Determination of nature of polyploidy in Argemone ochroleuca ssp. ochroleuca Sweet

Abstract

Cytogenetical and molecular studies in Argemone mexicana Lin. (2n = 28) and A.ochroleuca ssp. ochroleuca Sweet. (2n = 56) showed exclusive bivalent pairing at meiois; their triploid hybrid had, univalents, bivalents and trivalents; autotetraploid of diploid A. mexicana had bivalents and quadrivalents and polyhaploid of A. ochroleuca showed bivalency. Random amplified polymorphic DNA analyses did not support the autotetraploid nature of A. ochroleuca. The dendrogram based on pair-wise genetic similarity coefficients showed distinct grouping of two species into two clusters. The conflicting data are resolved by deducing that sufficient similarities existed between one of the ochroleuca and the diploid species genome; the remainder of the ochroleuca genome had homologous chromosomes. Apparently, A. ochroleuca carried enough cryptic intergenomic homologies which ordinarily remained unexposed. In ochroleuca ‘hemizygous-ineffective’ mechanism is suggested. Further a diploidizing genetic mechanism is envisaged. Alternatively an acute propensity to preferential pairing caused bivalent formation. Such a system or systems caused meiotic isolation of various genomes and instituted normal fertility. Thus repression of genetic control is of evolutionary significance in the creation of reproductive isolation and sterility barriers for further speciation. The segmental allotetraploid nature of A. ochroleuca is inferred.