Early Pod-filling Stage Research Articles

First Report of White Mold Caused by Sclerotinia sclerotiorum on Faba Beans in North Dakota

Faba bean (Vicia faba L.) is a pulse crop grown for its nutritional value for both human and animal consumption worldwide. In addition to its nutritional value in terms of high protein content (≈28%), faba bean improves soil fertility by fixing atmospheric nitrogen (Sahile 2011). With the decline in the total hectares planted to field pea (Pisum sativum L.) owing to root rots, faba bean research has recently been initiated to determine its adaptability to North Dakota agroecosystems and the feasibility of using it as an alternative to field pea. Faba bean plants exhibiting white mold symptoms, characterized by white cottony mycelium of the pathogen growing on stems and bleached disease tissues, on the cultivar Tabasco were observed at the early pod-filling stage in research plots during late July 2017 at Langdon, North Dakota, with a general incidence of 6%. Dark, round sclerotia, characteristic of those produced by Sclerotinia sclerotiorum (Lib.) de Bary, were observed by opening infected stems. Sclerotia were collected from infected stems, and each sclerotium was cut in half after surface sterilization with 5% NaOCl. One half of the sclerotium was plated on potato dextrose agar (PDA) media in Petri plates and incubated at room temperature in the dark for 7 days on the laboratory bench. All isolates were tentatively identified as S. sclerotiorum (Kohn 1979) based on the mycelial color, growth, and transformation of white masses of the mycelia toward the edge of the plates into dark-colored sclerotia. Identity of five isolates was confirmed by performing a multiplex polymerase chain reaction (PCR) assay designed to discriminate four species of Sclerotinia (Abd-Elmagid et al. 2013). Amplicons of ≈171 bp were observed on a 1% agarose gel, confirming the identity of the isolates as S. sclerotiorum. Pathogenicity tests were conducted using four representative isolates of confirmed S. sclerotiorum based on molecular tests to fulfill Koch’s postulates and repeated. Faba bean cultivar Tabasco seeds were planted in 13-cm-deep, 10 × 10-cm square plastic pots filled with Sunshine Mix No. 1 (SunGro Horticulture, Agawam, MA) and grown for 4 weeks in a greenhouse maintained at 21°C with a 16-h photoperiod. Four-week-old plants were inoculated by wrapping a 5-mm-diameter mycelial plug removed from the leading edge of a 3-day-old actively growing colony on PDA. The mycelial plug was affixed to the stem approximately 2.5 cm above the soil with clear tape. Four pots, each containing two plants, were inoculated for each isolate. Plants inoculated with noncolonized PDA plugs served as controls. Necrotic lesions appeared 2 days postinoculation. Lesions expanded rapidly, resulting in death of plants within 7 days postinoculation. The plants were maintained in the greenhouse for an additional 2 weeks to allow sclerotia production. Control plants remained healthy. Dark black sclerotia were produced on dead stems by 3 weeks postinoculation. Pure cultures were reisolated from sclerotia collected from dead stems, and the identity was confirmed by morphology and PCR-based analysis. White mold is endemic in North Dakota and causes economic losses on many economically important broad leaf crops including dry bean, canola, soybean, and sunflower. To our knowledge, this is the first report of white mold occurrence on faba bean in North Dakota. Growers considering inclusion of faba bean in their rotations should consider the history of white mold in the fields to be planted.

Response of lentil to high temperature under variable water supply and carbon dioxide enrichment

