Les oïdiums des cucurbitacées. II. Mise au point d'une technique de conservation des souches en culture axénique

Abstract

La formation de cals et même de racines (cas de la courgette et du concombre) assure à la feuille une survie d'environ 2 mois (4 mois si elle n'est pas contaminée par l'oïdium). Après isolement d'une souche donnée, son repiquage « in vitro », à l'aide d'un pinceau, d'une feuille infectée à une feuille saine ne pose aucune difficulté.Cette technique est comparée aux diverses méthodes utilisées pour la conservation des parasites obligatoires.Mots clés additionnels : Sphaerotheca fuliginea, Erysiphe cichoracearum, Leveillula taurica, formation de cals, rhizogenèse, culture de tissus, courgette, concombre, tabac, piment, HgCl 2 , technique de désinfection. SUMMARYPowdery mildews of cucurbits. II. A method for preserving isolates in axenic culture.The following powdery mildews were preserved actively on detached adult leaves of different plants in a culture medium, in axenic conditions : Sphaerotheca fuliginea on squash or cucumber ; Erysiphe cichoracearum on squash, cucumber or tobacco ; Leveillula taurica on pepper. Detached leaves were first disinfected by soaking for 3 minutes in an aqueous solution of 0.05 % HgC' 2 , and their petioles planted into an agar medium (tissue culture). Leaves were then sprayed with spores of different powdery mildews, disinfected by an original technique involving HgC' 2 for less than 2 min. Spores were readily transferred from diseased to healthy leaves with a soft paint brush in axenic conditions. Callus and root formation (with cucumber and squash) allowed the leaves to survive as long as 2 months, or 4 months if not infected with powdery mildews. This technique is compared with other methods of conservation already in use for obligate parasites.

Novel sources of resistance to powdery mildew (Leveillula taurica (Lév.) Arnaud) in pepper

“…Three main inoculation techniques are commonly used: i) natural infection, ii) artificial inoculation by directly brushing conidia on leaves; iii) spraying conidia suspensions of variable concentration (10 5 -2.5 × 10 4 ml -1 ) with Triton X 100 1µl ml -1 (Molot et al, 1990;Daubeze et al, 1995;Zheng et al, 2013;Albert et al, 2017;Özer et al, 2018;McCoy and Bosland, 2019). Controlled screenings have been performed using a wide range of temperatures (16-27 °C, Molot et al, 1987;Zheng et al, 2013), humidity (30-70% ± 15 RH, Bai et al, 2003;Zheng et al, 2012) and photoperiod (12-14 h light and 12-10 h dark, Molot et al, 1987;Özer et al, 2018). To evaluate properly the response to infection some authors have suggested semi-quantitative scoring system or variants (Molot et al, 1987).…”

“…Controlled screenings have been performed using a wide range of temperatures (16-27 °C, Molot et al, 1987;Zheng et al, 2013), humidity (30-70% ± 15 RH, Bai et al, 2003;Zheng et al, 2012) and photoperiod (12-14 h light and 12-10 h dark, Molot et al, 1987;Özer et al, 2018). To evaluate properly the response to infection some authors have suggested semi-quantitative scoring system or variants (Molot et al, 1987). Such methodology ranks the plants using a scale from 0 to 5, where 0 = to healthy plant (i. e., no infested leaves) and 5 = 80-100% plant foliage infested.…”