Identification of Raspberry–Blackberry Hybrid Seedlings by Isozyme Staining and Soluble Protein Banding Patterns

Abstract

Isozyme staining and SDS-PAGE of soluble proteins were performed using leaf homogenates from 6- to 8-month-old field-grown seedlings resulting from the cross of either `Heritage' or `Nova' raspberry with ARK-577 diploid blackberry, the latter used as the pollen-donor parent. Four enzyme systems were tested: ADH, PGM, MDH, and PGI. Of these, ADH and PGM did not show any activity; MDH was monomorphic in both raspberry and blackberry parents, with activity at the same migration distance. PGI was polymorphic in the two raspberry cultivars, showing three dimeric bands, but monomorphic in blackberry; the allele for PGI in blackberry being common to that allele coding for the most cathodal band in raspberry. This phenomenon, in addition to poor resolution of bands (due, perhaps to low enzyme activity) and evidence of accidental self-pollination in our populations, prevented us from positively identifying the hybrid offspring using isozymes. By SDS-PAGE of soluble proteins, two bands were detected that seemed to be unique to ARK-577 blackberry and were also expressed in some of the offspring, suggesting a hybrid origin of these seedlings. Morphological comparisons indicated that those seedlings possessing the two unique bands highly resemble the blackberry male parent, greatly supporting their hybrid origin. Unless additional analysis shows otherwise, SDS-PAGE can be used to identify Raspberry–Blackberry hybrids during their vegetative stage of development, and might prove applicable to other interspecific hybrids of Rubus.