Flowering Node Research Articles

Genetic mapping of QTLs for horticulture traits in a F2-3 population of bitter gourd (Momordica charantia L.)

An extensive genetic linkage map was constructed for bitter gourd (Momordica charantia L.) via the study of F2 progenies derived from two cultivated inbred lines (gynoecia Z-1-4 and 189-4-1). The map included 194 loci on 11 chromosomes consisting of 26 EST-SSR loci, 28 SSR loci, 124 AFLP loci, and 16 SRAP loci. This map covered 1005.9 cM with 12 linkage groups. A total of 43 quantitative trait loci (QTLs), with a single QTL associated with 5.1–33.1 % phenotypic variance, were identified on nine chromosomes for 13 horticulture traits by analyzing the F2-3 families and the genetic linkage map. The 13 horticulture traits which were investigated in three environments included female flower ratios (FFR), first female flower node (FFFN), fruit length, fruit diameter, flesh thickness, fruit shape, fruit pedicel length, fruit length pedicel ratios, fruit weight (FW), fruit numbers per plant (FPP), yield per plant (YPP), stem diameter (SD), and internodes length (IL). One QTL cluster region was detected on Lg-5 which contained the most important QTLs for YPP, FPP, FFFN, FFR, and FW with high contributions to phenotypic variance (5.8–25.4 %).

Evaluation of some okra (Abelmoschus spp L.) germplasm in Ghana

Twenty-five accessions of okra collected from different parts of Ghana were evaluated for their horticultural and agronomic attributes in the major and minor cropping seasons of 2008 at the crop and soil sciences experimental field, Kwame Nkrumah University of Science and Technology (KNUST) Kumasi, Ghana, using a randomized complete block design (RCBD) with four replications. The objectives of the experiment were to investigate the horticultural characteristics and performance of all the okra entries. Data collected included fruit and leaf characteristics; Days to first flowering, first flowering node, first fruit-producing node, fresh fruit weight, fruit length at maturity, fruit width, maximum plant height, number of internode, number of seeds per fruit, number of total fruits per plant, seed yield, 100 seed weight. The accessions KNUST/SL1/07Nkrumahene, DA/08/02Dikaba and GH 5787Asontem, GH6102Fetri and ‘Asontem’ showed number of days from sowing to first-flowering at between 44.00 and 48.00 days, first flowering and fruiting nodes at between 5.00 and 6.00th nodes, days to 50% emergence at 8 days after sowing, the average number to total fruits per plant at 60.00 to 145.00 fruits and green immature fruit colour. The results showed that most of the okra displayed symptoms of okra mosaic virus (OMV) and okra leaf curl virus (OLCV). Fruit size varied among the entries. A correlation of the characters with the total fruit production showed that plant height, days to flowering and nodulation, fruit yield and seed yield recorded positive and significant associations, which generally mean that they influenced fruit production or yield. Specific accessions; KNUST/SL1/07Nkrumahene, DA/08/02Dikaba and GH 5787Asontem, GH6102Fetri and ‘Asontem’, identified in this study, could be passed on to breeders for utilization in the okra improvement programmes in Ghana. Key words: Accessions, assessment, okra mosaic virus (OMV), okra leaf curl virus (OLCV), susceptibility, vegetables.

Morphological indicators and the time of transition to flower in Ptilotus nobilis (Amaranthaceae)

Floral initiation of Ptilotus nobilis (Lindl.) F.Muell. was investigated by both scanning electron and light microscopy to develop a template for the transition from vegetative to reproductive growth. Four developmental stages were identified, including two vegetative and two reproductive stages. Bract initiation was accompanied by a significant increase in meristem area and diameter, and was defined as the onset of flowering. At the transition, meristem diameters and areas increased 1.5 and 2.3 times, respectively. Most morphological traits, including leaf number, mean leaf area and total leaf area, increased gradually at the time of transition and were further investigated in a subsequent glasshouse trial. Floral initiation occurred very early and at 25 days after sowing all plants had entered the reproductive phase. At the onset of flowering leaf and node number increased significantly with 3.6 and 4.2, respectively. Branching and leaf area expansion were identified as post-initiation processes, and increased by 2.8 (total foliage area), 3.3 (total leaf area) and 1.8 (mean leaf area). During the vegetative phase a discolouration of the shoot apical meristem was noted and underlying reasons are discussed.

