Late-season Flowers Research Articles

Effect of temperature, flowering time and inflorescence length on yield and productivity of litchi (Litchi chinensis) cv. ‘Shahi’

The present study was carried out in 2017–18 at ICAR-NRC on Litchi, Muzaffarpur to assess the effect of temperature, flowering time and inflorescence length on yield of litchi (Litchi chinensis Sonn.) cv. Shahi. The study revealed that the temperature, flowering stage as well as length of inflorescence were positively correlated with florescence width (0.98) while fruit set was negatively correlated with temperature (-0.863). There was a strong correlation between fruit set and size of the inflorescence. Early-season flowering had higher fruit set (8.56%) as compared to mid (7.58%) and late-season (4.05%) flowering. Fruit set was critically reduced by 50% in late floweringplants resulting in drastic reduction in the total fruit yield. A strong positive correlation (0.84) was found between inflorescence hickness and fruit weight. Fruit and pulp weight were influenced by stage of flowering, as early flowering exhibited highest fruit weight (24.56 g) compared to mid and late flowering in which fruit weight was reduced by 35.42% and 50%, respectively.

Plasticity in floral longevity and sex-phase duration of Lobelia siphilitica in response to simulated pollinator declines.

Pollinator declines can reduce the quantity and quality of pollination services, resulting in less pollen deposited on flowers and lower seed production by plants. In response to these reductions, plant species that cannot autonomously self-pollinate and thus are dependent on pollinators to set seed could plastically adjust their floral traits. Such plasticity could increase the opportunity for outcross pollination directly, as well as indirectly by affecting inflorescence traits. To test whether plants can respond to pollinator declines by plastically adjusting their floral traits, we simulated declines by experimentally reducing pollinator access to Lobelia siphilitica plants and measuring two traits of early- and late-season flowers: (1) floral longevity; and (2) sex-phase duration. To test whether plasticity in these floral traits affected inflorescence traits, we measured daily display size and phenotypic gender. We found that experimentally reducing pollination did not affect female-phase duration, but did extend the male-phase duration of early-season flowers by 13% and the longevity of late-season flowers by 12.8%. However, plants with an extended male phase did not have a more male-biased phenotypic gender, and plants with an extended floral longevity did not have a larger daily display. Our results suggest that plants can respond to pollinator declines by plastically adjusting both the longevity and sex-phase duration of their flowers. If this plasticity increases the opportunity for outcross pollination, then it could be one mechanism by which pollinator-dependent plant species maintain seed production as pollinators decline.

Flower forcing possibilities in Hemerocallis hybrids

Daylilies (Hemerocallis hybrids) are one of the most important ornamental perennial plants nowadays used in gardens and parks. Flower forcing of daylily hybrids in early spring or autumn could broaden their application and marketing possibilities. There is very limited data available on this topic. In our early flower forcing experiment ‘Moonlit Masquerade’, for late flowering ‘Mary Todd’ were used. During the study we have sought answer for the following questions: the amount of growing degree-day required for flower stalk induction and for flowering and whether the day length has an effect on these values or not. In the early flower forcing experiment 4 treatment groups were established: plants of the first treatment group were placed in a moderately heated greenhouse without assimilation lighting. The second treatment group were placed in the same greenhouse but artificial light was used to extend the day length for 15 h. The examination of the third group happened in a plant growth chamber with 15 h day length and a daily average temperature of 20°C was provided for the plants, and there was also a control group in open field environment. For late flowering the bare rooted dormant plants were stored in refrigerator and were planted to open-field in late spring and summer. During the experiments temperature data were logged and plant morphology characteristics were measured in two following year. According to the results it can be stated that the differentiation of inflorescence is not depending on the day length rather on the leaf surface area. Growing degree-day is the main factor which influences the speed of inflorescence development once it has already differentiated, so temperature is the key factor in flower bud opening and it also defines the number of the developing flower buds. The data from late flowering experiment show that bare-rooted daylily plants are suitable for long-term cold storage and this method offers late season flower forcing.

