Pod Abortion Research Articles

Drought stress effect on carbohydrate concentration in soybean leaves and pods during early reproductive development: its implication in altering pod set

To advance our understanding of the physiological mechanisms by which pod abortion is regulated in soybean ( Glycine max L. Merr.), leaf photosynthetic rates, carbohydrate concentrations and soluble invertase activities in leaves, flowers and pods were determined in plants subjected to drought stress during early reproductive development. Soybeans were grown in pots in an environmentally controlled glasshouse. Drought stress was imposed from −11 to 10 days after anthesis (DAA). Drought decreased photosynthetic rates and water potentials in leaves, flowers and pods. Drought decreased leaf sucrose and starch concentrations but increased hexose (glucose+fructose) concentrations. Drought did not affect the activity of soluble invertase in leaves. In flowers and pods, sucrose concentrations were higher under drought as compared with well-watered controls. Hexose and starch concentrations of flowers and pods were also higher under drought until 7 and 3 DAA, respectively; thereafter they were significantly lower than those of the well-watered controls. Soluble invertase activity was decreased by drought in pods 5–10 DAA. Although the concentrations of non-structural carbohydrate (sucrose+hexose+starch) were higher in droughted flowers and pods, the total amount of non-structural carbohydrate accumulated in pods during the sampling periods was substantially reduced by drought. Pod growth was decreased by drought 3–5 DAA, which coincided with a decrease in hexose to sucrose ratio, when a significant reduction of pod set was occurred. Collectively, the results indicate that both source and sink restrictions are involved in regulating pod set in drought-stressed soybeans. It is suggested that a low availability of current and reverse photosynthate in leaves coupled with an impaired ability to utilize the incoming sucrose by pods resulted in a decreased carbohydrate flux from leaves to pods, together with a decreased hexose to sucrose ratio in pods are potential factors contributing to pod abortion in drought-stressed soybeans.

Root signal controls pod growth in drought-stressed soybean during the critical, abortion-sensitive phase of pod development

Abstract Root-originated chemical signals have been shown to regulate the response of vegetative shoot to drought in soybeans ( Glycine max L. Merr.). However, their roles in the growth of soybean reproductive structures under drought stress have not yet been investigated. To explore this, a glasshouse experiment was conducted in which potted soybeans were either well-watered (WW) or subjected to six levels of drought stress. Irrigation was withheld in pots at six different dates before anthesis to induce drought of different severity (D1–D6) at sampling, viz. 4 days after anthesis (DAA). Root water potential, leaf water potential, pod water potential, xylem sap [ABA], pod fresh weight (FW), and pod set percentage were determined. Soil water status in the pot was expressed as the fraction of transpirable soil water (FTSW). Pod FW started to decrease at FTSW=0.43±0.02, when pod water potential was similar to that in the WW plants, while root water potential had decreased to −0.15 MPa and xylem sap [ABA] had increased 9-fold as compared with the WW plants. Pod set started to decrease at FTSW=0.30±0.01, and coincided with the decrease in pod water potential. Pod set started to decrease only when pod FW had decreased ca. 30%. Based on the results, a potential role of drought-induced increase in xylem sap ABA in affecting pod growth was suggested. We proposed that a low pod water potential, which might have led to disruptions in metabolic activities in the pods, is important in determining pod abortion.

Effect of Foliar Application of Urea on Reproductive Abscission and Grain Yield of Soybean