English

An F2 population derived from the hybrid of Lycopersicon esculentum Mill.XF98-7×Lycopersicon pimpinellifolium LA2184 was used for genome-wide linkage analysis for yield traits in tomato. The genetic map, spanning the tomato genome of 808.4 cM long was constructed with 112 SSR markers distributing on 16 linkage groups. Main and epistatic effect QTLs controlling first flower node, number of flowers per truss, fruit set percentage and fruit weight were located using Bayesian model selection method. A total of 20 significant main effect QTLs and 16 pairs of epistatic QTLs were identified on 16 linkage groups. The proportions of phenotypic variation explained by the detected QTLs ranged from 1.9 to 25.9% and from 0.00 to 17.4% for main-effect and epistatic QTLs, respectively. Most QTL effects were predictable from the parental phenotypes. Additionally, one QTL was found to be pleiotropic, governing simultaneously first flower node and number of flowers per truss.   Key words: Tomato, SSR marker, yield traits, QTL, Bayesian model selection.

Deferring flowering of nobile dendrobium hybrids by holding plants under low temperature after vernalization

Orchids are currently the most valuable potted crop in the United States. To date, no studies focused on making possible the year-round greenhouse production of flowering nobile dendrobium orchids. This experiment was aimed at developing a strategy to defer flowering of nobile dendrobium orchids by holding them under low temperature. Mature Den. Red Emperor ‘Prince’ and Den. Sea Mary ‘Snow King’ were held at 10 °C for various durations (0, 4, 8, 12 or 16 weeks) after vernalization (4 weeks at 10 °C). Plants were forced in a greenhouse after holding. Time to flower, flower differentiation (flowering node percentage, number of aerial shoot and aborted bud) and flower quality (total flower number, flower diameter, flower number per flowering node and flower longevity) were determined. Increase of low temperature holding duration from 0 to 16 weeks extended time to flower up to 3 months and did not affect parameters of flower except producing larger flowers and reducing flower number per flowering node for Den. Red Emperor ‘Prince’. Notably, the flower longevity was not adversely affected. Defoliation was aggravated in Den. Red Emperor ‘Prince’ by longer duration of cooling and was considered a detrimental effect of low temperature holding.

Quantitative trait loci (QTL) mapping for inflorescence length traits in Lablab purpureus (L.) sweet

Lablab purpureus (L.) sweet is an ancient legume species whose immature pods serve as a vegetable in south and south-east Asia. The objective of this study is to identify quantitative trait loci (QTLs) associated with quantitative traits such as inflorescence length, peduncle length from branch to axil, peduncle length from axil to lowermost flowering node, rachis length, node number of inflorescence, rachis internode length, node order of the first inflorescence and node order of lowest inflorescence, which are key characters affecting the output of vegetable cultivars of lablab. A molecular linkage map was constructed using a F 2 population derived from the cross (Meidou2012 × Nanhui 23). The map covers 1302.4 cm with 131 loci (122 RAPD and nine morphological markers) and consist 14 linkage groups. In the F 2 population and derived F 3 families, a total of 46 QTLs explained from 8.1 to 55.0% of phenotypic variance of the traits. Of them, 16 QTLs were detectable in the same linkage regions among different generation/season combinations, and 10 QTL clusters were mapped. It suggests that, genes which control inflorescence growth were pleiotropic or coincident involving more than one trait. Thus, these QTLs may be tagged for marker assisted selection to improve yield of lablab. Key words: Inflorescence length, lablab, linkage map, quantitative trait loci (QTLs), random amplification of polymorphic DNA (RAPD).

Computational analysis of flowering in pea (Pisum sativum).

