Resistance to broomrape (Orobanche spp.) in sunflower (Helianthus annuus L.) is temperature dependent

The effects of various temperature regimes in the range 29-17/21-9 degrees C day/night on each stage of the parasitism process of Orobanche cumana and O. aegyptiaca on sunflower were studied under controlled conditions in polyethylene bags. The response of the resistant sunflower variety 'Ambar' was expressed as the degeneration of the parasite tissues after its establishment in the plant roots, and this stage was found to be temperature dependent. The degeneration rate of Orobanche tubercles in the resistant sunflower variety was also found to be temperature dependent and was about five times as great as that in the sensitive variety in the highest temperature regime tested of 29/21 degrees C day/night. The ability to reject the parasite by causing its degeneration and death is the main factor that determines the resistance. As the temperature rises, more tubercles degenerate and die, that is the sunflower plant expresses higher levels of resistance.     

Bacterial antagonists of Sunflower (Helianthus annuus L.) fungal pathogens

Bacteria isolated on nutrient agar and King's medium B from sunflower leaves, crown and roots inhibited in vitro growth of the leaf spot and wilt pathogens Alternaria helianthi, and Sclerotium rolfsii, respectively, and also the root rot pathogensRhizoctonia solani and Macrophomina phaseolina. Antagonistic bacteria from leaves were mainly actinomycetes and pigmented Gram-positive bacteria, while those from roots and crowns were identified asPseudomonas fluorescens-putida, P. maltophilia, P. cepacia, Flavobacterium odoratum andBacillus sp. In soil bioassays, when used as seed inoculum in the presence ofS. rolfsii, P. cepacia strain N24 increased significantly the percentage of seedling emergence. Bacterial strains which exhibited broad spectrum in vitro antagonistic activity were tested for colonisation of sunflower roots, when used as a seed inoculum. Good colonisers (10⁴ to 10⁶ bacteria/g root) were consistent in their ability to reduce disease and fungal wilt. A seedling having a primary root length < 5 cm with fewer lateral roots, necrosed cotyledons or crown and a wilted shoot indicated its diseased status. On an average, only 30% of seedlings were diseased when treated with the antagonistic strains, in the presence of the pathogen, while 60% of the seedlings were diseased in the presence of the pathogen alone. In microplots treated with strain N24, only 1 to 3% of the seedlings were wilted, while 14% of the seedlings were wilted in the presence of the pathogen alone. The results obtained show that bacterial antagonists of sclerotial fungi can be used as seed inocula to improve plant growth through disease suppression     

Pre-haustorial resistance to broomrape (Orobanche cumana) in sunflower (Helianthus annuus): cytochemical studies

Sunflower broomrape (Orobanche cumana Wallr.) is a root holoparasitic angiosperm considered as one of the major constraints for sunflower production in Mediterranean areas. Breeding for resistance is regarded as the most effective, feasible, and environmentally friendly solution to control this parasite. However, the existing sources of genetic resistance are defeated by the continuous emergence of new more virulent races of the parasite. In this work, the interaction between sunflower and O. cumana has been analysed in order to gain insights into the mechanisms involved in resistance. Two sunflower genotypes were selected showing different behaviour against the new race F of O. cumana, HE-39998 (susceptible) and HE-39999 (resistant), and both compatible and incompatible interactions were compared. Pot and Petri dish bioassays revealed that only HE-39998 plants were severely affected, supporting a high number of successfully established broomrapes to mature flowering, whereas in HE-39999 root tubercles were never observed, resistance being associated with browning symptoms of both parasite and host tissues. Histological aspects of the resistance were further investigated. Suberization and protein cross-linking at the cell wall were seen in the resistant sunflower cells in contact with the parasite, preventing parasite penetration and connection to the host vascular system. In addition, fluorescence and confocal laser microscopy (CLM) observations revealed accumulation of phenolic compounds during the incompatible reaction, which is in agreement with these metabolites playing a defensive role during H. annuus-O. cumana interaction.     

Distribution of Nitrogen during Growth of Sunflower (Helianthus annuus L.)

