Bud Appearance Research Articles

CACTUS PHYSIOLOGICAL ECOLOGY, EMPHASIZING GAS EXCHANGE OF PLATYOPUNTIA FRUITS

Net CO2 uptake and transpiration help characterize how plants and their organs respond to the environment. To interpret environmental responses of fruits of platyopuntias, comparisons with the gas exchange and water potentials of the underlying cladodes are also important. Fruits of Opuntia ficus-indica have substantial amounts of chlorophyll, photosynthetic enzymes, nocturnal stomatal opening, and net CO2 uptake. The higher water potential of the fruits for six species of platyopuntias implies that water moves from the underlying cladodes to the fruits via the phloem, not the more expected pathway of the xylem. The phloem delivers a dilute solution supplying most of the photosynthate required for fruit growth (90% midway in the period between floral bud appearance and fruit maturation) and all of the water required. The net CO2 uptake ability of fruits of O. ficus-indica decreases 10-fold from anthesis to fruit maturation 75 days later. To understand why the total daily net CO2 uptake by fruits of this species varies and what happens to soluble sugars and polymers during the final stage of fruit ripening requires further research.

Endogenous gibberellins and their effects on flowering and stem elongation in cabbage (Brassica oleracea var. capitata)

SummaryEndogenous gibberellins were extracted from cabbage shoots and were analysed using gas chromatography and mass spectrometry. Nine gibberellins (GA1, GA19, GA20, GA44, GA12, GA4, GA15, GA24 and GA25) were identified. Two gibberellin biosynthesis pathways were suggested, an early-13-hydroxlyated pathway and a non-13-hydroxylated pathway, to operate in cabbage shoots. GA1, GA4 and prohexadione calcium, a gibberellin biosynthesis inhibitor, were applied to the shoot tip of cabbage ‘Sousyu’ and ‘Kinkei No.201’ with or without cold treatment. Without cold treatment, stem elongation was increased by gibberellins and was suppressed by prohexadione calcium in both cultivars. But prohexadione calcium treatment, followed by gibberellin, promoted stem elongation more than gibberellin alone. Flowering was not induced by gibberellin or prohexadione calcium without cold treatment. When gibberellin and prohexadione calcium were applied during a cold treatment, stem elongation after the cold treatment was increased by gibberellins and was suppressed by prohexadione calcium in both cultivars. Flower bud appearance was promoted by GA1 and GA4 in ‘Sousyu’, but in ‘Kinkei No. 201’ only GA4 was markedly effective. Inhibition of stem elongation and delay of flower bud appearance by prohexadione calcium were overcome by applying GA1 or GA4. Neither gibberellin nor prohexadione calcium treatment changed the number of leaf nodes at anthesis. These results indicated that stem elongation and flower bud development are regulated by gibberellins, but gibberellins might have little effect on flower induction.

Cultivation of cut flower and bulb species with saline water

The long-term effect of saline water irrigation on flower yield and quality was investigated in three herbaceous cut flower crops of commercial importance, the Emily cultivars of Japanese limonium, Trachelium caeruleum and Eustoma grandiflorum (lisianthus), and in two bulb species, Hippeastrum hybridum and Ornithogalum arabicum. Among the tested crops, limonium showed the highest resistance to salinity. Irrigation water with an electrical conductivity of up to 11.5 dS m −1 had little or no effect on stem yield and length of limonium flowering stems. In Trachelium, salinity had no effect on the yield of flowering stems or the size of the inflorescence, but it markedly reduced stem weight and length. The concomitant reduction in the number of nodes to flowering was reflected in earlier flower initiation. Since delayed flower differentiation and over-elongation of Trachelium stems is a serious problem during the winter months, application of mildly saline irrigation for winter production could be used to induce earlier flower initiation and to control stem height. In lisianthus subjected to salinity from bud appearance onwards, a salinity level of 6.0 dS m −1 increased stem weight and the number of flowers per stem without affecting other quality parameters. The work carried out with Trachelium and lisianthus, although limited, indicates that salinity may be used for improving the quality of some cut flowers. In contrast to its beneficial effect on the herbaceous species, salinity led to a significant reduction of bulb, leaf, and root weight of the two bulbous species, H. hybridum and O. arabicum.

