Biochemical changes associated with downy mildew infection in sunflower revealed an increase in the total soluble proteins, 0-40% ammonium sulfate fractionated proteins and total soluble sugars. Molecular sieve chromatography of 0-40% ammonium sulphate fraction revealed for presence of a high molecular weight protein and polysaccharide in the downy mildew infected sunflower leaves. Antibodies raised against the high molecular weight protein and polysaccharide were used in the western blot/dot blot analysis. It has been shown that the downy mildew disease also induces PR proteins, which have antigenic homology with PR-S protein, a member of the PR-5 class of proteins. An increase in iPA (isopentenyl adenosine) content in the infected sample was observed. A positive correlation exists between iPA level, 0-40% protein and total sugar content. Histological studies revealed that the downy mildew fungal mycelium extensively proliferates, ramifies extensively the leaf tissue and forms a nutritional link with the host cell by producing the intracellular haustorium.

In 1998, a number of Ambrosia artemisifolia individuals located in the vicinity of a sunflower breeding nursery at Bicsérd, south Hungary, showed disease symptoms resembling downy mildew and/or white rust. Sporangia of both Plasmopara and Albugo have been isolated from the affected plants. Microscopical observations and subsequent inoculation experiments revealed the existence of Plasmopara halstedii on the affected A.artemisifolia plants. Following inoculations on a set of sunflower differentials, the Ambrosia isolates of P.halstedii consistently showed a virulence formula of 730 that is equal to pathotype 4.

Downy mildew caused by the fungus Plasmopara halstedii is the main disease on sunflower in Bulgaria. In recent years a number of authors have reported the occurrence of new more virulent races of the pathogen. According to other authors these races demonstrate resistance to the fungicides used up to now. This fact is rather alarming and imposes the necessity of annual researches with the aim of following the changes in the downy mildew race variability.

In the period 1995-1997 downy mildew isolates were collected from the following locations: Bourgas, Boyanovo, Karnobat, Ognyanovo, Selanovtsi, Kroushari, Lovech, Koubrat, Brashlyan, Sitovo, Tervel, Targovishte, IWS “Dobroudja” and Dobrich. The samples were assessed for virulence on a set of sunflower differential - lines under greenhouse conditions.

The obtained results do not reveal a great race variability of downy mildew population in Bulgaria. In the period of study two races of the pathogen were identified: race 1 which infects the differential lines without genes for resistance to the pathogen. It is distributed in all sunflower production areas of the country. The other one is race 2. It is of limited distribution and has been registered in individual fields of north-east and north-west Bulgaria. It attacks the differential lines carrying the resistance gene Pl-1.

Six cultivars and one hybrid were evaluated for resistance to broomrape in the period 1988-1999. It was found that the resistance varied in the range from 0 to 100%. The evaluation was carried out under greenhouse conditions. Infestations were induced by mixed broomrape populations collected from different regions in Bulgaria. Different lines obtained from three cultivars, Progress, Oktjabr (Russia) and Vega (Bulgaria), and the hybrid Sorem 80 (Romania) showed stable resistance (80-100%) after ten years of evaluation, in spite of the occurrence and distribution of new races (D+E) of the parasite in Bulgaria.

A review of the racial situation of Orobanche cumana in Spain and of several studies on sunflower resistance to broomrape is presented. In the nineties, populations of O.cumana attacking sunflower crops in Spain have evolved first towards the increase in frequency of race B simultaneous to the decrease of race A. Later, race E has appeared with increasing frequency. However, the subsequent change to resistant hybrids carrying the Or5 gene has prompted the recent appearance of a new race (race F) that overcomes this resistance gene, and is expanding mainly in southern Spain. Collections of cultivated P.I. accessions tested for resistance to races E or F indicated a low frequency of entries resistant or segregating for resistance. A low frequency of resistance was also observed in accessions of wild annual species. Among 18 species, only H.agrestis and H.anomalus showed full resistance to both races, whereas H.debilis ssp. cucumerifolius and H.exilis segregated. Lines breeding true for resistance, derived from H.anomalus, H.exilis and H.debilis have been produced. In contrast, inoculation of races E and F to wild perennials resulted in complete resistance in 74% of the species, and segregation for resistance to race F in 11%. The transference of resistance from wild perennial species into cultivated sunflower is, however, much more difficult than that of annuals. Embryo rescue and chromosome doubling techniques were often required. Although inheritance studies indicated dominance and one single gene involved in the resistance to races A and E in most crosses, two dominant genes, epistatic interactions and reversal in the dominance were observed in some cases.

