Subsequent Flowering Research Articles

Effects of Plant Stages on bolting of the Breeding Line 'Leafy Green Parental Line No.2' (Brassica rapa L. pekinensis group)

Bolting characteristics of a late bolting breeding line 'Leafy Green Parental line No.2' (PL-No.2, previously known as Ano No.3 or FNC31·63) of Brassica rapa L. pekinensis group, syn. B. campestris L. pekinensis group, or Chinese cabbage, were examined with regard to its plant stages. Seedling sensitivity to low temperatures was very low, irrespective of plant stages ; differentiation of flower buds occurred very late. Bolting and flowering were induced by a 16-hr photoperiod. However, a long-day with supplementary lighting was ineffective in initiating bolting and subsequent flowering. Seedlings grown under 16-hr photoperiod required nearly 70 days to anthesis. As the plants grew, the time from the onset of the long-day treatment to flowering became less than 50 days. The long-day sensitivity of 'PL-No.2' increased as the plants grew.

Bushiness and cytokinin sensitivity in micropropagated Zantedeschia

Bushiness, the development of short, multiple stems, has been reported in some commercial hybrids of Zantedeschia, particularly the yellow-flowered cultivar Florex Gold derived from tissue culture. This cultivar exhibited a greater sensitivity to 6-benzylaminopurine when compared to four other cultivars using an in vitro root length bioassay, suggesting it may be pre-disposed to bushiness. The carry-over effect of cytokinin from micropropagation on subsequent tuber formation and flower development, in three selections of the cultivar Florex Gold, was also investigated. Cytokinin levels used in commercial Zantedeschia micropropagation protocols did not alter tuber or flower development. However, excessively high levels did affect development, also indicating that cytokinin may influence bushiness. Multi-eyed tubers used to initiate in vitro cultures were shown to have a significant effect on first year tuber formation and subsequent flower weight, compared to few-eyed tubers, although these plants did not necessarily develop bushy symptoms. Plant location within the greenhouse also influenced flowering although these plants did not display multiple stemmed bushy symptoms.

Effects of drought on fruit set, yield and quality of custard apple (Annona spp. hybrid) ‘African Pride’ plants

SummaryStudies were conducted to evaluate the effects of drought during flowering for both container- and field-grown trees, and during fruit development for container-grown trees, on subsequent growth, flowering, yield and quality of the custard apple ‘African Pride’ in subtropical Australia. Moderate drought (ψL=–1.5 MPa) reduced shoot growth by 20–30% and increased the number of flowers per lateral by about 40% compared with well-watered controls due to reduced apical dominance and increased lateral branching. Overall fruit set was not adversely affected by drought. Drought also increased the number of fruit harvested per tree by 47% compared with well-watered controls. This response was mainly due to the increase in flower number per tree. Drought reduced average fruit size by 11% possibly due to effects on cell division in the first 4–6 weeks after fruit set or on net carbon assimilation. In summary, mild to moderate drought during the flowering period and fruit set increased flowering without adversely affecting fruit set, but decreased fruit size.

Fitness consequences of floral variation in Senecio jacobaea (Asteraceae): evidence from a segregating hybrid population and a resource manipulation experiment

The present study examines some of the ecological factors that might exert selection on floral morphology in Senecio jacobaea, a self-sterile composite which exhibits geographic variation in the frequency of rayed and discoid individuals. Regression analyses of phenotypic data from a large, segregating hybrid population, established in a semi-natural (garden) environment and studied over a 2-year period, revealed a negative relationship between the size of the rays and the average germination rate of the maternal seed crop, a pattern that can be attributed to the reduced germination speed of achenes from ray florets. There was no effect of ray size on the amount of cross-pollination achieved, the proportion of heads infested by larvae of seed flies (Pegohylemyia) and the amount of resources retained for the next flowering season. The lack of resource costs was also apparent in a manipulation experiment with greenhouse-grown plants of the rayed phenotype: artificial removal of all rays at the early bud or flowering stage had no detectable effect on subsequent flower and fruit development, regardless of whether the plants experienced high or low water stress. Given these and other observations, I hypothesize that plant-animal interactions and resource costs sometimes play a minor role in exerting selection on flower morphology and that spatially varying selection on germination behaviour accounts for some of the morph frequency variation in S. jacobaea.