Morfologia floral e biologia reprodutiva de genótipos de aceroleira

Estudos sobre morfologia floral e biologia reprodutiva de uma cultura contribuem para o desenvolvimento de técnicas de castração e polinização. Com este propósito, estudaram-se a estrutura e a biologia floral em cinco genótipos de aceroleira (Malpighia emarginata), em Jaboticabal, SP; no período de dezembro/97 a janeiro/99. Foi avaliada a morfologia floral, por caracterização e quantificação, e a biologia reprodutiva, desde o aparecimento dos primórdios do botão floral até a abertura. As flores da aceroleira são monóclinas, com cálice composto por seis a sete sépalas, corola de cinco pétalas, nove a dez glândulas presentes na base, androceu com dez estames e gineceu com três a quatro pistilos e distribuem-se em cimeiras axilares com 3 a 13 flores nos ramos do ano anterior e do mesmo ano. Verificaram-se de 6 a 7 floradas por ano, principalmente de janeiro a maio e de agosto a dezembro, registrando-se que desde o aparecimento do botão floral à antese decorrem 6,9 a 7 dias, com abertura floral entre 5h00 e 8h00 e das 14h00 às 16h00, com floração de 22,1 a 29,4 dias, decorrendo do florescimento à maturação do fruto 22 dias e duração da colheita de 19,7 a 28,8 dias.

Carbon and water balances for young fruits of platyopuntias

Questions relating to transpired versus retained water for fruits, the xylem versus the phloem as water supplier to the fruits, and the importance of fruit photosynthesis for fruit dry mass gain were examined in the field for 6 species of platyopuntias (Nopalea cochenillifera, Opuntia ficus‐indica, O. megacantha, O. robusta, O. streptacantha and O. undulata), cacti with flattened stem segments (cladodes). For plants with fruits midway between floral bud appearance and fruit maturation, transpiration was greater at night for the cladodes, as expected for Crassulacean acid metabolism (CAM) plants, but greater during the daytime for the fruits of all 6 species. Nevertheless, net CO2 uptake by fruits of these platyopuntias occurred predominantly at night, as expected for CAM plants. The water potential of the young fruits (average of −0.41 MPa) was higher than that of the cladodes (average of −0.60 MPa), indicating that water entered the fruits via the phloem rather than via the xylem. Solution entry into the fruits via the phloem supplied the water lost by transpiration and allowed for increases in fruit fresh mass (daily transpiration averaged 3.2‐fold higher than daily water content increases), while the accumulating solutes were apparently polymerized to account for the higher water potentials of the fruits compared with the cladodes. The phloem thus acts as the sole supplier of water and the main supplier of dry mass (90%) to such young fruits of platyopuntias.

198 Daylength and Temperature Affect Rate of Flowering in Primula obconica

Primula obconica (`Libre Light Salmon') was grown from transplant at 16 or 20 °C in combination with 8- or 16-h daylength. Irradiance was adjusted to 10 mol/'m2 per day. Germination took place at 20 °C and seedlings were transplanted into 10-cm (800-mL) containers. Growing conditions until treatment 58 days from seeding were 20 °C and 16-h daylength. Rate of flower bud formation was independent of photoperiod at 16 °C requiring 88-93 days from seeding. A similar rate was observed at 20 °C and 16-h daylength. However, short days (SD) delayed flower bud appearance with 10-15 d at 20 °C. Open flowers were first recorded 110 days from seeding at 20 °C and long days (LD). At 16 °C, 12 more days were required for flower development at LD and 22 days at SD. Open flowers did not develop by termination 145 days from seeding at SD and 20 °C. Treatments within each temperature were included where plants were moved weekly to the alternate photoperiod and allowed to flower. There was no significant difference in flower bud appearance among plants exposed to 16 °C or LD at 20 °C. Flower bud formation progressively slowed at increasing duration beyond 4 weeks of SD and 20 °C. Any duration of LD at 20 °C resulted in similar flowering time while more than 1 week at SD slowed or prevented flower appearance. At 16 °C, more than 6 weeks of exposure to SD delayed, while LD hastened flowering.

