Genetics of sweet chestnut castanea sativa mill. iii. genetic analysis of zymograms of single tree offspring
Fineschi, S.; Gillet, E.; Malvolti, M.E.
Silvae Genetica 39(5-6): 188-194
Genetic analysis of four enzyme systems (PGI [phosphoglucose isomerase], IDH [isocitric dehydrogenase], DIA [diaphorase], AP [aminopeptidase]) in European sweet chestnut (Castanea sativa MILL) is performed by a method utilizing single trees and their seed progenies, as offspring from controlled crosses were not available. A total of six variable gene loci with single-locus codominant modes of inheritance were intuitively postulated on the basis of adult zymograms alone. Subsequent genetic analysis supported the intuitive interpretation for only five of the six proposed loci. The results for the sixth, AP-A, demonstrate the necessity for genetic analysis of zymograms, the limitations of such analysis, and its usefulness for providing indications of distortive phenomena. These results are summarized as follows: Observation of adult zymograms suggests complete codominance for AP-A, but qualitative analysis of the single tree progenies compels rejection of this hypothesis, instead suggesting the presence of a (recessive) null allele, A0, in several maternal trees. The revised, null-allele-hypothesis is unequivocally supported by the qualitative tests in all maternal trees as well as by the quantitative tests in all maternal trees not possessing A0. It must, however, be rejected on the grounds of the quantitative test for heterozyous maternal trees presumably possessing the null allele. A0 was significantly overrepresented in two progeny sets, significantly underrepresented in a third, and showed no significant deviation from expectation for the remaining three. It is considered whether the null-allele-hypothesis must necessarily be false or whether other phenomena could have caused the seemingly erratic segregation distortion. Possible explanations are discussed in the light of the fact that, despite the apparently considerable frequency of A0 in the population, no adult trees nor any seeds were found to be homozygous for it.