Soybean (Glycine max L., Merr.) is considered to have relatively high level of reproductive abscission, but research information on how fertilizer use influences this problem is scanty. Field trials were therefore carried out for two seasons (1996 and 1998) to investigate the abscission levels of three soybean cultivars (TGX 536‐02D, TGM 579, and Samsoy 11) as affected by foliar application of urea during the early reproductive stages. Flowering was not significantly increased by urea application, although all fertilized plants had fewer flower abortions than control. Fertilizing twice at full‐flowering and pod‐setting (R2–R3) or thrice at first‐flowering, full‐flowering, and pod setting (R1–R2–R3) stages gave the least flower abortion. In TGX 536‐02D the average flower abortion was 61% in 1996 and 57% in 1998. The abortion rate was about 60% for TGM 579 in 1996 and Samsoy 11 in 1998, respectively. Percentage pod abortion was generally reduced especially at the R1–R2–R3 stage, while the proportion of aborted grains was highest in the unfertilized plants. Fertilizing at R2–R3 and R1–R2–R3 reduced seed abortion by about 8% in TGX 536‐02D. The grain yield of fertilized soybean was between 6 and 68% higher than the control. These increases were attributed to higher number of pods and meaningful reductions in flower and pod abortions. Foliar applied urea at R2–R3 gave satisfactory results but the best stage of application was R1–R2–R3.

Loss of pod set caused by drought stress is associated with water status and ABA content of reproductive structures in soybean

Drought stress occurring during flowering and early pod expansion decreases pod set in soybean (Glycine max L. Merr.). The failure of pod set may be associated with changes in water status and ABA content in soybean reproductive structures under drought stress. To test this, pot experiments in an environmentally-controlled greenhouse were conducted, in which soybeans were exposed to drought stress around anthesis. In a preliminary experiment (Expt. I), irrigation was withheld at -6 (D1), -4 (D2) and -2 (D3) to 11 days after anthesis (DAA), then the droughted plants were re-watered to control levels until physiological maturity. Pod set percentage, seed yield and yield components were recorded. In the main experiment (Expt. II), irrigation was withheld from -11 to 10DAA. During the drying cycle, parts of the droughted plants were re-watered at 0, 3, 5, 7 and 10 DAA and kept well-watered until physiological maturity. In Expt. II, water status, ABA contents in xylem sap, leaves, flowers and pods were measured at 0, 3, 5, 7 and 10 DAA. The water potential in the flowers and pods was always lower than the leaf water potential. Turgor was decreased in leaves by drought 3 DAA, but remained at control levels in flowers and pods. Compared with well-watered plants, in severely droughted plants (10 DAA), xylem [ABA] increased about 60-fold; leaf [ABA] increased 9-fold; pod [ABA] increased 6-fold. During soil drying, flower and pod [ABA] was linearly correlated with xylem [ABA] and leaf [ABA], indicating that root-originated ABA and/or leaf ABA were the likely sources of ABA accumulated in the flowers and pods. In Expt. I, pod set and seed number per pod was unaffected by drought stress, while seed yield and individual seed weight was significantly decreased by drought. In Expt. II, significant reductions in pod set and seed yield were observed when re-watering the droughted plants at 3-5 DAA, re-watering the droughted plants later than this stage resulted in a similar pod set. Collectively, these results suggest that drought-induced decrease in water potential and increase in ABA content in flowers and pods at critical developmental stage (3-5 DAA) contribute to pod abortion in soybean.

Reactions of chickpea to water stress: yield and seed composition

AbstractDrought after podding is a common feature of chickpea production in south‐western Australia. We studied the effect of water stress, imposed after podding, on yield and on the accumulation of amino acids and soluble sugars in seeds. Although terminal water stress decreased the total plant dry mass and seed yield by 23% and 30% respectively, it had no effect on the mass of individual pods and seeds which remained on the plant after the imposition of stress treatment. The deleterious effect of water stress on yield was due to increased pod abortion and a decrease in pod formation. Water stress improved the seed's nutritive value in terms of higher accumulation of soluble sugars, amino acids and proteins.© 2001 Society of Chemical Industry

Analysis of Grain‐Yield Components and Inflorescence Levels in Winter‐Type White Lupin