During plant development, the transition from a vegetative to reproductive state is a critical event. For decades, pea (Pisum sativum) has been used as a model species to study this transition. These studies have led to a conceptual, qualitative model for the control of flower initiation, referred to as the 'classical' model. This model involves many inputs, namely photoperiod, genetic states and two mobile signals which interact to determine the first node of flowering. Here, we developed a computational model based on the hypotheses of the classical model. Accordingly, we converted qualitative hypotheses into quantitative rules. We found that new hypotheses, in addition to those already described for the classical model, were required that explicitly described the signals. In particular, we hypothesized that the key flowering gene HR interacts with the photoperiod pathway to control flowering. The computational model was tested against a wide range of biological data, including pre-existing and new experimental results presented here, and was found to be accurate. This computational model, together with ongoing experimental advances, will assist future modelling efforts to increase our understanding of flowering in pea.

Effects of Cooling Temperature and Duration on Flowering of the Nobile Dendrobium Orchid

The effects of cooling temperature [constant (10, 13, 15, or 18 °C, or 15, 18, or 21 °C)] and duration (2, 3, 4, 5, or 6 weeks, or 3, 4, 5, 6, or 7 weeks) at two separate locations (College Station and Weslaco, TX) on growth and flowering of Dendrobium Sea Mary ‘Snow King’, a Dendrobium nobile Lindl. hybrid, were investigated and the cooling requirement for flowering was quantified. Interactions between temperature and cooling duration were significant on time required to reach anthesis from either the beginning or completion of cooling, average flower number per flowering node, and percentage of nodes with aborted buds. Increasing cooling duration from 2 to 6 or 3 to 7 weeks resulted in less time to reach anthesis after the completion of cooling. However, the increased cooling durations extended the time needed for producing a flowering crop. Plants cooled at a relatively higher temperature among 10, 13, and 15 °C required less time to reach anthesis after the completion of cooling. Plants had more flowering nodes and total flowers when cooled at 10, 13, or 15 °C than at 18 °C in College Station or at 15 or 18 °C than at 21 °C in Weslaco. The results suggest that 3 weeks at 13 °C has saturated the cooling requirement, and 3 weeks at 13 or 15 °C is a recommended cooling treatment that saves production cost without retarding flower development.

Genetic mapping and QTL analysis of fruit and flower related traits in cucumber (Cucumis sativus L.) using recombinant inbred lines

A set of 224 recombinant inbred lines (RILs) derived from a narrow cross between two fresh eaten types (S94 (Northern China type) × S06 (Northern European type)) (Cucumis sativus L.) was used to construct a genetic linkage map. With the RILs a 257-point genetic map was constructed including 206 SRAPs, 22 SSRs, 25 SCARs, 1 STS, and three economically important morphological markers (small spines (ss), uniform immature fruit color (u), dull fruit skin (D)). The seven linkage groups covered 1005.9 cM with a mean marker interval of 3.9 cM. The ss locus was linked to D and u, and they were all on Linkage group 6. The RIL map contained a total of 51 sequence-specific markers, which made possible the comparison of molecular linkage maps developed in different laboratories. Using the F6:7 derived families, a total of 78 QTLs were detected with relatively high LOD scores (2.9–84.4) for nine fruit-related traits (fruit weight, length, and diameter, fruit flesh thickness, seed-cavity diameter, fruit-stalk length, fruit pedicel length, length/diameter and length/stalk ratio) and three flower-related traits (first flower node, first female flower node and female flower ratios). Several sequence-anchor markers (CSWCT25, CS30, CMBR41, CS08 etc.) were closely linked with some QTLs for fruit weight, fruit length, fruit flesh thickness and sex expression, which can be used for the future marker-assisted selection to improve the fruit traits in cucumber breeding.

Nitrogen, Phosphorus, and Potassium Requirements for Optimizing Growth and Flowering of the Nobile Dendrobium as a Potted Orchid