Organic farming supports spatiotemporal stability in species richness of bumblebees and butterflies

The spatiotemporal stability of wild organisms, such as flower-visiting insects, is critical to guarantee high levels of biodiversity in agroecosystems. Whereas the proportion of semi-natural habitats in the landscapes has been shown to stabilize the species richness of flower visitors, the effect of farming intensity has not yet been studied. In this study, we compared the temporal and spatial stability (continuity of species richness in space and time) of two groups of flower-visiting insects (butterflies and bumblebees) between nine conventional and ten organic farms, distributed along a gradient of semi-natural grassland proportion. We surveyed bumblebees, butterflies and local flower cover during the growing season, covering multiple years and several habitat types per farm (cereal fields, temporary grasslands and semi-natural grasslands). At the field scale we found that within-year stability of bumblebee species richness was higher in organic than in conventional temporary grasslands (leys), because of a higher continuity of in-field flower resources. Further analyses showed that late-season flower resources in organic ley fields were critical to maintain a high within-year stability of bumblebee species richness by reducing resource bottlenecks during that period, when most bumblebee colonies produce new queens. The among-year stability of bumblebee species richness was higher in organic than in conventional cereal fields, whereas the within and among-year stability of butterfly species richness was not influenced by farming system. On the farm scale, we found that the spatial stability of butterfly and bumblebee species richness was higher in organic than in conventional farms, but this was not explained by a greater spatial continuity of flower resources. Our study shows that organic farming reduces the spatiotemporal fluctuations in bumblebee and butterfly species richness. In addition, increasing floral resources as such benefits bumblebees and butterflies irrespective of farming system. Organic farming and increasing availability in floral resources therefore contribute to maintaining the within and between-year stability of bumblebees and butterflies in agricultural landscapes.

Cumulative herbivory outpaces compensation for early floral damage on a monocarpic perennial thistle.

Floral herbivory represents a major threat to plant reproductive success, driving the importance of plant tolerance mechanisms that minimize fitness costs. However, the cumulative insect herbivory plants experience under natural conditions complicates predictions about tolerance contributions to net fitness. Apical damage can lead to compensatory seed production from late season flowering that ameliorates early season fitness losses. Yet, the compensation realized depends on successful development and herbivore escape by later season flowers. Using monocarpic perennial Cirsium canescens, we quantified seed-reproductive fitness of plants with vs. without experimental damage to the early-developing large apical flower head, with and without a 30-40% herbivory reduction on subsequent flower heads, for two flowering cohorts. Plants with reduced herbivory clearly demonstrated the release of apical dominance and compensation, not overcompensation, for apical damage via greater seed maturation by later flower heads. In contrast, plants that experienced ambient herbivory levels on subsequent heads undercompensated for early apical damage. Individuals had lower total seed set when the apical head was damaged. Compensation was, therefore, possible through a small increase in total flower heads, caused by a higher rate of floral bud survival, and a higher seed maturation rate by subsequent heads, leading to more viable seeds per matured flower head. With ambient cumulative floral herbivory, compensation for apical damage was not sufficient to improve fitness. Variation in the intensity of biological interactions played a role in the success of plant tolerance as a mechanism to maximize individual fitness.

Measurements of Oleic Acid among Individual Kernels Harvested from Test Plots of Purified Runner and Spanish High Oleic Seed

ABSTRACT Normal oleic peanuts are often found within commercial lots of high oleic peanuts when sampling among individual kernels. Kernels not meeting high oleic threshold could be true contamination with normal oleic peanuts introduced via poor handling, or kernels not meeting threshold could be immature and not fully expressing the trait. Beyond unintentional mixing, factors contributing to variation in oleic acid concentration in peanut kernels include market type, environment, maturity and/or kernel size; however, the relative influence of these factors, and their interactions, is not quantitatively well understood on the single kernel level. To better understand these factors while simultaneously excluding variation from unintentional mixing, seed from a high oleic spanish cultivar and seed from a high oleic runner cultivar were carefully purified via NIR technology. The purified seed were planted in environmentally controlled test plots to analyze the progeny for oleic acid chemistry. Post flowering, plot sections were either chilled (3.8 -5.0 C below ambient), maintained at ambient or heated (3.8-5.0 C above ambient) in the pod zone to characterize soil temperature effects on oleic acid chemistry development. Fully randomized (4 reps) plots included the purified high oleic spanish and runner cultivars, three soil temperatures, seed maturity (profile board), commercial kernel size classifications, and a late season flower termination protocol. At harvest, the oleic acid concentration of approximately 24,000 individual kernels were measured via NIR technology. Market type, temperature, maturity and size had a significant effect on high oleic chemistry among kernels. Late season flower termination significantly, and positively, influenced high oleic chemistry of runner peanuts, minimized the number of immature kernels not meeting high oleic threshold and resulted in elevated and more consistent distributions in this key chemistry; distributions that were more similar to those of the more botanically determinate, but lower yielding, spanish market type. Data from this study improves our understanding of expected natural variation in high oleic chemistry and suggests late season flower termination of runner peanuts is a viable strategy to maximize high oleic chemistry on the single kernel level.