Two accessions of the wild species Helianthus annuus L., GT-E-112 and GT-E-126, carried genes for resistance to Plasmopara helianthi Novot., Phomopsis helianthi Munt.-Cvet. et al. and Orobanche cumana Wallr. The material produced by interspecific hybridization with susceptible cultivated sunflower showed resistance to the three pathogens. Some progenies were resistant to two pathogens simultaneously. Self pollination helped to increase the percentage of resistance up to 100%. Accessions GT-E-112 and GT-E-126 of the wild species Helianthus annuus could be successfully used as donors for resistance to Plasmopara helianthi, Phomopsis helianthi and Orobanche cumana.

The genetics of anodal esterase (Est), cathodal esterase (cEst), cathodal acid phosphatase (cAcp) and malate dehydrogenase (Mdh) has been studied in mature seeds and leaves (genetics of cAcp and Mdh has not been studied in leaves) of sunflower (Helianthus annuus L.). A total of ten loci (four loci of anodal esterase, two loci of cathodal esterase, three loci of malate dehydrogenase and one locus of cathodal acid phosphatase) have been identified and described. Five esterase loci (Est1, Est2, Est3, Est4, cEst5), three malate dehydrogenase loci and one locus of cathodal acid phosphatase are expressed in seeds. Three esterase loci (Est2, cEst5 and cEst6) are expressed in leaves. The analysis of linkage between these loci has been made. Two linkage groups have been found. The sequence of the loci in the first linkage group was Mdh2-Est1-Est2-Est3-cEst5. In the second linkage group it was Est4-cAcp1. Linkages have been analyzed between three isoenzymatic loci expressed in leaves and between two loci controlling morphological traits (branched stem and male fertility restoration). The linkage between morphological traits and isoenzymatic loci has not been revealed. It has been revealed in Br-Rf pair.

The genetic control of the high saturated fatty acid content in sunflower seed oil has been studied in the high palmitic acid (C16:0) mutant line CAS-5, and in the high stearic acid (C18:0) mutant line CAS-3. This review summarizes the pertinent results. The high saturated fatty acid content in sunflower seed oil is controlled by partially recessive alleles at two loci (Es1, Es2) for the high C18:0 content and at three loci (P1, P2, P3) for the high C16:0 content. The high C16:0 and the high C18:0 traits are not inherited independently. When their combined segregation was studied, the expected phenotypic expression of both high C16:0 and high C18:0 levels was not observed. This fact was attributed to the existence of an epistatic effect of the loci controlling the high C16:0 trait on the loci controlling the high C18:0 trait. The results obtained indicate that sunflower hybrids with a high saturated fatty acid content in their seed oil can be developed and will be in cultivation in a few years.

This work was aimed to study, under different levels of radiation intercepted by the plants during the seed filling stage, the relationship between yield and vascularization in three concentric positions of the capitulum. At the end of flowering, we applied shading (to reduce intercepted radiation) and thinning (to increase it) to three culture plots: a shaded plot, a thinned plot and a shaded and thinned plot. One additional untreated plot was used as control. We harvested heads at flowering and at physiological maturity. We delimited on them three positions: outer, middle and inner. Portions of each position were extracted from physiological maturity heads and their yield components were determined. The remaining heads were fixed in F.A.A., soaked in paraffin, and transversely cut at seed insertion to measure vascularization variables (phloem and sieve tubes area, number of tranverse and longitudinal bundles and sieve pores diameter). The head area unit was used as a base in all measurements. Shading reduced dry weight in the three positions. The middle position showed the highest yield and the inner showed the lowest in the four plots. The yield of the former was high because its lower individual seed weight (decreasing from periphery to center in all plots) was compensated by a higher number of filled seeds. However, average sieve pores radius was similar among positions, and phloem and sieve tubes areas were similar among positions and treatments, which could not account for the differences in yield per head area unit between positions. This enables us to conclude that this variation would not be produced by vascularization lack.