The accumulation, distribution and redistribution of dry matterand nitrogen is described for Helianthus annuus L. cv. Hysun21 grown on 6 mM urea in glasshouse culture. Seed dry matterand nitrogen were transferred to seedlings with net efficienciesof 40 and 86 per cent respectively. At flowering, the stem hadmost of the plant's dry matter and the leaves most of its nitrogen.About 35 per cent of the plant's nitrogen accumulated afterthree-row anthesis. The amount of protein in vegetative parts,especially leaves, declined after flowering. Concentrationsof free amino compounds also decreased during growth. Matureseeds had 38 per cent of the total plant dry weight and 68 percent of the total nitrogen. Seeds acquired 33 per cent of theirdry matter and nitrogen from redistribution from above-groundplant parts. The stem was most important for storage of carbohydrate,leaves the most important for nitrogen. Over 50 per cent ofthe nitrogen in the stem and leaves was redistributed. Plantsthat received 6 mM nitrate accumulated more dry matter thanurea-grown plants. Seeds from nitrate-grown plants were heavier(58 mg) than those of urea-grown plants (46 mg), and their percentageoil was greater (50 and 41 respectively). The amount of nitrogenper seed was the same. Little or no urea was detected in xylem sap of plants suppliedwith 5 mM urea, but it was detected in sap of plants which received25 mM. Concentrations of urea and amino compounds in the sapdecreased up the stem. Plants supplied with nitrate had mostof the nitrogen in xylem sap as NO₂^–, suggesting littlenitrate reduction in roots. Plants grown on 6 mM nitrate andchanged to high levels of urea-nitrogen for 14 days still hadhigh levels of nitrate; little nitrate remained in plants receivinglow levels of urea. When urea is applied in irrigation waterto field-grown sunflower, the nitrogen is subsequently takenup as nitrate due to rapid nitrogen transformations in the soil. Helianthus annuus L., sunflower, urea, nitrate, nitrogen transport, xylem sap, nitrogen accumulation nitrogen distribution     

Plantlet Regeneration from Electrostimulated Protoplasts of Sunflower (Helianthus annuus L.)

Hypocotyl protoplasts from Helianthus annuus L. were electrically stimulated using different parameters and subsequently cultivated in agarose droplets with weekly changes of the liquid media. Macroscopic visible calli (0.1-0.3 mm) were transferred onto solid media supplemented with different concentrations of NAA, BAP, and GA₃. Colonies reaching a size of about 3 mm were isolated and further cultivated under the same conditions. Several calli originating from electrically stimulated protoplasts and especially those cultured on relative high auxin concentrations, generated somatic embryos which were characterized by a green globular shoot tip and a developing root. Later on differentiation of the shoot tip occurred on kinetin-containing MS medium leading to plantlets with stunted shoot axis. No somatic embryos were initiated in control experiments with non-stimulated protoplasts.     

Effect of Mechanical Stress on Sunflower (Helianthus annuus L.) Hypocotyl Growth

Etiolated seedlings of Sunflower (Helianthus annuus L.) weresubjected to mechanical stress by longitudinally compressingthe hypocotyl with approx. 0·05 N force (equivalent to0·025 MPa for a 1·6 mm diameter hypocotyl). Thisrelatively low compressive stress effected an increase in relativegrowth rates (RGR) of the hypocotyl for a period of 1-2 h, followingwhich RGR returned to the pretreatment rate. RGR was also increasedby an equivalent compressive stress treatment (0·025MPa) for 4 h in water or in 10^-10 mol l^-1 IAA. These resultsare discussed in the context of a possible role for mechanicallyinduced stress in the initiation and maintenance of nutationalgrowth movements.Copyright 1994, 1999 Academic Press Helianthus annuus, Sunflower, hypocotyl growth, mechanical stress, seedling growth, nutational growth movements, circumnutation     

Quantitative trait loci for growing degree days to flowering and photoperiod response in Sunflower (Helianthus annuus L.)

