Articles
CYTOLOGICAL STUDIES OF TETRA-, HEPTA- AND OCTOPLOID INTERSPECIFIC HYBRIDS BETWEEN P. CERASIFERA, P. SPINOSA AND P. DOMESTICA.
An other genomic hypothesis was suggested for hexaploid plums: D1D1D2D2CC.
The following cytological study was carried out on two tetraploid forms and on two polyploid forms, one heptaploid (2n = 7x = 56) and the other octoploid (2n = 8x = 64).
The two tetraploid types (P. domestica x P. cerasifera) x P. spinosa and P. spinosa x [(P. domestica x P. cerasifera)] x P. spinosa, exhibit an identical meiotic behaviour to that of the P. spinosa species and (P. domestica x P. cerasifera) tetraploid hybrids, ie a formation of bivalent associations for approximately 98% of their chromosomes.
Such results are not in agreement with Crane and Lawrence hypothesis (SSS1S1CC). However they do not help to identify the genomic structure of P. spinosa (SSS1S1 ou SSCC).
The behaviour of hybrids from the second tetraploid group is in agreement with the genomic formula SSCC of P. spinosa.
The hepta and octoploid hybrids (2n = 56 ou 64) are issued from non-reduced gametes of the same pentaploid parent (P. domestica CV. 742 x P. spinosa 106) fertilized by P. spinosa and P. domestica respectively.
The heptaploid hybrid is characterized by an average of 24 bivalents and 6.48 univalents per cell.
This meiotic behaviour suggests the formula SSS1S1 for P. spinosa and D1D1D1D2CC for P.domestica.
The octoploid hybrid is characterized by an average of 2.40 univalents, 30.20 bivalents, 0.13 trivalent and 0.13 quadrivalent, per cell.
Only one genomic formula fits with such behaviour and agrees with the same genomic composition mentionned above for the two species.
None of the above results agree with the Crane and Lawrence hypothesis, however there is a contradiction concerning the genomic structure of P. spinosa. These results point out the limit of such study which relies exclusively on the analysis of meiotic behaviour;