Osmotic adjustment in chickpea (Cicer arietinum L.) results in no yield benefit under terminal drought

Variation in osmotic adjustment (OA) among chickpea (Cicer arietinumL.) cultivars has been observed when exposed to terminal drought,but some studies suggest that this benefits yield while otherssuggest it does not benefit yield in water-limited environments.In the present study, parents differing in OA were crossed anda set of advanced breeding lines (ABLs) developed for yieldtesting. The variation in OA during podding was measured underterminal drought in the F₂, F₃, F₇, and F₈ progeny and in theparents by either rehydrating the leaves before sampling forosmotic potential (OP) or by measuring the relative water content(RWC) and OP on adjacent leaves for the calculation of the OPat full turgor. Yields were measured in the F₈ progeny underterminal drought in Australia and India. While differences inOA were measured in the chickpea lines and parents, OA variedfrom year to year and did not consistently benefit yield whenmeasured in the field under terminal drought. In Australia,differences in OA were not associated with any yield benefitin any year, while in India early flowering resulted in higheryields at three of the four sites, and OA had an inconsistenteffect on seed yields. A comparison of OP at full turgor measuredafter rehydration and from measurements of RWC and OP showedthat the rehydration technique underestimated OA. The lack ofcontribution of OA to yield of chickpea is discussed. Key words: Advanced breeding lines, early flowering, phenology, terminal drought, yield components     

Genotypic variability in physiological,biomass and yield response to drought stress?in pigeonpea

Three pigeonpea (Cajanus cajan L. Millsp.) genotypes- GT-1, AKP-1 and PRG-158 with varying crop duration, growth habit and flowering pattern were evaluated for variability in their response for drought stress. Drought stress was imposed at initiation of flowering and the observations on biomass and seed yield parameters were recorded at harvest. The magnitude of response of individual component to drought stress was found to be genotype specific. Drought stress significantly decreased photosynthetic rate (P_N), transpiration rate (Tr) and relative water content (RWC) in all the genotypes, however the magnitude of reduction differed with genotype. With drought stress, the reduction of P_N was highest in GT-1 while reduction in Tr was highest in PRG-158. The genotype AKP-1, accumulated significantly higher concentrations of osmotic solutes especially proline under water deficit stress, this facilitated it to maintain higher relative water content (RWC) and lower malondialdehyde (MDA) content as compared to other genotypes. Drought stress also impacted biomass production and their partitioning to vegetative and reproductive components at harvest. There was significant variability between the genotypes for seed yield under drought stress while it was non-significant under well-watered condition. Drought stress enhanced flower drop and decreased flower to pod conversion resulting in reduced pod number and seed number in PRG-158 and GT-1. The genotype AKP-1 recorded superior performance for seed yield under stress environment due to its ability in maintaining pod and seed number as well as improved test weight (100 seed weight). Under drought stress, significant positive association of seed yield with proline, seed number, pod number and test weight clearly indicating their role in drought tolerance.     

A conservative pattern of water use, rather than deep or profuse rooting, is critical for the terminal drought tolerance of chickpea

Chickpea is mostly grown on stored soil moisture, and deep/profuse rooting has been hypothesized for almost three decades to be critical for improving chickpea tolerance to terminal drought. However, temporal patterns of water use that leave water available for reproduction and grain filling could be equally critical. Therefore, variation in water use pattern and root depth/density were measured, and their relationships to yield tested under fully irrigated and terminal drought stress, using lysimeters that provided soil volumes equivalent to field conditions. Twenty chickpea genotypes having similar plant phenology but contrasting for a field-derived terminal drought-tolerance index based on yield were used. The pattern of water extraction clearly discriminated tolerant and sensitive genotypes. Tolerant genotypes had a lower water uptake and a lower index of stomatal conductance at the vegetative stage than sensitive ones, while tolerant genotypes extracted more water than sensitive genotypes after flowering. The magnitude of the variation in root growth components (depth, length density, RLD, dry weight, RDW) did not distinguish tolerant from sensitive genotypes. The seed yield was not significantly correlated with the root length density (RLD) in any soil layers, whereas seed yield was both negatively related to water uptake between 23-38 DAS, and positively related to water uptake between 48-61 DAS. Under these conditions of terminal drought, the most critical component of tolerance in chickpea was the conservative use of water early in the cropping cycle, explained partly by a lower canopy conductance, which resulted in more water available in the soil profile during reproduction leading to higher reproductive success.     

