Low temperature exotherms of winter buds of hardy conifers

Differential thermal analysis (DTA) of winter buds and the excisedprimordial shoots of sub-alpine or sub-cold firs revealed thatthese buds had all low temperature exotherms around –30?C.However, no low temperature exotherm below –15?C was detectedin the spring buds. In the winter bud of Abies firma, a temperatefir native to Japan, a low temperature exotherm was detectedaround –20?C, which is higher by 10?C than that of sub-alpineor sub-cold firs. The low temperature exotherms of these firsoccurred at nearly the same temperatures that result in thedeath of these primordial shoots. On the other hand, littleor no low temperature exotherm was detected in the winter budsof sub-cold spruces. In larch winter buds, numerous small exothermswere observed, which are probably due to the many leaf primordiain the buds. Unlike many temperate deciduous broad-leaved trees,no low temperature exotherm was detected below –15?C inwinter twig xylem of conifers such as Abies, Picea, Pinus, Larixand Pseudotsuga. Thus, very hardy coniferous twigs can tolerateextracellular freezing to –70?C. ¹ Contribution No. 1907 from the Institute of Low TemperatureScience. (Received June 8, 1978; )     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18°C). With a temperatureregime of 35°C day, 25°C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35°C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acidinvertase, heat stress, reproductive organs, sink leaves. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves.     

Effect of Heat Stress on Assimilate Partitioning in Tomato

Differences in assimilate partitioning in response to heat stresswere observed between the heat-sensitive tomato cultivar, RomaVF and the heat-tolerant cultivar, Saladette. Transport of carbonto the trusses and apex was inhibited in both cultivars, particularlyin Roma VF. Basipetal transport to the roots was inhibited inRoma VF only. Assimilate partitioning within the young trusswas also affected by heat stress in both cultivars, but wasmore pronounced in Roma VF: at higher temperatures more ¹⁴Cwas found in the peduncle and in the older flower buds thanin the younger flower buds. The youngest flower buds were moresensitive than other parts of the truss to heat stress. Theuptake of [¹⁴C]sucrose by detached flower buds from agar mediumwas lower at higher temperatures. Alteration of assimilate partitioningwas also observed following the application of GA₃+Kinetin tothe first truss. The possible relationship between flower-setin tomato and carbohydrate stress is discussed. Lyeopersicon esculentum Mill., carbon translocation, starch     

Effect of Heat Stress on Assimilate Metabolism in Tomato Flower Buds

Assimilate import by flower buds in two cultivars of tomato(Lycopersicon esculentum Mill.) was inhibited by heat stress.With increasing temperature, levels of sucrose in the sourceorgan increased while levels of starch decreased. The transportof radioactive carbon was correlated with the starch contentof the flower buds. In Saladette, a heat-tolerant cultivar,conversion of the imported carbon to starch occurred to a greaterextent than in Roma VF, a heat-sensitive cultivar. Uptake ofsucrose from agar medium by detached flower buds was negativelycorrelated with their internal ratio of sucrose to hexoses.Glucose uptake from agar medium by detached flower buds decreasedwith increasing temperatures. Sucrose hydrolysis was negativelyaffected by high temperatures, and this was more pronouncedin the heat-sensitive than in the heat-tolerant cultivar. Theeffect of heat stress on assimilate translocation from the leavesto the sink organ is discussed. Lycopersicon esculentum Mill., starch, sucrose, heat stress     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18 °C). With a temperatureregime of 35 °C day, 25 °C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35 °C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves     

Freezing avoidance mechanism of primordial shoots of conifer buds

Excised winter buds of very hardy fir supercooled to —30or — 35?C, though primordial shoots excised from thesewinter buds (freezing point: about —5.5?C) supercooledonly to —12 to — 14?C. Also, excised primordialshoots did not tolerate freezing, but were rather resistantto desiccation. Differential thermal analysis (DTA) of primordialshoots revealed that the capability of supercooling increasedwith decreasing water content and that no exotherm could bedetected in the primordial shoots with a water content belowabout 20%. When excised whole buds were cooled very slowly,the exotherm temperature shifted markedly to a lower value andthe exotherm became much smaller. Also, masses of needle icewere observed, mainly beneath the crown of the primordial shoot.From these results, it may be concluded that most of the waterin primordial shoots gradually migrates out through the crownand freezes as the temperature decreases (extraorgan freezing),which enables primordial shoots to survive at very low temperatures.Winter buds of Abies balsamea held at — 20?C for 30 daysand then slowly cooled down to —50 or —60?C remainedalive. Thus, there seems to be no low temperature limit to thisfrost avoidance mechanism, if the primordial shoots can resistintensive freeze-dehydration. Low temperature exotherms wereobserved in all genera which belong to Abietoideae and Laricoideaeof Pinaceae, all of which have a crown in the primordial shoots,but not in other conifers. ¹ Contribution No. 2037 from the Institute of Low TemperatureScience. (Received June 25, 1979; )     