Seed germination of six sunflower (Helianthus annuus L.) hybrids was investigated across a range of eleven constant temperatures between 5°C and 45°C. Large temperature differences in germination rate 1/t (d -1), cardinal temperature (°C) and thermal time θ (°cd) were observed among hybrids. Base temperatures (Tb) varied between 3.3°C and 6.7°C whereas maximum germination temperatures (Tm) varied between 41.7°C and 48.9°C. Final germination fraction was attained at 15°C - 25°C whereas the maximum rate of germination was attained at 30.4°C - 35.6°C. The maximum germination rate of hybrid USDA 894, the cultivar with the slowest germination rate, was only 50% of that of hybrid EX 47. The low Tb and high Tm of sunflower appear to be one of the factors which explain the successful adaptation of sunflower to a wide range of temperature. These findings are discussed in relation to the origin of the crop and its wide adaptations in diverse habitats and climatic zones.

Sunflower and other Helianthus ssp. produced, among other secondary metabolites, the coumarins scopoletin, scopolin and ayapin. In the most general sense they can be defined as stress metabolites, their synthesis being induced in response to adverse environmental condition, both biotic and abiotic. The pattern of coumarin synthesis and accumulation depends on plant variety, it is tissue dependent and developmentally regulated. Coumarin synthesis in sunflower seems to be part of the defence strategy against microorganisms, insect and parasitic plants. From an agricultural point of view the defensive potential of these compounds can be exploited in order to develop resistant varieties (either by classical plant breeding or by biotechnology) or crop protection strategies involving the use of chemicals which induced coumarin synthesis

Studies have been carried out on the quality and utilization of sunflower seed and cake. Sunflower hybrids have been examined for their proximate composition, micronutrients, fatty acid profile and tocopherol content. The major fatty acids namely oleic and linoleic acids, were 36-50% and 42-54%, respectively. Micronutrients like zinc, copper, manganese and iron were analyzed in various genotypes; zinc content ranged from 50 to 107.2 g/g, copper 24.4-39.6 g/g, manganese 28.2-89.6 g/g and iron between 305 and 392 g/g. Alpha, beta and gamma tocopherols ranged between 406 and 485, 35 and 56 and 4 and 10 mg/kg, respectively. MSFH 8 had high levels of tocopherols and micronutrients.

Sunflower cake flour and protein isolates were utilized in the preparation of biscuits and some snack food items like pakodi and chapati. Protein isolates added at 5% levels increased protein content of biscuits from 12 g/100g to 16 g/100g. At 10% level the protein content was 20 g/100g. Taste panel acceptability was 75-80% for the biscuits and snack foods against 100% for the control. There is thus a good opportunity for utilization of sunflower seed and cake flours and their protein isolates as food ingredients in India

Experiments were laid out to investigate the germination ability of immature sunflower seeds. Seeds of different age after fertilization were planted directly into bags filled with soil mixture. The experiments, conducted in the period 1984-1986, proved the possibility of sunflower cultivation with immature seeds directly in soil, without artificial nutritive media. Seeds are removed from a head 10 or 12 days after fertilization and immediately planted (do not permit them to dry) into bags with soil mixture. Our method is simple and easy. It does not demand special equipment, tools and specially prepared nutritive media and allows getting six vegetative cycles per year. It permits to obtain different line analogues in a single year instead of 6 or 7 years.