Uses and usefulness of endosperm balance number

The Endosperm Balance Number (EBN) hypothesis was developed in the early '8 0s to explain the basis for normal seed development after intra- and inter- specific crosses, first in the potato and then in several other crop specie s. According to this hypothesis, each species has a genome-specific effecti ve ploidy, the EBN, which must be in a 2:1 maternal to paternal ratio in th e hybrid endosperm for normal development of the endosperm itself. This pap er reviews how the EBN may act as a powerful isolating mechanism in sexual reproduction, maintaining the genome integrity of the species and playing a n important role in the speciation of polyploids from diploids. We also pro vide further evidence that EBN is more important than chromosome ploidy in determining the successor failure of interspecific crosses. In fact, result s from interploidy and inter-EBN crosses to infuse 1EBN Solanum commersonii into 4EBN S, tuberosum demonstrated that the knowledge and manipulation of EBN is a useful tool in designing breeding schemes and in predicting the o ffspring ploidy and EBN. In this paper we also discuss the exceptions to th e 2: 1 EBN ratio, and report the evidence for endomitosis in the polar nucl ei to explain exceptions to the EBN model in the potato.