569 Photoselective Filters Affect Flowering and Stem Extension In Viola ×wittrockiana and Pisum sativum

For many plants, light quality has a pronounced effect on plant morphology; light with a low red (R, 600 to 700 nm) to far-red (FR, 700 to 800 nm) ratio promotes stem elongation and a high R: FR, or blue light (B, 400 to 500 nm), suppresses it. In addition, FR light is required for rapid flowering in some species, particularly for long-day plants. Our objective was to quantify how flexible spectral filters, which selectively reduce FR, B, or R, influence plant height and flowering of the quantitative long-day plants Pisum sativum L. `Utrillo' and Viola ×wittrockiana Gams. `Crystal Bowl Yellow'. Plants were grown at 20 °C with reduced FR, B, or R environments or with a neutral density control (C) filter. Calculated phytochrome photoequilebria were 0.78, 0.73, 0.71, or 0.46 for the altered FR, B, C, or R environments, respectively. All filter treatments transmitted a similar photosynthetic photon flux. Sixteen-hour photoperiods were created with natural daylight supplemented with high-pressure sodium lamps positioned above filters. Viola grown under the FR filter never reached 100% flowering within 8 weeks, and visible bud appearance was delayed by at least 17 days compared to all other filters. The R and B filters enhanced peduncle length by at least 25% compared to the C or FR filters. In Pisum, average internode length was 2.2, 2.9, 3.4, and 3.7 cm under the FR, C, B, and R filters, respectively, all statistically different. Fresh and dry shoot weights were similar under the C and FR filters but were at least 35% greater under the B filter and 35% lower under the R filter.

Spectral Filters Affect Growth, Flowering, and Postharvest Quality of Easter Lilies

The role of light quality on growth, flowering, and postharvest characteristics of `Nellie White' Easter lilies (Lilium longiflorum Thunb.) was evaluated in two growing seasons using 4% CuSO4 and water (control) as spectral filters. The CuSO4 filter significantly reduced plant height and internode length. However, the height reduction was smaller in the 1994-95 season (9%) than in the 1995-96 growing season (32%). The number of days to flower bud appearance and flower opening, and the number and diameter of flowers were not significantly affected by the spectral filters in either season. The CuSO4 filters reduced flower longevity by 3 days in nonstored plants, and by 5 days when plants were subjected to 1 week storage at 4 °C prior to placing in the postharvest room. Results suggest that spectral filters are effective in controlling height and producing compact Easter lily plants without causing a delay in flowering or reducing number of flowers per plant but flower longevity can be adversely affected.

Spectral Filters Affect Growth, Flowering, and Postharvest Quality of Easter Lilies

The role of light quality on growth, flowering, and postharvest characteristics of `Nellie White' Easter lilies (Lilium longiflorum Thunb.) was evaluated in two growing seasons using 4% CuSO4 and water (control) as spectral filters. The CuSO4 filter significantly reduced plant height and internode length. However, the height reduction was smaller in the 1994-95 season (9%) than in the 1995-96 growing season (32%). The number of days to flower bud appearance and flower opening, and the number and diameter of flowers were not significantly affected by the spectral filters in either season. The CuSO4 filters reduced flower longevity by 3 days in nonstored plants, and by 5 days when plants were subjected to 1 week storage at 4 °C prior to placing in the postharvest room. Results suggest that spectral filters are effective in controlling height and producing compact Easter lily plants without causing a delay in flowering or reducing number of flowers per plant but flower longevity can be adversely affected.

