural fruit set or final fruit number. For ‘Delicious’, temperatures of the previous fall also explained a significant amount of variation in final fruit set and final fruit number. For ‘Gala’, carbon balance from bloom to shortly after petal fall and when fruits were about 18 mm were the two main periods, which were more sensible to carbohydrate deficiency triggering fruit abscission. A later susceptible period was also observed for ‘McIntosh’, suggesting a larger thinning window for this cultivar.

Sensitivity of potted ornamental peppers to ethylene

Many environmental factors affect the post-production shelf life of potted ornamental plants. Exposure to ethylene can reduce the quality of many species, inducing flower, fruit and leaf abscission and senescence. The present study identified ethylene-resistant pepper genotypes during post-production shelf life testing. Potted plants of eleven pepper cultivars were transferred o a 90-L sealed container when they had 30% of ripe fruits and treated with 10 μL L-1 of ethylene for 48 hours. Number of leaves and fruits were counted at the beginning of ethylene exposure and after 48, 96 and 144 hours. The experimental design was completely randomized, with five replicates of individual pots. The cultivars showed varied rates of foliar and fruit abscission. ‘Peloteira’ showed higher resistance to ethylene, with foliar abscission of 19%, after 144 hours. For fruit abscission, the cultivars ‘Peloteira’, ‘Jalapeño’, ‘Stromboli ornamental’, ‘Malagueta’ and ‘Rocoto Vermelha’ presented a lower percentage of leaf drop, varying between 9 and 34%, after 144 hours of exposure to ethylene. This study showed that ornamental peppers have high genetic diversity regarding ethylene sensitivity.

Hormonal interactions during early physiological partenocarpic fruitlet abscission in persimmon (Diospyros Kaki Thunb.) ‘Triumph’ and ‘Shinshu’ cultivars

Fruitlet abscission is typical to many fruit trees, including persimmon, (Diopyros kaki Thunb.), and often results in unstable fruit production and yield. We documented massive parthenocarpic fruitlet abscission in the persimmon cultivars 'Triumph' and 'Shinshu', which initiated soon after anthesis and peaked at 45 days post anthesis. In contrast, abscission of mature fruitlets 45–65 days after anthesis was minor. The early parthenocarpic fruitlet abscission in 'Shinshu' and 'Triumph' took place in the abscission zone located at the calyx-pedicel junction. Differentiation of the abscission layer occurred during flower development and preceded fruitlet abscission. Endogenous analysis of gibberellins, cytokinins and auxin levels in the abscission zone of 'Triumph' and 'Shinshu' during the developmental stages preceding abscission revealed a reduction in cytokinin endogenous levels in both cultivars. In addition, a decline in GA3 and IAA levels was found in 'Triumph' and 'Shinsu' respectively during flower development. Gibberellin, auxin and cytokinin application to inhibit early fruitlet abscission were analyzed and gibberellin treatment exhibited the highest and most consistent inhibition effect in 'Triumph' and 'Shinshu'. An increase in endogenous levels of gibberellins, cytokinins and auxin in the flower abscission zone was found following GA application in both cultivars. Our results suggest that gibberellin application inhibits early fruitlet abscission by elevating cytokinins, and auxin levels and that a reduction in gibberellins, cytokinins and auxin levels may induce abscission during parthenocarpic fruitlet development in 'Shinshu' and 'Triumph' cultivars.

Ectopic Expression of Two FOREVER YOUNG FLOWER Orthologues from Cattleya Orchid Suppresses Ethylene Signaling and DELLA Results in Delayed Flower Senescence/Abscission and Reduced Flower Organ Elongation in Arabidopsis

