CHROMOSOME DOUBLING VIA TUBER DISC CULTURE IN DIHAPLOID POTATO AS DETERMINED BY CONFOCAL MICROSCOPY

The potential of tuber disc culture for chromosome doubling was invest igated in somaclonal populations of four dihaploid genotypes and one t etraploid cultivar of potato (Solanum tuberosum). Laser scanning confo cal microscopy (LSCM) was used for rapid determination of the ploidy l evel based on the number of chloroplasts in stomatal guard cells of le aves. Factorial analysis of chloroplast number in 58 clones and two le af types showed that somaclones were clearly divided in two groups. Cl ones with 5-7 chloroplasts per cell as observed in tuber derived diplo id controls were classified as 2X (not doubled), while those with 9-14 chloroplasts resembled the tuber derived tetraploid controls and were considered 4X (doubled). A high frequency of spontaneous chromosome d oubling, 42% - 50%, was detected in 3 dihaploid genotypes, whereas no doubling was observed in one of the dihaploids as well as the tetraplo id cultivar Yukon Gold. Effects of leaf type on chloroplast number was also significant. The middle leaf showed significantly higher chlorop last number than the younger leaves.