Apospory Expressivity and Segregation in Intraspecific Hybrids of Paspalum notatum Flügge

Background/Objectives: Apospory is a key component of gametophytic apomixis in Paspalum notatum and is relevant to breeding because, together with parthenogenesis and appropriate endosperm development, it can enable clonal seed reproduction. This study determined reproductive phenotype at the embryo-sac level, quantified apospory expressivity, and evaluated segregation in tetraploid intraspecific hybrids. Methods: Inflorescences were collected from 84 hybrids from 11 crosses between sexual female and aposporous male parents. Cleared ovaries were examined by differential interference contrast microscopy. Hybrids were classified as facultatively aposporous when at least one ovule contained an aposporous embryo sac; expressivity was calculated as A/(S + A) × 100. Results: Reproductive phenotype was determined in 80 hybrids: 48 were facultatively aposporous and 32 were sexual; four were indeterminate. Expressivity ranged from 3% to 69%. Pooled segregation did not deviate significantly from 1:1 (χ2 = 3.20; p = 0.0736), whereas the largest family, KF4 × KF6, deviated from 1:1 (15 S:32 facultatively aposporous; exact p = 0.0186). Between-family heterogeneity was not significant (Monte Carlo exact p = 0.1444). Conclusions: Apospory showed substantial variation in expressivity and family-level segregation. Because parthenogenesis and maternal progeny origin were not evaluated, these results characterize apospory rather than complete apomictic seed reproduction.