Fitness consequences of floral variation in Senecio Jacobaea (Asteraceae): evidence from a segregating hybrid population and a resource manipulation experiment

The present study examines some of the ecological factors that might exert selection on floral morphology in Senecio jacobaea, a self-sterile composite which exhibits geographic variation in the frequency of rayed and discoid individuals. Regression analyses of phenotypic data from a large, segregating hybrid population, established in a semi-natural (garden) environment and studied over a 2-year period, revealed a negative relationship between the size of the rays and the average germination rate of the maternal seed crop, a pattern that can be attributed to the reduced germination speed of achenes from ray florets. There was no effect of ray size on the amount of cross-pollination achieved, the proportion of heads infested by larvae of seed flies (Pegohylemyia) and the amount of resources retained for the next flowering season. The lack of resource costs was also apparent in a manipulation experiment with greenhouse-grown plants of the rayed phenotype: artificial removal of all rays at the early bud or flowering stage had no detectable effect on subsequent flower and fruit development, regardless of whether the plants experienced high or low water stress. Given these and other observations, I hypothesize that plant–animal interactions and resource costs sometimes play a minor role in exerting selection on flower morphology and that spatially varying selection on germination behaviour accounts for some of the morph frequency variation inS. jacobaea.

The effects of low temperatures on the vegetative growth and flowering of the primocane fruiting raspberry ‘Autumn Bliss’

SummaryThe effects of low temperatures on subsequent vegetative growth and flowering in the raspberry ‘AutumnBliss’ were investigated. In the first experiment, a number of lifting dates were used to determine the seasonal pattern of dormancy and the effect of natural chilling on plant development. In the second, different durations of artificial chilling(0, 2, 4, 6, 8 and 10 weeks at 0˚C) were combined with two lifting dates to investigate the effect of natural and artificial chilling. In these experiments, plants which received little chilling grew slowly and failed to develop beyond short rosettes of leaves but as chilling increased, the rate of vegetative growth increased. This coincided with a decline in the time toflowering. These two responses, however, were distinct. In a third experiment, the effect of vernalization of actively growing canes was tested in an attempt to separate the effects of cold on time to flowering, and on the removalof dormancy. The plants responded significantly to cold treatment and flowering was advanced, indicating a distinct vernalizing effect

254 Stem Extension and Subsequent Flowering of Plugs Grown Under A Far-red-deficient Film

Environments with a low red (R, 600 to 700 nm) to far-red (FR, 700 to 800 nm) ratio (e.g., with high plant density) promote stem elongation, and a high R: FR suppresses it. While FR light promotes stem extension, it is also required for rapid, uniform flowering of many long-day plants. We investigated how a new FR filter [creating a FR-deficient (FRd) environment] influenced plug growth and subsequent flowering of pansy (Viola ×wittrockiana `Crystal Bowl Yellow'), petunia (Petunia ×hybrida `Carpet Pink'), impatiens (Impatiens wallerana `Accent Rose'), snapdragon (Antirrhinum majus `Liberty Scarlet'), and tomato (Solanum lycopersicon `Beefmaster'). One-week-old seedlings were placed under three filter treatments with 16-h photoperiods: the FRd filter, a neutral-density filter (N) that transmitted a similar PPF, and transferring plugs from the N to the FRd filter when leaves of each species began to touch (7 to 11 days later). The predicted phytochrome photoequilibria under the FRd and N filters was 0.80 and 0.72, respectively. After 25 to 35 days at 20 °C, node number and stem (or petiole for pansy) length were collected. Twenty plants of each species and filter treatment were then transferred to 4-inch pots and grown under natural photoperiods (14 to 15 h) at 20 °C until flowering. Compared to plants continually under the N filter, stem length under the FRd filter was significantly reduced in impatiens (by 11%), pansy (by 18%), petunia (by 34%), snapdragon (by 5%), and tomato (by 24%). Flowering of plants from plugs under the FRd filter was delayed by 2 to 3 days for snapdragon, petunia, and pansy. Filter treatment of plugs had no significant effect on flower number or plant height at flower.