Experiments were conducted to determine how nitrogen (N), phosphorus (P), and potassium (K) rate and fertilizer termination time affect the growth and flowering of a Dendrobium nobile Lindl. hybrid, Dendrobium cv Red Emperor ‘Prince’. Nitrogen, P, and K were tested in separate experiments as a factorial combination of five rates and three termination dates (1 Sept., 1 Oct., and 1 Nov. 2005). Nitrogen and K rates were 0, 50, 100, 200, and 400 mg·L−1. Phosphorus rates were 0, 25, 50, 100, and 200 mg·L−1. Levels of the nutrients not being tested were held constant. For all nutrients, ending fertilization on 1 Sept. resulted in greater or similar pseudobulb thickness compared with ending fertilization on 1 Oct. or 1 Nov. Pseudobulbs grew taller as the N rate increased, peaking at 100 and 200 mg·L−1. There were interactions between the N rate and fertilizer termination time on all reproductive characteristics. For all fertilizer termination times, flower number increased once N was applied. When ended on 1 Nov., 200 and 400 mg·L−1 N caused a delay to reach anthesis. All P rates resulted in taller plants with equally more nodes when compared with 0 mg·L−1. As the K rate increased from 0 to 100 mg·L−1, plant height increased, with no further increase at higher rates. The number of leaves remaining increased as N and K rates increased up to 200 mg·L−1. Total flower number and flowering node number increased as the K rate increased to 100 mg·L−1 (terminated on 1 Sept.) or 50 mg·L−1 (terminated on 1 Oct. or 1 Nov.). In the fourth experiment, only N was ended at four termination times, whereas all other nutrients continued to be supplied until flowering. Control plants received all fertilizer elements until flowering. The duration of N application did not affect vegetative or flowering characteristics. No aerial shoots were observed as a result of prolonged application of N at all rates. In summary, 100 mg·L−1 N, 25 mg·L−1 P, and 100 mg·L−1 K are recommended for optimal vegetative growth and reproductive development of Dendrobium cv Red Emperor ‘Prince’.

In vitro Propagation and Plantlet Regeneration from Doritaenopsis Purple Gem ‘Ching Hua’ Flower Explants

The effects of four types of explants removed from 10-cm flower stalks of Doritaenopsis Purple Gem ‘Ching Hua’ (immature apical flower buds, immature lateral flower buds, flower stem nodes, and flower pedicel sections) and combinations of two plant growth regulators [naphthalene acetic acid (NAA) and thidiazuron (TDZ)] on direct in-vitro shoot induction and multiplication were studied. Immature apical flower buds were the only explants that showed induction and multiplication of shoots in vitro. NAA at 5.4 and 10.7 μm combined with either 4.5 or 9.1 μm TDZ provided the fastest and greatest percentages of shoot induction (27% to 40%) and the greatest numbers of shoot multiplication (111–160 shoots per explant). In vitro–induced shoots were rooted on medium containing 5.4 μm NAA and developed into plantlets with normal vegetative and reproductive morphology. Regenerated plantlets were acclimatized, showing 100% survival and establishment in greenhouse. Plantlets were grown to maturity and showed normal flower morphology. No floral off-types were observed. The high rates of shoot multiplication obtained offer a means for mass clonal propagation of this and possibly other related Doritaenopsis hybrids.

Rapid in vitro propagation of Dendrobium hybrids through direct shoot formation from foliar explants, and protocorm-like bodies

In vitro propagation protocol for Dendrobium hybrids Sonia 17 and 28, two highly priced commercial cut flower cultivars through direct organogenesis from in vitro derived foliar explants was established. Rapid clonal propagation was achieved by subsequent induction of protocorm-like bodies (PLBs) and its conversion to shoots. No significant differences were observed in the induction of direct shoots, shoot multiplication, PLBs formation and subsequent shoot development and rooting of shoots between the two cultivars. Leaf explants from flower stalk node derived shoots cultured on half-strength Murashige and Skoog (MS) medium supplemented with 44.4 μM N 6-benzyladenine (BA) developed more than seven shoots per explant. The isolated shoots transferred onto the same medium induced more than eight PLBs from the base within 60 days, which upon transferral to fresh medium having the same level of BA facilitated rapid proliferation. More than 200 PLBs were yielded from fifth subculture. Half-strength MS medium containing 6.97 μM kinetin (Kn) facilitated conversion of more than 90% PLBs to shoots. PLBs exhibited proliferation without decline up to the 15th subculture. Half-strength MS medium with 2 g l −1 activated charcoal was the best for in vitro rooting. Plantlets of the hybrids exhibited more than 80% ex vitro establishment.