Chemical Interruption of Late Season Flowering to Improve Harvested Peanut Maturity

ABSTRACT Peanut (Arachis hypogaea) is a botanically indeterminate plant where flowering, fruit initiation, and pod maturity occurs over an extended time period during the growing season. As a result, the maturity and size of individual peanut pods vary considerably at harvest. Immature kernels that meet commercial edible size specifications negatively affect quality during processing due to their increased propensity for off flavors, higher moisture and water activity, and variable roasting properties. As peanuts progress toward maturation, late season flowers set within 40 days till harvest will not have sufficient time to develop into mature, marketable pods prior to harvest. Research was conducted to determine the effect of late season flower termination on peanut yield, grade, and seed germination. Diflufenzopyr-Na (Diflufenzopyr) (BASF Biosciences), a synthetic auxin transport inhibitor, and the herbicide glyphosate were applied at three sub-lethal rates along with a “hand flower removal” and a non-treated control in both irrigated and non-irrigated plots. No differences in non-irrigated pod yield across all treatments were detected. Glyphosate at 56 and 112 g/ha increased non-irrigated sound mature kernels plus sound splits (SMK+SS) and decreased other kernels (OK). Non-irrigated seed germination was negatively affected by glyphosate. Diflufenzopyr at 17 and 25 g/ha increased irrigated peanut yield. Glyphosate at 112 and 168 g/ha increased irrigated SMK+SS and decreased OK and germination.

Pollination consequences of simulated intrafloral microbial warming in an early-blooming herb

In habitats where low ambient temperature limits entomophilous pollination of early-blooming plants, intrafloral warming facilitates pollinator visitation and enhances plant reproductive success. A novel mechanism for intrafloral warming was described recently for the early-blooming, bumblebee pollinated herb Helleborus foetidus (Ranunculaceae) where the warming agent was the metabolic heat dissipated by dense populations of the nectar-specialist yeast Metschnikowia reukaufii. This paper reports results of field experiments conducted over three consecutive years aimed at (1) ascertaining whether flowers of H. foetidus with warmed interiors differed in pollination success from flowers experiencing natural intrafloral microclimate; and (2) testing the hypothesis that the pollination effects of intrafloral warming should be stronger during the early stages of the H. foetidus flowering season, when inclement weather and low ambient temperatures often limit pollinator activity. Intrafloral warming resulted in increased number of pollen tubes per style and reduced probability of pollen limitation early in the flowering season, while these effects were reversed in late-season flowers. Since the number of pollen tubes was directly correlated with number of pollen grains on the stigma, fruit set and number of seeds produced by individual flowers, results of this study are interpreted as indicating that yeast-induced intrafloral warming has the potential to influence reproductive success in H. foetidus via effects on pollinator activity, although the nature of effects will vary depending on environmental conditions. Results also stress the importance of ambient and floral temperature for the pollination of early-blooming plants.

Tolerance and phenological avoidance of herbivory in tarweed species.

