Flower Abortion Research Articles

INTERACTIVE EFFECT OF NUTRIENT CONCENTRATION AND CONTAINER VOLUME ON FLOWERING, FRUITING, AND NUTRIENT UPTAKE OF SWEET PEPPER

Flower abortion and low fruit set has long been a problem in sweet pepper (Capsicum annum L.), especially when the flowers are cross-pollinated. Restrictions of nutrient element supply and root volume affect plant vigor and size. To study the interactive effects of nutrient element supply and container volume on pepper flowering and fruiting, a complete interactive experiment (3 × 3) containing three concentrations of nitrogen (N), phosphorus (P), and potassium (K) at a constant ratio and three volumes of containers were conducted using a hydroponic system in a temperature control-greenhouse during a autumn-winter season. The cultivar of sweet pepper was cv. ‘Hazera’ 1195 and only cross-pollinated flowers were allowed to set fruits. The mean minimum root zone temperature was maintained at 16.3–16.6°C in the middle (18-dm3) and big (33-dm3) containers at night during the fruit developing stage, it dropped at night to 14.1°C in the small (9-dm3) container. The low concentration nutrient solution containing 3-0.5-1.25mM of N-P-K, when combined with the small container induced an early flowering and short duration of flowering, that led to early fruit set and maturation. No difference in flowering, fruit set and total fruit yield of pepper was found between middle (6-1-2.5 mM) and high (9-1.5-3.75 mM) nutrient element level when the small and middle containers were used. Plants in the large container significantly delayed the flowering and fruit set when high concentration of nutrient elements was applied, but the total number of fruit set and total plant yield was higher than in the small container. High nutrient element concentration and larger container size produced high fruit yield only when allowed to grow and set fruits for a long period.

Flowering Responses of Petunia Plants to Photoperiod and Irradiance.

Various flowering responses in Petunia × hybrida Vilm. 'Garden Party White' and 'Snow Cloud White' were studied under different photoperiods and irradiance levels. In particular, leaf number below the first flower bud (LNBFB) on the main stem, time to macroscopic flower bud visibility (MFBV), time to anthesis, time to flower bud development, and the percentage of flower bud abortion were examined. LNBFB increased significantly (P<0.001) only under a combination of short-day (SD) and low irradiance, but each had little effect alone. Time to MFBV and time to anthesis decreased, as photoperiod or irradiance increased. One of the main factors on late anthesis under unfavourable light condition appears to be flower bud abortion. In this study, photoperiod or irradiance had no effect on LNBFB, but they influenced the time to anthesis either singly or together, indicating that long-day (LD) and/or high irradiance is necessary for minimizing a production period of petunia plants.

A New Ilarvirus Isolated from Grapevine in Greece

In 1994, characteristic viruslike symptoms on grapevine were reported in the collection of the Grapevine Institute in Athens, Greece, on the hybrid Baresana × Baresana. The symptoms were sharp angular mosaic, leaf crinkle, and little leaf. The affected vines showed gradual decline and severe stunting or death. Such vines produced abortive flowers or very few berries with smaller, wrinkled, and nongerminating seeds. Serological testing, by enzyme-linked immunosorbent assay (ELISA), of the affected vines against the most common grapevine viruses Alfalfa mosaic, Arabis mosaic, Grapevine fanleaf, Grapevine fleck, Grapevine A, Rasberry ringspot, and grapevine leafroll-associated viruses gave negative results. A virus was isolated from affected grapevine young leaves by mechanical inoculation of Gomphrena globosa and single lesioned. The virus host range included G. globosa (local and systemic dark red or necrotic lesions), Chenopodium quinoa (necrotic local lesions and systemic mottle), and three tobacco cultivars (sharp necrotic local lesions, 1 to 3 mm in diameter). Pollination of C. quinoa with pollen from infected plant gave about 30% infected seedlings. The virus was purified from C. quinoa by differential centrifugation using 0.02 M phosphate buffer pH 8.0, containing 0.01 M DIECA and 0.01 M sodium thioglycolate as extraction buffers. In a purified preparation, quasisphaerical virus particles of about 29 nm were observed. Electrophoretic mobility of the viral coat protein showed a molecular weight of 30 kDa. Using purified preparations, an antiserum was obtained with a titer of 1:1024 in microprecipitin test and an optimum IgG dilution in ELISA of 1:10,000 for maximum absorption at OD405 nm Using degenerate primers designed from homologous regions in RNA-2 corresponding to a fragment of the polymerase gene of Ilarviruses, the expected 381-bp polymerase chain reaction product was obtained. This product was cloned and sequenced. Comparisons with sequence data from the homologous regions of RNA-2 of other known Ilarviruses, showed that the sequence of the above 381-bp amplicon shared 72% sequence similarity with Tobacco streak virus, 67% of Citrus variegation virus and Spinach latent virus, 66% of Asparagus virus 2 and Elm mottle virus, and 65% of Citrus leaf rugose virus. Based on the above data, it is concluded that the isolated virus is an Ilarvirus with closest similarity to Tobacco streak virus. From the relative bibliography (1-3) it appears that the virus reported here is different from Grapevine line pattern virus, a possible Ilarvirus, previously reported from Hungary.