Cultivar differences in yield distribution patterns in okra [Abelmoschus esculentus (L.) Moench

A total of 15 okra cultivars of Indian, Turkish, West African, and United States origin with diverse plant traits were selected to investigate the distribution patterns of yield throughout the harvest period. The proportion of fruits harvested up to mid-harvest period (FMH) was calculated for each cultivar and taken as a criterion in transforming yield distribution patterns into numerical variables. Cultivars showed a gradation for FMH values ranging from 64.5% to 30.7%. High FMH values were exclusively found in the Indian cultivars, whilst there was no origin-specificity for lower FMH values. Most parts of the plant architecture were associated with FMH. When moving from lower to higher FMH values, the number of lateral branches and consequently the proportion of yield carried by the lateral branches decreased (both at P < 0.001) and flowering initiated earlier (P < 0.001). However, plants showed reduced mean stem diameter (P < 0.05), leaf area (P < 0.001), and fruit weight (P < 0.05). Hence, fewer generative nodes per plant were formed (P < 0.001). However, the proportion of generative nodes translated into fruits was higher (P < 0.001), and consequently a greater number of fruits per plant was harvested (P < 0.01). Coefficient of determination (R 2) analysis revealed that a multiple regression model containing the 3 traits most correlated with FMH [number of days to flowering (r = –0.89), first flowering node (r = –0.84), proportion of generative nodes translated into fruits (r = 0.80)] explained 85% of the variation in FMH. Number of days to flowering alone explained 79% and a complex regression model containing all variables (10 variables) explained 90%. Traits associated with yield distribution patterns may be considered in introducing cultivars to different ecological and production systems, as well as in selection for breeding lines.

Construction of a genetic map and localization of QTLs for yield traits in tomato by SSR markers

Abstract Using F2 population derived from the hybrid of Lycopersicon esculentum Mill. ‘XF 98-7’ × Lycopersicon pim pinellifolium LA2184, a SSR genetic linkage map of tomato is constructed. The map contains 112 markers and spans 808. 4 cM with an average distance of 7.22 cM between loci. Two quantitative trait loci (QTLs) for first flower node on chromosomes 5 and 11, two QTLs for number of flowers per truss on chromosomes 2 and 5, and five QTLs for fruit weight on chromosomes 1, 2, 3, 9 and 12 are identified.

Temporal profiles of pod production and pod set in soybean

The distribution of flower and pod production during flowering may be an important determinant of pod and seed number in grain crops. We characterized the dynamics of small pod production and survival to maturity on indeterminate and determinate soybean [ Glycine max (L.) Merrill)] cultivars growing in the field or greenhouse. Two soybean cultivars (maturity group IV, indeterminate and determinate) were grown in the field near Lexington, KY (38°N latitude) in 2001 and 2002 in 0.76 cm rows using late May and late June (2002 only) planting dates, and normal (24 plants m −2) and low (9 plants m −2, 2002 only) plant populations. Cultivar Elgin 87 (indeterminate, maturity group II) was grown in a greenhouse in 3.0 L pots with one plant per pot. All unmarked pods that were ≥10 mm long were marked with acrylic paint at the base of the pod at 3-day intervals. Paint color was changed at each marking to provide a temporal profile of pod production and pod survival. The pod production (marked pods) period was longer in the indeterminate cultivar (nearly 50 days after R1) than the determinate cultivar (≤40 days after R1). Delayed planting shortened the pod-production period, but a two- to three-fold difference in pods per plant, created by changing plant population, did not affect it. The temporal distribution of small pods that survived to maturity (full sized pods with at least one normal seed) closely followed the distribution of pod production in all experiments. Some surviving pods initiated growth after the beginning of seed filling (i.e., between growth stage R5 and R6), but most of the pods were initiated in a much shorter interval (up to 84% were initiated in <40% of the period) before R5. Abortion of pods >10 mm long was relatively low (20–30%), so production of a pod ≥10 mm long seems to be a key event in the pod set process. The average length of the pod set period at individual nodes on the main stem was larger for the determinate cultivar (14 days) than for the indeterminate (9 days), so the longer total period in the indeterminate cultivar resulted from the delay in initating pod production at the upper nodes on the main stem. Temporal profiles of pod production and pod set seem to be more sensitive to changes in flower and main stem node production than to changes in photosynthesis per plant (created by varying plant population). These results provide some of the information needed to integrate time into models predicting pod and seed number.

