LOOKING BACK - Origin of Male Sterilities and Sunflower Hybrid Varieties in France and Worldwide
by: Bernard VIVIER, INRAE – Agri-Obtentions, Clermont-Ferrand, France (retired)
"The edible oil most widely used in France before 1970 was obtained from imported groundnuts. During the 1960s, the French government decided to develop oil crops that could be produced in France, to replace these importations. INRAE was asked to undertake research programmes concerning rapeseed and sunflower. The latter species was not grown in France at this time, except for small areas in South-Eastern France, mainly for bird feed (mostly the variety Gris Strié de Provence) and in gardens during World War 2, to provide a small amount of oil. In the 1960s, the sunflower crop was most important in the USSR, mainly in southern Russia and Ukraine, using open pollinated varieties bred for their high oil contents by V. PUSTOVOIT at Krasnodar.
Discovery of Genic Male Sterility
Simone LENOBLE, who was in charge of the sunflower programme at INRAE, Clermont-Ferrand, contacted the VNIIMK at Krasnodar to obtain samples of their different varieties. Collaborations were implemented with the French Association of oil seed multipliers (USGOS/AMSOL) and the CETIOM (now Terres Inovia), the technical institute, to multiply, test and distribute this material. In 1962, the first samples were grown in the INRAE sunflower nursery, and one plant producing no pollen was observed, it was male sterile. Such plants are very rare and its observation was the equivalent of some medical discoveries.
This male sterile plant showed no particular coloration (it was described as “green”). An old French variety, “Nain Noir”, present in the 1962 sunflower nursery, showed red coloration on stems, petioles and leaf edges, due to the presence of anthocyanins (defined as “red”). Pollen from this variety was applied on the male sterile plant. The seeds obtained were sown in the greenhouse in October 1962. At emergence, all the seedlings showed the red coloration. This character was therefore considered to show dominant inheritance.
In February 1963, I joined the sunflower laboratory at INRAE, Clermont-Ferrand. With S. Lenoble, when the plants in the greenhouse flowered, we observed that they all produced pollen (they were male fertile). They were self-pollinated, by covering the heads with bags. The seed harvested was sown in spring 1963 and at flowering, the ¾ plants, which were all “red”, were all male fertile whereas the ¼ plants which were “green” were all male sterile. The two characters followed the laws of Mendel for major genes and were very closely linked genetically. This was the discovery of what is known as genic male sterility in sunflower, marked by the presence or absence of red coloration (Leclercq, 1966). However, since the male sterile character shows recessive inheritance, it was not possible to obtain a progeny with 100% male sterile plants. To permit crossing with another line to produce uniform hybrids, it was necessary to remove all the “red” plants before flowering. Lines developed from various Russian and Bulgarian varieties were used as male parents to pollinate the male sterile plants. To permit research and breeding on a larger scale, the sunflower team was enlarged with the arrival of two technicians.
Development of the First Hybrid Variety
Field trials to compare the yield and oil content of the experimental hybrids led to the registration in 1970 on the French Official Catalogue of the first sunflower hybrid in the world, INRA 6501. In the same period, a very early open pollinated variety, ISSANKA, was registered by INRAE at Montpellier.
Large scale cropping of sunflower in France started in about 1968 using the open pollinated varieties imported from the USSR by USGOS/AMSOL and recommended after study by CETIOM/Terres Inovia. Production of INRA 6501 and field trials of other hybrids were developed by collaboration between INRAE and seeds firms in areas of France with climates adapted to sunflower: Limagne, Rhone valley, western and southwestern France.
Pollination of sunflowers is mainly carried out by bees, which can collect pollen and nectar quite far from their hives. Large scale hybrid seed productions and checks of the uniformity of the seed produced made it possible to determine the distance, about one kilometre, necessary to isolate hybrid production from other sunflower crops.
Multiplication of the female parent required the seed to be sown very densely before removal of all the « red » plants in the bands designated « female », from which the seed was harvested and all the « green plants » in the bands designated « male » which produced the pollen. This required a large amount of manual labour as was also the case for the female parent in commercial hybrid production.
Discovery of Cytoplasmic Male Sterility
At the same time as the commercial development of « genic hybrids », under the direction of André CAUDERON, Patrice LECLERQ, who succeeded Simone LENOBLE (who transferred to Lusignan to work on forage crops), made some interspecific crosses in the nursey, between cultivated sunflower (Helianthus annuus) and related wild species, samples of which were provided by the American scientist C. HEISER.
From a cross between the wild species Helianthus petiolaris and H. annuus, he obtained plants with a cytoplasmic male sterility (a character determined in the cytoplasm, under maternal inheritance). Published by Leclercq (1969), this male sterility gives progenies with 100% of the plants producing no pollen, and thus largely simplifying hybrid seed production. The male parents of cytoplasmic hybrids must carry restorer genes, which were obtained from several Helianthus species (Kinman, 1970, Leclercq, 1971). The first cytoplasmic hybrid in the world, registered in France in 1973 was called RELAX to indicate the simplicity of its production.
This cytoplasmic male sterility, distributed with no limitation or patent is still used freely and almost exclusively used throughout the world and has been the basis of an enormous extension of the sunflower crop in very many countries (Vear 2010). This development was also helped by pioneer research in sunflower agronomy and mechanisation.
These discoveries of male sterilities in sunflower made it possible to obtain hybrid varieties showing much more uniform height and maturity dates, compared with the old open-pollinated varieties, simplifying agronomic procedures. They also made possible more rapid progress in breeding for characters such as disease resistance and oil quality which can be rapidly fixed in parental lines (Vear 2016). They were the basis of the many breeding programmes developed in Europe, North America, South America and, more recently Asia.
The sunflower crop should continue to have a good future as it requires few inputs other than seed, is quite drought resistant and produces several sorts of edible oil much appreciated by consumers."
Bernard Vivier in an advertisement for an INRAE variety in about 1978
Kinman ML. 1970. Letter to Participants. Proc 4th Int Sunflower Conf, Memphis, TN, USA, June 23–25, 1970
Leclercq P. 1966. Une stérilité male utilisable pour la production d’hybrides simples de tournesol. Ann. Amélior.Pl. 16 :135-144.
Leclercq P. 1969. Une stérilité mâle cytoplasmique chez le tournesol. Ann. Amelior.Pl. 19: 99–106.
Leclercq P. 1971. La stérilité mâle cytoplasmique du tournesol 1. Premières études sur la restauration de la fertilité. Ann Amélior Pl. 21: 45–54.
Vear F. 2010. Classic Genetics and Breeding. In “Genetics, Genomics and Breeding of Sunflower” ed. Kole C. Science Publishers Inc. Jersey, N.H, USA. : 51-77.
Vear F. 2016. Changes in sunflower breeding over the last fifty years. OCL 2016, 23(2) D202.