Rhizome dormancy and shoot growth in myoga ( Zingiber mioga Roscoe)

After the senescence of above ground plant parts the rhizomes of myoga undergo a period of dormancy. The length of this dormancy period and the requirement for chilling to break dormancy are examined in this paper. Myoga rhizome segments were capable of initiating shoot growth 6 weeks after excision from a recently senesced dormant mother plant. A period of chilling was not required for shoot growth, but chilling at 4°C for 3 weeks immediately after excision resulted in shoot development in newly divided myoga rhizome segments which would otherwise not have sprouted until after a 6-week dormancy phase. Longer storage periods before planting and increased duration of chilling treatments decreased the variability in the sprouting response of rhizome segments. Chilling at 4°C for 2–4 weeks was the most effective treatment for promoting uniform sprout emergence and subsequent flower production. Shoot growth rate and the number of vegetative shoots produced by the rhizome was not affected by chilling treatments. Increasing the length of chilling, promoted earlier sprouting and flowering, but may have decreased the weight of the flower buds produced.

Environmental regulation of flowering and growth of Cosmos atrosanguineus (Hook.) Voss

This study investigated the factors affecting the emergence and subsequent flowering and growth of the tuberous perennial Cosmos atrosanguineus. A first experiment showed the time of emergence of overwintered plants raised from micro-propagated tubers was highly related to temperature, but not photoperiod, such that at 11.5°C shoots emerged 17 days later than those at 27.2°C. Subsequent growth was also significantly affected by temperature. Plant height doubled and flower area halved as temperature increased from 13°C to 26°C. However, the response of time to flowering from emergence to temperature was small, increasing temperature from 13°C to 21.5°C only advanced flowering by 9 days. In terms of the overall response to photoperiod, flowering was advanced by long-days; plants at a daylength of 17 h per day flowered 33 days earlier than those at 8 h per day. Photoperiod also dramatically affected plant morphology, with long photoperiods (17 h per day) leading to a greater than 7-fold increase in plant mass compared to short-days (8 h per day). The experiments described suggest that out of season forcing of Cosmos is horticulturally attainable at a relatively small cost.

Effect of temperature and light on rooting in vitro and subsequent flowering of pot alstroemeria

SummaryA clone of dwarf alstroemeria cv. Rosalina propagated in vitro was used in experiments to develop a method for pot alstroemeria production. The aim of this study was to optimize the in vitro rooting conditions of the rhizomes so as to obtain early flowering after transplanting to a greenhouse. The effects of cooling in darkness or in light, the addition of paclobutrazol to the rooting medium and the effect of stage of rhizome development on subsequent flowering were studied. The in vitro rhizome cultures maintained on the rooting medium were cooled at 10°C for 2–5 weeks and at 5°C for five weeks in darkness or under a 16 h photoperiod. To allow root formation and growth, the rhizomes were kept for 10 d at 20°C and 16 h photoperiod before cooling at 5°C and 10°C. Pretreatment with 20°C for 10 d and 16 h photoperiod applied during cooling resulted in superior rooting in vitro and better plant survival in the greenhouse. The faster flowering and most plants flowering were obtained after five weeks of cooling at 10°C under a 16 h photoperiod using pre-rooted rhizomes. Paclobutrazol markedly decreased flower stem length.

The history of fruit thinning.

The history of fruit thinning is reviewed, beginning with hand removalof fruits, the effects upon subsequent flowering, and current attemptsto develop mechanical methods of fruit removal. Early experiments withcaustic compounds and growth regulators and their subsequent developmentas commercial practices are discussed, as well as the modes of action ofgrowth regulators. Brief reviews of methods of application, factorsaffecting response, modeling to improve efficiency, and the economicvalue of thinning to the grower are also included.

