Plant regeneration from immature inflorescence-derived callus of Italian ryegrass [Lolium multiflorum Lam.]: chromosome number and fertility of regenerated plants

Twenty field-grown genotypes of diploid Italian ryegrass (Lolium multiflorum Lam., 2n = 2x = 14) were tested for their ability to induce callus and regenerate plants. Callus cultures were initiated from segments of immature inflorescences cultured on the MS medium supplemented with 4.0 mg L⁻¹ 2,4-D. The calluses were subcultured first on the maintaining medium (MS medium with 2.0 mg L⁻¹ 2,4-D) and later on the rooting medium (MS medium with 0.2 mg L⁻¹ 2,4-D). The frequency of callus induction varied depending on the source of explant and the initial genotype. A total of 473 green plantlets were regenerated, of which 420 were established in the soil. All these plants had the morphological characteristics of Italian ryegrass. Among 372 regenerants analysed cytologically, 302 (81.2%) had the expected diploid chromosome number (2n = 2x= 14), 65 (17.5%) were tetraploid (2n = 4x = 28); several aneuploids and mixoploids were also observed. All diploid and tetraploid regenerants were male and female fertile. However, a great variation of female fertility within and between both groups of regenerants was observed.