The population genetics of sporophytic self-incompatibility in Senecio squalidus L. (Asteraceae) I: S allele diversity in a natural population

Abstract

Twenty-six individuals of the sporophytic self-incompatible (SSI) weed, Senecio squalidus were crossed in a full diallel to determine the number and frequency of S alleles in an Oxford population. Incompatibility phenotypes were determined by fruit-set results and the mating patterns observed fitted a SSI model that allowed us to identify six S alleles. Standard population S allele number estimators were modified to deal with S allele data from a species with SSI. These modified estimators predicted a total number of approximately six S alleles for the entire Oxford population of S. squalidus. This estimate of S allele number is low compared

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

“…In contrast to predictions that an extreme population bottleneck and subsequent invasion should favour the breakdown of SI in favour of uniparental reproduction (Pannell and Barrett, 1998), S. squalidus shows a strong SSI system (Hiscock, 2000;Brennan et al, 2005). Nevertheless, the SSI system of S. squalidus does show features consistent with a recent population bottleneck, such as relatively few S alleles compared with other wild SSI species, a high frequency of S allele dominance interactions and some selfing due to the presence of PSC (Hiscock, 2000;Brennan et al, 2002Brennan et al, , 2005Brennan et al, , 2006. Both S allele dominance and PSC increase cross-compatibility for a given number of S alleles and have been proposed as a means by which the SSI system of invasive S. squalidus escapes the constraints of limited S allele number (Brennan et al, 2002(Brennan et al, , 2003(Brennan et al, , 2006.…”

“…Nevertheless, the SSI system of S. squalidus does show features consistent with a recent population bottleneck, such as relatively few S alleles compared with other wild SSI species, a high frequency of S allele dominance interactions and some selfing due to the presence of PSC (Hiscock, 2000;Brennan et al, 2002Brennan et al, , 2005Brennan et al, , 2006. Both S allele dominance and PSC increase cross-compatibility for a given number of S alleles and have been proposed as a means by which the SSI system of invasive S. squalidus escapes the constraints of limited S allele number (Brennan et al, 2002(Brennan et al, , 2003(Brennan et al, , 2006. Here we investigate the genetic regulation of the SSI system of S. squalidus in greater detail by characterizing S allele dominance interactions more completely and exploring the expression and inheritance of partial selfing (PSC).…”

“…Other individuals with known homozygous S genotype; OS-Bill-4, and A34-4-23 (here referred to as B4 and A23 respectively) were previously identified from controlled crossing studies of selfed progenies derived from individuals originally sampled from a different wild Oxford population (Hiscock, 2000). Crosses were therefore performed to cross-classify S alleles identified in the two studies and cross-classified S alleles then followed the nomenclature of Brennan et al (2002). Thus the genotypes of B4 and A23 were identified as S 1 S 1 and S 6 S 6 , respectively.…”

“…Plants of known S phenotype included five individuals sampled directly from a wild Oxford population and assigned five different S phenotypes based on diallel crossing studies (Brennan et al, 2002). These Ox individuals and their S phenotypes were Ox2 ¼ S 2 ; Ox4 ¼ S 3 ; Ox22 ¼ S 4 ; Ox27 ¼ S 4 S 5 (S genotype ¼ S 4 S 5 ) and Ox19 ¼ S 6 (here referred to as; O2, O4, O22, O27 and O19 respectively).…”

“…Progeny arrays were generated by performing controlled crosses between parental plants of known S phenotype (that is, with one dominant S allele identified) or known S genotype (that is, both S alleles identified) based on the results of previous controlled crossing experiments (Hiscock, 2000;Brennan et al, 2002). Plants of known S phenotype included five individuals sampled directly from a wild Oxford population and assigned five different S phenotypes based on diallel crossing studies (Brennan et al, 2002).…”