Review in vitro-induced flowering in bamboos

The majority of bamboos (Graminae) are arborescent and perennial. The erect stems (culms) of woody bamboos are useful for a wide variety of purposes. Most bamboos flower only once at the end of very long vegetative growth phases and die afterwards. Flowering in bamboos is thought to be under genetic control, occurring somewhat like an alarm clock, going off at a preset time. The nature of this genetic clock and any interaction between the ‘internal clock’ and the environment are not yet known. Because of this ‘peculiar’ flowering behavior, bamboo seeds are available only at very long intervals. Obtaining concurrent flowering in two or more species (or varieties) in space and time is difficult, making perennial seed propagation and genetic improvement by breeding nearly impossible. Besides, this peculiar flowering behavior of bamboos is also believed to have brought the giant pandas to the verge of extinction. One of the spectacular developments in the area of bamboo genetic improvement has been the precocious in vitro induction of flowering. By this method it has been possible to rapidly accelerate the reproductive development (within 3–6 mo. versus 30–60 yr in nature). This has opened the possibility of perennial seed propagation and hybridization. In vitro induction of flowering can be obtained by diverse methods which show some similarities and differences. Induction of flowering is possible in cultures derived from both juvenile and mature explants. The proportion of seedlings induced to flower is possibly influenced by genotypic variation, though the role of methods used cannot be ruled out. A cytokinin or a shift in the auxin-cytokinin equilibrium is believed to bring about in vitro induction of flowering. The pH of the media also has an influence. Induction of flowering and rhizogenesis is considered to be an antagonistic phenomenon in vitro. A comparison between in vitro and in vivo flowering in Bambusa arundinacea has shown that though smaller, in vitro-induced florets are comparable to normal florets. There is reduced pollen fertility and some impairment in pollen wall development. Biochemical studies on the in vitro-induced flowering in bamboos have shown (1) selective expression of esterase and peroxidase isozymes during transition of nonembryogenic calluses to embryogenic calluses, somatic embryo development, germination and subsequent flowering of somatic embryo derived shoots, and (2) minimal peroxidase activity before rhizogenesis and induction of flowering in vitro. There are reports of published and comparable methods having failed to induce flowering in vitro.

Effects of nitrogen nutrition on Sandersonia cut flower and tuber production in a soil‐less medium

The effects of five nitrogen (N) application rates—14.2, 28.4, 56.8, 113.6, and 227.2 g N/ m2 (equivalent to 37.5, 75, 150, 300, and 600 ppm of N as a daily liquid feed), on greenhouse cut flower production and outdoor tuber production in Sandersonia aurantiaca (Hook.) were compared in two experiments using a peat:pumice medium. Stem length and weight declined with increasing N rate. Tuber weight declined slightly along with tuber quality with increasing N rate. High N rates resulted in an increased incidence of tuber disorders including secondary tuber formation and tuber rots. Leaf N concentration increased with N rate to a maximum of 56.8 g N/m2, but tuber N continued to increase (from 0.68 to 2.01% dry weight) with increasing N rate. The effects of the N rates on tuber storage and subsequent cut flower production were assessed at two N rates (28.4 and 113.6 g N/m2) in a third experiment. Leaf nutrient concentrations were not affected when tubers were forced at the two N rates in the third experiment nor was vase‐life of stems. This study indicates that sandersonia requires low‐medium amounts of nitrogen and that an N rate of c. 28.4 g/m2 would optimise both tuber quality and stem production for sandersonia grown in a soil‐less medium. Tuber and leaf nutrient concentrations at this N rate could be used for crop cultural guidelines for both flower and tuber production.

Influence of soil mulching on winter chilling of kiwifruit

The influence of soil temperature during winter and early spring on subsequent budbreak and flowering of kiwifruit vines (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson ‘Hayward') was studied at three sites during a 2‐year period. Soil under kiwifruit vines was mulched for 28‐day periods by laying sheets of clear polythene under vines. Mulching in June or July increased soil temperatures at 0.1 m depth by 1–2°C compared to control vines, whereas mulching in August and September elevated soil temperatures by 3–6°C. Increases in soil temperature were directly proportional to the amount of solar radiation incident on the orchard (r 2=0.97). Mulching did not substantially alter the time of budbreak, the amount of budbreak, the rate of shoot growth, the number of flowers per shoot, or the number of flowers per winter bud. However, in one season the proportion of shoots that produced flowers was reduced when vines at the warmest site were mulched during late winter (August), but increased when vines at another warm site were mulched during early spring (September). These data suggest that the performance of kiwifruit vines is not very sensitive to soil temperature.