Biosynthesis of Volatiles in Brown Boronia Flowers after Harvest: Effect of Harvest Time and Incubation Conditions

Brown boronia flowers (Boronia megastigma)were incubated at25 °C after harvest, increasing the concentration of a solventextracted product by up to 25% (d. wt basis) and floral volatilesby up to 300% (d. wt). Open flowers produced more volatilesduring post-harvest incubation than flower buds, whole flowersproduced more than flowers treated to simulate harvester damage,and fresh flowers produced more than frozen and thawed flowers.Flowers incubated in bags purged with air produced more extractand volatiles than those purged with nitrogen gas; ß-iononewas particularly depleted in nitrogen-purged flowers. Flowersand buds from three successive harvests (68, 82 and 90% openflowers) were incubated at several temperatures for up to 24h. The greatest increase in the concentration of floral extractoccurred in flowers harvested when 90% were open and incubatedfor 4 h at 12 °C, or 14 h at 23 °C. The largest increasein total volatiles occurred in material harvested at 82% openflowers and incubated for 25 h at 12 °C, or 13 h at 23 °C.The concentration of extract and volatiles declined after prolongedpost-harvest incubations. Brown boronia flowers produce volatilesand other components of the floral extract after harvest whenflowers with mature, intact enzyme systems are well suppliedwith oxygen, at temperatures at or below 25 °C. As flowersbecome visibly senescent, their ability to produce volatilesafter harvest declines.Copyright 1998 Annals of Botany Company Boronia megastigma(Nees); brown boronia; essential oils; floral volatiles; ß-ionone; phenology; post-harvest storage.     

Cold Hardiness and Acclimation Intensity in Flower Buds for Fall Bloom and Spring Bloom Clones in Rhododendron kiusianum, a Dwarf Evergreen Azalea

The relationship between the degree of cold hardiness (supercoolingability of florets) and the acclimation intensity in flowerbuds was investigated in the fall bloom and the spring bloom(typical) clones of Rhododendron kiusianum, a hardy dwarf evergreenazalea. Supercooling ability or exotherm temperature distribution(ETD) in florets was determined by differential thermal analysis(DTA) and the intensity of bud acclimation or the rate of deacclimationwas judged by the changes in ETD profiles resulting from thedehardening temperature treatment. Although the two clone typesshowed no significant differences in ETDs and water contentsin florets, they differed in their rates of bud deacclimation.The flower buds of fall bloom clones generally tend to deacclimatemore quickly than the spring bloom ones throughout the seasons.It is concluded that the degree of cold hardiness in flowerbuds of R. kiusianum does not differ between the fall bloomand spring bloom clones but the intensity of bud acclimationdoes; acclimation intensity is higher in the spring bloom clonesand the rate of deacclimation is greater in the fall bloom ones. (Received October 14, 1985; Accepted February 5, 1986)     

The Effect of Fruit Load, Defoliation and Night Temperature on the Morphology of Pepper Flowers and on Fruit Shape

The shape and regularity of bell pepper (Capsicum annuumL.)fruit are known to be determined at a very early stage of flowerdevelopment. Small, flattened fruit which are commonly parthenocarpicdevelop under low-temperatures (below 16 °C) from flowerswith enlarged ovaries. In such flowers self-pollination is notefficient because of the large distance between the stigma andstamens. Flower deformation of this kind is common during thewinter season. In the present study it was found that deformationsof flowers, similar to those found under low temperatures, wereinduced in 15 d by complete removal of fruit from plants growingunder night-time temperatures of 18 °C. Only flowers whichwere at the pre-anthesis stage at the time of fruit removalwere deformed by this treatment. Removal of leaves from thelower part of the plant (source leaves) partially reduced theeffect of fruit removal on the shape of the flowers and on subsequentfruit morphology. Fruit removal induced significant increasesin the concentrations of starch and reducing sugars, but notsucrose, in the flower buds. Likewise, flower buds of plantswhich grew under a night-time temperature of 12 °C containedmore carbohydrate than those which grew at 18 °C. Theseresults suggest that flower morphology in pepper is at leastpartly controlled by source-sink relationships. Assimilateswhich are normally transferred to developing fruit may be transported,upon fruit removal, to the flower buds which subsequently swell.A similar increase in assimilate translocation to flower budsmay occur under low temperatures, subsequently causing deformationof fruit.Copyright 1999 Annals of Botany Company Pepper, (Capsicum annuumL), flower shape, low temperatures, source-sink relationship, fruit shape, seeds, reducing sugars, sucrose, starch.     