Lentil (Lens culinaris Medik.) production in arable, Mediterranean-type climates is limited by heat waves and unreliable rainfall. Under climate change scenarios, increased atmospheric carbon dioxide (CO2) concentration will increase plant growth; however, the net effect of increasing occurrence and intensity of heat waves and drought is unclear. This study tested the response of combined acute high temperature (>32°C) at the early pod-filling stage and (i) crop-available soil water, and (ii) elevated CO2 on three lentil genotypes in two experiments. The three lentil genotypes selected were commercial cultivar PBA Bolt and two landraces sourced from the Australian Grains Genebank, AGG 71457 and AGG 73838. High soil-water availability (0.42 Mg m–3) throughout the growing season increased yield by 28% compared with low soil-water availability (0.35 Mg m–3). Across contrasting water treatments, there was no difference in patterns of crop response to high temperature during the early pod-filling phase (5 days at 42°C daytime, 25°C night), where yields were reduced by 45%. A significant interaction between high temperature response and genotype was observed, where reduction in grain number was higher for AGG 73838 (0.20% per degree-hour >32°C) than for AGG 71457 (0.07% per degree-hour >32°C) or PBA Bolt (0.10% per degree-hour >32°C). For heat and CO2 effects, there was no significant interaction between high temperature (3 days at 38°C daytime, ambient night temperature) and CO2 treatment on yield components. There was, however, an overall trend of increased biomass, grain number and yield due to elevated CO2. Although non-limiting soil water did not reduce the impact of high temperature in this study, the range in response across genotypes to high temperature supports opportunity for increased adaptation of lentil toward increasing yield stability under effects of climate change.

Impact of rhizobial inoculation and reduced N supply on biomass production and biological N2 fixation in common bean grown hydroponically.

Testing rhizobial inoculation of common bean (Phaseolus vulgaris L.) in hydroponics enables accurate quantification of biological N2 fixation (BNF) and provides information about the potential of reducing inorganic N fertilizer use. In view of this background, common bean grown on pumice was inoculated with Rhizobium tropici CIAT899 (Rt) and supplied with either full-N (total nitrogen 11.2 mmol L-1 ), 1/3 of full-N or N-free nutrient solution (NS). BNF was quantified at the early pod-filling stage using the 15 N natural abundance method. Full-N supply to Rt-inoculated plants resulted in markedly smaller nodules than less- or zero-N supply, and no BNF. Rt inoculation of full-N-treated plants did not increase biomass and pod yield compared with non-inoculation. Restriction (1/3 of full-N) or omission of inorganic N resulted in successful nodulation and BNF (54.3 and 49.2 kg N ha-1 , corresponding to 58 and 100% of total plant N content respectively) but suppressed dry shoot biomass from 191.7 (full-N, +Rt) to 107.4 and 43.2 g per plant respectively. Nutrient cation uptake was reduced when inorganic N supply was less or omitted. Rt inoculation of hydroponic bean provides no advantage when full-N NS is supplied, while 1/3 of full-N or N-free NS suppresses plant biomass and yield, partly because the restricted NO3- supply impairs cation uptake. © 2017 Society of Chemical Industry.

Effect of Synthetic Auxin Herbicides on Seed Development and Viability in Genetically Engineered Glyphosate-Resistant Alfalfa

Feral populations of cultivated crops have the potential to function as bridges and reservoirs that contribute to the unwanted movement of novel genetically engineered (GE) traits. Recognizing that feral alfalfa has the potential to lower genetic purity in alfalfa seed production fields when it is growing in the vicinity of foraging pollinators in alfalfa seed fields, industry has established production standards to control feral plants. However, with the commercialization of GE glyphosate-resistant (GR) alfalfa and the need to support the coexistence of both GE and conventional production, effective methods to control transgenic feral alfalfa need to be developed. Therefore, a study was conducted in 2012, 2013, and 2014 to determine the effect of several synthetic auxin herbicides on seed development in GR alfalfa. GR alfalfa, var. Genuity (R44BD16), was treated with dicamba, 2,4-D, triclopyr, and aminopyralid when alfalfa plants contained green seed pods. Two weeks after herbicide application, plants were harvested, air dried, and seed yield, seed germination, and seedling emergence from the soil were determined. In 2013, dicamba, triclopyr, and 2,4-D decreased alfalfa seed yield per plant compared wih nontreated plants, whereas in 2014, all four herbicides decreased alfalfa seed yield per plant 24 to 49% (by weight) compared with nontreated plants. The same trend was evident in 2012, but seed yield was variable and was not significantly different among treatments. Seed germination averaged 43, 50, and 72% in 2012, 2013, and 2014, respectively, and was not affected by the four herbicides applied at early pod-fill stage. However, seeds harvested from plants treated with dicamba, 2,4-D, and triclopyr often produced deformed and abnormal seedlings, and when planted in soil, frequently failed to emerge. The combined effects of dicamba, 2,4-D, and triclopyr in reducing seed yield, seedling emergence, and seedling growth could contribute to managing feral alfalfa populations.