In winter‐type white lupin (Lupinus albus L.), an improved understanding of the importance of inflorescence levels and yield components among environments could be useful when considering selection criteria for breeding. We examined inflorescence levels and yield components of indeterminate, determinate, and dwarf accessions among a broad range of environments. Data were acquired from date‐of‐seeding (DOS) and dry matter partitioning (DMP) studies. The DOS studies were conducted from 1991 to 1993 in north, central, and south Alabama, USA. The DMP studies were conducted for 2 yr in western France and central Alabama. We used principal‐component analysis to reduce the number of yield components for further consideration in future breeding. The first four principal components had Eigenvalues >1 and contributed ≥74% of the variance. Pod number m−2, seed number m−2, pod yield m−2, and seed yield m−2 were highly correlated (r ≥0.80, P ≤0.01) with most principal components. The first two to four principal components also had biological meaning because yield components that were highly correlated with each principal component were associated with a specific inflorescence level. Mainstem and primary‐branch inflorescence levels were most important for yield and yield‐component development. Basal branches were important in the southeastern USA, but these inflorescence levels should be selected against in France. Pod number m−2 and seed weight had the greatest effect on grain yield. Breeding for higher seed weight will improve cold tolerance and stabilize grain yield in western France, but further testing is needed in Alabama. Selecting germplasm with low pod abortion will help increase pod number potential.

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

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

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

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

Potencial de rendimento da soja em razão da disponibilidade de fósforo no solo e dos espaçamentos

O objetivo deste trabalho foi avaliar o potencial produtivo de grãos da soja nos estádios fenológicos R2 (florescimento), R5 (início de enchimento de grãos) e R8 (maturação). O experimento foi conduzido durante o ano agrícola 1994/95 na EEA/UFRGS, Eldorado do Sul, RS, em solo Podzólico Vermelho-Escuro (Paleudult). O delineamento utilizado foi o de blocos casualizados, com quatro repetições, com os tratamentos arranjados em parcelas subdivididas. Os tratamentos originaram-se da combinação de dois níveis de P no solo (3 e 15 ppm), e dois espaçamentos entre linhas (20 e 40 cm). Foi utilizada a cultivar precoce, determinada, OCEPAR 14. Na média dos tratamentos, o potencial de rendimento alcançado em R2 foi de 18 t/ha e de 10 t/ha em R5, sendo o rendimento obtido em R8 de 4,6 t/ha. O tratamento com 15 ppm de P apresentou maior potencial de rendimento, nos três estádios fenológicos, em decorrência do menor aborto de flores e de legumes. O espaçamento de 20 cm entre linhas apresentou maior potencial que o de 40 cm nos três estádios fenológicos avaliados, mas os valores percentuais de diminuição do rendimento pelo aborto de flores e de legumes foram similares.

Effects of the Dt 2 and S Alleles on Agronomic Traits of F 1 Hybrid Soybean

Agronomic evaluation of F1 hybrid soybean [Glycine max (L) Merr.] will be useful for germplasm evaluation, recurrent selection, and estimating heterosis. We anticipated that vegetative heterosis, commonly observed in soybean, could increase early lodging and pod abortion, reducing grain yield. Under these circumstances, observed hybrid grain yield would not reflect the true potential of the hybrid as expressed in later generations. The Dt2 (semideterminate stem type) and S (short internode stem type) alleles have been shown to reduce excessive vegetative growth and lodging in narrow-row production of inbred soybean. Our objectives were (i) to determine the per se effects and effects on heterosis, for agronomic traits, of the semideterminate (Dt2_) and short (S_) stem types in hybrid soybean, (ii) to assess their potential in facilitating germplasm evaluation and recurrent selection, and (iii) to determine if either stem type would be agronomically desirable in commercial hybrid soybean production. Near-isogenic inbred lines and hybrid (F1) lines were evaluated replicated three-row plots. The Dt2 and S alleles affected agronomic traits of hybrids and inbreds similarly. The Dt2 and S alleles hastened maturity, decreased plant height and lodging, and increased harvest index per se values. The Dt2 allele decreased seed weight and protein content. Both the per se and heterosis data suggest that the Dt2 and S alleles would not be consistently beneficial to germplasm evaluation or recurrent selection. The per se data suggest that the S allele might be useful for both inbred and commercial hybrid soybean.

