Fertility changes in inbred families of self-incompatible Chrysanthemums (Dendranthema grandiflora)

Chrysanthemum [Dendranthema xgrandiflora Tzvelv. (syn. Chrysanthemum xmorifolium Ramat.)] breeding programs have been selecting for reduced expression of self-incompatibility (via pseudo-self-compatibility) to create inbred families with selected genotypes to serve as parents for F₁ hybrid chrysanthemum seed production. However, it is not known to what extent inbreeding is affecting fertility in this outcrossing, heterozygous species. The objective of this research was to assess male/female fertility changes (gain/loss) in successive inbred generations of chrysanthemums. Pseudo-self-compatible chrysanthemum parents (n = 41 inbred, noninbred, and recombinant inbred) were chosen for fertility analyses. As many as three generations of inbreds (I₁, I₂, and I₃) from self-pollinations were created using rapid generation cycling. Female and male fertility levels of the parents and all derived inbred populations were assessed using outcross seed set and pollen stainability, respectively. Average seed set ranges were 0.3% to 96.1% (inbred parents), 24.5% to 38.5% (noninbred parents), and 0.9% to 85.1% (recombinant inbred parents); these began decreasing in the I₁ and continued to decline steadily into the I₃. Statistically significant (P < 0.05) decreases in seed set occurred in n = 23 (56.1%) inbred families; the remaining inbred families had similar or higher fertility than the parents. Pollen stainability was >50% for the parents, but began declining in some inbred families as inbreeding progressed. Fertility reductions were attributed to inbreeding depression. Lack of significant fertility losses in other inbred families demonstrates the opportunity of selection of fertile inbred parents for use in hybrid seed production.