Early osmotic adjustment responses in drought- resistant and drought-sensitive oilseed rape

The impact of osmotic stress on growth, physiolo- gy, and metabolism of winter oilseed rape （Brassica napus L.） was investigated by detailed analysis of biomass traits, hormone metabolites and osmolytes in two genetically unrelated drought-tolerant genotypes and two unrelated drought-sensitive genotypes. Seedlings were grown in vitro under controlled conditions and osmotic stress was simulated by applying a gradual treatment with polyethylene glycol （PEG 6ooo）, followed by hypo-osmotic treatment of variants used for metabolite determination. The results provide a basis for the identification of reliable selection criteria for drought resistance in oilseed rape. The in vitro cultivation system established during this study enabled effective discrimination of early osmotic stress responses between drought-resistant and -susceptible oilseed rape genotypes that also show large differences in relative seed yield under drought conditions in the field. Clear physiological and metabolic differences wereobserved between the drought-resistant and drought-sensitive genotypes, suggesting that osmotic adjustment is a key component of drought response in oilseed rape. Unexpected- ly, however, the drought-resistant genotypes did not show typical hormonal adjustment and osmolyte accumulation, suggesting that they possess alternative physiological mech- anisms enabling avoidance of stress symptoms.     

Varying phosphorus supply and development,growth and seed yield in narrow-leafed lupin

Narrow-leafed lupin (Lupinus angustifolius L.) is usually grown in sandy, acidic and phosphorus (P) deficient soil with low yield and variable harvest index. This study aimed to examine the effects of varying P supply on lupin growth, seed yield and harvest index. Non-abscission plants (cv. Danja) were grown in Lancelin sand at seven rates of P supply (5, 10, 15, 20, 25, 30 or 40 mg kg^–1) in a naturally-lit glasshouse. The rate of leaf emergence, flowering time and flower number were decreased or delayed by low P supply (5, 10 or 15 mg kg^–1), with no differences at P rates higher than 20 mg kg^–1. High P supply (25, 30 or 40 mg kg^–1) increased plant seed yield and harvest index largely by increasing the number of pods and consequently yield on the lateral branches, but had less effect on the number of seeds per pod and seed size. Seed yield and seed P concentration continued to increase up to 40 mg P kg^–1but harvest index plateaued at 25 mg P kg^–1, indicating that low P supply decreased reproductive growth more than vegetative growth in narrow-leafed lupin.     

Early osmotic adjustment responses in drought-resistant and drought-sensitive oilseed rape

The impact of osmotic stress on growth, physiology, and metabolism of winter oilseed rape(Brassica napus L.)was investigated by detailed analysis of biomass traits,hormone metabolites and osmolytes in two genetically unrelated drought-tolerant genotypes and two unrelated drought-sensitive genotypes. Seedlings were grown in vitro under controlled conditions and osmotic stress was simulated by applying a gradual treatment with polyethylene glycol(PEG6000), followed by hypo-osmotic treatment of variants used for metabolite determination. The results provide a basis for the identification of reliable selection criteria for drought resistance in oilseed rape. The in vitro cultivation system established during this study enabled effective discrimination of early osmotic stress responses between drought-resistant and -susceptible oilseed rape genotypes that also show large differences in relative seed yield under drought conditions in the field. Clear physiological and metabolic differences were observed between the drought-resistant and drought-sensitive genotypes, suggesting that osmotic adjustment is a key component of drought response in oilseed rape. Unexpected ly, however, the drought-resistant genotypes did not show typical hormonal adjustment and osmolyte accumulation suggesting that they possess alternative physiological mech anisms enabling avoidance of stress symptoms.     

Trigonelline Concentration in Field-Grown Soybean in Response to Irrigation

Trigonelline (TRG) is a conjugate of nicotinic acid, and is postulated to function as a compatible solute in response to salinity- and water deficit-stresses. TRG concentrations and several agronomic characteristics were measured under irrigated field and non-irrigated field conditions within 18 soybean (Glycine max) genotypes using leaves taken from different growth stages (vegetative, flowering and pod development). Under irrigation, relative water content (RWC) ranged from 90.0 to 99.6 %. Under non-irrigation, RWC ranged from 86.3 to 97.5 %. TRG concentration ranged from 364 to 555 μg g⁻¹(d.m.) under irrigation, and from 404 to 570 μg g⁻¹(d.m.) under non-irrigation. TRG concentrations increased in the majority of genotypes (15 of 18) under non-irrigation even though RWC did not significantly differ in many genotypes between treatments. TRG decreased as plants progressed to pod development and seed filling. Mean seed yield under non-irrigated conditions declined 55 % relative to the irrigated controls. TRG concentrations among all genotypes were significantly correlated with seed yield. This revised version was published online in July 2006 with corrections to the Cover Date.     

