Regulatory Effects of Plant Growth Inhibitors on Delaying Bolting and Improving Yield and Quality of Asparagus Lettuce (Lactuca sativa var. angustana)

Plant growth inhibitors are a class of chemical substances that regulate plant growth and development; yet, their effects on the bolting, yield, and quality of asparagus lettuce remain largely unexplored. In this study, the cultivar ‘Bihongfeng’ of asparagus lettuce was used as the test material to investigate the regulatory effects of the foliar application of different concentrations of plant growth inhibitors (paclobutrazol, uniconazole, and prohexadione-calcium) on the growth yield and quality of asparagus lettuce. The results showed that the foliar application of plant growth inhibitors significantly inhibited the increase in plant height, promoted the thickening of fleshy stems, and improved the yield and quality of asparagus lettuce. The results are reported as estimated marginal means (±SE) derived from a fitted general linear model. Among them, compared with the control (CK), the foliar application of 300 mg·L−1 paclobutrazol (A3), 135 mg·L−1 uniconazole (B3), and 600 mg·L−1 prohexadione-calcium (C4) reduced the bolting rate by 77%, 72.5%, and 69.4% and increased the yield by 24.1%, 28.6%, and 25.3%, respectively. The quality of asparagus lettuce was also significantly improved under the A3, B3, and C4 treatments. In comparison with CK, the soluble solids content increased by 84.6%, 42.3%, and 61.5%, the soluble protein content increased by 159.3%, 169.1%, and 140.6%, the nitrate content decreased by 22.4%, 18.9%, and 11.3%, and the cellulose content increased by 40.9%, 23.8%, and 31.7%, respectively. Principal component analysis (PCA) was performed on the key indicators of asparagus lettuce under different concentrations of plant growth inhibitor treatments, and the results revealed that the 135 mg·L−1 uniconazole (B3) treatment exhibited the optimal comprehensive performance. In conclusion, the foliar application of plant growth inhibitors at an appropriate concentration is an effective agronomic practice for delaying bolting and improving the yield and quality of asparagus lettuce, which provides a technical basis for the high-quality and high-yield cultivation of this crop.