MORPHOGENIC RESPONSE FROM LEAF EXPLANT OF Dendranthema grandiflora VAR MICROMARGARA

Background: Chrysanthemum is one of the most popular landscape plants worldwide. Introducing desirable traits into this plant by conventional breeding has limitations due to cross-incompatibility. An approach to this problem is the introduction of resistance or tolerance traits via plant genetic transformation. In vitro regeneration of plants is necessary for implementing genetic transformation systems; therefore, regeneration via morphogenesis is required before any genetic transformation attempt. Objective: To induce morphogenesis from the leaf explant of Dendranthema grandiflora var Micromargara. Methodology: Micropropagation from node cuttings was induced from node cuttings of 3 cm in length from 6 months-old plants that were used as explants to produce seedlings as source explants. Morphogenesis experiments were done using leaf segments of 1 cm2 from 8-weeks-old in vitro seedlings. The explants were transferred to basal medium Murashige and Skoog at 4.4 gL-1 supplemented with different plant growth regulators. During the morphogenic process, leaves samples were collected to detect which morphogenic process was induced. Results: Node cuttings culture on Murashige and Skoog medium at 3.3 gL-1 supplemented with benzylaminopurine at 2.2 µM yielded a vegetative growth increase from 1 to 7 shoots, 2 to 12 leaves per node cutting, and the stem length of 3 to 9.5 cm. The leaf explant induced three ways of in vitro morphogenesis: direct and indirect roots organogenesis (rhizogenesis) and, shoot organogenesis. Direct rhizogenesis was induced in plant growth regulator-free Murashige and Skoog medium (18 roots/explant). Indirect rhizogenesis from leaf explant was less efficient than direct rhizogenesis, get obtaining six roots per leaf explant cultured on Murashige and Skoog medium at 4.4 g L-1 supplemented with 0.4 µM thidiazuron and 4.5 µM 2,4-dichlorophenoxyacetic acid, and three roots per leaf explant cultured on Murashige and Skoog medium supplemented with 0.4 µM thidiazuron and 9.05 µM 2,4-dichlorophenoxyacetic acid. Indirect shoot organogenesis was induced from leaf explants cultured on Murashige and Skoog at 4.4 g L-1 supplemented with 13.32 µM benzylaminopurine and 4.83 µM naphthalene acetic acid; 50% of explants with callus formed shoots (2 shoots/leaf explant). Through histological analysis it was possible to verify that the morphogenic response obtained was organogenesis. Implications: Regeneration of Dendranthema grandiflora var. Micromargara establi