The effect of boron (B) deficiency in sunflower (Helianthus annuus L.) plants on early capitulum development was studied. Plants were grown under artificial conditions on an 18 h long-day photoperiod in B-deficient soil mixture (<0.1 ppm B) irrigated with B-deficient or complete Hoagland’s solution (0.27 ppm B). B-deficient plants were transferred 25 days after seedling emergence (DAE) to a B-rich soil mixture (2.0 ppm B) and irrigated with complete B Hoagland’s solution. Compared with controls, plants grown in B-deficient soil mixture had 18% less leaf area, 25% less receptacle area, and 33% less shoot dry weight; all differences were statistically significant. In both treatments the generation of new floret primordia started at the capitulum rim at 35 DAE and continued towards its center. Each floret primordium differentiated gradually and cen tripetally over space and time, first as a slight dome that became a two-part structure, the bract and the floret corolla. Capitulum damage was observed in B-deficient plants early during floret differentiation, resulting in the onset of surface splits on the receptacle at floral stage (FS) 4 (28-30 DAE). The edges of these splits acted as centres of floret primordium differentiation which devel oped centrifugally and resulted in aberrant capitula and the development of ray flowers and involucral bracts in abnormal positions on the inflorescence. This paper provides a detailed description of the beginning of floret primordium dif ferentiation during the floral morphogenetic process in sunflower capitula where damage was observed in plants grown under boron stress.

Basic in vitro techniques, linked with the increase of genetic variability and acceleration of the breeding process, have been mastered and applied in sunflower breeding programs at Dobroudja Agricultural Institute, Bulgaria. The method of direct organogenesis has been succesfully used for genetic modifications of fertility restorer lines RHA-857, 147 R and Z-8-A and for over coming the inability for crossing between H. annuus (hybrid Albena) and Helianthus tuberosus, Helianthus salicifolius, Helianthus maximiliani, Helianthus silphioides, Verbisina helianthoides and between H. mollis and H. annuus. The method of γ-induced parthenogenesis has been successfully applied to the cultivated sunflower (H. annuus L.) for obtaining doubled haploid lines. The parthenogenetic ability of both maternal and paternal parents and the gamma-irradiation effect on parthenogenic embryo development have been studied. A number of researches have been focused on the genetic potential of wild species from the genus Helianthus. Our studies investigated the possibilities of the methods for cultivation of embryos and anthers from interspecific origin. They included the use of the embryo cultivation technique under in vitro conditions until the production and testing of finished lines that could directly par ticipate in the breeding process. Embryos were isolated from interspecific hybrids (cultural x wild and wild x cultural) with the participation of the species H. resinosus M-046, H. strumosus M-059, H. salicifolius M-045, H. ciliaris M-092, H. giganteus M-030, H. maximiliani M-087 and H. glaucophylus M-012. The studies included and investigated 51 new lines which originated from embryos of the above interspecific crosses. A number of lines obtained from embryos of the above interspecific crosses exibited valuable economic indices and high combining ability. They were included as components in highly productive hybrids.

The experiment was conducted in order to study the regeneration potential of cotyledon explants from some Iranian inbred lines of sunflower (Helian thus annuus L.) and their F1 hybrids. Cotyledons of 2-day-old seedlings of three cytoplasmic male sterile inbred lines used as female (CMS 24, CMS 31 and CMS 60/52) and five inbred lines used as male (R-81.1, R-92, R-97, R-201 and R-232) and finally their 15 F1 hybrids were plated on shoot induction medium, Murashige and Skoog (MS) containing 3% sucrose, 0.5% agar-agar and different concentrations of BAP and NAA. Analysis of variance showed significant differences for all organogenesis traits studied among parental geno types and F1 hybrids, hormone combination treatments and genotype × hormone combination treatment interaction. Shoot organogenesis was optimized on MS medium with 1 mg l-1 BAP and 1 mg l-1 NAA. Interaction “(CMS 24 × R-201) × T2” showed the highest values for number of explants shooting per 100 explants plated (55%). Interaction “R-92× T2” showed the highest value for average number of shoots per explants plated (8.65). Interaction “R-81.1 × T2” showed the highest value for average number of shoots per explants shooting (23). Interaction “CMS 24 × T2” showed the highest value for number of explants rooting per 100 explants plated (35%).

This study was conducted to quantify crop water stress index (CWSI) based on single leaf temperatures of sunflower and to determine if CWSI values were correlated with other measures of plant water stress. Plant were grown under furrow irrigation and subjected to five water treatments ranging from 100 to 0% (100, 75, 50, 25, 0%) replacement of evapotranspirational losses within 0.90 m soil profile. The yield and water use of fully irrigated sunflower were highest in both years. Trends in CWSI values were consistent with the soil water contents induced by deficit irrigations. An average CWSI of 0.59 before irrigation times produced maximum yield. An equation for calculating yield potential of sunflower was developed using the relationship between yield and seasonal mean CWSI. Moreover, statistically significant correlations were found between CWSI calculated from single leaf temperatures and stomatal resistance, leaf area index (LAI) and available water in the root zone.

