Development and characterization of an adapted form of droopy, a diploid potato mutant deficient in abscisic acid

A cultivated diploid potato breeding population has been selected for adapt ation to growing, tuberizing (under relatively long days), and storing (inc luding long dormancy) under New Brunswick conditions. In this population, a mutant was discovered that appeared similar to the earlier described droop y mutant, which is deficient in abscisic acid and is unable to regulate wat er loss from its leaves. The physiology and genetics of the newly discovere d mutant were studied and compared in detail with the description of droopy . This mutant has a longer tuber dormancy than the original droopy. In fami lies segregating for droopy and normal, similar dormancies and endogenous a bscisic acid levels in tubers were observed between droopy and normal genot ypes. The effect of the mutant gene appears to be tissue specific, affectin g aboveground plant parts only. A test for allelism indicated that this mut ant is allelic to droopy. Classical linkage analyses confirmed previously r eported close linkage between the Dr (droopy) and the S (incompatibility) l oci. The Dr locus has been mapped in this study to the top of chromosome I. Several test crosses indicated reciprocal differences in the segregation r atios between droopy and normal. In keeping with the droopy (drdr) genotype , drought-stressed leaves of the mutant were incapable of increasing abscis ic acid production compared to the normal. This mutant, with its apparent d evelopmentally restricted expression, may be useful in elucidating the gene tic and physiological processes associated with such major events as tuberi zation, response to drought stress and tuber dormancy.