Leaf starch accumulation and seed set at phloem-isolated nodes in soybean

There is usually a linear relationship between pod and seed number per unit area and assimilate supply in soybean ( Glycine max L. Merrill) communities. In contrast, the relationship is curvilinear at single phloem-isolated nodes. To further investigate this curvilinear relationship, we evaluated photosynthesis, leaf starch levels and pod and seed number at phloem-isolated nodes of cultivar Elgin 87 in three greenhouse experiments. The main stem was girdled between the fifth and sixth nodes (unifioliolate node was node one) when the first flowers opened at the sixth node. The main stem above the sixth node was removed and defoliation (five or six levels from 0 to 100%) created a range in assimilate supply. Girdling increased leaf starch levels 3- to 7-fold over non-girdled plants within 7 days. In two experiments starch decreased to control levels within 14–27 days after girdling, but in a third experiment the increase was maintained for 28 days. Defoliation reduced leaf starch levels, with 66–91% defoliation lowering it to the level in the non-girdled controls. Pod and seed number were directly related to assimilate supplies at low levels of assimilate availability when there was no accumulation of starch. There were only relatively small increases in pod and seed number at high levels of assimilate availability, but there were large accumulations of starch in the leaves. Flower and pod abortion was always above 50%, so pod set was not limited by flower availability. The failure of pod and seed number to respond to high levels of assimilate availability suggests that there may be other processes involved in determining pod and seed number at isolated nodes in soybean.

Differentiation of the timing of flower abortion in Tilia japonica

AbstractThe sex expression of Tilia japonica is functional andromonoecy (an andromonoecious system with abortion of perfect flowers). Some of protandrous flowers are aborted after shedding pollen grains and thus are functionally male flowers (FMF). When both male and female organs are retained in a flower, the plants can more flexibly regulate sex allocation, or resource allocation to male and female functions than true andromonoecious plants, which is considered as an adaptive significance of functional andromonoecy. However, the plants have to pay some costs of female organ in FMF. For functional andromonoecious plants, there is a conflict between flexibility and cost in determining the timing of flower abortion, or arrest investing in female functions in a flower. We clarified that (i) differentiation of the timing of flower abortion caused two types of FMF: short‐style (SS) and normal‐style (NS) flowers; (ii) SS can be produced at a lower cost than NS, and (iii) plants having NS can flexibly regulate sex allocation following a sudden change in conditions. Hence, we concluded that differentiation of the timing of flower abortion makes a compromise of the conflict. We also found that NS is more frequent than SS, and we discuss the adaptive significance of keeping potential fertility.

RELATIONSHIP OF FLOWER AND POD NUMBERS PER INFLORESCENCE WITH SEED YIELD IN LENTIL

This study, quantifying variation in flower and pod production in lentil (Lens culinaris), aimed to answer the question: Will selection for more pods per inflorescence increase seed yield? In Season 1 (1992–93) all open flowers were tracked to maturity in a field experiment with two lentil genotypes sown on two dates. Genotype Talia 2 had a higher rate of flower abortion than pod abortion, in contrast to genotype ILL 2581 which showed the reverse. Flower abortion accounted for 15% of flowers opened in early sowing and increased to 22% in the late sowing. Pod abortion was 19% (of flowers opened) in early sowing and 23% in the late sowing. These are the first quantitative estimates of flower and pod abortion in lentil. From the data, a rapid sampling method was developed to estimate the average number of pods per inflorescence at maturity. In Season 2 (1993–94) an experiment was conducted at two locations to estimate the average number of pods per inflorescence of 81 genotypes and to relate this to seed yield. Although the broad-sense heritability (h2) of the number of pods per inflorescence was 0.68 and its phenotypic correlation with seed yield was r = 0.71, the highest-yielding genotypes were not those with the most pods per inflorescence. Selection for the number of pods per inflorescence cannot be recommended for increasing seed yield in lentil.