Pod removal responsive change in phytohormones and its impact on protein degradation and amino acid transport in source leaves of Brassica napus

To characterize the hormonal regulation of nitrogen remobilization from source to pod filling in Brassica napus, the hormonal level, proteolytic process, and amino acid transport were assessed in mature leaves of pod-removed or control at the early pod-filling stage. Pod (sink) removal decreased salicylic acid (SA), and significantly increased jasmonic acid (JA). The SA/JA ratio decreased with pod removal, accompanied by low degradation of foliar proteins and Rubisco content. A significant decrease in protease activity was observed in pod-removed leaves, confirmed by in-gel staining of protease. Pod removal reduced the expression of four amino acid transporter genes (BnAAP1, BnAAP2, BnAAP4, and BnAAP6) in mature leaves and reduced amino acid loading into phloem. These results indicated that a decrease in SA resulting from pod removal down-regulated nitrogen remobilization accompanied by a decrease in proteolytic activity and amino acid transport in mature leaves at the pod-filling stage.

Evidence of Salicylic Acid-Mediated Protein Degradation and Amino Acid Transport in Mature Leaves of Brassica napus

Brassica napus is characterized by low nitrogen remobilization efficiency from source leaves to seed filling, which is mainly due to poor hydrolysis of foliar proteins. To investigate the roles of salicylic acid (SA) in the proteolytic process in source organ at the early pod-filling stage, the SA concentration, protein profile, protease activity, and amino acid transporter genes were measured in mature leaves sprayed with SA or control at four and 30 days after treatment. Exogenous SA application resulted in an increase in SA concentration, accompanied with a significant decrease in protein with concomitant increase in amino acid concentration. Rubisco proteins were largely degraded in the SA-applied leaves. A significant increase in protease activity (up to 98 % at day 30) in the SA-applied leaves was observed. The increased proteolytic activity was confirmed in-gel staining of protease. Three amino acid permeases, BnAAP1, BnAAP2, and BnAAP6, were identified in mature leaves. Exogenous SA application enhanced the expression of three amino acid transporter genes. The present study clearly indicates that the SA level increased by exogenous SA application could improve N remobilization efficiency by up-regulating protein degradation and amino acid transport in source leaves at the pod-filling stage.

Variability of root traits in common bean genotypes at different levels of phosphorus supply and ontogenetic stages

Selection of common bean (Phaseolus vulgaris L.) cultivars with enhanced root growth would be a strategy for increasing P uptake and grain yield in tropical soils, but the strong plasticity of root traits may compromise their inclusion in breeding programs. The aim of this study was to evaluate the magnitude of the genotypic variability of root traits in common bean plants at two ontogenetic stages and two soil P levels. Twenty-four common bean genotypes, comprising the four growth habits that exist in the species and two wild genotypes, were grown in 4 kg pots at two levels of applied P (20 and 80 mg kg-1) and harvested at the stages of pod setting and early pod filling. Root area and root length were measured by digital image analysis. Significant genotype × P level and genotype × harvest interactions in analysis of variance indicate that the genotypic variation of root traits depended on soil nutrient availability and the stage at which evaluation was made. Genotypes differed for taproot mass, basal and lateral root mass, root area and root length at both P levels and growth stages; differences in specific root area and length were small. Genotypes with growth habits II (upright indeterminate) and III (prostrate indeterminate) showed better adaptation to limited P supply than genotypes of groups I (determinate) and IV (indeterminate climbing). Between the two harvests, genotypes of groups II and III increased the mass of basal and lateral roots by 40 and 50 %, respectively, whereas genotypes of groups I and IV by only 7 and 19 %. Values of the genotypic coefficient of determination, which estimates the proportion of phenotypic variance resulting from genetic effects, were higher at early pod filling than at pod setting. Correlations between shoot mass and root mass, which could indicate indirect selection of root systems via aboveground biomass, were higher at early pod filling than at pod setting. The results indicate that selection for root traits in common bean genotypes should preferentially be performed at the early pod-filling stage.