The number of days from seedling emergence to flowering (DTF) is a major consideration in sunflower breeding programs. This is a complex trait determined by the genotype, environmental conditions and interactions. Photoperiod and temperature have major effects on DTF and could be important sources of genotype× environment interaction. The objectives of this study were to locate quantitative trait loci (QTLs) associated with growing degree days (GDD) to flowering and photoperiod (PP) response in an elite sunflower population. Two hundred and thirty five F₂-generation plants and their F_2:3 and F_2:4 progenies of a single-cross population of two divergent inbred lines were evaluated in six environments (locations, years and sowing dates) with photoperiods known to elicit a PP response between the inbred lines. Detection of QTLs was facilitated with a genetic linkage map of 205 RFLP loci and composite interval mapping. The 205 restriction fragment length polymorphism (RFLP) loci covered 1380 cM and were arranged in 17 linkage groups, which is the haploid number of chromosomes in this species. The average interval size was 5.9 cM. Six QTLs in linkage groups A, B, F, I, J and L were associated with GDD to flowering and accounted for 76% of the genotypic variation in the mean environment. QTLs in linkage groups A and B accounted for 72% of the genetic variation. QTL×environment (QTL×E) interactions were highly significant for linkage groups A, B, F and J (P<0.01). QTLs in linkage groups A and B were highly dependent on PP. Also, QTL mapping of the ratio of the GDD required by a progeny to flower at a PP of 12.1 and 15.0 h, defined as the photoperiod response (PPR), suggested that alleles at QTLs in linkage groups A and B were responsive to PP. QTLs in linkage groups F and J showed QTL×E interaction but the LOD values were not associated with PP. QTL×E interactions for additive effects were highly significant (P<0.01) for linkage groups A, B and F. QTL×E interactions for QTLs with dominant effects were significant (P<0.01) for linkage groups A, B and J. The dominant effect of QTLs in linkage group B increased in environments with a longer PP. The knowledge of how these QTLs influence the GDD for flowering and how they interact with the environment will facilitate marker- assisted selection and backcross conversion of photoperiod-sensitive germplasm. Received: 7 February 2000 / Accepted: 13 June 2000     

Membrane-bound Plastid Inclusions and Chloroplast Thylakoid Formation in Sunflower (Helianthus annuus L.)

The ultrastructure, distribution and frequency of membrane-boundplastid inclusions present in the epidermal cells of leavesof intact sunflower plants (Helianthus annuus L.) and in theepidermal and mesophyll cells of sunflower leaf discs culturedin darkness have been studied. These inclusions appear to bedilated thylakoids containing a granular material which, undernormal conditions, is probably involved in chloroplast membraneformation. It is suggested that this material accumulates, andinclusions form, in the chloroplasts of sunflower leaves intwo specific situations. Firstly, in the completely differentiatedcells of the epidermis where the chloroplasts, although at arelatively immature stage, have nevertheless reached a terminalstage of development. Secondly, in the mesophyll cells of youngleaves when chloroplast development has been arrested at animmature stage by a 5-day dark period. In the latter situationthe material can be remobilized if plastid development is restimulated.The plastids of sunflower leaf discs cultured in darkness containboth membrane-bound inclusions and prolamellar bodies, indicatingthat they are separate and distinct structures possibly containingdifferent membrane components. Helianthus annuus L., sunflower, chloroplast, ultrastructure, plastid inclusions, thylakoid formation     

油用向日葵主要农艺性状的遗传分析

对10个油用向日葵品种的主要农艺性状进行遗传分析的结果表明,株高、单株粒数、百粒重、盘径和单株粒重等农艺性状具有较大的遗传率,可以在早代单株选择或直接选择;出苗-现蕾、现蕾-开花、开花-成熟、皮壳率等性状的遗传率较低,应根据各性状间相关关系进行间接选择或将选择推迟到晚期世代进行。遗传变异幅度较大的性状有皮壳率、单株粒数、小区产量、单株粒重等。由于性状的遗传改良效果主要由该性状的遗传率和变异幅度及选择强度所决定,因此,在选择率确定为5%情况下,遗传改良效果较好的性状为单株粒数和单株粒重。 Abstract:The genetic analysis of main agronomic characters was conducted with 10 varieties of oil sunflower(Helianthus annuus L.).The results showed that direct selection can be carried out at early generation for characters with higher heritability such as plant height,grain number pere plant,100-grain weight,diameter of disc and grain weight per plant.For maturity and percentage of shell with lower heritability,indirect selection correlated with other characters or late generation selection can be utilized.The characters showing wide genetic variation were those as percentage of shell,grain number per plant,grain yield per plot and grain weight.Since the successful improvement of a character mainly depends on its heritability,variation of heritability and intensity of selection,we suggest that the characters which may give better genetic improvement are grain number and grain weight per plant under condition of 5% selection pressure.     

Combined linkage and association mapping of flowering time in Sunflower (Helianthus annuus L.)