Linkage Mapping of QTL for Seed Yield, Yield Components, and Developmental Traits in Pea

Seed yield in pea (Pisum sativum L.) is a physiologically complex trait that is strongly influenced by both genotype and environment. Seed yield can be described in terms of its components, which include plant number per unit area, seed weight, and seed number. These yield components show interdependence and plasticity in response to environment; therefore, selection based on a single component is unlikely to succeed in increasing yield in breeding programs. To improve our understanding of the genetic basis of seed yield determination in pea and to identify genetic loci involved, quantitative trait loci (QTL) for yield per se, yield components (seed weight, seed number, and harvest index [HI]) and developmental traits (node of first flower [NFF], number of flowering nodes [NFN], total node number [TNN]) were mapped. The QTL mapping was conducted using F2–derived families of a cross between Primo, a marrowfat cultivar, and OSU442‐15, a blue pea breeding line. Linkage maps containing 108 loci on 11 linkage groups (LGs) were constructed for 227 families derived from this cross. Traits were measured in three replicated field trials conducted in New Zealand during the summers of 1997–1998, 1998–1999, and 2002–2003. The trials were managed to ensure maximum expression of yield potential. The QTL affecting yield‐related traits were associated with 19 genomic regions on LGs I, II, III, IV, VI, and VII. The QTL for different yield‐related traits were colocalized, suggesting some basis for understanding the reproductive plasticity that is observed in pea at the genetic level.

Influence of Day Length on Stem Growth, Flowering, Morphology of Flower Clusters, and Seed-Set in Buckwheat (Fagopyrum esculentum Moench)

The effects of day length on main stem growth, flowering, morphology of flower clusters and seed-set were examined in three buckwheat cultivars Shinanonatsusoba (summer eco-type), Miyazakizairai (autumn eco-type) and BLO 1999 (a long cluster line which usually develops DM clusters at Kade Research Ltd., Canada). Long-day treatment prolonged the stem elongation period, elevated the first flowering node, delayed the first flowering day, increased the numbers of nodes, flower clusters and flowers on the main stem, and decreased the increase rate of flowering-cluster number, the number of seeds and the seed-set ratio on the main stem. It also increased the frequency of DM clusters, the length of the flower clusters and the number of sub-flower-clusters per cluster in Shinanonatsusoba and Miyazakizairai as well as in BLO 1999. The effects of day length varied among the growth parameters and there were three types of responses to day length. The difference between the summer and autumn eco-type cultivars in the responses to day length was elucidated in four groups of parameters; (1) main stem elongation; (2) first flowering node and first flowering day; (3) increase rate of flowering-cluster number on the main stem; and (4) the number of seeds and seed-set ratio.

Characterizing the Vernalization Response of Campanula `Birch Hybrid' to Temperatures Between -2.5 to 20 °C

Campanula `Birch Hybrid' has an obligate vernalization requirement, though little is known about the vernalization response as a function of temperature and duration. The objective of this study was to characterize the qualitative and quantitative effects of exposure to -2.5 to 20 °C on C. `Birch Hybrid' flowering. Plugs were bulked at 20 °C for 4 weeks and then transferred to -2.5, 0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5 or 20 °C for 0, 3, 5, 7, 9, or 12 weeks. Plugs were then potted and grown at 20 °C under 16-h photoperiod. Nine plants were used per treatment. Date of first open flower and the number of open flowers and flowering nodes 7 d later were recorded. No plants flowered after 0 or 3-week treatments. One plant held at 20 °C flowered and no plants flowered after exposure to 17.5 °C. After 5 weeks at 0 to 7.5 °C, 100% of plants flowered with the fastest flowering after 2.5 to 7.5 °C. The number of flowering nodes and open flowers were similar for plants held at -2.5 to 10 °C for 5 weeks. All plants flowered following 7 weeks at -2.5 to 12.5 °C, though flowering was quickest after exposure to 2.5 to 7.5 °C. After 7 weeks, plants held at -2.5 to 10 °C produced similar number of flowering nodes and open flowers. Following 9 weeks, all plants at -2.5 to 12.5 °C flowered and 2.5 to 7.5 °C treated plants flowered first. The number of flowering nodes was uniform across -2.5 to 12.5 °C and the highest number of flowers was produced at 12.5 °C. All plants held at -2.5 °C died after 12 weeks. After 12 weeks, all plants flowered following 0 to 15 °C. However, following 15 °C, plants produced fewer flowers and flowering nodes. Overall, the optimal vernalization response was between 0 to 7.5 °C.

