Hybridity, polyploidy and change in breeding system in a Ruellia hybrid

Area of Science:

• Plant genetics
• Reproductive biology
• Evolutionary botany

Background:

• Ruellia tweediana and R. tuberosa are diploid chasmogamous species with normal meiosis and fertility.
• Hybridization between these species yields a sterile, cleistogamous F1 hybrid with chromosomal irregularities.
• Artificial amphidiploids derived from these hybrids exhibit restored fertility despite cleistogamy.

Purpose of the Study:

• To investigate the genetic and cytological basis of breeding system changes in Ruellia hybrids.
• To understand the role of hybridization and polyploidy in the evolution of cleistogamy.
• To analyze the relationship between floral morphology, fertility, and breeding system in Ruellia.

Main Methods:

• Controlled crosses between Ruellia tweediana and R. tuberosa.
• Cytological analysis of meiosis in F1 hybrids and artificial amphidiploids.
• Assessment of fertility, breeding system (chasmogamy vs. cleistogamy), and floral morphology.

Main Results:

• F1 hybrids (R. tweediana x R. tuberosa) were cleistogamous, sterile, and showed meiotic irregularities.
• Artificial amphidiploids (n=34) were cleistogamous but fertile, with preferential chromosome pairing.
• Floral deformities were linked to sterility in F1 hybrids and fertility in amphidiploids.

Conclusions:

• Hybridization and polyploidy can induce a shift from chasmogamy to fertile cleistogamy.
• Sterility in F1 hybrids is chromosomal, while fertility is restored in amphidiploids.
• This study presents a novel case of a true-breeding, fertile cleistogamous taxon originating from chasmogamous parents via hybridization.