, Volume 187, Issue 3, pp 359-368
Date: 25 Apr 2012

Evidence for second division restitution as the basis for 2n + n maternal chromosome transmission in a sugarcane cross

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Abstract

Chromosome doubling in megaspores of sugarcane was first reported over 70 years ago and was seen primarily in interspecific crosses between Saccharum officinarum and Saccharum spontaneum. Since then, there has been robust debate on the mechanism(s) responsible for this doubling with hypotheses ranging from second division restitution (SDR), post-meiotic restitution to fusion of the two innermost cells of the megaspore tetrad. In the present study, we sought to answer this question using molecular marker data from a cross which demonstrated 2n + n chromosome transmission between an S. officinarum clone (IJ76-514; 2n transmission) and a commercial hybrid (Q165 ; n transmission). Molecular marker data from four other bi-parental crosses were used to form a “base-line” for expected segregation ratios (n + n transmission). Comparison of segregation ratios showed that 2n transmission from the S. officinarum clone could be identified by the increased segregation ratios, a characteristic of both SDR and tetrad cell fusion. Simulation was then undertaken based on current understandings of sugarcane meiosis, to determine if the observed segregation ratios matched those simulated for SDR/tetrad cell fusion. Analysis of the simulation confirmed that most and perhaps all progeny appear to have been formed from a mechanism akin to SDR/tetrad cell fusion. The genetic consequences of this are discussed.