Assessment of transpiration efficiency in peanut (Arachis hypogaea L.) under drought using a lysimetric system

Transpiration efficiency (TE) is an important trait for drought tolerance in peanut ( Arachis hypogaea L.). The variation in TE was assessed gravimetrically using a long time interval in nine peanut genotypes (Chico, ICGS 44, ICGV 00350, ICGV 86015, ICGV 86031, ICGV 91114, JL 24, TAG 24 and TMV 2) grown in lysimeters under well-watered or drought conditions. Transpiration was measured by regularly weighing the lysimeters, in which the soil surface was mulched with a 2-cm layer of polythene beads. TE in the nine genotypes used varied from 1.4 to 2.9 g kg⁻¹ under well-watered and 1.7 to 2.9 g kg⁻¹ under drought conditions, showing consistent variation in TE among genotypes. A higher TE was found in ICGV 86031 in both well-watered and drought conditions and lower TE was found in TAG-24 under both water regimes. Although total water extraction differed little across genotypes, the pattern of water extraction from the soil profile varied among genotypes. High water extraction within 24 days following stress imposition was negatively related to pod yield ( r ²   =   0.36), and negatively related to water extraction during a subsequent period of 32 days ( r ²   =   0.73). By contrast, the latter, i.e. water extraction during a period corresponding to grain filling (24 to 56 days after flowering) was positively related to pod yield ( r ²   =   0.36). TE was positively correlated with pod weight ( r ²   =   0.30) under drought condition. Our data show that under an intermittent drought regime, TE and water extraction from the soil profile during a period corresponding to pod filling were the most important components.     

低水势下冬小麦胚芽鞘长度与叶片的渗透调节能力及大田产量关系的研究

本文以７个抗旱性不同的冬小麦品种（系）为材料,研究了低水势下芽鞘长度与大田干旱条件下叶片的渗透调节能力及大田产量的关系。结果表明：低水势下芽鞘长度与叶片的渗透调节能力及产量有极为密切的关系。为冬小麦抗旱鉴定及抗旱个体筛选提供了一个良好的指标。     

Interactive effect of cytokinin and potassium on sink-source relationships in Lupinus angustifolius

This study examined whether increased K supply in conjunction with BAPcould increase lupin seed yield and harvest index by enlarging sink volume (podnumber), increasing assimilate and improving assimilate partitioning to filltheadditional pods induced by BAP treatment. Narrow-leafed lupin(Lupinusangustifolius, cv. Danja abs^– mutant) was grown inaglasshouse, in pots containing sandy soil with four K treatments (0, 15, 60 and120 mg K/kg soil). BAP (2 mM) was applied daily toallmain stem flowers throughout the life of each flower from opening to senesced.BAP application did not affect assimilate production (as measured by totalabove-ground biomass), but changed assimilate partitioning. On BAP-treatedplants, there were greater proportions of seed to pod wall dry weight on themain stem but smaller proportions on the branches, and an increased weightratioof seed to pod wall overall which meant more assimilate was used for seedgrowthrather than pod wall growth. BAP increased the number of pods per plant by35% and this more than compensated for the decreases in seeds per podandseed weight. Therefore, there was an increased harvest index (+11%)and seed yield per plant (+13%) in BAP-treated plants. BAP alsoincreased the number of pods with filled seeds (146%) on the main stemand main stem seed K⁺ concentration (from 0.81% to0.87%). Added K increased biomass but only slightly affected assimilatepartitioning. As applied K increased, relatively more assimilate was used forpod wall growth rather than seed growth. Added K increased seed yield per plantby about 14% due to increases in seed weight and the number of pods onthe main stem. Moreover, K⁺ concentration in seeds and shootsincreased with increasing level of applied K. Seed yield was enhanced more byBAP when K was supplied at high levels. Increasing K supply interactedpositively with added BAP by increasing narrow-leaf lupin seed yield andharvestindex through increases in assimilate supply and its partitioning into seeds.     