The effect of temperature on inflorescence initiation and subsequent development in chrysanthemum cv. Snowdon ( Chrysanthemum× morifolium Ramat.)

The relationships between temperature and time to inflorescence initiation and subsequent development in chrysanthemum cv. Snowdon ( Chrysanthemum× morifolium Ramat.) were investigated. From pinching, flowering occurred most rapidly in plants grown at a mean temperature of 20.4°C, whilst those grown at 10.9°C had the lowest leaf number at flowering. The final leaf number, from the pinch to the inflorescence, increased with increasing temperature above 10.9°C. This could be attributed to a marked sigmoidal increase in the rate of leaf initiation with temperature, not delayed initiation. Above 20°C temperature had little effect on the time of floral initiation (plants initiating after 8–9 days), although temperatures below this led to a considerable delay in floral initiation (20.5 days at 9.6°C). Once initiated the inflorescences developed most rapidly at 20.2°C, however, unlike the process of flower initiation, subsequent flower development was delayed by both warmer and cooler temperature regimes.

INTERACTIVE EFFECTS OF POLLINATION AND HEAVY METALS ON RESOURCE ALLOCATION INPOTENTILLA ANSERINAL.

We studied resource allocation between sexual reproduction and clonal propagation in a perennial stoloniferous clonal plant, Potentilla anserina, an obligate outcrosser. We manipulated reproductive effort of Potentilla anserina either by hand-pollinating all flowers or by preventing pollination. To test the effect of resource-limiting conditions on resource allocation and reproductive output, we used a control and two levels of heavy metals (copper and nickel) to limit plant growth. The experiment was conducted as a 2 × 3 factorial design to reveal possible interactions between reproductive manipulation and resource limitation. Heavy metals decreased the total biomass of the plants and number of flowers and ramets produced. Only 50% of the plants grown with the higher level of heavy metals produced flowers. Pollination treatment interacted significantly with the heavy-metal treatment. In the metal control (no metals added) and lower heavy-metal treatment, there were no significant differences in total vegetative biomass between the two pollination treatments. Costs of reproduction in terms of subsequent flowering in the later season appeared to be clear, because the number of flowers per whole plant was lower if the plants were hand-pollinated and because the proportion of flowering ramets decreased due to hand-pollination. However, flowering may also be partly hormonally controlled. In contrast, hand-pollinated plants exposed to high concentrations of heavy metals tended to have greater biomass of vegetative plant structures and higher number of flowers compared to nonpollinated plants. Together, these results suggest that environmental factors may alter costs of reproduction but do not support the idea that these costs are more acute in resource (photosynthate)-limiting conditions.

Timing and Severity of Summer Pruning Affects Flower Initiation and Shoot Regrowth in Sweet Cherry

To examine the effect of timing and severity of summer pruning on flower bud initiation and vegetative growth, 4-year-old `Bing' cherry trees (Prunus avium L.) were pruned at 31, 34, 37, 38, or 45 days after full bloom (DAFB) with heading cuts 20 cm from the base of current-season lateral shoot growth, or at 38 DAFB by heading current-season lateral shoot growth at 15, 20, 25, or 30 cm from the base of the shoot. The influence of heading cut position between nodes also was examined by cutting at a point (≈20 cm from the shoot base) just above or below a node, or in the middle of an internode. Summer pruning influenced the number of both flower buds and lateral shoots subsequently formed on the shoots. All of the timings and pruning lengths significantly increased the number of both flower buds and lateral shoots, but differences between pruning times were not significant. There was significantly less regrowth when shoots were pruned just below a node or in the center of an internode, rather than just above a node, suggesting that the length of the remaining stub may inhibit regrowth somewhat. The coefficient of determination (r2) between flower bud number and regrowth ranged from -0.34 to -0.45. In young high-density sweet cherry plantings, summer pruning may be useful for increasing flower bud formation on current-season shoots. The time of pruning, length of the shoots after pruning, and location of the pruning cut can influence subsequent flower bud formation and vegetative regrowth.

