Abstract:
To screen plant growth retardants that effectively inhibit autumn shoot growth and enhances the ornamental value of fruits in
Ilex verticillata ‘Oosterwijk’, three-year-old potted seedlings of
I.
verticillata ‘Oosterwijk’ were used as experimental materials. Foliar applications were conducted with solutions of paclobutrazol (PP333) at four concentrations (50, 100, 150 and 250 mg·L
−1), uniconazole (S3307) at four concentrations (1, 2, 3 and 6 mg·L
−1), and chlormequat chloride (CCC) at four concentrations (200, 400, 600 and 1200 mg·L
−1), each with three spray frequencies (1, 3 and 5 times), and with water spraying serving as the control (CK) so as to investigate the effects of these retardants on autumn shoot and fruit characteristics. The results showed that three retardants exhibited inhibitory effects on the sprouting and growth of autumn shoots. Among all treatments, PP333 at 250 mg·L
−1 applied five times achieved the strongest inhibition, with a shoot sprouting rate of 16.15%( a reduction of 63.34% compared to CK) and the shortest mean autumn shoot length (0.34 cm). The fruit set rate responded differently to the three retardants: overall, the fruit set rate under PP333 treatment (79.53%) was lower than CK(84.28%), whereas S3307 (85.87%) and CCC (87.18%) treatments both exceeded CK. Among all treatments, CCC at 1 200 mg·L
−1 applied three times yielded the highest fruit set rate (94.30%), representing a 10.02% increase over CK. The three retardants also differentially affected the fruit morphology of
I.
verticillata ‘Oosterwijk’, with little effect on fruit transverse diameter and an increase on fruit longitudinal diameter. The maximum increase in longitudinal diameter was observed with 1 mg·L
−1 S3307 sprayed five times (10.79 mm, an increase of 1.50 mm over CK). All three retardants altered the ratio of transverse to longitudinal diameter, making fruits more rounded compared to CK. The effects on fruit density also varied: PP333 and S3307 applications increased fruit density, whereas CCC applications suppressed it. Among all treatments of the three plant growth retardants on fruit density and hundred-fruit weight, 150 mg·L
−1 PP333 sprayed once maximized fruit density, significantly increasing by 49.02% over CK, yielded the greatest promotion of hundred-fruit weight, with a 7.32% increase over CK. Principal component analysis combined with membership function analysis indicated that five applications of S3307 at 1 mg·L
−1 yielded the optimal enhancement of fruit ornamental value of
I.
verticillata ‘Oosterwijk’, followed by three applications of PP333 at 150 mg·L
−1 when the new shoot length, fruit morphology, fruit density, and hundred-fruit weight were considered collaboratively.