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

Flowering plants have evolved a multitude of mechanisms to avoid self-fertilization and promote outbreeding. Self-incompatibility (SI) is by far the most common of these, and is found in ca. 60% of flowering plants. SI is a genetically controlled pollen-pistil recognition system that provides a barrier to fertilization by self and self-related pollen in hermaphrodite (usually co-sexual) flowering plants. Two genetically distinct forms of SI can be recognized: gametophytic SI (GSI) and sporophytic SI (SSI), distinguished by how the incompatibility phenotype of the pollen is determined. GSI appears to be the most common mode of SI and can operate through at least three different mechanisms, two of which have been characterized extensively at a molecular level in the Solanaceae and Papaveraceae. Because molecular studies of SSI have been largely confined to species from the Brassicaceae, predominantly Brassica species, it is not yet known whether SSI, like GSI, can operate through different molecular mechanisms. Molecular studies of SSI are now being carried out on Ipomoea trifida (Convolvulaceae) and Senecio squalidus (Asteraceae) and are providing important preliminary data suggesting that SSI in these two families does not share the same molecular mechanism as that of the Brassicaceae. Here, what is currently known about the molecular regulation of SSI in the Brassicaceae is briefly reviewed, and the emerging data on SSI in I. trifida, and more especially in S. squalidus, are discussed.

Understanding genetic mechanisms of self-incompatibility (SI) and how they evolve is central to understanding the mating behaviour of most outbreeding angiosperms. Sporophytic SI (SSI) is controlled by a single multi-allelic locus, S, which is expressed in the diploid (sporophyte) plant to determine the SI phenotype of its haploid (gametophyte) pollen. This allows complex patterns of independent S allele dominance interactions in male (pollen) and female (pistil) reproductive tissues. Senecio squalidus is a useful model for studying the genetic regulation and evolution of SSI because of its population history as an alien invasive species in the UK. S. squalidus maintains a small number of S alleles (7-11) with a high frequency of dominance interactions. Some S. squalidus individuals also show partial selfing and/or greater levels of cross-compatibility than expected under SSI. We previously speculated that these might be adaptations to invasiveness. Here we describe a detailed characterization of the regulation of SSI in S. squalidus. Controlled crosses were used to determine the S allele dominance hierarchy of six S alleles and effects of modifiers on cross-compatibility and partial selfing. Complex dominance interactions among S alleles were found with at least three levels of dominance and tissue-specific codominance. Evidence for S gene modifiers that increase selfing and/or cross-compatibility was also found. These empirical findings are discussed in the context of theoretical predictions for maintenance of S allele dominance interactions, and the role of modifier loci in the evolution of SI.

Canola varieties exhibit variation in drought avoidance and drought escape traits, reflecting adaptation to water‐deficit environments. Our understanding of underlying genes and their interaction across environments in improving crop productivity is limited. A doubled haploid population was analysed to identify quantitative trait loci (QTL) associated with water‐use efficiency (WUE) related traits. High WUE in the vegetative phase was associated with low seed yield. Based on the resequenced parental genome data, we developed sequence‐capture‐based markers and validated their linkage with carbon isotope discrimination (Δ13C) in an F2 population. RNA sequencing was performed to determine the expression of candidate genes underlying Δ13C QTL. QTL contributing to main and QTL × environment interaction effects for Δ13C and yield were identified. One multiple‐trait QTL for Δ13C, days to flower, plant height, and seed yield was identified on chromosome A09. Interestingly, this QTL region overlapped with a homoeologous exchange (HE) event, suggesting its association with the multiple traits. Transcriptome analysis revealed 121 significantly differentially expressed genes underlying Δ13C QTL on A09 and C09, including in HE regions. Sorting out the negative relationship between vegetative WUE and seed yield is a priority. Genetic and genomic resources and knowledge so developed could improve canola WUE and yield.

Senecio squalidus (Oxford Ragwort) is being used as a model species to study the genetics and molecular genetics of self-incompatibility (SI) in the Asteraceae. S. squalidus has a strong system of sporophytic SI (SSI) and populations within the UK contain very few S alleles probably due to a population bottleneck experienced on its introduction to the UK. The genetic control of SSI in S. squalidus is complex and may involve a second locus epistatic to S. Progress towards identifying the female determinant of SSI in S. squalidus is reviewed here. Research is focused on plants carrying two defined S alleles, S(1) and S(2). S(2) is dominant to S(1) in pollen and stigma. RT-PCR was used to amplify three SRK-like cDNAs from stigmas of S(1)S(2) heterozygotes, but the expression patterns of these cDNAs suggest that they are unlikely to be directly involved in SI or pollen-stigma interactions in contrast to SSI in the Brassicaceae. Stigma-specific proteins associated with the S(1) allele and the S(2) allele have been identified using isoelectric focusing and these proteins have been designated SSP1 (Stigma S-associated Protein 1) and SSP2. SSP1 and SSP2 cDNAs have been cloned by 3' and 5' RACE and shown to be allelic forms of the same gene, SSP. The expression of SSP and its linkage to the S locus are currently being investigated. Initial results show SSP to be expressed exclusively in stigmas and developmentally regulated, with maximal expression occurring at and just before anthesis when SI is fully functional, SSP expression being undetectable in immature buds. Together these data suggest that SSP is a strong candidate for a Senecio S-gene.