Biochemical and immunocytochemical localization of a BAPAase in developing and mature lupin cotyledons

Summary Activity measurements and specific antibodies were used to detect and localize in developing and mature cotyledons ofLupinus albus seeds an endopeptidase, active on BAPA, previously isolated from the same seeds. Total activity and enzyme amount were highest at full seed maturation and then declined during germination. Protein bodies were isolated from mature dry cotyledons under anhydrous conditions with a yield of intact organelles of about 80% as assessed by dot blotting with antibodies to lupin legumin-like storage globulin. Activity assays on the isolated protein bodies indicated that 72% of BAPAase activity was associated with these organelles. Quantitative immunocytolocalization with antibodies to the enzyme on thin sections of mature lupin cotyledons confirmed that 75% of the enzyme was located inside the protein bodies. The possible involvement of the BAPAase in the proteolytic processing of the storage proteins during seed ontogeny is discussed.Abbreviations BAPA N-benzoyl-L-arginine-4-p-nitroanilide - DAF days after flowering - EM electron microscopy - NaPi sodium phosphate buffer - LRW London resin white - SDS sodium dodecylsulphate - PAGE polyacrylamide gel electrophoresis     

Relationship between grain yield, osmotic adjustment and benzoxazinone content in Triticum aestivum L. cultivars

Fifteen wheat genotypes were grown under water deficit to ascertain the role of osmotic adjustment (OA) and the concentration of benzoxazinones in sustaining grain yield. A positive correlation between osmotic adjustment capacity and yield was observed in wheat genotypes cultivated under field conditions. The weight gain of plants exposed to drought was in agreement with the OA values (R(2) = 0.93). However, when wheat plants were infested by cereal aphids, this correlation was not found. The benzoxazinones 2,4-dihydroxy-1,4-benzoxa-zin-3-one (DIBOA) and 2,4-dihydroxy-7-methoxy-1,4 benzoxazin-3-one (DIMBOA) are defensive secondary metabolites present in wheat and others cereals. The content of these compounds varied in wheat genotypes and increased with drought and aphid infestation. A positive correlation between weight gain of irrigated-infested plants and drought-infested plants and the contents of benzoxazinones was observed. These results suggest that plants with better OA capacity and high benzoxazinone content should have better field yields.     

开花后光照长度对大豆农艺性状的影响

在人工控制条件下,研究了开花后的光照长度对大豆农艺性状的影响及大豆不同发育阶段长度与农艺性状的相关性．结果表明,开花后长日照可提高大豆的干物质积累量,在正常成熟的前提下可明显提高产量．试验进一步证明鼓粒期长度与粒重和产量呈正相关,花荚期长度对产量形成相当重要．认为东北大豆花荚期及以前的长日照有助于干物质的积累和较多花荚数量的形成,鼓粒开始后迅速缩短的日照条件可促进干物质向籽粒的运转,并加快籽粒的整齐成熟．     

内生真菌与苍术粉对连作花生根际微生物区系和微量元素的影响

通过盆栽试验,研究了内生真菌拟茎点霉B3(Phomopsis liquidambari)及苍术(Atractylodes lancea)粉联合施用对连作花生根际土壤微生物区系、酶活性及有效态微量元素(Mo、B、DTPA-Fe、Zn、Cu、Mn)含量的影响。结果表明:内生真菌B3和苍术粉复合处理比内生真菌B3处理的荚果和秸秆产量分别增加10.28%和14.11%,内生真菌B3处理与正常施肥相比显著提高了根瘤数量、荚果和秸秆产重,各处理组与正常施肥对照相比分枝数和根长无显著差异。B3处理与对照相比显著提高了种子期、结荚期和成熟期根际土壤可培养细菌和放线菌数量,B3和苍术粉复合处理与对照相比显著提高种子期、花期和成熟期可培养真菌和放线菌数量;细菌DGGE指纹图谱聚类分析表明,B3和苍术粉复合处理相对于正常施肥处理,显著改变种子期、苗期、花期和成熟期花生根际土壤细菌群落结构,同时苗期、花期和结荚期的细菌条带数和香农指数也有所提高,真菌DGGE指纹图谱聚类分析表明,B3和苍术粉复合处理对真菌群落影响较大,除种子期以外的生育期真菌条带数和香农指数都有明显提高,花期真菌群落结构变化最大,相似度仅为49.6%。花生关键生育期(花期和结荚期)根际土壤脲酶和蔗糖酶活性B3处理和复合处理都显著高于正常施肥对照,促进了连作花生生态系统的物质循环和能量流动。B3和苍术粉复合处理促进了花生生长发育必需微量元素Mo、B、Fe、Zn、Mn的活化,花生叶片和籽粒中微量元素Mo、B、Fe的积累显著增加。研究结果表明,内生真菌和苍术粉联合施用能有效改善连作花生根际微生物区系,提高土壤酶活性,促进微量元素的活化和吸收,对缓解花生连作障碍具有重要意义。     