Pod Elongation and Seed Growth as Influenced by Nodal Position on Stem and Raceme Order in a Determinate Type of Soybean Cultivar.

Pod elongation and seed growth in a determinate type of soybean were investigated in relation to nodal positions and raceme orders. Pods began to elongate on day 16 after the beginning of flowering, and seed growth was started on day 14 after the beginning of pod elongation(i.e., it took 30 days). The lower the raceme orders, the higher the final pod length and seed dry weight. The floral organs on the 4th and 5th orders of racemes began to flower on day 21 after the flowering of basal buds, but started to elongate on day 10 after the beginning of elogation of basal pods. Furthermore, the increase in seed weight began on day 6 after the beginning of the growth of basal pod seeds. The rate of pod elongation was highest on order 3 raceme and the rate of dry matter accumulation in seeds on order 2 raceme was higher than on the basal order raceme. Flower or pod abortion was observed most frequently just before the period of pod elongation. Although soybean had a long flowering period according to raceme orders, both the pod elongation and the seed growth were synchronous among raceme orders; thus seeds were matured at the same time.

Water Use and Yield of Canola under Dryland Conditions in the Central Great Plains

Reduced tillage systems, compared with conventional tillage methods, have increased precipitation storage efficiencies and increased the amount of available water for crop production in the central Great Plains. Increased available water affords producers the opportunity to diversify and intensify their production systems from the traditional wheat (Triticum aestivum L.)-fallow system. This study was conducted to determine canola (Brassica napus L.) production potential under the limited and variable precipitation patterns found in dryland agricultural systems in northeastern Colorado. Water stress timing effects on canola yield components were determined under a rainout shelter in 1993 and 1994, with water withheld during either the vegetative, reproductive, or grain-filling growth stage. All treatments received the same total water application, equal to the long-term average growing season precipitation. Rooting depth was determined from water extraction patterns monitored with a neutron probe. A water use-yield function was determined for canola grown under a line-source gradient irrigation system. A non-water-stressed baseline was determined for future water stress research using an infrared thermometer in canola. Timing of water stress did not significantly affect yield. Canola can extract water from soil depths of 65 in., but 92 to 95% of total seasonal water use comes from growing season precipitation and water extracted from soil depths above 47 in. An examination of the growing season precipitation records indicates that canola yields could range from 284 to 2358 lb/acre (averaging 1020 lb/acre), assuming 4 in. of stored soil water use in addition to precipitation. Dryland canola production may not be economically viable for northeastern Colorado at current market prices and yields.

Influence of photosynthetic restriction due to defoliation at flowering on seed abortion in lucerne (Medicago sativaL.)

The seed yield of lucerne is poor, in contrast to its good vegetative growth. This is partly due to a lack of pollination under natural conditions, pod abortion and the production of only a few seeds per pod. In this study, lucerne plants were grown in controlled conditions and about 30% of the inflorescences were pollinated manually. There were about 10 ovules per flower, which remained constant throughout the flowering period. There were 4.5 seeds per pod, indicating over 50% seed abortion. One group of plants was defoliated and the lack of recent assimilates at flowering caused a small but significant decrease in the number of seeds per pod (4.1). The effect of defoliation varied with seed age; the youngest fertile inflorescences were the most affected and there was no effect at around 400°C d - - 1 . This stage marked the end of the lag phase, which was determined separately in control plants. Thus, it is assumed that this date is the abortion limiting stage (ALS) for this species. The long lag phase for lucerne could be a key influence on seed yield. The longer the ALS, the greater the risk of vegetative competition, thus reducing reproductive development.