Spectral Filters Affect Growth, Flowering, and Postharvest Quality of Easter Lilies

The role of light quality on growth, flowering, and postharvest characteristics of `Nellie White' Easter lilies (Lilium longiflorum Thunb.) was evaluated in two growing seasons using 4% CuSO4 and water (control) as spectral filters. The CuSO4 filter significantly reduced plant height and internode length. However, the height reduction was smaller in the 1994—95 season (9%) than in the 1995—96 growing season (32%). The number of days to flower bud appearance and flower opening, and the number and diameter of flowers were not significantly affected by the spectral filters in either season. The CuSO4 filters reduced flower longevity by 3 days in nonstored plants, and by 5 days when plants were subjected to 1 week storage at 4 °C prior to placing in the postharvest room. Results suggest that spectral filters are effective in controlling height and producing compact Easter lily plants without causing a delay in flowering or reducing number of flowers per plant but flower longevity can be adversely affected.

Cyclamen Leaf Unfolding Rate in Response to Temperature

Nine-week-old plants of Cyclamen persicum `Miracle Salmon' were transplanted into 10-cm pots and placed in growth chambers at 8, 12, 16, 20, or 24 °C. The irradiance was 10 mol/day per m2 during a 16-h day length. After 8 weeks, the temperature was changed to 16 °C for all plants. Expanded leaves (1 cm or larger) were counted at weekly intervals for each plant. The rate of leaf unfolding increased with temperature to 20 °C. The fastest rate at 20 °C was 0.34 ± 0.05 leaf/day. Flower buds were visible 55 ± 7 days from start of temperature treatments (118 days from seeding) for the plants grown at 12, 16, or 20 °C. Flower buds appeared 60 ± 6.9 days from initiation of treatments for plants grown at 24 °C and 93 ± 8.9 days for cyclamens grown at 8 °C. Although there was no significant difference in rate of flower bud appearance for cyclamens grown at 12, 16, or 20 °C, the number of leaves, flowers, and flower buds varied significantly among all temperature treatments. Leaf number at flowering increased from 38 ± 4.7 for plants at 12 °C to 77 ± 8.3 at 24 °C. Flowers and flower buds increased from 18 ± 2.9 to 52 ± 11.0 as temperature increased from 12 to 24 °C. Plants grown at 8 °C had on average 6 ± 2 visible flower buds, but no open flowers at termination of the study (128 days from start of treatments).

The Influence of Fruit and Bud Volumes on Eucalypt Flowering—An Exploratory Analysis

The appearance of buds and development of fruits in 51 species of Eucalyptus L’Hér. were examined to determine whether bud and fruit volume had an influence on flowering. These variables exert an influence on eucalypt flowering as individuals and as members within an umbel. Flowering earlier in the growing season is characteristic of species with large, individual bud and fruit volume and those that have a large umbel volume. The number of buds and fruits in an umbel is influenced by volume of the individuals. Development time of buds was longer in umbels which had a larger total volume. Bud and fruit umbel volume was positively correlated with the timing of bud appearance as was seed maturity with individual fruit and fruit umbel volume. A threshold of bud and fruit volume was indicated below which seed maturity and time of flowering is not reflected by volume. Discriminant analysis used nine predictors to assign 80% (overall) of section members of Adnataria (91%), Bisectaria (60%), Maidenaria (67%) and Renantheria (87%) to their true groups. Across groups examination adduced the possibility of each group having a distinct bud development period and a discernible cessation of flowering. Five clusters were revealed whose members were significantly differentiated on seed maturity, section, individual fruit volumes, bud and fruit umbel volumes. Factor analysis outlined four factors—buds, fruits, timing and development—which accounted for 78.9% of the variance.

Topophysis affects the Potential of Axillary Bud Growth, Fresh Biomass Accumulation and Specific Fresh Weight in Single-stem Roses ( Rosa hybridaL.)