Low-Density Co-Inoculation of Myanmar <i>Bradyrhizobium yuanmingense</i> MAS34 and <i>Streptomyces griseoflavus</i> P4 to Enhance Symbiosis and Seed Yield in Soybean Varieties

This study examined whether low-density co-inoculation of Myanmar Bradyrhizobium yuanmingense strain MAS34 and Streptomyces griseoflavus P4 would enhance nodulation, N2 fixation, and seed yield in two soybean varieties. A field experiment was conducted during the July to November 2012 growing season at Kyushu University Farm, Japan, using a split-plot design with three replications and the following four treatments: T1, an uninoculated treatment with peat moss (uninoculated); T2, a single inoculation with S. griseoflavus P4 (P4); T3, a single inoculation of B. yuanmingense MAS34 (MAS34); and T4, a dual inoculation of P4 with MAS34 (P4 + MAS34). Two varieties of soybean, Yezin-3 (Rj4) and Yezin-6 (non-Rj), were used. The N2 fixation activity of soybean was evaluated by the relative ureide method using xylem solute from root bled sap at the early pod-fill stage (R3.5). Dry matter production, N2 fixation, and seed yield were significantly (P 0.01) different between the inoculated treatments. The effect of variety was also significant (P 0.05) for nodule dry weight at the V6 stage, percentage of N derived from the atmosphere at the R3.5 stage, and seed yield at the maturity stage. The number of nodules on the tap roots was significantly higher in Yezin-3 than in Yezin-6. The single inoculation of P4 did not have a significant effect on dry matter production, N2 fixation, and seed yield in either soybean variety. The dry matter production, relative ureide index, percentage of N derived from the atmosphere, and seed yield were significantly (P 0.01) enhanced by a single inoculation of MAS34 in Yezin-3 and by dual inoculation of P4 + MAS34 in Yezin-6. These results indicate that low inoculum concentrations (105 cells seed-1) increase N2 fixation and seed yield in these soybean varieties under open field conditions. Myanmar B. yuanmingense MAS34 and S. griseoflavus P4 are expected to be useful biofertilizers for soybean production.

Effects of endophytic actinomycetes and Bradyrhizobium japonicum strains on growth, nodulation, nitrogen fixation and seed weight of different soybean varieties

Effects of endophytic actinomycetes and two Bradyrhizobium japonicum (Kirchner 1896) Jordan 1982 strains on growth, nodulation, nitrogen (N) fixation and seed weight of different soybean (Glycine max L. Merr.) varieties from Myanmar (Hinthada), Thailand (SJ5) and Cambodia (DT84) were studied in pot experiments in Thailand. The six treatments consisted of an uninoculated control (T1), a single inoculation with endophytic actinomycetes (Streptomyces sp. strain, P4) (T2), a single inoculation with Bradyrhizobium japonicum strains, USDA110 (T3) or THA7 (T4) and a dual inoculation of P4 with USDA110 (T5) or THA7 (T6). Sterile soil was used for cultivation of all treatments under open field conditions, using tap water for irrigation. N2 fixation activity of soybean was evaluated by the relative ureide method using xylem solute from the root bleeding sap at the early pod-fill stage. It was found that the single inoculation of P4 did not show significant effects on nodulation, N2 fixation, shoot dry weight and seed weight at harvest of all soybeans compared with the uninoculated control. In the Hinthada soybean, single inoculation of USDA110 or THA7 increased seed weight while USDA110 improved N2 fixation (P < 0.05). Dual inoculation of USDA110 and P4 showed the highest shoot N accumulation and seed weight among treatments. In the SJ5 soybean, similar trends to Hinthada were shown, although the THA7 and P4 combination showed the highest shoot N accumulation and seed weight. On the other hand, in the DT84 soybean, there were no significant differences of N2 fixation and seed weight between USDA110 and THA7 (both single and dual inoculation). In conclusion, dual inoculation of endophytic actinomycetes strain P4 may increase the nodulation and nitrogen fixation in some varieties; however, it is not effective for other varieties.

