Seed Formation Promoted by Paclobutrazol, a Gibberellin Biosynthesis Inhibitor, in pat-2 Parthenocarpic Tomatoes

Seed production in pat-2 parthenocarpic tomatoes is sufficiently low for the propagation of parthenocarpic tomato cultivars. To establish the technology to promote seed formation in pat-2 parthenocarpic tomato plants, we examined the effects of paclobutrazol, a gibberellin biosynthesis inhibitor, on seed formation. The parthenocarpic F1 cultivar ‘Renaissance’, that has the homozygote recessive gene pat-2, was treated with paclobutrazol at 0 (control), 0.2, 1, 5, or 25 mg per pot (5.1 L) by irrigation to the culture medium. With increasing application of paclobutrazol, stem diameter increased, while stem length, leaf length, leaf width, and fruit fresh weight decreased. The percentage of fruits with seeds increased with increasing levels of paclobutrazol, and it reached 100% with 1 mg/pot and higher. Seed number per fruit increased from 12 at 0 mg/pot of paclobutrazol to 52 and 74 at 1 and 5 mg/pot, respectively. To confirm the practicality of this technology, the parthenocarpic purebred strain ‘PASK-1’, the seed parent of ‘Renaissance’, was treated with 0 (control), 1, or 5 mg/pot of paclobutrazol. All flowers of ‘PASK-1’ were emasculated before flowering and crossed at flowering with pollen of the parthenocarpic purebred strain ‘PF811K’, the pollen parent of ‘Renaissance’. The percentage of fruits with seeds increased from 59% at 0 mg/pot of paclobutrazol to higher than 95% at 1 and 5 mg/pot. Seed number per fruit increased from 21 at 0 mg/pot of paclobutrazol to 45 and 46 at 1 and 5 mg/pot, respectively. From these results, we concluded that paclobutrazol promotes seed formation in pat-2 parthenocarpic tomato plants.