Topophysis, the effect on growth and differentiation of position of axillary buds along the shoot, was studied by propagating five-leaflet-leaf single-node cuttings which were excised from seven stem positions and grown as single stemmed plants. In Rosa hybrida‘Korokis’ Kiss®, ‘Tanettahn’ Manhattan Blue®, and ‘Sweet Promise’ Sonia®, following release of the buds from apical dominance by excision, morphogenetic development was studied until anthesis. The time from excision/planting until onset of bud growth, visible flower bud appearance, and anthesis was generally shorter in plants originating from apical bud positions than from basipetal positions. Topophysis mainly affected the onset of axillary bud growth; the earliest growth and development was found in cuttings from the second uppermost node position. This node tended to have the lowest plastochron value, which indicated the existence of a transition between sylleptic and proleptic buds. Stem length at visible flower bud and at anthesis generally increased as the cutting position changed basipetally until the second lowest position, and the number of five-leaflet-leaves at anthesis and the total number of nodes generally increased basipetally. For internode length, growth rate, and fresh biomass efficiency the cuttings taken from the uppermost and lowermost positions generally had significantly lower values than cuttings from all medial positions. At anthesis, plants originating from cuttings excised from lower medial positions generally had a higher fresh weight, greater flower stem diameter, and a significantly higher specific fresh weight than those plants originating from apical or basal positions. Among the cultivars, Sonia was the most efficient in increasing fresh biomass and had the highest growth rate, whereas Manhattan Blue possessed the highest specific fresh weight, indicating a higher plant quality. It is suggested that topophysis in Rosais an independent phenomenon intrinsic to the axillary bud.

Control of Leaf Senescence of Easter Lily using Plant Spacing and Early Applications of Promalin

Easter lilies (Lilium longiflorum Thunb. `Nellie White') were placed at three spacings of about 11, 22, or 44 plants per square meter (plants/m2). Above canopy light intensities, measured weekly at noon, ranged from 107.3 to 704.5 μmol·s–1·m–2 and were not significantly different among spacings. Mid canopy light intensities ranged from 16.5 to 229.0, 43.0 to 458.5, and 77.5 to 535.3 μmol·s–1·m–2 at spacings of 44, 22 and 11 plants/m2, respectively. On February 5, 1996, three plants from the 22 plants/m2 spacing were sprayed with a solution of 0.5 ml·L–1 of 1.8% (a.i.) of each of N-(phenylmethyl)-IH-purine-6-amine and gibberellins A4A7; and on March 5, three additional plants from each spacing were similarly sprayed. Beginning 5 Mar., weekly counts were made of yellow and brown leaves on all treated and control plants. Average per plant numbers of brown leaves increased on control plants at all spacings but increased on treated plants only at the 11 plants/m2 spacing. On 25 Mar., control plants averaged 15.6, 12.1, and 15.3 brown leaves per plant at spacings of 11, 22, and 44 plants/m2, respectively, while plants treated on March 5 averaged 10.7, 9.0, and 10.7 brown leaves. Plants treated on 5 Feb. averaged 3.5 brown leaves per plant and had an average mid leaf length of 13.8 cm compared to about 10.5 cm for all other plants. Spacing had no effect on average yellow or brown leaves per plant. This study demonstrated that early applications of Promalin can reduce leaf senescence which may occur during forcing time before bud appearance to opening of first bud. Some leaf enlargement may occur on plants treated very early.

