Self-incompatibility genetics (Brassica) — Sporophytic self-incompatibility (SSI) in Brassica is governed by which genetic system?

Introduction / Context:
Self-incompatibility prevents self-fertilization and promotes outcrossing. In Brassica, SSI is controlled by a highly polymorphic S-locus encoding determinants on both pollen and stigmatic tissues that trigger pollen rejection when S specificities match.

Given Data / Assumptions:

• SSI phenotype is determined by the diploid genotype of the pollen parent (sporophyte).
• S-locus receptor kinase (SRK) and S-locus cysteine-rich protein (SCR/SP11) are key components.
• Recognition causes signaling that arrests incompatible pollen.

Concept / Approach:
Because the incompatibility is sporophytic, the phenotype of pollen reflects the parental anther tissue genotype at the S-locus. Extensive allelic diversity at the S-locus underlies strong SI reactions in Brassica.

Step-by-Step Solution:

Verification / Alternative check:
Molecular mapping and functional studies of SRK/SCR confirm S-locus control of SSI in Brassica.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing gametophytic SI (pollen haplotype-determined) with sporophytic SI; Brassica shows SSI.

Final Answer:
S alleles (S-locus polymorphism).