First Report of Anthracnose Caused by Glomerella cingulata on Passion Fruit in Argentina.

Passion fruit (Passiflora edulis Sims.) is a subtropical fruit recently cultivated in Misiones Province, Argentina. In spring 1997, a severe epidemic of anthracnose was observed. Disease incidence was ≍95%, causing high yield losses. Sunken, gray lesions on the whole surface of young fruits were observed. Under humid conditions, acervuli containing masses of spores and dark setae were found within lesions. On leaves, tendrils, and twigs, circular and irregular brown spots with darker edges were observed. Abortion of flowers also was recorded. Cultures on potato dextrose agar yielded abundant, gray aerial mycelium and one-celled, hyaline, oblong conidia with obtuse or rounded ends (11.2 to 15.0 × 3.8 to 4.6 μm). Perithecia were scarce (90.2 to 220.0 μm). Asci were not conspicuous, and ascospores measured 10.8 to 23.4 × 3.5 to 7.0 μm. Based on morphological characteristics, the fungus was identified as Glomerella cingulata (anamorph Colletotrichum gloeosporioides) (2). Fruits and leaves of P. edulis with and without wounds were sprayed with a conidial suspension (106/ml) and incubated in plastic bags for 48 h. Lesions similar to original symptoms were observed after 2 weeks only on wounded leaves and fruits. G. cingulata was reisolated, confirming Koch's postulates. This disease has been recorded in Brazil and Japan (1). This is the first report of G. cingulata on passion fruit in Argentina. Reference: (1) E. Francisco Neto et al. Summa Phytopathol. 21:25, 1995. (2) J. A. von Arx. Phytopathol. Z. 29:413, 1957.

Epidemiology and control of Botrytis cinerea in tomato crops grown under cover in Greece

Out-of-season tomatoes grown in unheated glasshouses in Greece annually suffer considerable losses from grey mould induced by Botrytis cinerea. Characteristic soft rots of young fruit by the calyx end, flower abortions and stem lesions or cankers are the most commonly occurring symptoms of the disease. Severe ghost spots on fruit only appear when fungicides inhibiting spore germination are not applied. Conidia produced on plant debris of the previous year's crop serve as primary inoculum. Disease starts in late autumn, increases rapidly during the winter period and ceases abruptly at the end of April. Infections caused by isolates resistant to dicarboximides or to both dicarboximides and benzimidazoles are uncommon at the beginning of each new crop cycle. These increase substantially as the season progresses and decline after cessation of fungicide sprays. By contrast, infections caused by benzimidazole-resistant strains are stable throughout the growing season. Efficient disease control implies use of proper glasshouse covering material, adequate indoor air circulation, partial night heating, strict indoor and outdoor hygiene and regular fungicide sprays. When disease pressure is low, application only of conventional compounds like dichlofluanid and chlorothalonil is recommended. Under conditions favourable to Botrytis infections, mixtures of conventional compounds with reduced strength specific botryticides should preferably be applied. Such regimes efficiently minimize losses from fungicide resistance development and ghost spot.

Effect of Punica granatum Linn. (flowers) on blood glucose level in normal and alloxan-induced diabetic rats

‘Gulnar farsi’, male abortive flowers of Punica granatum L., are used for the treatment of diabetes mellitus in Unani medicine. Oral administration of its aqueous-ethanolic (50%, v/v) extract led to significant blood glucose lowering effect in normal, glucose-fed hyperglycaemic and alloxan-induced diabetic rats. This effect of the extract was maximum at 400 mg/kg, b.w.

Spread of Tomato yellow leaf curl virus Sar from the Mediterranean Basin: Presence in the Canary Islands and Morocco.