Effects of Habitat, Plant Size, and Floral Display on Male and Female Reproductive Success of the Neotropical Orchid Brassavola nodosa

We examined correlatively the joint effects of light, supporting plant characteristics, plant size, and floral display on pollinia removal and fruit production of 103 individuals of the orchid Brassavola nodosa (L.) Lindl. at Peter Douglas Cay, Belize, Central America. This orchid is epiphytic on red mangroves (Rhizophora mangle L. [Rhizophoraceael), and grows from 1-300 cm above ground. Light levels above each orchid, measured as direct site factor using hemispherical canopy photography, were 6-46 percent of potential direct sunlight. To characterize plant size, we counted the number of leaves of each plant and measured its longest leaf and the leaf subtending each inflorescence. The largest orchids were found in areas of high light availability, high above ground, and on large support structures. From June through early August 1993, and again in December 1993, orchids were surveyed every 3-4 days for reproductive status and success (removal of pollinia and/or fruit production). The 48 plants that flowered during these 7 months had more and longer leaves than the 55 plants that did not flower at any time in this time period. Plants flowered continuously throughout the summer; a complete reproductive cycle (bud appearance to fruit set) lasts 2-5 weeks. Pollinia were removed from 12 percent, and fruits were set by 30 percent, of the flowers produced in the summer. Because fruit set was much lower in the fall, the total proportion of fruit production relative to flower production over the 7-month study period was only 13 percent. Path analysis indicated that direct site factor, height above ground, and diameter of supporting structures significantly contributed to plant size and floral display area. In turn, floral display significantly affected both male and female reproductive success. We condude that resources limit flower production and components of floral display, whereas pollinator availability likely limits reproductive success in Brassavola nodosa.

Effects of waterlogging at different growth stages on physiological characteristics and seed yield of winter rape ( Brassica napus L.)

A study on physiological and yield effects of waterlogging of rape plants at different stages of growth was conducted in specially designed experimental tanks. Waterlogging at seedling and floral bud appearance stages significantly decreased leaf chlorophyll content, superoxide dismutase and catalase activities, the accumulation of leaf malondialdehyde and ethylene production, and leaf photosynthetic rate and root oxidizability. The experiment confirmed that the physiological function of rape plants was retarded during the time of waterlogging, and its adverse effect remained afterwards. Also, plant height, stem width and the number of primary branches per plant were significantly decreased by waterlogging at seedling and floral bud appearance stages. Pods per plant and seeds per pod were also significantly reduced, giving 21.3% and 12.5% decrease of seed yield from the control for treatments at the seedling and floral bud appearance stages, respectively. No significant difference in yield components and seed yield was observed between the control and treatments applied at flowering and pod formation stages. The paper also analyses the relationships between the physiological reactions of waterlogging, morphological characteristics, and yield components and discusses ways to alleviate waterlogging damage in plants.

Effects of Photoperiod on Reproductive Development in Velvetleaf (Abutilon theophrasti)

When velvetleaf plants from Mississippi and Minnesota populations were maintained in growth chambers with day/night temperatures of 29/23 C and photoperiods of 11, 12, 13, 14, and 15 h, flower buds and open flowers appeared first in the 12 h photoperiod. Buds and flowers appeared 2 to 4 d later at photoperiods of 11, 13, or 14 h. Increasing the photoperiod beyond 14 h to 15 h delayed bud appearance an additional 7 d in the MN plants and 12 d in the MS plants. Open flowers appeared four to five nodes higher, 10 d later at 15 than at 14 h in the MN plants and 20 d later in the MS plants. Vegetative shoot weight and fruit weight 73 d after emergence were greater in 13 h or longer photoperiods than at 11 or 12 h. In shorter photoperiods, MN plants produced more vegetative growth than MS plants, but the reverse occurred at longer photoperiods where MS plants were taller than MN plants. These growth differences occurred because earlier shifts in allocation to reproductive growth in MN plants limited their vegetative growth, particularly in the longest photoperiods. Differences in rate of reproductive development between populations were not evident until photoperiod exceeded 13 h. Reciprocal transfer of plants of the MS population between short and long photoperiods revealed the durations of the juvenile (pre-inductive), inductive, and post-inductive phases to be 3 to 5, 7 to 8 (short day) or 30 (long day), and 10 to 11 d, respectively. Differences in competitive ability among latitudinal biotypes of photoperiodically-sensitive weeds may depend on time of emergence in the field and consequent photoperiod exposure. Weed growth simulation models to be used in development of expert systems for weed management should take photoperiodic sensitivity into account.