Freezing Avoidance Mechanisms by Supercooling in Some Rhododendron flower Buds with Reference to Water Relations

Excised florets of some hardy Rhododendron species did not toleratefreezing at –5°C when ice-inoculated due to intracellularfreezing. Florets in intact December buds, however, could besupercooled to about –30°C. When flower buds of R.japonicum were slowly cooled with daily decrements of 5°Cto temperatures ranging from 0 to –20°C, the exothermtemperatures of the florets drastically decreased. This wasaccompanied by a decrease in water content of florets and peduncleand an increase in that of scales. The water in florets andthe peduncle is thought to migrate to scales and other tissuesduring the early stages of freezing; the dehydrated floret hasa lower freezing point which enhances its supercooling abilityand the dehydrated peduncle helps to maintain the supercooledstate of the florets. This hypothesis would explain the dependenceon the cooling rate of supercooling in Rhododendron flower buds.Water migration within flower buds was observed in other hardyRhododendron species with some variation in ice formation siteand the quantity of migrated water. The exotherm temperatureof excised florets was inversely proportional to their watercontent. Dehydration of flower buds by wind at 0°C alsoenhanced their supercooling ability. Mechanisms of freezingavoidance by supercooling in Rhododendron flower buds and therelationship of supercooling to freezing tolerance are discussed. ¹ Contribution No. 2254 from the Institute of Low TemperatureScience ² This is a revised form of the master's thesis of the seniorauthor (M.I.) which is cited in the present and previous papers(Sakai 1979a, b, etc.). (Received August 11, 1980; Accepted June 1, 1981)     

Freezing Events within Overwintering Buds of Blackcurrant (Ribes nigrum L.)

Overwintering buds of blackcurrant cultivars 'Ben Lomond' and'Ben More' were examined by differential thermal analysis (DTA).Photographic evidence relates the first (primary) exotherm tothe freezing of water in the basal pith and bud scales. Thenumber of secondary exotherms either matched, or was fewer than,the number of floral racemes within the bud. There is evidencein the structure of the secondary exotherms that the freezingof individual primordia was being recorded.Copyright 1993, 1999Academic Press Differential thermal analysis, freezing injury, buds, Ribes nigrum, blackcurrant     

Supercooling ability of Rhododendron flower buds in relation to cooling rate and cold hardiness

The freezing process and supercooling ability in flower budsof 11 native Rhododendron species were examined with referenceto the cooling rate and cold hardiness by differential thermalanalysis. The freezing patterns of the excised whole buds variedwith the season: in autumn, buds froze as whole units, whilein winter, freezing was initiated in the scales and propagatedto each floret. The supercooling ability of florets was enhancedduring winter. The freezing patterns in winter buds were stronglyinfluenced by the cooling rate (1 to 30°C/hr). Althoughthe first exotherm in scales occurred at –5 to –10°Gand was rate-independent, the occurrence of several floret exothermsshifted considerably to lower subzero temperatures at slowerrates. The most reliable cooling rate for testing maximum supercoolingability was l°C/hr. The exotherm in florets of hardier speciesoccurred at –20 to –25°C and at –7 to–20°C for less hardy ones, and were well correlatedwith their killing temperatures. Water relations within budtissues in response to freezing are briefly discussed. (Received June 26, 1980; )     

Hardening and Dehardening of Lolium perenne in Response to Fluctuating Temperatures

Hardening and dehardening responses of two contrasting varietiesof Lolium perenne, measured as LT50 estimates, were followedin fluctuating temperature environments. Unhardened seedlingswere exposed to hardening environments for 7, 14, and 21 d inall combinations of 2, 4, 6, 8 and 10 C with either high dayand low night temperatures or low day and high night temperatures.Seedlings hardened for 28 d at 2 C were exposed to dehardeningenvironments in all combinations of 4, 6, 8, 10, and 12 C withhigh day and low night temperatures. A low day, or night, temperature of 2 C in combination withany other temperature increased hardening compared with theconstant higher temperature. For Premo, a hardy variety, thisincrease was 3 C when night temperature was reduced from 10to 2 C in combination with a day temperature of 10 C. Similarly,a low night temperature reduced the dehardening response ofPremo to higher day temperatures. At 12 C this effect on LT60was greater than 2 C. Much smaller responses to daily periodsof low temperature were found for the less hardy variety, GrasslandsRuanui. During each 24-h period, exposures to 2 C of longer than 4h were required to achieve greater hardening than that achievedin continuous 10 C treatments. Hardiness was not improved furtherby exposures longer than 8 h. Responses to diurnal temperature fluctuations were discussedin relation to possible mechanisms and to changes in hardinessduring the winter under different weather systems. Lolium perenne, cold hardening, cold dehardening, diurnal temperature fluctuations, varieties     

