In vitro technique for selecting onion FOR white rot disease- resistance

Abstract

In vitro selection is one of the most effective and efficient techniques for plant improvement. This is due to its ability to isolate plants with the desired character(s), either by applying a selection agent on the culture media to drive the selection of somaclones with the required character(s), or by establishing particular conditions that change in the genomes of somaclones toward the required character. The objective of this study was to identify a suitable protocol for in vitro selection of Allium white rot disease ( Sclerotium cepivorum ) tolerance in commercial Egyptian onion varieties, namely Giza 20, Giza 6 and Beheri Red. Oxalic acid (OA), the phytotoxin produced by Sclerotium cepivorum, was used as the selective agent. Seeds of the three Egyptian varieties were germinated on four concentrations (0.0, 0.02, 0.2, 2 and 20 mM) of Oxalic acid. Among the tested cultivars, Beheri Red had the highest germination frequency (52%) at all concentrations tested, followed by Giza 20 (42.6%), and Giza 6 at (32%). Cotyledon explants from the varieties were cultured on toxic MSBDK> medium, supplemented with 0, 3, 6 and 12 mM OA. The survival of calli on MSBDK free toxic medium was 70.7% for all tested cultivars; however, MSBDK-stressed medium, with 3 mM OA reduced the viable calli to 42.1%. The highest OA concentration (12 mM) completely inhibited calli induction from cotyledons explants. A medium supplement with 3 mM OA retarded 80% of calli growth. Among 156 tested calli of Beheri Red, only 23 calli (14.7%) survived on toxic medium for 45 days. Similarly, there was 15.6% survival for Giza 20 calli, while 40.1% of the Giza 6 calli survived. Plantlets were regenerated from surviving calli and transplanted onto ex vitro, and formed bulb after acclimatisation.La selection In vitro est l\u2019une des techniques les plus efficaces en amelioration des plantes. Ceci est d\ufb \ue1 la capacit\ue9 qu\u2019\ue1 cette technique de permettre l\u2019isolation des plants avec des caract\ue8res d\ue9sir\ue9s. Ceci se fait de deux mani\ue8res; soit en appliquant un agent de selection sur le milieu de culture afin d\u2019orienter la s\ue9lection somaclonale de fa\ue7on \ue1 pr\ue9server le caract\ue8re desir\ue9, ou, en cr\ue9ant des conditions particuli\ue8res visant \ue1 modifier le genome afin dans le sens des caract\ue8res voulus. L\u2019ojectif de l\u2019\ue9tude \ue9tait d\u2019identifier un protocole ad\ue9quat pour la selection in vitro de la tol\ue9rance \ue1 la maladie de pourriture blanche ( Sclerotium cepivorum ) chez les vari\ue9t\ue9s commerciales d\u2019oignon en Egypte, en loccurence, Giza 20, Giza 6 et Beheri Red. L\u2019acide oxalique (OA), la phytotoxine produite par Sclerotium cepivorum, ont \ue9t\ue9 utilis\ue9s comme agent de s\ue9lection. Les semences des trois vari\ue9t\ue9s Egyptienne d\u2019oignon ont \ue9t\ue9 cultiv\ue9es sur quatre milieu de culture de diff\ue9rentes concentrations d\u2019acide oxalique (0.0, 0.02, 0.2, 2 et 20 mM). parmi les cultivars test\ue9s, Beheri Red avait la fr\ue9quence de germination la plus (52%) sur tous les quatre milieu de culture, puis vint Giza 20 (42,6%) et Giza 6 (32%). Des explants de cotyledons ont \ue9t\ue9 cultiv\ue9s sur milieu toxique MSBDK, additionn\ue9 de 0, 3, 6 et 12 mM de OA. Les calls survivants sur milieu toxique mais ne contenant pas de MSBDK \ue9tait de 70.7% pour tous les cultivars test\ue9s; n\ue9anmoins, le milieu contenant MSBDK, avec 3 mM de OA a caus\ue9 la r\ue9duction des calls viables de 42.1%. la plus forte concentration de OA (12 mM) a caus\ue9 une inhibiton complete de la r\ue9g\ue9ration des calls \ue1 partir des explants de cotyledons. Un milieu additionn\ue9 de 3 mM de OA \ue1 retard\ue9 la croissance des calls de 80%. Parmi les 156 calls de Beheri Red test\ue9s, seuls 23 calls, soit 14,7%, ont surv\ue9cu sur milieu toxique pendant 45 jours. De m\ueame, il y avait 15,6% de calls survivants Giza 20 calli, tandis que 40,1% des calls de Giza 6 ont surv\ue9cu. Des plantules ont \ue9t\ue9 r\ue9g\ue9n\ue9r\ue9 \ue1 partir des calls survivants et ceux ci ont \ue9t\ue9 transplant\ue9 sur milieu naturel, ils forment des bulbes d\u2019oignons apr\ue8s un temps d\u2019acclimatation