Association mapping and linkage mapping were used to identify quantitative trait loci (QTL) and/or causative mutations involved in the control of flowering time in cultivated sunflower Helianthus annuus. A panel of 384 inbred lines was phenotyped through testcrosses with two tester inbred lines across 15 location × year combinations. A recombinant inbred line (RIL) population comprising 273 lines was phenotyped both per se and through testcrosses with one or two testers in 16 location × year combinations. In the association mapping approach, kinship estimation using 5,923 single nucleotide polymorphisms was found to be the best covariate to correct for effects of panel structure. Linkage disequilibrium decay ranged from 0.08 to 0.26 cM for a threshold of 0.20, after correcting for structure effects, depending on the linkage group (LG) and the ancestry of inbred lines. A possible hitchhiking effect is hypothesized for LG10 and LG08. A total of 11 regions across 10 LGs were found to be associated with flowering time, and QTLs were mapped on 11 LGs in the RIL population. Whereas eight regions were demonstrated to be common between the two approaches, the linkage disequilibrium approach did not detect a documented QTL that was confirmed using the linkage mapping approach.     

Water Stress in Sunflower (Helianthus annuus L.): I. Effect on Plant Development

Development of sunflower plants grown in pots under controlledconditions was monitored at frequent intervals. Two separatewater stresses, which reached a minimum of –1.7 MPa, wereimposed at specified developmental stages on two separate batchesof plants. Leaf initiation and leaf unfolding were significantlyreduced by water stress. Inflorescence primordium initiation,involucre bract formation, disc and disc floret developmentwere not affected. The mitotic index was reduced by water stressin unfolding leaves from 5 to 0.5 per cent. In other leaves,the mitotic index was reduced to a lesser extent. This reducedmitotic index helps explain reduction in leaf development. Thetime between seed germination and inflorescence primordium initiationremained relatively constant despite the reduced leaf numberassociated with water stress. The discussion evaluates the complicationsthat this may cause in the comparison of leaves in the upperhalf of the leaf profile. Helianthus annuus L., sunflower, water stress, mitotic index, leaf development     

Effect of Flooding on Starch Accumulation in Chloroplasts of Sunflower (Helianthus annuus L.)

Chloroplasts in leaves of sunflower (Helianthus annuus L. cv hybrid 894) whose roots were flooded for 4 days showed an increase in the level of starch in chloroplasts when examined with the electron microscope. Starch determination showed significantly higher levels in leaves of flooded plants. Chloroplast and mitochondrial structure seemed otherwise normal.     

Histopathological Studies of Resistance of Sunflower (Helianthus annuus L.) to Downy Mildew (Plasmopara halstedii)

Histopathological studies of the infection of sunflower seedlings by downy mildew ( Plasmopara halstedii ) have shown that penetration of roots and the lower part of the hypocotyl occurs for both compatible combinations (suseptibility) and incompatible combinations (resistance). After penetrating susceptible genotypes, the parasite develops intercellular hyphae and intracellular haustoria, leading to systemic invasion. In contrast, in resistant plants, as soon as colonization develops, hypersensitive-like reactions occur in the parenchyma, with the appearance of necrotic zones surrounded by dividing cells. Growth of the parasite is strongly inhibited and most hyphae are blocked before they reach the cotyledonary node.     

Water Stress in Sunflower (Helianthus annuus L.) 3. Responses of Cypsela Size

Six water stress treatments were applied before, during andafter anthesis of the sunflower inflorescence. The effects ofthese stresses on leaf and inflorescence size, cypsela number,pericarp and embryo weight were examined. Water stress accelerated leaf senescence and reduced leaf number.Leaf area and inflorescence diameter were reduced in some treatments.Total cypsela weight may be related to leaf area. All stresstreatments reduced pericarp weight at all positions. Embryoweight at central positions was similarly affected. Post-anthesisstress did not affect embryo weight at peripheral positions.The effects of water stress on embryo weight may involve a criticalstage in development but this differs from that envisaged forleaves. Helianthus annuus L., sunflower, water stress, cypsela, inflorescence, embryo, pericarp     

Unsaturated fatty acid synthesis in sunflower (Helianthus annuus L.) seeds in response to night temperature

The incorporation of ¹⁴CO₂ into unsaturated fatty acids during seed development was measured in sunflowers grown in controlled environments with day temperatures of 28°C and night temperatures of 15°C or 22°C. While the average temperatures to which the plants were exposed did not differ greatly, the ratio of linoleic acid to oleic acid synthesized was much greater at a night temperature of 15°C than at 22°C. These results support the proposal (Harris et al. 1978) that the mean minimum temperature experienced during seed development is the major environmental factor influencing the unsaturated fatty acid composition of sunflower seed oil.     

A Quantitative Study of the Resistances to Transpirational Water Movement in Sunflower (Helianthus annuus L.)