Two orthologues of Arabidopsis FOREVER YOUNG FLOWER (FYF), CaFYF1 and CaFYF2, were identified from Cattleya intermedia. To investigate the function of these two genes, we performed ectopic expression of CaFYF1/2 in Arabidopsis. Delayed flower senescence and abscission were observed in 35S::CaFYF1/2 transgenic Arabidopsis plants. Furthermore, once CaFYF1/2 was fused with the strong repressor domain SRDX, severe delayed flower senescence and abscission were observed in 35S::CaFYF1/2+SRDX transgenic Arabidopsis plants. In contrast, when 35S::CaFYF1/2 was converted to a potent activator by fusion with the VP16-AD motif, flower senescence and abscission were promoted in these 35S::CaFYF1/2+VP16 transgenic dominant-negative mutant Arabidopsis plants. These results indicated that similar to Arabidopsis FYF, CaFYF1/2 also act as repressors in controlling floral organ senescence and abscission in transgenic Arabidopsis plants. The delayed senescence and abscission of the flower organs in 35S::CaFYF1/2 and 35S::CaFYF1/2+SRDX transgenic Arabidopsis plants were unaffected by ethylene treatment. Genes of the ethylene signaling and abscission-associated pathways, such as EDF1/2/3/4, BOP1/2, and IDA, were repressed in 35S::CaFYF1/2 and 35S::CaFYF1/2+SRDX transgenic Arabidopsis plants. Furthermore, 35S::CaFYF1/2 and 35S::CaFYF1/2+SRDX transgenic Arabidopsis plants showed additional morphological defects, such as short sepals and petals, which were correlated with the upregulation of the DELLA genes RGA, GAI, RGL1, and RGL2. These results suggested a possible role for Cattleya orchid CaFYF1/2 in controlling floral senescence/abscission by suppressing ethylene signaling and abscission-associated genes as well as controlling flower organ elongation through negative regulation of GA response by activating the expression of the DELLA genes during flower development.

Uniconazole and diethyl aminoethyl hexanoate increase soybean pod setting and yield by regulating sucrose and starch content.

Uniconazole (S3307) and diethyl aminoethyl hexanoate (DA-6) are known plant growth regulators (PGRs). However, it is unknown if their regulation of sucrose and starch content can affect pod setting and yield in soybean. Herein, S3307 and DA-6 were foliar sprayed on soybean Hefeng50 and Kangxian6 at the beginning of the bloom cycle in field tests conducted over two years. PGRs promoted the accumulation and distribution of plant biomass and significantly improved leaf photosynthetic rates. Sucrose and starch content increased after PGR treatment across organs and varieties. Accumulation and allocation of sucrose and starch content in soybean source organs are enhanced by PGRs, which supply high levels of assimilate to sink organs. Moreover, sucrose and starch contents in source and sink organs are positively correlated. S3307 and DA-6 also significantly increased pod setting rates and reduced flower and pod abscission rates, leading to increased yield. S3307 and DA-6 promoted the accumulation and availability of sucrose and starch content in source organs and increased sucrose and starch content in flowers and pods or seeds, thereby maintaining the balance between source and sink organs and contributing to increased pod setting rates and soybean yield. © 2018 Society of Chemical Industry.

Gibberellic acid affects the functioning of the flower abscission zone in Lupinus luteus via cooperation with the ethylene precursor independently of abscisic acid

The abscission of plant organs is a phytohormone-controlled process. Our study provides new insight into the involvement of gibberellic acid (GA3) in the functioning of the flower abscission zone (AZ) in yellow lupine (Lupinus luteus L.). Physiological studies demonstrated that GA3 stimulated flower abortion. Additionally, this phytohormone was abundantly presented in the AZ cells of naturally abscised flowers, especially in vascular bundles. Interesting interactions among GA3 and other modulators of flower separation were also investigated. GA3 accumulated after treatment with the ethylene (ET) precursor 1-aminocyclopropane-1-carboxylic acid (ACC). Abscisic acid (ABA) treatment did not cause such an effect. Furthermore, the expression of the newly identified LlGA20ox1 and LlGA2ox1 genes encoding 2-oxoglutarate-dependent dioxygenases fluctuated after ACC or ABA treatment which confirmed the existence of regulatory crosstalk. GA3 appears to cooperate with the ET precursor in the regulation of AZ function in L. luteus flowers; however, the presented mechanism is ABA-independent.