Severe outbreaks of tomato yellow leaf curl disease occurred during summer and autumn 1999 in tomato (Lycopersicon esculentum Mill.) crops in the Vecindario Region of Gran Canaria (Canary Islands, Spain) and Agadir (southwestern Atlantic coast of Morocco). Symptoms of the disease included upward curling of leaflet margins, reduction of leaflet area, and yellowing of young leaves, as well as stunting and flower abortion. High populations of whiteflies, Bemisia tabaci Gen., were present on tomatoes in Agadir, and analysis of adult individuals by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) identified them as the biotype Q. Samples were collected from symptomatic tomato plants: 5 plants from Gran Canaria and 22 from three areas in Agadir, (7 from Agadir/1, 12 from Agadir/2, and 3 from Agadir/3) in the Koudya Region. Samples were analyzed for Tomato yellow leaf curl virus (TYLCV) Sar or Is (genus Begomovirus, family Geminiviridae) infection by squash blot hybridization under high stringency conditions with digoxigenin-labeled DNA probes specific to TYLCV-Sar or -Is, as described previously (1,3). The TYLCV-Sar probe hybridized to the five samples from Gran Canaria, and the TYLCV-Is probe hybridized to the 22 samples from Agadir. The TYLCV-Sar probe also hybridized to the three samples from Agadir/3. Primer pairs MA-14/MA-15 and MA-30/MA-31, designed for specific amplification of the intergenic region (IR) of TYLCV-Sar or -Is reported from Spain, respectively (1), were used in PCR to amplify one sample each from Gran Canaria, Agadir/1, and Agadir/3. A fragment of the expected size was obtained from the samples from Gran Canaria and Agadir/3 using MA14/MA15 (342 bp) and from the two samples from Agadir using MA30/MA31 (357 bp). PCR products were directly sequenced (GenBank Accession nos. AF215819 to AF215822). The nucleotide sequences of the IR fragments amplified from the Gran Canaria and Agadir/3 sample using MA-14/MA-15 indicated their closest relationship (99.0 and 96.7% identity, respectively) was to the corresponding region of a TYLCV-Sar isolate reported from Spain (GenBank Accession no. L27708). The nucleotide sequences of the IR fragments amplified from the Agadir/1 and Agadir/3 samples using MA-30/MA-31 indicated their closest relationship (98.1% identity) was to the corresponding region of the TYLCV-Is isolate reported from Spain (GenBank Accession no. AF071228). Based on the hybridization and sequence data, we conclude that the symptomatic plants from Gran Canaria were infected by TYLCV-Sar, those from Agadir/1 and Agadir/2 were infected by TYLCV-Is, and those from Agadir/3 had mixed infections with TYLCV-Is and TYLCV-Sar. The presence of TYLCV-Is in Morocco has been described recently (2). However, this is the first report of TYLCV-Sar in the Canary Islands and Morocco and extends its geographic range beyond the Iberian Peninsula and Italy.

POLLEN-MEDIATED SELECTIVE ABORTION IN YUCCAS AND ITS CONSEQUENCES FOR THE PLANT–POLLINATOR MUTUALISM

Mutualistic interactions contain an underlying evolutionary conflict, in that natural selection favors individuals better at exploiting their mutualistic partner, thus potentially destabilizing the mutualism. In the obligate mutualism between yuccas and yucca moths, selective abortion of flowers that receive many moth eggs or receive poor pollen load has been suggested as a mechanism that can prevent evolution of excessive exploitation by moths. Using controlled pollinations, varying pollen amount and source, we asked whether variation in pollination quality of the magnitude seen among moths affects patterns of selective abortion. Pollination experiments in two Yucca filamentosa populations revealed that both pollen quantity (large/small) and quality (self/one-outcross/two-outcross donors) affected fruit retention, seed set, and seedling growth rate. A pollen load larger than that typically provided by moths increased fruit retention. Outcrossed flowers were selectively retained to fruit, and flowers receiving a mixed outcross load were selectively retained over single-outcross flowers in one population. Seed set per fruit was significantly lower with a small pollen load, and lower when a single outcross source was used than in self or mixed outcross treatments. Outcross seeds germinated at a greater frequency and produced plants that grew faster than those that resulted from self-pollination, yielding a cumulative inbreeding depression of 0.73–0.81. Early fruit abortion is a major mortality factor to the yucca moth's progeny, and the female can increase retention by providing high-quality pollinations. Nonetheless, individual pollen loads are usually below levels that provide higher probability of retention, and commonly observed geitonogamous pollinations also appear to conflict with expected strong selection on moths to provide pollinations that give high retention probability. Other factors, such as combined visits by multiple females, floral position effects on retention, and possible costs of moth movement among plants, may interact with the pollination-mediated effects in molding female behavior. These factors do not diminish the potential of selective abortion to promote evolutionary stability of the interaction as they do not provide the moth with a mechanism to circumvent selective abortion.