Sunflower (Helianthus annuus L.) is an important oil seed crop grown quite often in drylands. The variability in rainfall occurrence in these regions makes crop production risk and the crop experiences moisture stress at different growth stages. Crop simulation models help to assess such production risks. This paper described the development and testing of a combination of mechanistic and empirical models of sunflower. The model uses a few conservative relationships to define leaf area development as a function of leaf number and in turn leaf number as a function of accumulated thermal units. Biomass accumulation was simulated as a function of fraction of photosynthetically active radiation interception and radiation use efficiency. Seed growth was simulated from linear increase in harvest index with time. The model was calibrated empirically to predict the growth and yield of sunflower as influenced by irrigation and moisture stress effects by developing suitable sensitive factors. The model performed satisfactorily in predicting the aboveground biomass, leaf area and final yield of sunflower as influenced by irrigation and moisture stress.

Seed of three sunflower genotypes (Oro9, Flamme and Albena) were germinated in petri dishes placed in an incubator maintained at 28°C. Six NaCl concentrations (0, 50, 75, 100, 125 and 175 mM) were used to moisten seeds. Results showed a decline in seed germination of the three genotypes as NaCl concentration was increased in the medium. After six days of incubation, significant differences were observed between control and treatments. Mean com parison of treatments did not reveal a significant differences neither between 50 mM and 75mM treatments nor between 100 mM and 175 mM. Among the genotypes, Flamme was most sensitive. Average time of seed germination was significantly affected by both NaCl concentration and genotype.

A field experiment was conducted on medium black clayey soils under rainfed conditions at Main Research Station, University of Agricultural Sciences (UAS), Dharwad, India, during kharif 1999 to study the effect of different levels and ratios of nitrogen and phosphorus on seed yield and nutrient uptake of the sunflower hybrid DSH-1. The experiment consisted of nine treatments, i.e., N/P ratios with two N/P ratios of <1.0 (0.67 and 0.80), N/P ratio of 1.0 consisting of two ratios and four N/P ratios of >1.0 (1.20,1.30,1.60 and 2.00) along with control (no nitrogen and phosphorus) as keeping potassium level (60 kg K2O ha-1) as constant. The results showed that nitrogen and phosphorus applied in N/P ratios of >1.0 with 2.00 : 1.25 : 1.00 fertilizer level and N/P ratio of 1.0 with 2.00 : 2.00 : 1.00 fertilizer level produced 21 and 27 percent higher seed yield over the UAS, Dharwad fertilizer recommendation, i.e., N/P ratio of <1.0 with 1.00 : 1.25 : 1.00 fertilizer level (2800 kg ha-1). At maturity, higher nitrogen (177.72 kg and 186.27 kg N ha-1), phosphorus (23.66 kg and 27.75 kg P2O5 ha-1) and potassium (124.85 kg and 126.68 kg K2O ha-1) uptakes were obtained in the treatment receiving N/P ratio of >1.0 with 2.00 : 1.25 : 1.00 (120 kg N, 75 P2O5 and 60 kg K2O ha-1) and in the treatment receiving N/P ratio of 1.0 with 2.00 : 2.00 : 1.00 (120 kg N, 120 P2O5 and 60 kg K2O ha-1) fertilizer levels as compared with the UAS, Dharwad fertilizer recom mendation, i.e., N/P ratio of < 1.0 with 1.00 : 1.25 : 1.00 (60 kg N, 75 P2O5 and 60 kg K2O ha-1).

A hydroponic study was conducted to investigate the role of sulphur application on K/Na selectivity by sunflower and alleviation effect of sulphur on plant growth under saline conditions. Three salinity levels (0, 75, and 150 mM sodium chloride) and two sulphur levels (1 and 4 mM magnesium sulphate) were maintained in the root medium. The treatments were replicated thrice and arranged on growth chamber bench according to a complete randomized design (CRD). Seeds of Helianthus annuus (cv. Hysun-33) were germinated in quartz sand under standard conditions. One-week old seedlings were trans ferred to pots containing 2.5 l continuously aerated half strength modified Hoagland's nutrient solution. The plants were provided optimum growth conditions. First harvest on 25th and second harvest on 30th day were taken after germination. Plants grown with 4 mM sulphur level showed significant growth whereas interaction between sulphur and salinity was highly significant (P<0.01) for growth parameters like fresh weight, dry matter yield of shoot and root, diameter and length of stem and root. The positive correlation of dry matter yield with sulfur (r=0.93), potassium (r=0.99) and calcium (r=0.83) were observed, whereas sodium had negative relationship (r=-0.99) with dry matter yield. Potassium/sodium selectivity in plants was significantly higher (P< 0.01) at 4 mM sulphur level than at 1 mM.

