This article comes from the journal Sciences et Avenir – La Recherche no. 893 of July and August 2021.
Lavender, “soul of Provence” wrote Jean Giono, who today develops his blue furrows in the Ili River Valley in the Uighur Autonomous Region of Xinjiang, in northwest China. This former stage of the Silk Road, located at the same latitude as Provence, inspired communist agricultural planners who introduced the first plants there in the 1960s. With success, since 8000 hectares of Huocheng County now provides 95% of the total production of lavender and essential oil in China. With a 12% share of the world market, it has become the third largest producer of official lavender (Lavandula angustifolia), behind Bulgaria (52%) and France (26%). But it has the ambition to solidify its position, especially by improving the quality of its essential oils. And for that, she wants to create “super-lavender”.
Genes associated with identified odors
It is in this perspective that researchers from the Academy of Sciences have just done work on sequencing the lavender genome – in this case the variety (varieties selected for cultivation) Jin-gxun 2. The team was led by botanist Lei Shi, who was already the father of four new varieties. he was interested in the families of genes associated with terpene biosynthesis, these volatile organic compounds derived from perfumes and essential oils. Thus, they found that these compounds in lavender are much more diverse than in other species in the family Lamiaceae (mint, oregano, sage, etc.). This first step of analyzing the principles of terpene biosynthesis is crucial for the transition to the second episode of genetic manipulation in order to obtain better quality lavender. The Chinese team also mapped the genetic distribution of various volatile compounds underlying plant-insect communication, a chemical communication that allows it to attract pollinators and repel herbivorous insects. This last aspect could prove crucial for French lavender crops.
Genetic sequencing of Jingxun 2 cultivar has made it possible to highlight the genes involved in the production of volatile organic compounds, which are much more diverse than in other species Lamiaceae, which includes lavender. Credit: JINGRUILIE TAL
Lavender is actually inseparable from the French Mediterranean terroir, where it naturally occupies dry and rocky soils. Since the 16th century, its essence has been distilled in Provence, which has long been a leading player in the world market of essential oil from the plant. About 22,000 hectares of lavender and lavender hybrids are currently cultivated in southeastern France. But for several decades their production declined, Provencal fields suffer from wear and tear diseases. It is caused by stalk, phytoplasma (bacteria) transmitted by deciduous trees, sucking and stinging insects that live especially with lavender. Infected plant eventually withered. More seriously: French lavender is doubly threatened by climate change. “Stolbur-bearing insects really have a shorter and shorter development cycle, remark by Stéphane Herbette, botanist and physiologist at the University of Clermont Auvergne . The more this insect reproduces, the more lavender withers. In some years, a quarter of the bushes die. And the rise of the impending drought is causing fears of even greater mortality. “ Among lavender growers, the threat is taken seriously. Especially because when a plant dies, its flower production is lost for several years, until the whole plot is mechanically planted …
“We have no way of direct control over October, notes Stéphane Herbette. You should be able to use insecticides, but it would also kill bees that produce lavender honey. One solution would be to improve the plant to obtain a resistant variety. “ Hence the interest of French researchers in sequencing the Chinese genome. “This paper offers the beginning of a solution, but it is not a solution, however tempers Stéphane Herbette. This genome does not tell us which genes, or which combinations of genes, respond to the problem. “ The Interprofessional Technical Institute for Perfumes, Medicinal, Aromatic and Industrial Plants (Iteipmai) is responsible for finding solutions by the Ministry of Agriculture (Iteipmai), so it decided to focus its research on more applied tools through Genolavanda, a program that creates hard lavender. Since 2018, researchers have had new molecular tools at their disposal to identify markers associated with essential oil yield and quality, bacterial resistance, and drought to create a superproductive and resistant variety. In June 2021, they also introduced a reference genetic map for lavender. “This will allow us to compare our results with the results of the Chinese, explains Guillaume Fremondière, head of the Iteipmai experimental station. We will compare the phenotype (set of observable traits of an organism) with the genotype (genetic data of an individual) of lavender plants to link their traits of interest. “
Physical and visual barrier against invasion
While waiting to create a super-lavender resistant to stolbur and drought, lavender growers reconcile with the enemy. “The insect needs open spaces to lay eggs in the ground, explains Stéphane Herbette. By including a grass cover between the rows of lavender, it slows down the progress of insects. “ These rows of grass create both a physical and visual barrier for the postman that flies low on the ground. “This insect is attracted to hot soils”, underlines Éric Chaisse, director of the regionalized interprofessional center for experimentation in perfume, aromatic and medicinal plants (Crieppam). In three to four years of testing, we have already noticed 50% less deaths in lavender fields. ” These plant covers are kept in rows for about five years, which also allows the soil to cool. They are colder, less attractive on deciduous trees, and also stay alive all year round, when bare soils are usually sterilized by summer temperatures.
“Increasing the biological diversity of the soil under the plant cover also implies an increase in predators of beetles (ladybugs, spiders, beetles, etc.), points out Éric Chaisse. We have been testing various plant covers for ten years. This year, 4 tons of grass seeds, legumes and legumes were purchased to test their effectiveness. “ But the appetite for water in these grassy areas is worrying. Also, to prevent them from competing with lavender, they are laid in late spring using mechanical rollers so that the plant uses all the water present in the soil. “Concerns about the survival of lavender are great, insists Stéphane Herbette. This plant is grown in arid countries, hot in summer and cold in winter, like the iconic plateau of Valensole, in the Alpes-de-Haute-Provence. If the lavender disappears, other cultivation will not be possible. “ Super lavender is eagerly awaited.
Vegetables from vegetables (here cereals) between rows of lavender (hybrid lavender) reduces plant death by 50% due to the postman, the vector of the disease, on the examined plots. Credit: THOMAS COSTES / CRIEPPAM
Perfume, medicine … sometimes dangerous
For more than 2500 years, different types of lavender have been used as a perfume, medicine or pesticide in the form of essential oil. Pharmaceutical studies have confirmed many of the properties already assigned to it. The only official lavender or real lavender (Lavandula angustifolia), thus showed its insecticidal (especially against lice), antibacterialEscherichia coli, Staphylococcus aureus, Salmonella) and antifungal. It also has analgesic, anti-inflammatory, anti-stress and sedative powers, including on horses. But its use is not without danger. Two studies published in 2018 and 2019 report children – girls and boys – aged 3 years and older with abnormal breast growth associated with exposure to scented products containing lavender oil: some components of essential oils mimic estrogen and block testosterone.