Effects of drought stress on seed sink strength and leaf protein patterns of common bean genotypes

Assimilate availability and the capacity to utilise them in the reproductive structures to a large extent determine reproductive sink establishment and yield of crops under drought stress. This study was carried out to investigate the effect of drought stress imposed at early pod-fill stage on seed sink strength of common bean (Phaseolus vulgaris L.) genotypes differing in drought resistance. Quantitative and qualitative changes in leaf protein patterns was assessed using 2D-gel electrophoresis. A drought-resistant inbred line (SEA 15) and a droughtsusceptible cultivar (BrSp) were grown under non-stress and drought stress conditions in a vegetation hall during the summer of 2004. Drought stress commenced at early pod-filling stage caused 53 and 30% seed yield reductions in BrSp and SEA 15, respectively. The effect of drought on seed yield was primarily due to the significant reduction in number of seeds per plant (48% for BrSp vs. 35% for SEA 15). Whereas seed sucrose concentrations of BrSp decreased by 29 to 47% under drought conditions, the stress resulted in an increase (up to 43%) in concentration of the carbohydrate in SEA 15 seeds. Despite the genotypic difference found for seed sucrose import, seed starch accumulations of the two genotypes decreased under drought stress. For both genotypes, none of the seed sink capacity parameters (numbers and volumes of cotyledonary cells and starch granules per seed) were significantly affected by the stress imposed implying that the drought-induced decrease in seed starch accumulation could be due to limitations in assimilate availability and/or other sink activity factors within theseed. A total of 230 leaf proteins were differentially expressed due to drought out of which 23.5, 15.1, 4.3 and 3.5% were down-regulated, up-regulated, newly appeared and disappeared, respectively. Identification and assigning possible functions in the crop’s response to drought of the stress-induced proteins warrant further study

Akumulasi dan distribusi bahan kering pada beberapa kultivar kacang tanah

This research was carried out in April–September 2007. The research objective was to study the dry matter distribution pattern of several peanut cultivars. Twenty cultivars were planted at two different locations, Cikarawang and Sawah Baru Experimental Field but at the same elevation (250 m above sea level). The cultivars were scored according to morphological and physiological characters, total N and total non-structural carbohydrates (TNC), yield and yield components. There were no statistically differences in pod yield, seed yield and harvest index between the cultivars, but there were differences in dry matter distribution between cultivars. TNC content in stem correlated positively with pod fi lling. Carbohydrates for pod fi lling presumed were derived from dry matter accumulation in early pod fi lling stage. It was concluded that the ideal growing type of peanut are early accumulated dry matter but almost no increase of dry matter accumulation in upper part of plant during seed development. Keywords: dry matter distribution, pod fi lling, peanut

The abundance and efficacy of Rhizobium leguminosarum bv. viciae in cultivated soils of the eastern Canadian prairie