Morphological variability between accessions of H. tuberosus collected in Montenegro and the USA was investigated as well as possible effect of long term cultivation or its absence and growing in different environmental conditions on morphological traits of this species. Results obtained showed that there is a large similarity between some populations collected in Montenegro and those collected in the USA. This, along with the presence of a great cluster formed exclusively from Montenegrin populations, supports the hypothesis that there were two ways of introduction of H. tuberosus to Montenegro. In a group of populations, the changes in morphology were found, probably due to absence of cultivation.

Immature zygotic embryos from a self-pollinated sunflower line 147 R (Helianthus annuus L.) were used for donor material to induce direct organo genesis. A portion of the isolated immature embryos were treated with gamma radiation (137Cs) at a dose of 5 Gy before plating. The range of the spontane ously induced somaclonal variation among the obtained regenerants was investigated and compared with that of the variants induced through irradiation. The genetic changes occurring spontaneously during the regeneration procedure included seventeen morphological and biochemical characters. The most significant changes were observed for the characters of plant height, stem diameter, head diameter, length of branches, oil content in seed (%) and 1000 seed weight. The researches showed that the somaclonal (R9) and the radiationinduced (M9R9) variants revealed similar spectra of morphological and biochemical modifications, thought with different frequency.

The analysis of variance of 51 inbreds and 3 checks revealed significant differences for all 15 characters studied. The range of variation was maximum for percent autogamy followed by plant height and oil yield, while it was lowest in the case of days to 50 percent flowering and stem girth. The magnitude of variation was maximum for oil yield, 100-seed weight, head diameter, percent autogamy, husk percentage, seed density, plant height, seed test weight and oil content. Except for oil content, all other characters studied were least affected by environment showing a close correspondence between phenotypic co-variance (PCV) and genotypic co-variance (GCV). High heritability estimates were obtained for all the characters studied except for oil content, the value of which was moderate. High heritability coupled with the high genetic advance was recorded for plant height, percent autogamy, percent seed set and yield per plant. High heritability along with low genetic advance was observed for the number of leaves per plant, head diameter, stem girth, days to 50 percent flow ering, 100-seed weight and oil yield, suggesting that these characters cannot be effectively improved by selection.

Genetic divergence of 51 inbreds and 3 checks of sunflower was assessed using the Mahalanobis D2 statistics. Fifty-one sunflower inbreds plus three checks, GAUSUF-15, TNASUF-7 and TNAU-1, of diverse geographical origin, were grouped into eight clusters which were not related to their geographic ori gin. Stem girth and seed yield per plant contributed the most to the total genetic divergence. Maximum inter-cluster distance was observed between the inbreds grouped in clusters I and V containing five and twelve inbreds, respectively, while the intra-cluster distance ranged from 0 to 2306.05. Based on mean performance, genetic divergence and clustering pattern, few inbreds namely CMS-234B, 7-1-B, CMS-597B, CMS-852B, ARM-250B, ARM-245B, HAM-69, ARM-284B, ARM-247B and HAM-174 were considered as potentially important for further breeding programs.

Fifty-one inbreds and three checks of sunflower were laid in a randomized complete block design following recommended package of practices. Correlation studies revealed that seed yield was positively and significantly associated with seed volume weight, hull percentage, percent autogamy, days to 50 percent flowering and oil yield. Oil content was positively associated with plant height, number of leaves per plant, seed volume weight, hull percentage, head diameter, percent autogamy, days to 50 percent flowering, 100-seed weight, seed yield and oil yield. Path coefficient analysis for seed yield at phe notypic level showed that the direct effect was maximum for oil yield followed by 100-seed weight. The maximum indirect effect for seed yield was minimum through oil yield, while it was through yield per plant for oil.

This study was conducted in order to improve new synthetic varieties having high yielding ability and to observe hybrid vigor in certain agronomic traits of these synthetics. Three Syn 1s, each composed of four inbred lines, (Syn 1A, Syn 1B, Syn 1C) and one Syn 1 derived from twelve lines (Syn 1D) were formed artificially by inter-crossing. Four experimental Syn 1s, their parental mixtures (Syn O's) and two check varieties (open pollinated Vniimk 8931 and commercial hybrid Sunbred-281) were evaluated in replicated field trials under Bursa conditions without irrigation in 1995, 1996 and 1997. The rates of heterosis observed in plant height, head diameter, seed number/head, 1000-seed weight, seed weight/plant (head) and seed yield/ha were found as 11.2, 14.7, 35.8, 15.7, 59.4 and 65.7%, respectively.

This study was conducted in order to estimate the gene effects which determine the inheritance of certain characters and to search the genetic structure of each group in a 9 x 9 diallel cross group established by crossing inbred lines of sunflower. (1) Significant positive heterotic effects were observed for all the characters studied but for different number of crosses. According to the results obtained, two to three parents were observed to be good general combiners for seed yield and eight hybrids were promising crosses for seed yield and plant height. (2) Both additive and dominance genetic variances were significant for all characters. Also, the overall mean dominance effect of heterozygous loci, h2 was significant for all characters. It was found that positive and negative alleles at these loci were not in equal proportions in the parents (i.e., H1>H2). The average degree of dominance showed overdominance for all characters.