INFLUENCE OF PAR FLUX AND TEMPERATURE ON THE FLOWER BUD ABORTION OF ROSE (ROSA HYBRIDA CV. FRISCO) AND THE CARBON BALANCE OF THE SHOOT

The occurrence of flower bud abortion for rose, especially during winter, is attributed to a disequilibrium between the carbohydrate production in the sources and the demand for the assimilates in the sinks, caused by a low light intensity or a limitation of the translocation pattern. Manipulating the source and the sink strength by the light intensity and the translocation by temperature may lead to a reduction of flower abortion and an improved flower stem quality. An experiment was set up for roses (cv. Frisco) in 3 growth chambers of the Laboratory of Plant Ecology, including a control treatment (day/night temperature of 18116 degrees C and 300 mu mol-PAR), a low night temperature combined with high light intensity (18/12 degrees C; 300 mu mol PAR) and a low night temperature and low light intensity (18/12 degrees C; 100 mu mol-PAR). Measurements of the photosynthesis rate at shoot level (for a shoot length of 6 cm, 10 cm and 15 cm) and the carbohydrate content of several plant parts (also for different shoot lengths, corresponding with different developmental stages of the apex), as well as observations of the degree of abortion and the flower stem quality were performed. From the results, it was shown that the treatments influenced the rate of development of the shoot. The low night temperature, combined with the non-limiting light intensity enhanced the quality of the flower stem and decreased the abortion rate. Moreover, for a shoot length of ca. 10 cm (the critical stage of flower bud abortion), the quantum efficiency of the shoot and the carbohydrate content of the most mature leaf on the shoot were significantly higher than in the other treatments. The results support that a sufficient supply of carbohydrates during the critical stage for abortion, in combination with a high light intensity, which is known to enhance the sink strength, leads to a reduction of flower abortion and better flower stem quality.

EFFECTS OF SUPPLEMENTARY LIGHTING AND BENDING TECHNIQUE ON GROWTH, FLOWERING AND CARBOHYDRATE STATUS OF ROSA HYBRIDA 'FRISCO'

The effect of 2 supplementary lighting regimes (30 and 60 mu mol/m(2).s) and 2 cultural techniques (bending or decapitation) on the development of the new stems, dry-matter distribution and carbohydrate content of Rosa hybrida 'Frisco' plants was evaluated. Experiments were performed with single shoot rooted cuttings in a greenhouse compartment. Plants were grown at 18/16 degrees C day/night temperature and received a photoperiod of 18 hours. At each light level (30 and 60 mu mol/m(2).s) plants were randomly split in two groups depending on the harvesting technique. The primary shoot was either decapitated above the two most basal leaves with five leaflets or bended. Development of two shoots per plant was allowed. The analysis were performed on those two emerging shoots. The experiment was performed from January until March 1996, and was repeated for the decapitation treatment only, from March until May 1996. Bending of the primary shoot resulted in significant longer stems and increased flower stem weight and flower stem diameter with no effect of the supplementary lighting on the flower stem quality at harvest. For decapitated plants, however, a supplementary lighting of 60 mu mol/m(2).s reduced significantly the percentage of flower abortion, increased the flower stem development rate and the flower stem weight in comparison with 30 mu mol/m(2).s. The bending technique, in comparison to the decapitation method, results in faster shoot growth rate associated to higher glucose and fructose concentration in the apical part of the stem during the differentiation of the flower primordia and the shoot elongation phase.

Effect of organic manure application on yield distribution over time and in truss position on the main stem in eggplants

Temporal distribution of yield over harvests and yield in various truss positions on the main stem in three West African eggplants were studied in the field under five poultry manure rates. Fruit yields were spread over 12-15 weeks, unless where the life of the crop was cut short due to insect pest or disease attack. Two peaks, the first major and a second minor one, were evident in the temporal fruit yield distribution, apparently arising from inherent flowering and fruiting periodicities of the eggplants and influenced by weather factors, especially rainfall. Multiple harvests were necessary as fruits were always at different stages of development, reaching maturity at different times. On the basis of time to first harvest, Marvelum was classified as early maturing, Roundgreen intermediate and Sweet Samaru late maturing. Flower abortion was generally high and increased with higher truss positions. Fruit set was higher with the lower trusses and decreased with higher truss positions. Although manuring benefited yields generally, it did not help much in enhancing assimilate distribution among truss positions or in stabilizing fruit yield values during different harvest periods.