Time to flowering of temperate pulses in vivo and generation turnover in vivo–in vitro of narrow-leaf lupin accelerated by low red to far-red ratio and high intensity in the far-red region

Understanding the role light quality plays on floral initiation is key to a range of pre-breeding tools, such as accelerated single-seed-descent. We have elucidated the effect of light quality on early flowering onset in cool-season grain legumes and developed predictive models for time to flowering under the optimised light conditions. Early and late flowering genotypes of pea, chickpea, faba bean, lentil and lupin were grown in controlled environments under different light spectra (blue and far red-enriched LED lights and metal halide). All species and genotypes showed a positive response to a decreasing red to far-red ratio (R:FR). In general, ratios above 3.5 resulted in the longest time to flowering. In environments with R:FR below 3.5, light with the highest intensity in the FR region was the most inductive. We demonstrate the importance of considering both relative (R:FR) and absolute (FR photons) light values for flower induction in grain legumes. Greater response to light spectra was observed in the later flowering genotypes, enabling a drastic compression of time to flowering between phenologically diverse genotypes. A novel protocol for robust in vitro germination of immature seeds was developed for lupin, a species known for its recalcitrance to in vitro manipulation. We show how combining this protocol with growth under conditions optimized for early flowering drastically speeds generation turnover. The improved understanding of the effect of light on flowering regulation and the development of robust in vitro culture protocols will assist the development and exploitation of biotechnological tools for legume breeding.     

长期水分胁迫对小麦生育中后期根叶渗透调节能力、渗透调节物质的影响

以 2个抗旱性强的和 2个抗旱性弱的小麦品种为材料 ,研究了中度及严重水分胁迫对根系及叶片渗透调节能力的影响。结果表明 :随着水分胁迫的加剧 ,叶片的渗透调节能力增强 ,但在籽粒迅速扩大的灌浆期 ,叶片的渗透调节能力下降。去穗处理明显地提高叶片的渗透调节能力。说明叶片渗透调节能力的高低与同化物的供应及分配有关。不同品种根系渗透调节能力与叶片基本一致 ,但根系的渗透调节能力低于叶片。开花、灌浆期根系的渗透调节能力大大降低 ,严重水分胁迫下根系的渗透调节能力低于中度水分胁迫。这一方面与同化物的供应有关 ,另一方面严重水分胁迫还会对根细胞造成损伤 ,对根系的渗透调节能力产生影响。渗透调节物质的变化趋势与渗透调节能力基本一致。叶片中 K+对渗透调节的贡献最大 ;其次是可溶性糖 ,6种渗透调节物质排列顺序为 K+>可溶性糖 >游离氨基酸 >Ca2 +>Mg2 +>Pro。根系中仍以 K+占绝大部分 ,但根系中 Ca2 +也是不可忽视的成分之一。     

Effect of Molybdenum and Inorganic Nitrogen on Molybdenum Redistribution in Black Gram (Vigna mungo L. Hepper) with Particular Reference to Seed Fill

Seeds used to plant a crop may contain sufficient molybdenum(Mo) to prevent subsequent Mo deficiency in the crop even whenthey are sown on Mo deficient soils. However, little is knownabout either the sources of the Mo acquired by the seed, orthe timing of its redistribution during seed development. Aglasshouse experiment was set up to examine the effect of Mosupply and nitrogen source on the redistribution of Mo withinblack gram, from full flowering to seed maturity. Treatmentscomprised two sources of N (symbiotic N₂fixation, NH₄NO₃), twolevels of Mo supply [nil (-Mo), 0.64 mg Mo kg^-1soil (+Mo)] andfour harvests (full flowering, early pod setting, late pod fillingand seed maturity). The redistribution of Mo in black gram wasexamined by determining changes over time in the content ofMo in plant parts at each growth stage. Molybdenum supply and the plant growth stage strongly affectedthe redistribution of Mo to the seed. In -Mo plants relianton symbiotic N₂fixation, Mo redistributed from roots, stemsand leaves was the only source of Mo for reproductive developmentsince, from full flowering until maturity, there was no netincrease in whole plant Mo. For pod and early seed development,the roots were the major source of Mo in -Mo plants. After latepod filling, nodules replaced roots as the major source of Mofor seed fill in -Mo plants. By contrast, for +Mo plants relianton symbiotic N₂fixation, Mo taken up from the soil after fullflowering could have supplied nearly 50% of the seed Mo. Themajor sources of Mo for seed filling in +Mo plants were middlestem leaves during early podding, and middle stems and pod wallsfrom late podding. Supplying NH₄NO₃to plants from sowing had little effect on Modistribution or redistribution in +Mo black gram plants. However,in -Mo plants it accelerated the loss of Mo from middle stemsand their leaves compared to nodulated plants. Black gram; Vigna mungo L. Hepper; distribution; molybdenum; nitrogen; nodules; redistribution; seed fill     