Reproductive biology of Vicia faba: role of pollination conditions

The effects of two different pollination conditions, self versus open, were studied in two consecutive years in 12 genotypes which showed wide variation for some reproductive characters related to plant structure, fertility and yield. Yield was not apparently limited by pollen availability. However, the first node to bear pods was lower in open- than in self-pollinated plants, which developed more flowers into young pods. The superabundance of flowers developed into young pods was compensated by adjustment of other yield components to achieve the physiological maximum yield. Open pollination may also have increased both pod and seed set, but only to a lesser extent, and depended on year and genotype. The results of these experiments also suggested that yield regulation operated by different mechanisms for the various genotypes; particularly, abortion of young pods, ovules and seeds, and seed-size adjustments. In some genotypes, many young pods were produced but few matured; in others, few ovules develop into seeds, or seeds remained small. Theoretically, such alternative strategies, present in different genotypes, could be combined to produce new high-yielding cultivars, in such a way that highly self-fertile genotypes respond optimally to the presence of pollinators.

Flower and pod abortion in chickpea as affected by sowing date and cultivar

Chickpea (Cicer arietinum L.) flowers abundantly but a large proportion of its flowers and pods abscise. The objective of this study was to quantify the variation in the flower number and the fate of flowers as affected by sowing date and cultivar, with the aim of understanding the significance of the variability to final yield. The production and fate of chickpea flowers were studied on two cultivars (Janta-2 and Lebanese Local) sown on 9 December 1992 and 17 February 1993 at the American University of Beirut Farm, Beka'a Valley, Lebanon. The pattern of flower production, pod rentention, number of flowers produced, and percentage of flowers and pods abscised varied with sowing date and cultivar. Winter sowing produced significantly more yield than spring sowing. Cultivar Janta-2 yielded more than Lebanese Local in the winter, but the difference disappeared under spring-sown conditions. In general, primary branches contributed 54% to final pod yield with the secondary branches contributing 27% and the main stem contributing 19%. Adjustments to yield from stress after flowering and during pod-filling came primarily from flowers on primary and secondary branches rather than from those on the main stem, from higher order primary and secondary branches rather than from those on basal branches, and from upper-most nodes of the main stem and primary and secondary branches. The primary and secondary branches on the basal nodes 1–3 on the main stem produced most of the pods that were retained.Mention of trade name, proprietary product, or vendor does not constitute an endorsement or warranty by the American University of Beirut, nor does it imply its approval to the exclusion of other products or vendors that may be suitable. Key words: Flower biology, pod retention pattern, Cicer arietinum L.

Isozyme markers for self-compatibility and yield in Theobroma cacao (cacao)

Self-incompatible cacao clones were observed to out-yield self-compatible clones in a 20-year trial. In another trial, self-compatible trees were seen to set three times more pods than did the self-incompatible trees. However, because of the abortion of young pods this difference had disappeared by the time the pods reached maturity. Isozyme analysis revealed that both the Acp and Idh loci were linked to one of the loci controlling compatibility type. Thus, isozyme screening of seedlings could be used to predict the compatibility type and hence pod-set and, possibly, yield of the mature tree.

Influence of sulphur and nitrogen on seed yield and quality of low glucosinolate oilseed rape (Brassica napus L)

AbstractInfluence of S and N application on seed yield and quality of a double low (low erucic acid and glucosinolate content) variety of winter oilseed rape (Brassica napus L) was examined in field experiments at both S‐sufficient and S‐deficient sites. At the S‐sufficient site, application of S had no significant influences on seed yield, yield components, seed protein and oil contents, and resulted in only a marginal increase in seed glucosinolate content. Application of N increased seed yield and protein content, but decreased oil content concurrently. A significant increase in seed glucosinolate content in response to the increasing N rate was obtained at this site, which was more noticeable in those treatments with applied S than without. In contrast, at the S‐deficient site, there were significant interactions between S and N on seed yield, protein and glucosinolate contents. Increasing the N rate beyond 150 kg ha−1 did not increase seed yield in the absence of applied S. However, with an application of 300 kg N ha−1, seed yield increased by 10·7% with an application of 50 kg S ha−1. The effect of N on seed yield was achieved mainly through enhanced pod formation, and that of S through reduced pod abortion. Sulphur application also increased seed protein content at the high N rate, and increased methionine content at the expense of aspartic acid. On average, a two‐fold increase in seed glucosinolate content in response to an application of 100 kg S ha−1 was obtained at the S‐deficient site. Also, increasing the N rate decreased seed glucosinolate content in the absence of applied S, but increased it when S was applied. The interaction between S and N on seed glucosinolate content was explained in terms of the allocation of S towards primary and secondary metabolites within plants.