ENVIRONMENTAL FACTORS AFFECTING FLOWERING AND FRUIT DEVELOPMENT OF OPUNTIA FICUS-INDICA CUTTINGS DURING THE THREE WEEKS BEFORE PLANTING

Opuntia ficus-indica(prickly pear) is a widespread desert perennial cactus shrub. The plants produce either lateral branches or flowers from the axillary meristems, depending on maternal and environmental influences.The flower buds develop from the axillary meristems mainly at the margin of the apical part of the terminal flat branch segments. Flower bud meristems start to be active and secrete mucus in January. The red-bracted flower buds start to appear in March/April, flowers open in May/June, and fruit matures in June/August.This study focused on the appearance of flower buds, flowers, and fruits after induction ofO. ficus-indicaone-segment branch cuttings by environmental factors during the 3-week healing period after cutting and before planting. The influence of treatments such as temperature, light intensity, and day length on flower bud appearance and fruit development is described.

Flower Morphogenesis in Rosa hybrida 'Mercedes' as Studied by Cryo-scanning Electron and Light Microscopy. Effects on Light and Shoot Position on a Branch

Flower bud development in Rosa hybrida cv. 'Mercedes' was studied in shoots grown at different irradiances and sprouting from axillary buds at different branch positions. Cryo-scanning electron microscopy and light microscopy were used to visualize, characterize and determine flower morphogenesis during early shoot development. Up to the moment of visible flower bud appearance on the plant, flower morphogenesis was divided into nine stages. This classification was based on external and internal characteristics of the primordium. All shoots of the rose 'Mercedes' whether positioned uppermost or second on a branch and whether grown at 300 or 150 μmol m-2 s-1 PAR (12 h d-1) developed equally up to flower stage 7, i.e. the stage just before visible initiation of stamen and pistils. Signs of flower bud abortion were the compactness of the flower bud at developmental stage 7 (height/width < 1·5) and the sprouting of axillary buds positioned just below the flower bud primordium. It was concluded that once a flower bud has reached a height to width ratio larger than 1·5, and once stamen and pistil developmental has started, it has passed the critical developmental stage in which abortion may occur. Flower developmental stage was closely related to shoot length. This relationship was not affected by irradiance level nor by shoot position on a branch. Therefore, cultivation treatments aimed to improve flower production by reducing flower abortion, such as supplementary lighting, will be most effective when applied during the first 2 weeks of shoot growth in which the flower develops up to stage 7.

Influence of water stress on photosynthesis, transpiration, water-use efficiency and yield of Brassica juncea L.

Abstract Indian mustard ( Brassica juncea L. cv. Parkash) grown in large containers was subjected to six watering treatments: (i) no watering after crop establishment; (ii) dry up to floral bud appearance and irrigated thereafter; (iii) dry up to full bloom and irrigated thereafter; (iv) early irrigation, dry during flowering period and irrigated during pod formation; (v) irrigated up to flowering and dry afterwards; (vi) irrigated control. Several plant processes were measured diurnally and seasonally on many clear days. Diurnally, canopy photosynthetic rate (P N ) followed photon flux density (PAR), and transpiration (T) followed air temperature ( T a ). At higher PAR, P N in dry treatments was greater during the first than the second half of the day. Photosynthesis attained compensation point at −4.0 MPa leaf water potential ( Ψ 1 ). Similarly, T during the first half of the day was greater than in the second half of the day at similar T a . Water-use efficiency (WUE) was quite low at high PAR during the second half of the day. Photosynthesis and WUE peaks were observed during the full bloom period while T gradually increased towards maturity. Seed yield was primarily reduced by water stress because of decrease in number of pods per plant and number of seeds per pod. The number of pods per plant and number of seeds per pod were linearly related to seed yield, and cumulative Ψ 1 and P N related to both seed yield and total biomass.