Relevance of sexual polyploidization for crop improvement – A review

Abstract

Colchicine induced polyploids have notdirectly contributed for crop improvementin the past. On the other hand, theso-called natural polyploids, derived fromthe functioning of numerically unreduced(2n) gametes have been shown to bemore relevant for crop improvement in manycases. Different types of cytologicalabnormalities during meiosis can give riseto 2n gametes and the geneticcomposition of these gametes is variable.Depending on the type meioticabnormalities, various types of 2ngametes, such as first division restitution(FDR), second division restitution (SDR),indeterminate meiotic restitution (IMR) andpost meiotic restitution (PMR) gametes,among others, have been described in recentyears. For the improvement ofautopolyploids such as potato, alfalfa,Vaccinium spp., and some of thefodder grasses, FDR gametes have beenproved to be highly useful. However, theuse of 2n gametes for the improvementof allopolyploid crops has received muchless attention so far. Some of theinvestigations on allopolyploids, derivedfrom Festuca-Lolium, Alstroemeria and Lilium specieshybrids, have revealed that 2ngametes can be most useful for theintrogression of alien genes andchromosomes into cultivars. An importantfeature of using sexual polyploidization inthe case of allopolyploids is thatintrogression can be achieved throughrecombination due to genetic crossing-overbetween alien chromosomes as well asaddition of alien chromosomes, which isextremely difficult or impossible toachieve in the case of colchicine inducedallopolyploids. Because of the recentdevelopments in the field of plantmolecular biology, methods have becomeavailable for the analysis of 2ngametes and sexual polyploid progenies moreaccurately and to develop systematicbreeding approaches. The methods includeDNA in situ hybridization (GISH and FISH)and molecular mapping (AFLP, RFLP, RAPDs).In addition to providing basic informationon the genetic and genome composition ofthe polyploid progenies, these methods canbe potentially useful for a more efficientcreation of desirable breeding material andcultivars.