Effects of mulching on soil temperature and moisture variations, leaf nutrient status, growth and yield of pistachio trees (Pistacia vera.L)

Abstract The objective of this study was to investigate the response of leaf nutrients concentration, growth and yield of pistachio trees affected by changes in soil moisture and temperature as a result of different mulching. The experiment was conducted in a randomized complete block design with five replications in Feyzabad, Khorasan Razavi, Iran, for two years in 2014 (‘off’ year) and 2015 (‘on’ year). Treatments included sub-soil plastic (SPM1 and SPM2), up-soil plastic (UPM), woodchips (WM), barley residue (BM) mulches and control (CK). Treatment of SPM2 recorded the highest shoot growth and nut splitting, and lowest bud abscission in ‘off’ year. However, in ‘on’ year, maximum bud abscission was found in SPM2. Treatments of BM and WM were effective in decreasing flower bud and fruit abscission than other treatments during ‘on’ year. Mulching affected leaf P concentration in ‘off’ year and N, P and Mg in ‘on’ year, with the highest rate of these nutrients recording in BM treatment. Yield variations were not significantly affected by treatments in ‘off’ year, but in ‘on’ year, SPM2, WM, BM and SPM1 treatments increased yield by 29.2%, 28.7%, 19.8% and 10.5% compared to CK, respectively. Unlike other treatments, UPM had negative effect on leaf N concentration, and yield during ‘on’ year. This difference is attributed to high soil temperature in this treatment, so that yield reduced in soil temperature ranges over 36–37 °C in mean depth of 20–60 cm. In general, sub-soil plastic mulches, despite increasing yield in ‘on’ year, could not control flower bud abscission in that year. Thus, due to the increase of leaf nutrient concentration, regulation of alternate bearing phenomenon and improvement of yield, organic mulches are better options in arid and semi-arid regions with traditional irrigation methods.

Benzyl adenine is more effective than potassium silicate on decreasing the detrimental effects of heat stress in pepper (Capsicum annum cv. PS301)

ABSTRACT- Heat stress causes flower and fruit abscission in pepper. This study was conducted in the greenhouses of Isfahan University of Technology to evaluate the effect of foliar application of Benzyl adenine (BA) and potassium silicate (K2SiO3) under heat stress condition on bell pepper. Two factorial experiments based on completely randomized design with four concentrations of BA (0, 0.06, 0.6 and 6 ppm) and the second with two levels of K2SiO3 (0 and 5 Mm) both in two temperature treatments (25±2 (optimum) 35±2 (high temperature)) with six replicates were conducted. The results of the study indicated that the use of BA (especially 6 ppm) promoted growth parameters and increased proline, phenol and antioxidant content. Also, application of BA 6 ppm improved cell membrane stability assessed via decreasing electrolyte leakage (EL) and also reduced flower abscission in bell pepper. BA at 6 ppm increased plant height, shoot and root dry weight, proline and total phenol, root fresh weight, potassium (K) concentration and decreased flower abscission. Antioxidant content increased with heat stress in all BA levels. Results of the study indicated that fresh and dry weight of root and K concentration increased with 5 mM K2SiO3. Moreover, root fresh weight and K concentration and antioxidant content increased in 5 mM K2SiO3 under heat stress.

The Tomato Hybrid Proline-rich Protein regulates the abscission zone competence to respond to ethylene signals

The Tomato Hybrid Proline-rich Protein (THyPRP) gene was specifically expressed in the tomato (Solanum lycopersicum) flower abscission zone (FAZ), and its stable antisense silencing under the control of an abscission zone (AZ)-specific promoter, Tomato Abscission Polygalacturonase4, significantly inhibited tomato pedicel abscission following flower removal. For understanding the THyPRP role in regulating pedicel abscission, a transcriptomic analysis of the FAZ of THyPRP-silenced plants was performed, using a newly developed AZ-specific tomato microarray chip. Decreased expression of THyPRP in the silenced plants was already observed before abscission induction, resulting in FAZ-specific altered gene expression of transcription factors, epigenetic modifiers, post-translational regulators, and transporters. Our data demonstrate that the effect of THyPRP silencing on pedicel abscission was not mediated by its effect on auxin balance, but by decreased ethylene biosynthesis and response. Additionally, THyPRP silencing revealed new players, which were demonstrated for the first time to be involved in regulating pedicel abscission processes. These include: gibberellin perception, Ca2+-Calmodulin signaling, Serpins and Small Ubiquitin-related Modifier proteins involved in post-translational modifications, Synthaxin and SNARE-like proteins, which participate in exocytosis, a process necessary for cell separation. These changes, occurring in the silenced plants early after flower removal, inhibited and/or delayed the acquisition of the competence of the FAZ cells to respond to ethylene signaling. Our results suggest that THyPRP acts as a master regulator of flower abscission in tomato, predominantly by playing a role in the regulation of the FAZ cell competence to respond to ethylene signals.

