REVERTANTS OF THE AMYLOSE-FREE POTATO CLONE 86.040 (2N = 1X = 12)

The amylose-free (amf) potato clone 86.040 (2n = 1x = 12), in which the enzyme granule bound starch synthase (GBSS) is affected, has been used for the induction and isolation of revertants with loosely branched amylopectin. Screening of 5500 microtubers, which were induced on stem segments of 685 irradiated buds gave in 44 cases reverted sectors from which 22 solid revertants were isolated. However, biochemical analysis showed in a revertants GBSS activity and a compound present in the starch granules which in all probability was amylose. The frequency of spontaneous reversions in tuber cells of the amf mutant 86.040 1x, 2x and 4x and of amf-mutations in wildtype AM 79.73221 1x, 2x and 4x was investigated indirectly by screening, after iodine staining, for starch granules with altered composition. The amf-mutation occurred at the monoploid- and diploid level. Spontaneous reversions occurred also at the tetraploid level and in high frequencies in older microtubers from monoploid shoots. The reversion frequency in microspores of fertile amfamf-plants appeared to be low. © 1990.