Pod and seed numbers as a function of photothermal quotient during the seed set period of field pea ( Pisum sativum) crops

The effects of radiation and temperature during the seed set period (SSP) on pod number per square metre (PN m −2) and seed number per square metre (SN m −2) and those of temperature during grain filling on unit seed weight (USW, milligram per seed) of field pea ( Pisum sativum L.) were examined in experiments involving irrigated crops of three or more cultivars of contrasting maturity sown on two or more dates per year from 1996 to 1998 at Buenos Aires, Argentina. The duration of the seed-setting phase was estimated from records of the progress of flowering on the main stem and an estimate (obtained using an optimisation procedure) of the thermal time from flowering at which the uppermost reproductive node reached the final stage of seed abortion (FSSA). The FSSA at a particular node was assumed to be achieved 200 °C day ( T b=4 °C) after flowering at the same node. The grain-filling phase was assumed to run from the achievement of FSSA at the first reproductive node through to 200 °C day ( T b=0 °C) after the date of achievement of the FSSA by the second flowering node. The treatments (cultivar, sowing date, year) produced important ranges of above-ground biomass (AGB) at maturity (271–782 g m −2), seed yield (SY, 119–331 g m −2), SN (1062–3698 seeds m −2) and USW (67–150 mg seed −1). Seed yield was strongly correlated with SN, and there was full compensation between SN and USW in large-seeded cultivars in the high SN range, but not at lower values of SN or in small-seeded cultivars. Both PN ( r=0.83) and SN ( r=0.87, P<0.0005) were strongly correlated with the mean daily value of the photothermal quotient (PQ=incident radiation/(mean temperature − base temperature)) for the seed-setting phase. Large- and small-seeded cultivars had PN/PQ and SN/PQ relationships with slopes which did not differ among categories but with significantly different intercepts. When the effects of low temperatures during flowering and early grain growth were allowed for, outliers on the PN/PQ and SN/PQ relationships for unstressed crops fell within the confidence limits of the respective linear regressions. Unit seed weight showed a negative response to mean temperature during the grain-filling phase in large- and small-seeded cultivars. We conclude that the relationships established in these experiments, taken together with previous work by other authors, constitute a robust basis for modelling the yield of unstressed field pea crops.

Can sucrose content in the phloem sap reaching field pea seeds (Pisum sativum L.) be an accurate indicator of seed growth potential?

The composition of the translocates reaching the seeds of pea plants having various nitrogen (N) nutrition regimes was investigated under field situations. Sucrose flow in the phloem sap increased with the node number, but was not significantly different between N nutrition levels. Because N deficiency reduced the number of flowering nodes and the number of seeds per pod, the sucrose flow bleeding from cut peduncles was divided by the number of seeds to give the amount of assimilates available per seed. The sucrose concentration in phloem sap supplied to seeds at the upper nodes was higher than that at the lower nodes. The flow of sucrose delivered to the seeds during the cell division period was correlated with seed growth potential. Seeds from the more N-stressed plants had both the highest seed growth rate and received a higher sucrose flux per seed during the cell division period. As seed growth rate is highly correlated with the number of cotyledonary cells produced during the cell division period, sucrose flow in phloem sap is proposed to be an important determinant of mitotic activity in seed embryos. The carbon (C)/N ratio of the flow of translocates towards seeds was higher under conditions of N-deficiency than with optimal N nutrition, indicating that N flux towards seeds, in itself, is not the main determinant of seed growth potential.