Avoidance and tolerance of herbivory are important components of plant interactions with herbivores. Their relationship to each other and to plant defense is important in understanding how plants maximize fitness in the face of herbivore pressure. Various tarweed species have populations comprised of both early-season and late-season flowering individuals. Late-season flowering individuals employ a recently described indirect defense against herbivores in which the accumulation of dead insects on their sticky surfaces attracts predatory insects that eat herbivores. In two tarweed species (Hemizonia congesta and Madia elegans), we observed that key herbivores rarely interact with early-season individuals in the field, and early-season individuals did not invest in dense glandular trichomes that cause indirect defense. We conducted field and greenhouse bud-removal experiments to assess tolerance of M elegans to herbivore damage. We found that late-season individuals were more tolerant of simulated herbivory than early-season individuals in both the field and the greenhouse. Late-season individuals that were forced into an earlier phenology with a 24-h light cue lost their tolerance to simulated herbivory. One possible mechanism linking phenological avoidance of herbivores with decreased tolerance is that early-season individuals invested less in below-ground biomass than late-season individuals, which may accumulate belowground resources for regrowth at the expense of early flowering.

Late-season mass-flowering red clover increases bumble bee queen and male densities

Spatiotemporal resource continuity promotes persistence of mobile animal populations. Current agricultural landscapes are poor in flowers resources for bumble bees. Available forage crops are predominantly early-season mass-flowering crops (MFC). It has been suggested, but not tested, that scarcity of late-season flower resources are limiting bumble bee populations. We examined whether addition of late-season flowering red clover affected worker, queen and male bumble bee densities. Bumble bees were surveyed in flower-rich uncultivated field borders across 24 landscapes (radius 2km) with or without a clover field in the centre, varying in semi-natural grassland (SNG) and early MFC availability. Clover fields had over ten times higher worker densities compared to field borders, suggesting red clover as favoured forage. Five times more queens and 71% more males were found in landscapes with clover fields compared to control landscapes, despite these fields constituting less than 0.2% of the landscape area. Both MFC and SNG increased the density of males, but only in the presence of clover fields. Our results suggest that late-flowering red clover positively affects bumble bee reproduction, likely by increasing temporal resource continuity. Interventions such as flower strips can thus have mitigating effects if they release population regulation by late-season resource bottle-necks.

Agri-environment management for corncrake Crex crex delivers higher species richness and abundance across other taxonomic groups

This study tested whether agri-environment scheme (AES) management for corncrakes in the UK is associated with higher diversity or abundance of non-target flora and fauna relative to similar land outside AES management. The species richness and abundance of forbs, butterflies, bumblebees and foliar arthropods were compared on 101 paired control-treatment plots across the two AES measures for corncrakes: provision of tall vegetation throughout the breeding season (Early and Late Cover; ELC) and delayed mowing (DM) of hay or silage fields. There were significant positive effects of AES management for the species richness of forbs, and abundance of late-season flowers, butterflies, bumblebees and the majority of foliar arthropod groups on one or both AES measures. Significant negative effects of AES were found in only two cases: forb species richness (ELC only) and the abundance of springtails (DM only). For the remaining species and groups studied there was either no effect of AES or no clear difference due to strong AES×season interactions. The magnitude of the AES effects varied substantially both between taxonomic groups and the two measures for corncrake. Most of the positive effects were for common and widespread species, except for two rare bumblebees. The benefits resulted from the reduction in farmland management intensity associated with AES. While not beneficial to all taxonomic groups these results demonstrate that, in the case of corncrakes in the UK at least, well-designed AES measures targeted at a specific species do yield wider biodiversity benefits.

