Number, frequency & dominance relationships of S-alleles in diploid Ipomoea trifida

Abstract

Self-incompatibility genotypes of 224 plants of Ipomoea trifida from six populations in Central America have been determined by genetic analysis of segregants in F1 families derived from crosspollinations with the most recessive homozygote. A total of 49 different S-alleles was identified in these populations. From analyses of S-allelic interactions in heterozygous plants which were generated from cross-pollinations between plants possessing different S-alleles, a linear dominance hierarchy with six levels has been established among 28 S-alleles in both pollen and stigma.Codominance of alleles occurred more frequently in the stigma (9.2 per cent) than in the pollen (4.9 per cent). Nonlinear dominance relationships were rarely observed. Unequal frequencies of Salleles have been found in all populations examined, the most common S-allele being, as expected, the most recessive. This suggests that recessive S-alleles are widely distributed throughout Central America. The diversity of the multiple S-alleles observed in the present study also suggests that the southern area of Mexico to Guatemala is a centre of genetic variation in diploid I. trijIda.

Sporophytic self-incompatibility in Senecio squalidus (Asteraceae): S allele dominance interactions and modifiers of cross-compatibility and selfing rates

“…This observation of increasing numbers of S alleles with increasing dominance level is in accordance with both theoretical expectations (Schierup et al, 1997;Schierup, 1998;Uyenoyama, 2000;Billiard et al, 2007) and empirical observations (Kowyama et al, 1994;Glemin et al, 2005;Prigoda et al, 2005;Schierup et al, 2006) for SSI systems with multiple S allele dominance classes. This difference in S allele diversity, dependant on the relative dominance level of individual S alleles, is due to stronger negative frequency-dependent selection acting upon more dominant S alleles because their S phenotypes are more frequently expressed and exposed to selection in different S genotype combinations than more recessive S alleles.…”

“…For example, in the well-studied Brassica (Brassicaceae) SSI system, S allele dominance in the pistil appears to be limited to two or three dominance levels, whereas in pollen, there are multiple dominance levels (Ockendon, 1974;Glemin et al, 2005). In contrast many largely coincident dominance levels have been observed for both pollen and pistil S alleles in other SSI systems within the Brassicaceae and other plant families such as the Convolvulaceae and Betulaceae (Kowyama et al, 1994;Mehlenbacher, 1997;Prigoda et al, 2005;Schierup et al, 2006). These differences may be a consequence of different molecular mechanisms of SSI in these groups of plants (Hiscock and McInnis, 2003).…”

“…No such constraints apply to SSI in which complex S allele dominance interactions are possible in both pollen and pistil, thereby introducing an additional level of mating system complexity relative to GSI (Schierup et al, 1997). Within SSI systems, different kind of dominance interactions are possible, including complete dominance and tissue-specific dominance, and S alleles can often be ranked into a dominance hierarchy consisting of dominance classes of S alleles with codominant interactions between alleles within the group and dominance interactions between alleles from different groups (for example, Ockendon, 1974;Kowyama et al, 1994;Mehlenbacher, 1997;Glemin et al, 2005). S alleles that are frequently recessive in S allele interactions (hereafter referred to as recessive S alleles) are subject to less intense negative frequencydependent selection than dominant or codominant S alleles leading to a 'recessive effect' whereby recessive S alleles are more frequent within populations than more dominant S alleles (Sampson, 1974;Schierup, 1998;Billiard et al, 2007).…”

Self-Incompatibility System of Ipomoea trifida, a Wild-Type Sweet Potato

“…In the SI system of I. trifi da , the self-recognition reaction between male and female S -determinants ( S -gene products) occurs rapidly after pollination. Kowyama et al ( 1980Kowyama et al ( , 1994 reported that the SI phenotype of I. trifi da segregates as a single multi-allelic S -locus, and the pollen phenotype of SI is regulated sporophytically with clear dominant-recessive relationships between S -haplotypes. These features are consistent with the general features of SSI.…”

“…Pollen tube germination is completely arrested during self-pollination ( left ), including crossing between plants with the same S -phenotype; however, pollen tube germination is not inhibited during cross-pollination ( right ) Kowyama et al ( 1994 ) identifi ed 49 different S -haplotypes from 224 individuals collected from six natural populations in Central America. S -haplotypes of I. trifi da showed a linear dominant-recessive hierarchy between S -alleles and could be placed into fi ve classes ( Fig.…”