Cytogenetic Studies in an Experimental Amphidiploid inLuffa

SUMMARYExperimental amphidiploids were induced by colchicine treatment of the F1 hybrids of Luffa acutangula x L. graveolens. These amphidiploids showed gigantism over the diploid F1 hybrids in all morphological features recorded, but fruit setting did not occur in spite of artificial pollination of the female flowers.Meiotic studies revealed the occurrence of univalents, bivalents, trivalents, quadrivalents and at times higher chromosome associations both at diakinesis and metaphase I. Consequently many irregularities were observed at anaphase I.The occurrence of high frequencies of multivalents in the amphidiploids in which on the basis of preferential pairing only bivalents are expected, indicates autosyndetic or intragenomic pairing between the chromosomes. This is an indication of considerable segmental homology between some pairs of chromosomes of the two species.Sterility in the amphidiploid may be partly chromosomal, due to univalents and multivalents, but mainly the sterility appears to be genic. The genic sterility originates as an isolating mechanism bringing about speciation. Between L. graveolens and L. acutangula, chromosomal differentiation as indicated by chromosome pairing in this interspecific hybrid being highly deficient. Genic sterility has therefore reinforced their specific isolation.