Nitrogen use for high productivity and sustainability in cashew

Interest in cashew production in Australia has been stimulated by domestic and export market opportunities and suitability of large areas of tropical Australia. Economic models indicate that cashew production is profitable at 2.8 t ha −1 nut-in-shell (NIS). Balanced plant nutrition is essential to achieve economic yields in Australia, with nitrogen (N) of particular importance because of its capacity to modify growth, affect nut yield and cause environmental degradation through soil acidification and off-site contamination. The study on a commercial cashew plantation at Dimbulah, Australia, investigated the effect of N rate and timing on cashew growth, nut production, N leaching and soil chemical properties over five growth cycles (1995–1999). Nitrogen was applied during the main periods of vegetative (December–April) and reproductive (June–October) growth. Commercial NIS yields (up to 4.4 t ha −1 from individual trees) that exceeded the economic threshold of 2.8 t ha −1 were achieved. The yield response was mainly determined by canopy size as mean nut weight, panicle density and nuts per panicle were largely unaffected by N treatments. Nitrogen application confined to the main period of vegetative growth (December–April) produced a seasonal growth pattern that corresponded most consistently with highest NIS yield. This N timing also reduced late season flowering and undesirable post-November nut drop. Higher yields were not produced at N rates greater than 17 g m −2 of canopy surface area (equating to 210 kg N ha −1 for mature size trees). High yields were attained when N concentrations in Mveg leaves in May–June were about 2%, but this assessment occurs at a time when it is not feasible to correct N deficiency. The Mflor leaf of the preceding November, used in conjunction with the Mveg leaf, was proposed as a diagnostic tool to guide N rate decisions. Leaching of nitrate-N and acidification of the soil profile was recorded to 0.9 m. This is an environmental and sustainability hazard, and demonstrates that improved methods of N management are required.

Coolamon subterranean clover (Trifolium subterraneum L. var. subterraneum)

Coolamon is a mid-season to late-season flowering F4-derived crossbred subterranean clover of var. subterraneum, developed by the collaborating organisations of the National Annual Pasture Legume Improvement Program. It is a replacement for Junee and has been selected for release on the basis of its greater herbage production and persistence, and its resistance to both known races of clover scorch. Coolamon is recommended for sowing in Western Australia, New South Wales, Victoria, South Australia and Queensland. It is best suited to well-drained, moderately acidic soils in areas with a growing season of 6.5–8 months that extends into November. Coolamon is best suited to phase farming and permanent pasture systems. It can also be used in cropping rotations, but at least 2 years of pasture are required between crops. Coolamon has been granted Plant Breeders Rights in Australia.

Complex segregation analysis of day-neutrality in domestic strawberry (Fragaria ×ananassa Duch.)

Thirty bi-parental progenies were generated using 45 genotypes from the University of California (UC) strawberry breeding population as parents. Both parent genotypes and their offspring were classified for photoperiod insensitivity, or day-neutrality, for flowering using a late-season flowering score and the number of inflorescences per plant recorded during late summer. Complex Segregation Analysis of these traits indicated that their distributions were best explained by a genetic model that postulates a single major locus with partial dominance for day-neutrality in combination with a background of polygenic and environmental variation. The frequency of the allele conferring day-neutrality was estimated as p = 0.59–0.62 in this experimental population. Genotypic values for the inferred major locus were estimated as a = 1.12 and d = −0.81 for the flowering score, and a = 4.93 and d = 2.41 for inflorescence number. Further resolution of inheritance patterns were obtained by comparing the phenotypic variance for each trait with estimates obtained by insertion of these genotypic class values and allele frequencies into standard quantitative genetic models, and by the comparing variance components estimated using a mixed model analysis with and without inferred genotypic classes as a fixed effect. These comparisons suggest that the major gene determines 80.5% and 73.9% of the additive genetic variance for flowering score and inflorescence number respectively. One complicating feature of the results obtained here is that a non-Mendelian model of segregation fit statistically better than a fixed Mendelian model. The genetic parameters estimated using this non-Mendelian model were essentially identical to those obtained with fixed segregation; hybrid and octoploid ancestry, selection affecting flowering response, and limited number of generations in the analysis are discussed as possible explanations of this result.

Effects of planting system, plant density and flower removal on yield and quality of hybrid seed in cotton

Seedling transplanting and plastic mulching are widely adopted intensive planting systems in cotton production in China. Manual removal of early- or late-season flowers may improve seed quality without sacrificing yield through the compensatory growth of cotton plants. Two experiments were conducted, in Yellow River Valley in China from 2002 to 2003, to test if the intensive systems and flower removal can be used for enhancing hybrid seed production. Results in the first experiment show that yields of seed cotton and seed, and seed quality parameters averaged across three plant densities (2.25, 3.00 and 3.75 plants/m 2), were significantly improved by either transplanting or plastic mulching relative to conventional planting. The improvements in yield and quality in two intensive planting systems were mainly attributed to longer and earlier flowering period. Transplanted plants did not differ significantly from mulched plants in seed yield, seed maturity and percentage germination, but transplanting decreased lint percentage and increased seed index relative to mulching. In terms of seed yield and quality, the optimum plant density for each planting system was 3.00 plants/m 2. At the optimum plant density, seed yields averaged across two years for transplanting and mulching systems were 31.3% and 32.6% higher than for conventional planting system, respectively. Flower removal did not significantly affect seed yield, but removal of late-season or both early- and late-season flowers significantly improved seed quality. It was concluded that transplanting or plastic mulching, low plant density (3.00 plants/m 2), and removal of late-season or both early- and late-season flowers can be integrated to enhance yield and quality of hybrid seed of cotton.