The influence of pre-floral growth and development on the pathway of floral development, dry matter distribution and seed yield in oilseed rape (Brassica napus L.)

Patterns of floral development, dry matter distribution and seed yield were examined in winter oilseed rape plants subjected to different pre-floral growth environments. The duration of pre-floral growth and plant size at flower initiation, measured in terms of total mainstem leaf number, were manipulated by varying the temperature between seedling emergence and flower initiation. Exposure of seedlings to low temperatures from cotyledon expansion onwards markedly reduced the duration of pre-floral growth and the number of leaves on the mainstem. The subsequent development pattern of plants was largely dependent on the date of flower initiation and therefore vernalisation requirement. Indeed, the period of growth from flower initiation to maturity, considered on the basis of thermal time, was directly related to the duration of pre-floral growth and mainstem leaf number. The thermal durations of the bud development phase and flowering period in plants exposed to different pre-floral cold treatments but with a common date of flower initiation were similarly linked to these two parameters. Plants exposed to prolonged periods of low temperature treatment from cotyledon expansion onwards initiated fewer mainstem leaves during a relatively short pre-floral growth phase and their yield potential was limited by a reduction in branch and flower numbers. Plants maintained at higher temperatures produced more mainstem leaves during an extended period of pre-floral growth and supported a greater number of branches and flowers. However, this additional yield potential was not realised due to a reduction in seed numbers and mean seed weight. It appeared that seed yield of these plants was limited by increased competition between an excessive number of lower branches and flowers, a problem apparently created by excessive pre-floral growth. Minimal competition for available assimilates between the limited number of branches of plants with a shorter pre-floral growth phase and fewer mainstem leaves, resulted in lower levels of pod abortion, greater seed production and ultimately increased seed yields.

Irrigation and water use in leafless peas (Pisum sativum)

SUMMARYField trials at the University of Nottingham, UK, in 1979 and 1980 investigated the effect of moisture stress on the growth and yield of the leafless dried pea Filby. In the absence of drought, the crop photosynthetic area was increased and maturity delayed. Seed yield was increased by the production of a greater number of reproductive nodes and a reduced abortion of flowers and pods.In the second season, two sowing dates were also tested. Later sowing reduced the seed yield under the high and low moisture treatments by 14 and 33% respectively, due to an increased abortion of flowers and pods. The high moisture treatment reduced the water use efficiency (WUE) in this season and WUE was lower for the later sown crops, but there was no effect on WUE in the previous season.The seed yield and water use of pot-grown leafless peas were lower than were those of a nearisogenic line of leafed peas. Moisture stress reduced the yield of both phenotypes but the effect on the leafless pea was greater. Moisture stress imposed at flowering reduced yields more than it did at pod filling and there was an additive effect of moisture stress at both times.

Effects of cycocel on growth and seed yield ofLotus uliginosusSchk. cv. Grasslands Maku

Abstract Field experiments were conducted in two successive seasons to investigate the effects of the plant growth retardant cycocel applied at 1.25 and 2.50 kg a.i./ha at different plant growth stages on the vegetative and reproductive growth, yield components, and seed yield of Lotus uliginosus Schk. cv. Grasslands Maku. Cycocel did not retard internode length or affect total dry matter, flowering pattern, or seed weight. Significant seed yield increases were recorded in both years, although responses differed with application rate and time. Cycocel at 2.50 kg/ha applied in early October before reproductive initiation, increased seed yield by 108 and 92% in 1989 and 1990 respectively. Later applications (floral bud appearance; onset of flowering) produced less-consistent results. The seed yield increases recorded were in response to increased pods per umbel and seeds per pod. Cycocel reduced pod abortion from the mid-season flowers, but abortion rates did not differ in the early- and late-season flowers.