INFLORESCENCE DEFICIENT IN ABSCISSION-like is an abscission-associated and phytohormone-regulated gene in flower separation of Lupinus luteus

Abscission is a natural process that occurs to facilitate shedding of no longer needed organs, but on the other hand, can be triggered by certain environmental conditions, e.g. biotic or abiotic stresses. Regardless of the stimuli, organ shedding takes place specifically at the abscission zone (AZ). A signaling pathway that controls this process in Arabidopsis thaliana from ligand to receptors has been proposed. However, knowledge concerning the influence of plant hormones on these molecular elements still remains enigmatic. Excessive and premature flower abscission in the crop species Lupinus luteus L. is a process of substantial interest to the agricultural industry, as it can affect yield. Our strategy combined molecular studies, comprehensive ultrastructural and histological analysis, as well as exogenous hormone treatment to describe the contribution of the Lupinus IDA-like gene in flower abscission. In the AZ of the naturally abscised flowers, the differentiation of morphologically distinct cells characterized by progressive degradation processes was accompanied by LlIDL mRNA accumulation. A similar effect was observed following early steps of AZ activation and after abscisic acid or ethylene treatments. These phytohormones, previously pointed out as key stimulators of flower separation, altered the temporal expression pattern of LlIDL. Exogenous EPIP peptide synthesized on the basis of LlIDL sequence, significantly increased flower abortion rate, which indicates that this motif governs protein activity. In conclusion, our data provide new evidence for LlIDA involvement in both the early and late events of flower abscission supported by detailed spatiotemporal characterization of AZ cell structure and ultrastructure.

Screening for Chilling‐Tolerant Soybeans at the Flowering Stage Using a Seed Yield‐ and Maturity‐Based Evaluation Method

ABSTRACTCold weather damages soybean [Glycine max (L.) Merr.] crops in high‐latitude countries. The decreased seed yields caused by low temperatures are attributed to three main factors: poor growth during the early growth stage, abscission of flowers and pods at the flowering stage, and insufficient grain filling at the pod‐filling stage. The abscission of flowers and pods is the most important factor that contributes to reduced yields. There are differences in chilling tolerance among cultivars developed in Japan at the flowering stage. This study screened for chilling‐tolerant (CT) soybeans developed in high‐latitude countries, such as Canada, Switzerland, Poland, and the Czech Republic. For the screening, plants were subjected to a 28‐d chilling‐temperature treatment after flowering in a phytotron, and six CT cultivars, ‘Maple Arrow’, ‘AC Proteus’, ‘Ceresia, Pelvoux’, ‘Silvia’, and ‘Mazowia’, were found by focusing on seed yield and maturity. These six CT cultivars matured earlier and had greater yields than Japanese cultivars in the field under severe chilling conditions. Moreover, we developed five breeding lines derived from a cross of the CT cultivars Mazowia and ‘Toyoharuka’ (TH). All five breeding lines matured earlier than TH and had yields similar to that of TH in the field under normal conditions. Phytotron tests revealed that the chilling tolerance levels of two of the breeding lines were slightly greater than that of TH. The six CT cultivars found in this study will be useful for chilling tolerance breeding.

Substrate Water Content Influences the Flowering of Doritaenopsis Queen Beer ‘Mantefon’