Pollination of English Walnuts: Practices and Problems

English walnut (Juglans regia, L.) is a monoecious species bearing staminate and pistillate flowers separately on the same tree. Walnuts are generally self-fruitful, cross-compatible and dichogamous, having incomplete overlap of pollen shed and female receptivity. It is this characteristic which led to the recommendation that about 10% of the trees in a commercial planting be a cultivar with a pollen shed period overlapping pistillate flower receptivity of the main cultivar. Excessive pollen load has been implicated in the `Serr' cultivar in pistillate flower abortion (PFA), the loss of the female flowers early in the season before fruit drop due to lack of pollination. PFA can be reduced and yield improved in `Serr' orchards by reducing pollen load. This can be accomplished by pollinizer removal, or catkin removal at the beginning of pollen shed by mechanical shaking. In years of significant bloom overlap between staminate and pistillate bloom, PFA can be further reduced and yield improved by removing `Serr' catkins. PFA occurs to a lesser extent in other cultivars such as `Chico', `Chandler', `Vina' and `Howard'. This information has led to the reevaluation of pollinizer recommendations. Research focused on optimum pollinizer levels in `Chandler', a cultivar of increasing importance to the California walnut industry, has been inconclusive. Lack of pollinizers may impact yields to a greater extent in the in the northern San Joaquin Valley and Sacramento Valley than in the southern San Joaquin Valley. In any case the previously recommended 10% appears to be excessive. Two to three percent is probably adequate to limit losses due to lack of pollination without resulting in excessive PFA, and is currently being recommended by extension farm advisors and specialists. Factors to consider when determining the number of pollinators to plant include: cultivar susceptibility to PFA, walnut pollen load in the area and local pollination and fruit set experiences.

Bushy, a dominant pea mutant characterised by short, thin stems, tiny leaves and a major reduction in apical dominance

The spontaneous, single-gene dominant, pea (Pisum sativum L.) mutant bushy is characterised by short, thin stems, tiny leaves and a proliferation of basal lateral branches. We symbolised the dominant mutant allele bsh and the recessive wild-type allele BSH. Some effects were very large, e.g. the reduction in internode length was around 10-fold in pure mutant plants. The effect on branching was qualitative under our conditions as the wild-type did not branch and the mutant branched extensively. Analysis of epidermal cells indicated the reduction in internode length arose principally from a reduction in cell length. The bushy mutation also altered root morphology with a reduction in the number and length of lateral roots. Time to first open flower was increased but node of flower initiation was not affected. In a few cases, bushy plants died before producing an open flower even though tiny abortive flower buds were produced in the upper leaf axils. In pure mutant plants, individual seed weight was reduced by 30%, number of seeds per pod was reduced 3-fold, and seed number per plant was reduced 4-fold. However, pod size was essentially normal for a given seed content, and the flowers were fertile and of normal structure. Grafting studies showed the primary action of the bushy mutation occurred in the shoot. In summary, the reduced cell and shoot elongation, loss of apical dominance and a primary action in the shoot, all point toward auxin deficiency (or perceived deficiency) as a possible cause of the bushy phenotype. The overall characteristics of bushy make it a useful mutant for research on plant development.

Parthenocarpy induced by N-(2-chloro-4-pyridyl)- N′-phenylurea (CPPU) prevents flower abortion in Chinese white-flowered gourd ( Lagenaria leucantha)