For optimum production, the use of commercial rhizobial inoculant on pea ( Pisum sativum L.) at seeding is necessary in the absence of compatible rhizobial strains or when rhizobial soil populations are low or symbiotically ineffective. Multiple site experiments were conducted to characterize the abundance and effectiveness of resident populations of Rhizobium leguminosarum bv. viciae ( Rlv) in eastern Canadian prairie soils. A survey of 20 sites across a broad geographical range of southern Manitoba was carried out in 1998 and was followed by more intensive study of five of the sites in 1999 and 2000. Appreciable nodulation of uninoculated pea was observed at all sites which had previously grown inoculated pea. However, uninoculated pea grown at two sites, which had not previously grown pea, had negligible nodulation. Likewise, wild Lathyrus sp. and Vicia sp. plants collected from uncultivated areas adjacent to agricultural sites were poorly nodulated. In the more intensively studied sites, there was a tendency towards higher nodulation in pea plants receiving commercial inoculant containing Rlv strain PBC108 across all site-years (e.g., 4.7% in nodulation and 22% in nodule mass), but the effect was significant at only 2 of 10 site-years. Despite a relatively high range of soil pH (6–8), regression analysis indicated that decreasing soil pH resulted in lower nodulation rates. Likewise, electrical conductivity (EC) was correlated to nodulation levels, however the effect of EC was likely more indicative of the influence of soil texture and organic matter than salinity. As with nodulation, commercial inoculation tended to increase above-ground dry matter (DM) and fixed-N (estimated by the difference method) at the early pod-filling stage, but again the effects were significant at only 2 of 10 site-years. Specifically, above-ground DM and fixed-N levels were up to 29 and 51% greater, respectively, in inoculated compared to non-inoculated treatments at these sites. Addition of N-fertilizer at a rate of 100 kg N ha −1 decreased nodulation at almost all site-years (by as much as 70% at one site), but rarely resulted in increases in above-ground DM compared to inoculated plots. The study indicates for the first time that populations of infective, and generally effective strains of Rlv occur broadly in agricultural soils across the eastern Canadian prairie, but that there is a tendency for increased symbiotic efficiency with the use of commercial inoculant.

Effects of Paclobutrazol on Dry Matter Distribution and Yield in Peanut

Paclobutrazol (PB), an inhibitor of endogenous gibberellin synthesis, was applied to peanut plants altered dry-matter distribution and increased seed yield. PB solution at a concentration of 100, 200 or 400 ppm was sprayed on foliage at the beginning of the pod formation stage (BPFS), the early pod filling stage (EPFS) and the middle pod filling stage (MPFS) .The height of the plants treated with PB at BPFS and EPFS was shorter than that of the control plants by more than 10 and 5 cm, respectively. The pod number of the plants treated with 100 or 200 ppm PB at any developmental stage was higher than that of the plants treated with 0 or 400 ppm PB. The seed yield was increased by PB applied at any stage, and the yield after the treatment with 100 or 200 ppm PB at BPFS or EPFS was approximately 370 gm~2.

Time course of N 2 fixation and growth of chickpea

The 15N isotopic dilution technique was used to assess N2 fixation in desi chickpea (Cicer arientinum L.) cv. Myles at different growth stages as influenced by inoculation method. In this growth chamber study, no significant differences in nodule dry weight, amount of N2 fixed and plant dry matter were observed between seed inoculation with seed-applied peat inoculant and soil-applied granular inoculant placed 2.5 cm below the seed. However, seed inoculation with liquid inoculant was inferior to the seed-applied peat or the granular inoculant for all parameters measured at all sampling dates. The seed-applied peat and granular inoculant treatments fixed 4.8 and 4.1 mg N plant–1, respectively, by the late vegetative stage, and reached a maximum of 20.6 and 25.6 mg N plant–1, respectively, by the late pod-filling stage. These values accounted for 30.5% and 34.9% of the total plant N for the peat and granular inoculant, respectively, by late pod-filling. For the liquid inoculant treatment, the amount of N2 fixed increased from 2.3 mg N plant–1 by the late vegetative stage to a maximum of 9.6 mg N plant–1 which was 22.2% of total plant N by the mid pod-filling stage. The highest daily N2 fixation rate for the peat and granular inoculant was 0.9 mg N plant–1 and occurred between flowering and early pod-filling, whereas that for the liquid occurred between early and mid pod-filling stages (0.23 mg N plant–1). After the mid pod-filling stage, little or no N2 was fixed in all treatments. Plant dry matter increased from the late vegetative stage to physiological maturity but the greatest dry matter accumulation occurred between the late vegetative and early pod-filling stages in all treatments.

Rhizobial survival and nodulation of chickpea as influenced by fungicide seed treatment.

