Evaluation of genetic variability in in vitro sodium azide-induced Dendrobium 'Earsakul' mutants.

In vitro mutagenesis of Dendrobium 'Earsakul' was carried out by incubating the protocorm-like bodies in 0-5 mM sodium azide for 1 h. Twenty-eight putative mutants were evaluated for genetic variability compared to untreated control plants using inter-simple sequence repeat (ISSR) analysis. Polymorphic fragments were produced by 9 of 12 ISSR primers. A total of 173 amplified ISSR fragments varying in size from 140 to 5000 bp were obtained, 39 of which were polymorphic (22.5%). Of the 28 putative mutants, 15 (53.6%) showed altered genetic profiles compared to control and were identified as mutants. These results suggest that sodium azide can be effectively utilized to generate mutants in Dendrobium 'Earsakul', and ISSR provides a powerful tool that allows efficient early detection of these mutants. The identified mutants are currently being multiplied for further evaluation of their horticultural characteristics.

Association of RGA-SSCP markers with resistance to downy mildew and anthracnose in grapevines.

Downy mildew (Plasmopara viticola) and anthracnose (Sphaceloma ampelinum) are two major diseases that severely affect most grapevine (Vitis vinifera) cultivars grown commercially in Thailand. Progress of conventional breeding programs of grapevine for improved resistance to these diseases can be speeded up by selection of molecular markers associated with resistance traits. We evaluated the association between 13 resistance gene analog (RGA)-single-strand conformation polymorphism (SSCP) markers with resistance to downy mildew and anthracnose in 71 segregating progenies of seven cross combinations between susceptible cultivars and resistant lines. F(1) hybrids from each cross were assessed for resistance to downy mildew and anthracnose (isolates Nk4-1 and Rc2-1) under laboratory conditions. Association of resistance traits with RGA-SSCP markers was evaluated using simple linear regression analysis. Three RGA-SSCP markers were found to be significantly correlated with anthracnose resistance, whereas significant correlation with downy mildew resistance was observed for only one RGA-SSCP marker. These results demonstrate the usefulness of RGA-SSCP markers. Four candidate markers with significant associations to resistance to these two major diseases of grapevine were identified. However, these putative associations between markers and resistance need to be verified with larger segregating populations before they can be used for marker-assisted selection.