Increase of glycinebetaine synthesis improves drought tolerance in cotton

The tolerance to drought stress of the homozygous transgenic cotton (Gossypium hirsutum L.) plants with enhanced glycinebetaine (GB) accumulation was investigated at three development stages. Among the five transgenic lines investigated, lines 1, 3, 4, and 5 accumulated significantly higher levels of GB than the wild-type (WT) plants either before or after drought stress, and the transgenic plants were more tolerant to drought stress than the wild-type counterparts from young seedlings to flowering plants. Under drought stress conditions, transgenic lines 1, 3, 4, and 5 had higher relative water content, increased photosynthesis, better osmotic adjustment (OA), a lower percentage of ion leakage, and less lipid membrane peroxidation than WT plants. The GB levels in transgenic plants were positively correlated with drought tolerance under water stress. The results suggested that GB may not only protect the integrity of the cell membrane from drought stress damage, but also be involved in OA in transgenic cotton plants. Most importantly, the seedcotton yield of transgenic line 4 was significantly greater than that of WT plants after drought stress, which is of great value in cotton production.     

Internal recycling of respiratory CO2 in pods of chickpea (Cicer arietinum L.): the role of pod wall, seed coat, and embryo

It has previously been proposed that respiratory CO2 released from the embryo in grain legume pods is refixed by a layer of cells on the inner pod wall. In chickpea this refixation process is thought to be of significance to the seed carbon budget, particularly under drought. In this study it is reported that the excised embryo, seed coat, and pod wall in chickpea are all photosynthetically competent, but the pod wall alone is capable of net O2 evolution over and above respiration. The predominant role of the pod wall in refixation is supported by measurements of fixation of isotopically labelled CO2, which show that more than 80% of CO2 is fixed by this tissue when provided to the pod interior. Chlorophyll concentrations are of the same order for embryo, seed coat, and pod wall tissues in younger pods on both an area and a fresh weight basis, but decline differentially with development from 12-30 d after podding. Imaging of chlorophyll distribution in the pod wall suggests that less than 15% of chloroplasts are located in the inner layer of cells thought to refix CO2 in legumes; this would be sufficient to refix less than 40% of respired CO2. It is concluded that while all tissues of the pod are capable of refixing respiratory carbon, the entire pod wall is responsible for the majority of this process, rather than a specialized layer of cells on the inner epidermis. The role of this fixed carbon in the pod for reallocation to the seed is discussed     

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

The seed yield of lucerne is poor, in contrast to its good vegetativegrowth. This is partly due to a lack of pollination under naturalconditions, pod abortion and the production of only a few seedsper pod. In this study, lucerne plants were grown in controlledconditions and about 30% of the inflorescences were pollinatedmanually. There were about 10 ovules per flower, which remainedconstant throughout the flowering period. There were 4.5 seedsper pod, indicating over 50% seed abortion. One group of plantswas defoliated and the lack of recent assimilates at floweringcaused a small but significant decrease in the number of seedsper pod (4.1). The effect of defoliation varied with seed age;the youngest fertile inflorescences were the most affected andthere was no effect at around 400C d^–1 . This stage markedthe end of the lag phase, which was determined separately incontrol plants. Thus, it is assumed that this date is the abortionlimiting stage (ALS) for this species. The long lag phase forlucerne could be a key influence on seed yield. The longer theALS, the greater the risk of vegetative competition, thus reducingreproductive development. Key words: Lucerne, flowering, pollination, abortion limiting stage (ALS), seed production