The survival of Rhizobium ciceri on chickpea (Cicer arietinum cv. Myles) seed, treated separately with 1 of 4 commercial fungicides, i.e., Apron, Arrest 75W, Crown, or Captan, was examined under laboratory conditions using standard serial dilution and plate count techniques. The resulting effects of fungicide-Rhizobium interactions on nodulation, N2 fixation, and plant growth were assessed in a controlled environment. Fungicide treatment decreased the number of viable rhizobia on the seed. In general, the toxicity of the fungicides in terms of rhizobial viability increased in the following order: Control = Crown < Arrest = Apron < Captan. Although Crown had no effect on rhizobial viability assessed under laboratory conditions, it significantly reduced nodulation, percent N derived from the atmosphere (%Ndfa), and shoot dry matter. Seed treated with Arrest and Captan decreased nodule dry weight and %Ndfa, but only Arrest reduced dry matter yield. Apron had no effect on any of the parameters measured at the early pod-filling stage and was compatible with the chickpea inoculum used in this study.

Relationship of physiological characters to yield parameters in oilseed rape (Brassica napus L.)

The physiological basis of seed yield in oilseed rape (Brassica napus L.) still remains unclear, and conclusions on the contribution of such traits to seed yield are difficult to make. Nine cultivars, classified into three yield groups (high, medium and low) based on significant differences in seed yield from previous trials, were tested over two locations and years. Leaf chlorophyll content, net photosynthetic rate per unit leaf area (PA), per unit leaf dry matter (PDM) and per unit leaf chlorophyll (PC), transpiration rate (TR) and water use efficiency (WUE) were investigated on fully expanded leaf numbers 4 (vegetative), 6 (early flowering) and 8 (early podding stage) on the main stem and related to seed yield, total dry matter (TDM) and harvest index (HI) of each yield group. Differences among yield groups for seed yield, TDM and HI were significant. Chlorophyll content was lowest on leaf 4, but increased with leaf age. Correlations between net photosynthetic rate and seed yield were not found. However, cultivars in the high yield group maximized their net photosynthetic rates (PA, PDM, and PC) on leaf 6 during early flowering at the time when TR was lowest and WUE at its highest. In the medium and low groups, photosynthetic rates were highest on leaf 4, but decreased to lowest values on leaf 8, together with the high yield group. In general, the results indicate that the largest contribution to net photosynthesis by oilseed rape leaves occurred during the vegetative and early flowering stages compared with the early pod-filling stage. Key words: Total dry matter, harvest index, photosynthesis, chlorophyll

Time-course of dinitrogen fixation of promiscuous soybean cultivars measured by the isotope dilution method

Soybean cultivars capable of nodulating with indigenous Bradyrhizobium spp. have been developed by the International Institute of Tropical Agriculture (IITA) and national programs in Africa in order to avoid artificial inoculation by resource-poor farmers in Africa. The current selection procedure for enhanced N2 fixation is based on an assessment of nodule formation which does not directly quantify the proportions of crop N derived from the atmosphere. We have monitored N accumulation patterns and N2 fixation in nine promiscuous soybean cultivars with different maturity periods, using the 15N dilution technique. Nodule development generally peaked at the early podfill stage for all cultivars except Tgx 1519-1D and Tgx 1447-2D in which it continued to increase. The proportion of crop N derived from fixation (%NDFA) ranged between 51% and 67%, 77% and 84%, and 66% and 73% at full bloom, early podfill, and physiological maturity stages, respectively. Total N accumulation increased in all soybean genotypes with increasing plant age. Significant correlations (P<0.001) were established between nodule weight and %NDFA, even though this did not explain the relationship between nodule development and N2 fixation in cultivars such as Tgx 1519-1D. Promiscuous soybean cultivars retained between 10% and 19% of total N accumulated at the final harvest, in belowground biomass. Our results indicated that these soybean cultivars can derive substantial proportions of plant N from N2 fixation in soils where compatible indigenous bradyrhizobia populations are adequate and effective. Also, we have substantiated the claims that qualitative nodulation parameters currently used to select varieties with a high N2 fixation capacity need to be validated with other measurements of N2 fixation.

