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Downy mildew of sunflower, caused by the Oomycete, Plasmopara halstedii is at present controlled by major resistance genes. However, the pathogen has shown a considerable capacity for changes in virulence and these resistance genes are overcome only a few years after they have been introduced into new sunflower varieties. This paper presents research for quantitative, non-race-specific resistance independent of major genes. The reaction of cultivated sunflower genotypes to field attack by downy mildew was studied over 4 years in several environments and in the presence of the two most common races in France: 703 and 710. An experimental protocol with pre-emergence irrigation was developed, making it possible to observe downy mildew reaction whatever the weather conditions. Significant levels of partial resistance were observed in about 50 inbred sunflower lines among the 800 observed. These results suggest that it should be possible to select for non-race-specific downy mildew resistance and to include it in modern varieties. However, since this non-specific resistance is partial, it may be necessary to combine it with major gene resistance. Possible strategies are discussed to obtain durable resistance to downy mildew. [ABSTRACT FROM AUTHOR]

For sunflowers to be a profitable industrial-use crop, input costs must be as low as possible. Genetic resistance is therefore essential to control diseases without any spraying or seed treatment procedures. In France, Downy mildew is one of the most potentially important diseases. So far, complete, major gene resistance (Pl genes) has been used successfully, but with the appearance of seven new races since 2000, research on more durable resistance has been undertaken. Since 2003, methodologies for large-scale trials have been developed to study field reaction to Downy mildew attacks on genotypes which do not have Pl genes effective against the predominant races present. It has been shown that significant levels of partial resistance exist in cultivated sunflower lines (15% infection when susceptibles show 80-90% infection). This resistance appears independent of race (at least 710 and 703). Heredity is under additive control and the behaviour of hybrids can be quite well predicted from inbred lines. Present and future research programmes are discussed and suggestions are made for the use of partial resistance in breeding programmes. [ABSTRACT FROM AUTHOR]

Recurrent selection for resistance to Sclerotinia head rot was carried out for 15 cycles on a restorer sunflower population created in 1978. For the first 3 cycles a test measuring rate of extension of mycelium on the back of capitula was used; from the fourth cycle onwards, it was combined with a test based on ascospore infections, which repeat more closely natural infections. An 80% reduction in diseased area was obtained in 4 cycles, with the first test, thereafter the population remained stable and homogeneous for this character. In 12 cycles the latency index (measure of incubation period) of the ascospore test doubled, and the best relation with cycle was a simple regression, with a significant slope, indicating that further improvements should be possible. The hybrids made with the first, sixth and fifteenth generations of the population showed a halving of percentage attack in the field and hybrids with some of the best lines bred from several cycles presented even greater levels of resistance. This population is available to sunflower breeders and scientists. [ABSTRACT FROM AUTHOR]

Modern breeding of sunflower (Helianthus annuus L.), which started 100 years ago, increased the number and the diversity of cultivated forms. In addition, for more than 50 years, wild sunflower and other Helianthus species have been collected in North America where they all originated. Collections of both cultivated and wild forms are maintained in gene banks in many countries where sunflower is an important crop, with some specificity according to the availability of germplasm and to local research and breeding programmes. Cultivated material includes land races, open pollinated varieties, synthetics and inbred lines. The majority of wild accessions are ecotypes of wild Helianthus annuus, but also 52 other species of Helianthus and a few related genera. The activities of three gene banks, in USA, France and Serbia, are described in detail, supplemented by data from seven other countries. Past and future uses of the genetic resources for environmental adaptation and breeding are discussed in relation to genomic and improved phenotypic knowledge of the cultivated and wild accessions available in the gene banks.

The inheritance of resistance of sunflower to phomopsis (Diaporthe helianthi) was studied on 10 inbred lines representing a range of resistance and susceptibility levels, and 25 hybrids from a factorial cross of these lines. Analyses of observations over a 3-year period, of semi-natural infection (presence of stem lesions greater than 5 cm) on the hybrids indicated that additive gene control was predominant, with no significant interactions between parental effects. Correlations between infection of parental lines and the mean of their hybrids were not always significant, with certain inbreds which appeared quite susceptible giving hybrids with good levels of resistance. In order to predict hybrid values, it appears necessary to determine the general combining abilities of parental lines. Some inbreds gave very high levels of resistance, others gave very high levels of susceptibility. A test measuring the rate of extension of D. helianthi mycelium on leaves was significantly correlated with the results of natural infections. In particular, it permitted distinction of the most susceptible genotypes, and thus could be used in first generations of breeding to eliminate the most susceptible plants. [ABSTRACT FROM AUTHOR]

This study was made to determine the reactions of sunflower genotypes to artificial infections of Botrytis cinevea under netting tunnels with irrigation. The genotypes were the parents and F1 hybrids of a factorial cross between 5 female (male sterile) and 5 restorer lines. Their resistance levels were measured by the mean delay between infection and symptom appearance on the capitulum. Significant genotypic differences in reaction to B. cinerea were shown. The ratio of general combining ability to specific combining ability was 2.9, indicating that additive effects are important. However, there were some significant interactions between male and female parents. The mean parent-hybrid and parent-progeny regressions were both significant with correlation coefficients of r = 0.57 and r = 0.66 respectively. It is concluded that breeding programmes with tests for B. cinevea resistance in early generations should be effective in the development of sunflower hybrids with improved B. cinerea resistance. [ABSTRACT FROM AUTHOR]

Improvement of the feed value of sunflower seedmeal by hulling achenes before crushing is of economic importance and varieties with good hullabiIity (ease of hulling) would be economically significant. Knowledge of the genetics of this characteristic is therefore necessary. Studies of heritability were made on a factorial cross of six female and six restorer lines. Hullability was measured as the ratio of hull removed by a laboratory huller against the total quantity of hull in the achene. The genotypes studied showed a wide range huliabilities. There were considerable environmental effects but only small interactions; correlations between results in different locations were significant. Additive genetic effects predominated, although, there were some interaction between parental lines. Narrow-sense heritabilities were 073- 0.85 for genotype means, 0.52 when calculated from individual plants, and 0.36-76 From parent -parent-regressions. Early selection based on progeny means or a combination of individual and progeny values would appear to be the best method of breeding for improved hullability of sunflower achenes. [ABSTRACT FROM AUTHOR]

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