Effect of the Stages of Floral Development and Postharvest Temperatures to Flowering of Eremurus in Israel

The influence of postharvest temperature on the flowering response of Eremurus was studied. The plants were harvested at four different stages of development and were separated into three groups. The first group was immediately exposed to 2 °C, the second group to 20 °C followed by 2 °C, and the third group to 20 °C followed by 32 °C and, subsequently, 2 °C. Scanning electron microscopy (SEM) was used for concurrent morphological analysis of floral development. Application of 2 °C to the plants in the initial stage of floral development caused plant destruction and death, while the same treatment applied at the stage of full differentiation promoted normal flowering. Temperatures of 20 °C and, especially, 32 °C, significantly improved flowering of the plants harvested in the early stages of florogenesis, whereas the same treatment applied to the plants harvested at the end of flower differentiation did not affect the flowering process. A developmental disorder, which we term “Interrupted Floral Development” (IFD), was observed only in the plants harvested when the racemes were fully differentiated. This was probably caused by the very high air and soil temperatures that prevail in Israel during the summer. The extent of floral differentiation has a determinant role in subsequent scape elongation and flowering.

Vegetative plant development and seed production in cool-season perennial grasses

AbstractThe literature suggests that the establishment of seed yield potential in cool-season perennial grasses is based on developmental processes that take place before floral induction. The relationship between vegetative plant development to flowering and seed yield can be influenced by numerous factors, such as genotype, stand age, post-harvest regrowth environment, pests, management practices and juvenility. The objectives of our investigations and survey of literature were to identify characteristics of vegetative plant development present before floral induction (autumn regrowth period) that were related to flowering (yield potential) and seed yield (utilization of seed yield potential). The number of fertile tillers present at anthesis is a function of the number and developmental state (or biological age) of vegetative tillers present prior to floral induction. The number and size of vegetative tillers before induction was correlated with flowering and seed yield in young stands of orchardgrass (Dactylis glomerataL.) and tall fescue (Festuca arundinaceaSchreb.) (r= 0.93 and 0.95 for first-year stands of orchardgrass and tall fescue, respectively), but older stands did not exhibit this relationship. The basal diameter of vegetative tillers in autumn was related to flowering and seed yield in young stands of Kentucky bluegrass (Poa pratensisL.) and creeping red fescue (F. rubraL) As stands aged, basal diameter was not a primary indicator of subsequent flowering and seed yield. Tiller height at the end of the regrowth period was consistently related to flowering and seed yield in Kentucky bluegrass(r= −0.81,P< 0.01) and creeping red fescue (r= −0.87,P< 0.01), regardless of stand age. Increasing the rhizome:root ratio caused reduction of flowering in creeping red fescue. Vegetative characteristics were not related to flowering and seed production in perennial ryegrass (Lolium perenneL.) and dryland bentgrass (Agrostis castellanaBoiss. and Reut.). Green leaf number was a poor indicator of flowering and seed yield potential in all species tested. Ethylene production during autumn vegetative development has been implicated as a potential cause of reduced flowering in creeping red fescue. As much as 92% of the seed yield potential in several cool-season perennial grasses is set before the onset of conditions favouring vernalization of the crop. An increased understanding of developmental gateways in the formation of flowering and seed yield potential may be key to enhancing the economic and environmental sustainability of seed production enterprises.

Mineral nutrition of Zantedeschia plants affects plant survival, tuber yield, and flowering upon replanting

SummaryThe aim was to establish the carry-over effect of mineral nutrition of Zantedeschia (calla) plants on subsequent flowering of harvested, stored and replanted tubers during a second growth period. Factorial combinations of controlled-release N, P and K fertilizers, and dolomite at rates ranging from nil to exceeding those in commercial practice were applied to a bark-based growing medium before planting small, non-flowering tubers. Following harvesting, storage and replanting of the resulting tubers, N, P and K applied the previous growth period were found to affect the number of flowers per tuber fresh weight. Shoot development was most advanced and time to flower was shortened at low N. Most flowers and highest bloom fresh weight yield were obtained at low N. In addition, plant survival during the initial growth period was highest at low N and P, and at intermediate levels of K. The fresh weight of harvested tubers was highest at intermediate levels of N. Leaf N, P, Ca and Mg concentrations were affected by nutrient treatments. The significance of mineral nutrition for the three key factors of plant survival, tuber yield and subsequent flowering in the production of high quality calla tubers is demonstrated.