The effect of root damage caused by simulated white grub attack on the growth, yield and water-use of groundnut plants

White grubs (larval scarabaeids) are now recognized as being important pests of groundnut (peanut) in many parts of the world because of their ability to damage roots. A method of simulating white grub damage to groundnut plants was developed to obtain an indication of how the feeding activity of these insects influences plant growth. The effect of root cutting and drought stress on water uptake and biomass production was evaluated, with roots being cut at three depths in the late vegetative and early podfilling stages. As groundnut plants are often grown under conditions of drought stress, the effects of which would be accentuated by root damage, this factor was introduced into the experiment. Plant water-use measurements indicated that the root systems of plants cut 30 days after emergence (DAE) and watered twice a week became fully functional again after 40 days. Pod and total biomass production were however significantly less than those of the uncut control plants, with drought stress reducing yields below the well-watered controls, particularly when cut at 10 cm below the soil surface. The root systems of plants cut 51 DAE did not regrow to any appreciable extent, and rates of plant water-use remained less than half of the uncut control plants. Over all treatments, there was a strong positive correlation between total (and pod) biomass and plant water-use. It was concluded that the phenological stage of the plant at which root damage occurred had a profound influence on the subsequent recovery in root growth and function, and ultimately on pod yield.

Growth, yield and soil water extraction of irrigated and dryland peanuts in South Sulawesi, Indonesia

Irrigation at 35 and 70 mm of pan evaporation applied during the pre and/or post early podfilling stages increased pod yield of Spanish peanuts (100 day maturity) three fold compared to a dryland crop. There was no difference in pod yield in crops receiving 12 compared to 6 irrigations. Soil water sampling immediately after irrigations on selected treatments revealed that infiltration of irrigation water was probably restricted to less than ca. 20 cm, a response which resulted in poor soil water replenishment and low irrigation efficiency (Fig. 3). Even though roots extracted soil water below the compaction layer which was at 20 cm severe crop water deficits had developed by the end of irrigation cycles during later but not early stages of growth. The dryland crop, which received no rainfall during the season, presumably extracted significant amounts of soil water at depths to and below 1.2 m (Fig. 3). Despite producing ca. 2.9 t ha-1 of total dry matter yield, pod yield was extremely low (0.5 t ha-1) arising from low pod numbers and high percentage of empty pods.

Endogenous Gibberellins and Shoot Growth and Development in Brassica napus

Greenhouse-grown oilseed rape (Brassica napus, annual Canola variety ;Westar') plants were harvested at six dates from the vegetative phase until the early pod (silique)-fill/late flowering stage. Endogenous gibberellin (GA)-like substances were extracted from stems, purified, and chromatographed on silica gel partition columns prior to bioassay in serial dilution using the ;Tan-ginbozu' dwarf rice microdrop assay. The concentrations of total endogenous GA-like substances were low during vegetative stages (1 nanogram GA(3) equivalents/gram dry weight), and rose 300-fold by the time of floral initiation. After floral initiation the concentration of GA-like substances fell, then rose again during bolting to maximal levels during the early pod-fill stage (940 nanograms per gram dry weight). The qualitative profiles of GA-like substances varied across harvests, with higher proportions of a GA(1)-like substance at the early pod-fill stage. In a second study stems were similarly harvested at eight dates and the concentrations of endogenous GA(1), the principal bioactive native GA of oilseed rape, were determined by gas chromatography-selected ion monitoring using [17,17-(2)H]GA(1) as a quantitative internal standard. The concentration of GA(1) increased at about the time of floral initiation and then subsequently fell, thus confirming the pattern noted above for total GA-like substances. The exogenous application of paclobutrazol (PP333), a persistent triazole plant growth regulator (PGR) which blocks GA biosynthesis, or another triazole, triapenthenol (RSW0411), prevented flowering as well as bolting; plants remained at the vegetative rosette stage. These results imply a causal role for endogenous GA, in the control of bolting, which normally precedes anthesis. Further, the rise in the concentration of total endogenous GA-like substances, including GA(1), which was associated with floral initiation, and the prevention of visable floral development by the triazole PGRs, also indicates a role for endogenous GAs in the regulation of flowering in B. napus.