Chromosome doubling via tuber disc culture in dihaploid potato as determined by confocal microscopy.

The potential of tuber disc culture for chromosome doubling was investigated in somaclonal populations of four dihaploid genotypes and one tetraploid cultivar of potato (Solanum tuberosum). Laser scanning confocal microscopy (LSCM) was used for rapid determination of the ploidy level based on the number of chloroplasts in stomatal guard cells of leaves. Factorial analysis of chloroplast number in 58 clones and two leaf types showed that somaclones were clearly divided in two groups. Clones with 5-7 chloroplasts per cell as observed in tuber derived diploid 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 doubling, 42% - 50%, was detected in 3 dihaploid genotypes, whereas no doubling was observed in one of the dihaploids as well as the tetraploid cultivar Yukon Gold. Effects of leaf type on chloroplast number was also significant. The middle leaf showed significantly higher chloroplast number than the younger leaves.