Supercooling ability of Rhododendron flower buds in relation to cooling rate and cold hardiness

The freezing process and supercooling ability in flower budsof 11 native Rhododendron species were examined with referenceto the cooling rate and cold hardiness by differential thermalanalysis. The freezing patterns of the excised whole buds variedwith the season: in autumn, buds froze as whole units, whilein winter, freezing was initiated in the scales and propagatedto each floret. The supercooling ability of florets was enhancedduring winter. The freezing patterns in winter buds were stronglyinfluenced by the cooling rate (1 to 30°C/hr). Althoughthe first exotherm in scales occurred at –5 to –10°Gand was rate-independent, the occurrence of several floret exothermsshifted considerably to lower subzero temperatures at slowerrates. The most reliable cooling rate for testing maximum supercoolingability was l°C/hr. The exotherm in florets of hardier speciesoccurred at –20 to –25°C and at –7 to–20°C for less hardy ones, and were well correlatedwith their killing temperatures. Water relations within budtissues in response to freezing are briefly discussed. (Received June 26, 1980; )     

Development of Oilseed Rape Buds, Flowers, and Pods In Vitro

A technique for growing buds, flowers, and pods of oilseed rape(Brassica napus L. cv. Haplona) on stem explants in vitro hasbeen developed. Open flowers and young pods underwent normaldevelopment on a basal medium of minerals, vitamins, and sucrosebut the development of buds was less successful. Young buds(3 mm long) did not develop and only limited development ofthe older buds (5 mm long) took place. Some 3 mm-long buds wereinduced to develop to open flowers by adding naphthyl aceticacid or gibberellic acid. Pod and seed set in open flowers werenot affected by adding plant growth substances to the medium,but pod elongation and pod dry weight were promoted by gibberellicacid, 105 M, and benzyl amino purine, 10⁷ M, respectively. Reducingthe supply of sucrose or minerals to open flowers reduced seedset, pod elongation and pod weight but did not affect pod set.The physiological significance of the results is discussed. Key words: In vitro cultures, oilseed rape, pod development, flower development     

Effects of High Air and Soil Temperature Stress on Growth and Tuberization in Solanum tuberosum

Potato plants (Solanum tuberosum L.) were grown at differentair and soil temperatures to determine the effects of high-temperaturestress on root, tuber, and shoot growth. Cooling the soil (17–27C) at high air temperatures (30–40 C) relieved noneof the visible symptoms of heat stress on shoot growth; norwas the degree of induction to tuberize in leaves increased,as reflected in tuberization of leaf-bud cuttings. Heating thesoil (27–35 C) at cool (17–27 C) air temperatureshad no apparent detrimental effect on shoot growth or inductionof leaves to tuberize. However, in each case hot soil largelyeliminated tuber development. In one experiment stolons grewup out of the hot soil and formed aerial tubers upon reachingthe cool air. When leaf-bud cuttings from induced plants wereused as a model system, high soil temperatures inhibited tuberdevelopment from the buried leaf buds, in the absence of anyroot growth. Apparently the induction of leaves to tuberizeis affected principally by air rather than soil temperature,but expression of the signal to tuberize can be blocked by highsoil temperature. Solanum tuberosum L., potato, temperature stress, soil temperature, tuberization     

Determination of resistance to low temperatures of winter buds on lateral shoot present in Karaerik (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.) grape cultivar

This study aims to determine the low temperature resistance of dormant buds at nodes with or without lateral shoots of Karaerik grape cultivar, and explain the relationship between the resistance and biochemical parameters in this grape cultivar. In this study, the mean values of high temperature exotherms (HTEs), low temperature exotherms (LTEs), water, reducing sugar, total soluble protein contents and antioxidant enzyme activities of dormant buds taken from nodes with or without lateral shoots were determined. The experiment has been found that buds in nodes with lateral shoots showed HTE and LTE at higher temperatures (HTE average ?6.7 °C and LTE average ?8.3 °C) than buds (HTE average ?7.9 °C and LTE average ?11.5 °C) in nodes without lateral shoots; therefore, buds in nodes with lateral shoots had less tolerance to low temperature. Additionally, lower sugar (average 41.05 mg g^?1), protein (average 1.61 mg g^?1), superoxide dismutase (average 425.27 EU g^?1 tissue), peroxidase (average 2516.1 EU g^?1 tissue) and polyphenol oxidase (average 7283.1 EU g^?1 tissue) were determined for buds taken from nodes with lateral shoots. Due to the fact that dormant buds taken from nodes with lateral shoots decreased the resistance to low temperatures, this research suggests that these lateral shoots should be excised with the summer pruning at the regions, where low temperatures caused the damages.     

