RAPID METHOD FOR SCREENING THE TOLERANCE OF YEASTS TO ZINC (II) AND CHROMIUM (III)

Rapid screening of the tolerance of yeasts to zinc (II) and chromium (III) was performed by an agar diffusion test. A rapid and reliable procedure for the determination of metal ion concentration gradients on agar plates was developed. Different species of yeasts from the following genera were investigated: Arthroascus, Bulera, Dekkera, Debaryomyces, Dipodascopsis, Eremothecium, Candida, Hansenula, Kluyveromyces, Hormoacus, Geotrichum, Lipomyces, Pachysolen, Pichia, Saccharomyces, Schizosaccharomyces, Schizoblastosporion, Schwan-niomyces, Sporobolomyces, Yarrowia, Torulaspora, Zygosaccharomyces and Williopsis. The experimental conditions were defined as a constant volume of malt agar 32 cm³, and a temperature of 29C. After periods of 24, 47 and 72 h, the concentration intervals of growth inhibition were determined, and the yeasts investigated were grouped in different classes according to their tolerance to Zn (II) and Cr (III). Yeasts were found to be tolerant to significantly higher zinc (II) concentrations in the malt agar medium (5.9 mM to 20 mM) in comparison to chromium (III) (1.5 mM to 6.9 mM). Yeasts showed inter- and intra-generic differences in zinc (II) and chromium (III) tolerance.     

Strong resistance to potato tuber necrotic ringspot disease in potato induced by transformation with coat protein gene sequences from an NTN isolate of Potato virus Y

The potato cv. Igor is susceptible to infection with Potato virus Y (PVY) and in Slovenia it has been so severely affected with NTN isolates of PVY causing potato tuber necrotic ringspot disease (PTNRD) that its cultivation has ceased. Plants of cv. Igor were transformed with two transgenes that contained coat protein gene sequence of PVY^NTN. Both transgenes used PVY sequence in a sense (+) orientation, one in native translational context (N‐CP), and one with a frame‐shift mutation (FS‐CP). Although most transgenic lines were susceptible to infection with PVY^NTN and PVY^O, several lines showed resistance that could be classified into two types. Following manual or graft inoculation, plants of partially resistant lines developed some symptoms in foliage and tubers, and virus titre in the foliage, estimated by ELISA, was low or undetectable. In highly resistant (R) lines, symptoms did not develop in foliage and on tubers, and virus could not be detected in foliage by ELISA or infectivity assay. Four lines from 34 tested (two N‐CP and two FS‐CP) were R to PVY^NTN and PVY^O and one additional line was R to PVY^O. When cv. Spey was transformed with the same constructs, they did not confer strong resistance to PVY^O.