Hydroponic sunflower plants were used in a quantitative studyof the relationship between total plant and leaf resistancesto transpirational water movement and transpiration rate. Theresults demonstrate that both resistances are flux-dependentand decline 5–6-fold during a comparable increase in transpiration.The resistance of excised leaves including the petiole was approximatelyhalf the total plant resistance. Subsequent analyses of the water potential gradients and transpirationalfluxes in whole plants permitted calculation of the magnitudeof the partial resistances imposed by roots, stem, petiole,and leaf. The root and leaf resistances were approximately 50%and 30% of the total resistance respectively. Stem and petiolarresistances were relatively small and both influenced watermovement to the upper leaves similarly. The values obtainedare compared with previous published results obtained usingdiverse experimental techniques.     

Leaf and Floret Production in Sunflower (Helianthus annuus L.) as Affected by Nitrogen Supply

Both the vegetative and the floral meristems of glasshouse-grownsunflowers respond to nitrogen supply in the same way. The durationof leaf and floret production is unaffected but the rate ofproduction is decreased by low nitrogen supply. Thus both finalleaf number and floret number are lowest at the lowest nitrogensupply. The activity of the vegetative meristem is directlyrelated to the content of reduced nitrogen of the plant. Relief of nitrogen stress in the middle of the vegetative phaseallows final leaf number to reach the unstressed number. However,relief of nitrogen stress during floral initiation showed thatfloret number is a function of the plant's content of reducednitrogen at the beginning of floret production. Relief of nitrogenstress from the middle to the end of floret production did notincrease floret number. Nitrogen supply did not influence the duration but did affectthe rate of leaf expansion. Relief of nitrogen stress afterleaf and floral initiation were complete caused a larger finalarea in those leaves still expanding and also lessened apicaldominance so that some axillary buds developed into small flowers. Helianthus annuus L, sunflower, nitrogen supply, leaf production, leaf growth, floret production     

The Relative Magnitude of the Partial Resistances to Transpirational Water Movement in Sunflower (Helianthus annuus L.)

The effects on leaf water status of cooling entire root systemsor stem and petiolar segments were examined using hydroponicsunflower plants. Leaf water potential (^I) decreased by up to7 x 10⁵ Pa when root temperature was reduced to 10 °C orbelow; complete recovery occurred subsequently provided freezingwas avoided. Leaf water status was unaffected by cooling stemor petiolar segments unless freezing occurred, when severe irreversiblewater stress developed above the cooled zone. The leaves belowthe cooled zone were unaffected, demonstrating that the stressdid not originate from transmitted effects on the roots. Subsequent measurements using small heads of water applied toexcised petioles demonstrated that petiolar resistance was low(c. 0.04 Pa s cm_–4) except in immature and senescent petioleswhere resistance was up to 10 times larger. This trend reflectedthe developmental stage and condition of the xylem. Abrupt increases in evaporative demand, obtained by rapid reductionof relative humidity from 100% to 60 or 40%, induced transientdecreases in of approximately 4.5 and 2.5 x 10⁵ Pa, respectively,which were accompanied by simultaneous large increases in stomatalresistance. No simultaneous transient effects were observedin the stem xylem, demonstrating that the factor responsiblefor the formation of the transient foliar stress resides withinthe lamina. The results are discussed in relation to the relative magnitudeof the various partial resistances to transpirational watermovement.     

Salicylic acid-induced adaptive response to copper stress in sunflower (Helianthus annuus L.)

The ameliorative effect of salicylic acid (SA: 0.5 mM) on sunflower (Helianthus annuus L.) under Cu stress (5 mg l⁻¹) was studied. Excess Cu reduced the fresh and dry weights of different organs (roots, stems and leaves) and photosynthetic pigments (chlorophyll a, b and carotenoids) in four-week-old plants. There was a considerable increase in Chl a/b ratio and lipid peroxidation in both the roots and leaves of plants under excess Cu. Soluble sugars and free amino acids in the roots also decreased under Cu stress. However, soluble sugars in the leaves, free amino acids in the stems and leaves, and proline content in all plant organs increased in response to Cu toxicity. Salicylic acid (SA) significantly reduced the Chl a/b ratio and the level of lipid peroxidation in Cu-stressed plants. Under excess Cu, a higher accumulation of soluble sugars, soluble proteins and free amino acids including proline occurred in plants treated with 0.5 mM SA. Exogenous application of SA appeared to induce an adaptive response to Cu toxicity including the accumulation of organic solutes leading to protective reactions to the photosynthetic pigments and a reduction in membrane damage in sunflower.