The Control of Sex Expression in Cucurbits by Ethephon

Application of ethephon to field-grown plants of both bush andtrailing forms of Cucurbita maxima and C. pepo caused leaf epinasty,suppression of male flowers and earlier production and increasein numbers of female flowers. This gave rise to an increasein the ratio of female to male flowers per plant and a decreasein the total number of flowers. Observations of C. pepo showed that even at the two true leafstage there are several nodes present in the unexpanded shoot.Each node has one main and several secondary buds. The sex ofthe main bud at the first five to six nodes is usually determinedat this stage but the secondary buds still have bisexual potential.The change in sex expression was brought about by all male flowerbuds that had formed by the spraying time aborting, and allbuds that developed (both main and secondary) for at least 7days after spraying became female flowers. Thus, nodes fiveand six had male flowers in the controls, whereas in ethephon-sprayedplants the presumptive male flowers aborted at the bud stageat these nodes and secondary primordia developed into functionalfemale flowers. Cucurbita maxima, Cucurbita pepo, sex expression, ethephon, ethylene, flower abortion, flower differentiation     

Heat Stress-induced Abortion of Buds and Flowers in Pea: Is Sensitivity Linked to Organ Age or to Relations between Reproductive Organs?

A short period of heat stress can cause a significant increasein abortion frequency of floral buds and flowers in pea, buta large variability in sensitivity exists among reproductiveorgans (ROs) within a plant or between plants. We have analysedspatial distribution of abortion frequency in plants subjectedor not subjected to heat stress in: (1) four controlled environmentexperiments in which apex temperature was increased to 31 °Cfor 6 h per day for 4 d (moderate stress); (2) one field experimentwith a similar level of stress; and (3) one experiment with2 d with 33/30 °C day/night (severe stress) in additionto treatment (1). Influence of neighbouring organs on sensitivityto heat stress was analysed by partial flower removal. Severeheat stress caused rapid interruption of RO development followedby abscission while, in moderate stress, at leat 4 d elapsedbetween cessation of stress and first symptoms of abortion.In both moderate stress and control treatments, abortion frequencyfollowed a consistent pattern along the stem with no abortionon the lowest reproductive phytomeres, a temperature-dependentabortion frequency on intermediate phytomeres and 100% abortionon apical phytomeres. Regardless of temperature, this patternwas shifted by four positions if ROs were removed on the lowestfour reproductive phytomeres, and no abortion was observed ifyoung pods were sequentially removed. Moderate heat stress increasedthe effect of developing ROs on abortion frequency of youngerROs located above them. We suggest that the effect of mild stressshould be viewed as the acceleration of a programme linked tothe normal termination of phytomere production during the plantcycle, rather than as an abrupt event linked to stress. Pisum sativum; heat stress; abortion; abscission; age; organ-to-organ relations     

Photoperiodic Regulation of Flowering in Cowpeas (Vigna unguiculata (L.) Walp.)

To test the proposition that photoperiodic controls synchronizethe flowering of cowpeas, Vigna unguiculata (L.) Walp. [V. sinensis(L.) Savi], the day-length requirements for floral initiationand for flowering were investigated in several short-day accessions.No evidence was found of different critical photoperiods atdifferent stages of development, but exposure to only 2–4short days was required for floral initiation compared withabout 20 for development to open flowers. Pod setting was increasedafter exposure to even one short day more than the number requiredfor flower opening. Floral buds at higher nodes appeared to require fewer shortdays for development to flowering than buds at the lower nodes,and displayed faster rates of development. Inflorescence budsdid not resume development if they were exposed to 15 or morelong days following inflorescence initiation. Thus, any tendencytowards synchronous flowering in cowpeas is not due to the criticalday-length for flower development being shorter than that forflower initiation, but could be the result of cumulative photoperiodicinduction of plants and the more rapid development of later-formedflowers. Vigna unguiculata (L.) Walp., cowpeas, flower initiation, flower development, fruit set, photoperiodism