Automated irrigation systems based on soil moisture sensor measurements can reduce water and fertilizer use while adequately meeting plant water requirements. In this study, the effects of substrate volumetric water content (θ, v/v) on the flowering of 17-month-old Doritaenopsis Queen Beer ‘Mantefon’ (from the time of deflasking) were examined. The plants were transplanted in plastic pots (10.5 cm width × 9.5 cm height) filled with sphagnum moss and the θ of sphagnum moss was maintained at 0.2, 0.3, 0.4, or 0.5 m3·m−3 using an automated drip irrigation system. Plants grown at a θ threshold of 0.2 m3·m−3 had thinner leaves and lower SPAD value than those grown at higher θ thresholds. The net CO2 uptake of the uppermost fully expanded leaf increased with increasing θ between 0.2 and 0.4 m3·m−3, but there was no significant difference in the net CO2 uptake between plants grown at 0.4 and 0.5 m3·m−3 thresholds. The number of flower buds at the time of the first open flower was lower in plants grown at θ thresholds of 0.2 and 0.3 m3·m−3 as compared with that in the plants grown at 0.4 and 0.5 m3·m−3 thresholds. Early flower abscission, flower bud dropping, and flower senescence during the 2 weeks after flowering occurred in 55% and 30% of the plants at 0.2 and 0.3 m3·m−3 thresholds, respectively, whereas plants at θ thresholds of 0.4 and 0.5 m3·m−3 had negligible flower abscission. Although vegetative growth parameters were similar among θ thresholds of 0.3 m3·m−3 or higher, plants grown at a θ threshold of 0.3 m3·m−3 produced fewer flowers than those grown at 0.4 and 0.5 m3·m−3 thresholds. During the 83-day experimental period, the system irrigated the plants ≈0.79, 1.93, 2.46, and 2.84 L/pot at θ thresholds of 0.2, 0.3, 0.4, and 0.5 m3·m−3, respectively. Overall, 0.4 m3·m−3 was considered to be an optimal threshold θ level for producing high-quality Doritaenopsis Queen Beer ‘Mantefon’ during the flowering period with most efficient water use.

EARLY SPRING APPLICATION OF AMINOETHOXYVINILGLYCINE (AVG) INCREASES FRUIT SET AND YIELD OF ‘ROCHA’ PEARS

ABSTRACT The low fruit set is one of the main factors leading to poor yield of pear orchards in Brazil. Ethylene is associated with abscission of flowers and fruitlets. Then, the application of ethylene synthesis inhibitors, such as AVG, is a potential tool to increase fruit set of pears. The objective of this study was to evaluate the effect of AVG, sprayed at different rates and timings, on fruit set, yield and fruit quality of ‘Rocha’ pear. The study was performed in a commercial orchard located in the municipality of São Joaquim, SC, during the growing seasons of 2014/2015 and 2015/2016. Plant material consisted of ‘Rocha’ pear trees grafted on quince rootstock ‘BA29’. AVG was tested at different rates (60 mg L-1 and 80 mg L-1) and timings [full bloom, one week after full bloom (WAFB), and two WAFB), either alone or in combination. The experiment was arranged in a randomized block design, with at least five single-tree replications. The fruit set, number of fruit per tree, yield, estimated yield, fruit weight, return bloom, and fruit quality attributes were assessed. Fruit set and yield were consistently increased by single applications of AVG at 60 and 80 mg L-1 at both one and two weeks after full bloom, without negatively affecting fruit quality attributes and return bloom.

SlPIN1 regulates auxin efflux to affect flower abscission process

Solanum lycopersicum PIN-FORMED1 (SlPIN1), a major auxin efflux facilitator, contributes to the establishment of auxin maxima during organ initiation and development in tomato. However, the functions of SlPIN1 during organ abscission remain unclear. In our study, SlPIN1 expression decreased immediately after flower removal and increased following IAA treatment, indicating a high sensitivity to auxin depletion. 1-MCP (an ethylene inhibitor) delayed abscission and down-regulated SlPIN1, indicating that ethylene may positively regulate SlPIN1 and that low expression levels of SlPIN1 may delay abscission. The SlPIN1 protein levels were not consistent with the expression pattern, implying that in addition to transcription, protein degradation also affects SlPIN1 levels during abscission. The phosphorylation of SlPIN1 at Ser418, which significantly declined during abscission, was found to play roles in SlPIN1 localization and auxin transport. We also identified the interaction proteins of SlPIN1, which were involved in phosphorylation and ubiquitylation. Therefore, complex mechanisms mediate SlPIN1 auxin transport capability during abscission. The silencing of SlPIN1 expression accelerated abscission by increasing auxin accumulation in the ovary and decreasing the auxin content in the abscission zone (AZ), indicating that SlPIN1 plays a major role in mediating auxin source-sink transport and the establishment and maintenance of auxin maxima in the AZ.