Seasonal changes in pollen-packaging schedules in the protandrous plant Chamerion angustifolium.

The rate at which pollen is presented varies widely both among and within species of flowering plants. Although several studies have tried to explain between-species variation in this trait, few explanations exist for the variation that exists among individuals of the same species. I used protandrous fireweed, Chamerion angustifolium (Onagraceae), to examine seasonal changes in pollinator visitation, population sex ratio, and pollen presentation schedules. Most studies that make predictions about optimal pollen presentation assume conditions are constant throughout the flowering season. However, data presented here show that pollen presentation schedules vary seasonally: in early season flowers, anthers dehisce over a number of days, while late season flowers present all anthers simultaneously. I show that pollinator visitation rates to individual plants are higher but more variable early in the season than late in the season. Furthermore, per-male availability of female-phase flowers increases over the course of the flowering season in this population. I suggest that seasonal differences in the variability of pollinator visitation and the availability of female flowers has played an important role in selection for pollen presentation schedules.

Relative Attractiveness of Potential Beneficial Insectary Plants to Aphidophagous Hoverflies (Diptera: Syrphidae)

Establishing flowering plants in and around fields to provide pollen and nectar resources for natural enemies has shown promise as a strategy to enhance biological control of crop pests. Natural enemies are selective in their flower feeding, however, and show preferences for certain plant species. In this study the relative attractiveness of 11 flowering plant species to aphidophagous hoverflies (Diptera: Syrphidae) was evaluated at the Oregon State University Vegetable Research Farm. Six of these plant species were also evaluated at two other farm sites. Of the 12 species of hoverflies collected, Meliscaeva cinctella (Zetterstedt), Toxomerus marginatus (Say), Toxomerus occidentalis (Curran), Sphaerophoria sulfuripes (Thomson), and Scaeva pyrastri (L.) were common to all three sites. Attractiveness of flowering plants to foraging hoverflies was assessed by conducting timed observations of feeding-visit frequencies. Flowering periods varied between plant species and comparisons were made only for plant species flowering on a particular date. Relative attractiveness of plant species to hoverflies differed between dates and sites. Among early-season flowering species, coriander, Coriandrum sativum (L.), was fed from most frequently. Among late-season flowers, yarrow, Achillea millefolium (L.), fennel, Foeniculum vulgare (Miller), and Korean licorice mint, Agastache rugosa (Fischer & C. A. Meyer) were fed from most frequently. These results help in the selection of plants to enhance biological control, but final selection of plants for this purpose requires considering flower, natural enemy, and pest phenologies, and pollen and nectar quality and availability.

Effects of Day and Night Temperatures on Flower-bud Formation and Bolting of Japanese Bunching Onion(Allium fistulosum L.).

Effects of day and night temperatures on flower-bud formation and bolting of Japanese bunching onion (Allium fistulosum L.) were investigated by using mid-season flowering 'Kincho' and 'Asagi-kujo', and late-season flowering 'Cho-etsu'. Exp.1. Plants were grown at 3, 7, 11, and 15°C at night and 20°C during the day for 20 to 60 days. Flower-bud formation was promoted at 3°C and, especially, at 7°C in all cultivars. More than 50% of 'Kincho' and 'Asagi-kujo' plants formed flower buds at 15°C when grown for 60 days ; only 10% of 'Cho-etsu' bolted. Exp.2. Plants were grown at 7.0, 13.5, 20.0 or 26.5°C during the day and 7.0°C at night. Bolting of 'Kincho' and 'Asagi-kujo' plants at 7.0°C and 26.5°C was slightly retarded, compared to plants exposed to 13.5°C and 20.0°C. The bolting rate of 'Cho-etsu' was lower in all day temperatures than were those of 'Kincho' and 'Asagi-kujo', irrespective of the duration of treatments. Over 60% of 'Cho-etsu' bolted when grown at 7.0°C and 13.5°C for 75 days, whereas only 33.3% bolted at 20.0°C ; no plants bolted at 26.5°C. Thus, 'Cho-etsu' plants were devernalized at day temperature 20.0°C and 26.5°C. Based on these results, the optimum night temperature for flower-bud formation of Japanese bunching onion is 7°C at 20°C during the day. Devernalization occurs in 'Cho-etsu' at and above 20°C ; it rarely occurs in 'Kincho' and 'Asagi-kujo' below 26.5°C.