Flower abortion under unfavorable weather conditions is a serious problem in commercial production of cucurbitaceous crops in spite of artificial pollination. The effects of naphthaleneacetic acid (NAA), gibberellic acid (GA 3), N-(2-chloro-4-pyridyl)- N′-phenylurea (CPPU), 6-benzylaminopurine (BA), N, N′-diphenylurea (DPU) and N-(4-pyridyl)- N′-phenylurea (4-PU) on fruit set in unpollinated and pollinated ovaries of Chinese white-flowered gourd ( Lagenaria leucantha) were studied with the aim of increasing fruit set. Among the tested compounds, only CPPU showed high activity in inducing parthenocarpy and all the parthenocarpic fruit developed to normal size. The parthenocapy percentage induced by CPPU was as high as 100% within the tested concentration (10–100 mg l −1) and was not significantly altered by application time from 2 days before anthesis to two days after anthesis. NAA and GA 3 induced parthenocarpic fruit set in 37.5% and 45.5% of treated ovaries respectively, however, they could not induce parthenocarpic fruits of normal size. DPU, 4-PU and BA treatments had little effects on unpollinated ovaries. NAA, however, improved fruit set of pollinated ovaries but did not accelerate fruit growth. A contrary trend was observed in GA 3 treatment. CPPU also increased fruit set and fruit growth of pollinated ovaries. Treating all ovaries on a plant or alternate ovaries increased fruit yield by 91.3% and 83.3%, respectively, but reduced fruit size.

Recommendations for control of cone and seed insect pests of black spruce, Picea mariana (Mill.) B.S.P., with insecticides

Foliar sprays of dimethoate (1.25 g AI per tree) and permethrin (0.028 g AI per tree), applied to run-off one week prior to female flower bud flush, significantly reduced flower abortion, cone grazing, and shoot grazing caused by spruce budworm, Choristoneura fumiferna (Clem.), larvae as well as damage by the spruce cone maggot, Strobilomyia appalachensis (Michelsen). Treatment with Bacillus thuringiensis var. kurstaki (B.t.) (0.012 B.U.I, per tree) resulted in moderate protection from grazing damage to female flowers and cones as compared to treatment with dimethoate and permethrin. Systemic applications of acephate also reduced damage by spruce budworm larvae and the spruce cone maggot: fall and early spring applications were equal in efficacy, and the label rate (0.875 g acephate/3.2 cm dbh) provided similar protection to the half-label dose. Key words: Insecticides, black spruce, efficacy, recommendations, cone and seed insects

Yucca moth oviposition and pollination behavior is affected by past flower visitors: evidence for a host-marking pheromone.

Insect larvae such as those of yucca moths that feed on small, patchily distributed food items often face an elevated risk of intraspecific competition or cannibalism. For this reason, ovipositing females may assess a potential oviposition site for prior conspecific eggs or larvae before deciding whether to oviposit. Selective abortion of yucca flowers with high egg numbers prevents competition among larvae of the yucca moth Tegeticula yuccasella, but the same mechanism should select for female detection of and fewer ovipositions in flowers that already contain eggs. Female yucca moths presented with either virgin or previously visited flowers laid significantly fewer eggs in the latter flowers and pollinated them less often. A significant negative association was found between number of previous oviposition attempts in a flower and number of additional attempts by a female, suggesting a quantitative assessment of prior egg load, but the correlation coefficient was low. Factors contributing to this low correlation may include variation in signal quality, poor detection capability, uncertainty contributed by a variable oviposition attempt to egg ratio, and a variable response criterion based on recent female experience and physiological status. Females rationed their pollen by pollinating at decreasing frequency during a bout within a flower, and by depositing smaller pollen loads during later pollinations within a flower. Females ovipositing into a previously visited flower pollinated as frequently as would a first female for a given oviposition attempt within a flower, i.e., the probability of pollination after the nth oviposition was independent of whether it was performed by a first or a later moth. Experimental presentation of virgin flowers marked with a homogenate from female abdomens induced the same oviposition and pollination behavior as seen on previously visited flowers, suggesting the presence of a host-marking pheromone. Given that all eggs within a selectively aborted flower die, there may be selection among some yucca moths for providing a strong signal of floral egg status to conspecific females.

Characterization of a Tospovirus Isolate of Iris Yellow Spot Virus Associated with a Disease in Onion Fields in Brazil.

A tospovirus from onion causing a disease known as "sapeca" by growers in Brazil was characterized. Symptoms on onion consisted of numerous eyelike spots on the leaves and flower stalks resulting in flower abortion. Nicotiana benthamiana and N. rustica were the only systemic hosts experimentally found. Double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) experiments demonstrated that this virus was serologically related to iris yellow spot virus (IYSV), a tospovirus recently described in the Netherlands. This virus, from onion, based on an amino acid sequence identity of 90.5% for the N gene protein, is regarded as a strain of IYSV and is designated IYSVBR This 10% divergence in the nucleocapsid protein may represent an adaptation of the virus to distinct ecological niches.