Effect of photoperiods before, during and after vernalization on flower initiation and development and its varietal difference in Japanese bunching onion (Allium fistulosum L.)

SummaryTo control the bolting of Japanese bunching onion (Allium fistulosum L.) photoperiodically, the effect of photoperiods before, during and after vernalization on flower initiation and development and the varietal differences were investigated using the two mid-season flowering cvs Kincho and Asagi-kujo, and a late-season flowering cv. Cho-etsu. A long-day photoperiod (LD, 16 h) given before vernalization inhibited flower initiation. Especially, the bolting rate of ‘Asagi-kujo’ decreased by about a half, compared with the short-day photoperiod (SD, 8 h). The interaction between the effect of night temperature (3°C, 7°C, 11°C or 15°C) and the effect of the photoperiod (SD and LD) during vernalization was also investigated. In ‘Kincho’, LD did not affect flower initiation at 3°C, but inhibited flower initiation at 7°C, 11°C and 15°C. In ‘Asagi-kujo’, flower initiation was significantly inhibited by LD under all temperature conditions. This inhibitory effect was stronger at 11°C and 15°C than at 3°C and 7°C. In ‘Cho- etsu’, LD significantly inhibited flower initiation at 3°C and 7°C, and flower initiation rarely occurred at 11°C and 15°C. In this study, generally, LD during vernalization inhibited flower initiation in all cultivars. Thus Japanese bunching onion required a short-day photoperiod in flower initiation, which was stronger in ‘Asagi-kujo’ and ‘Cho-etsu’ than in ‘Kincho’. From these results, we conclude that low temperature and a short-day photoperiod complementarily induce flower initiation in Japanese bunching onion. Varietal differences exist in the requirement of low temperature and a short-day photoperiod: the primary requirement in ‘Kincho’ is low temperature and that in ‘Asagi-kujo’ is a short-day. After flower initiation, the early stage of flower development is day-neutral, and after the floret formation stage, a long-day photoperiod promotes flower development and elongation of the seedstalk.

Cotton Response to Seasonal Patterns of Flower Removal: I. Yield and Fiber Quality

Cotton (Gossypium hirsutum L.) yield and quality can be affected by altered fruiting patterns related to the abscission of fruiting forms. This field study quantified the effects of flower removal during various stages of reproductive development on subsequent yield development, boll development, and fiber properties. Effects of early‐, mid‐, and late‐season flower loss on cotton reproductive development was determined. Various flower removal treatments were imposed on two cultivars at Clayton, NC, during 1991 and 1992. Early flower removal treatments (3rd week and earlier) delayed boll development, but no significant reduction in yield was found at season's end. Later flower removals (4th week and later) significantly reduced total fiber yields (13–33%) compared with early‐season removals (1st, 2nd, and through 3rd week) and no removal. Boll weight was positively correlated with fiber properties and was related to the amount of competition among developing bolls. The largest bolls resulted from treatments that had the largest negative effect on yield. Micronaire was the only fiber variable affected by flower removal, with increased values associated with later removal. Data indicate that late‐season flower losses (4th week and later) are the most injurious to yield, with significant yield reductions occurring from even the least severe, late‐season removal treatment of 6th week and later flowers. Early loss (3rd week and earlier) of fruit can be tolerated if the season allows sufficient time for compensatory reproductive growth and if further losses due to plant stress or insect damage are controlled.