Luz e ventilação no cultivo in vitro da batata-doce (Ipomoea batatas (L.) Lam. cv. Ufla 1440)

Abstract

Sweet potato (Ipomoea batatas (L) Lam.) is a crop of great nutritional and socioeconomic importance, with wide adaptability in tropical and subtropical regions. Conventional propagation of this species presents limitations, such as disease transmission and genetic heterogeneity, which makes in vitro cultivation an efficient alternative for the production of healthy plantlets. The objective of this study was to evaluate the effects of light conditions and a natural ventilation system on the in vitro growth ofsweet potato. A completely randomized design (CRD) was adopted. For light intensity, five levels (26, 51, 69, 94, and 130 µmol m⁻² s⁻¹) provided by LEDs were tested, with 4 replicates and 7 plantlets per replicate, totaling 140 plantlets. In the light quality experiment, eight treatments were used: white LED, 100% red, 100% blue, 100% green, 100% yellow, and combinations of blue and red in the proportions of 70%B:30%R, 30%B:70%R, and 50%B:50%R, with five replicates and five tubes per replicate, totaling 200 plantlets. The Natural Ventilation System (NVS) was carried out using flasks without filters (control – NVS0) and with 1 (NVS1), 2 (NVS2), and 4 (NVS4) porous membrane filters, in five replicates with 10 tubes each, totaling 200 plantlets. Nodal segments were cultivated in MS medium supplemented with 30 g L⁻¹ of sucrose, 6 g L⁻¹ of agar, pH 5.7 ± 0.1, for 60 days, at 26 ± 1 °C, under a 16-hour photoperiod. The length of the longest shoot, number of leaves, and dry mass of leaf, stem, root, and total were evaluated. Regarding light intensity, the ranges of 94 and 130 µmol m⁻² s⁻¹ promoted greater shoot elongation (6.52 and 6.29 cm) and accumulated the most significant amounts of leaf (35.68 mg), stem (16.97 mg), root (13.98 mg), and total (65.53 mg) dry mass, in addition to higher protein (5.78 mg g⁻¹) and starch (25.98 mg g⁻¹) contents, whereas the intensities of 26 and 51 µmol m⁻² s⁻¹ stimulated the synthesis of photosynthetic pigments. In relation to spectral quality, the combinations 70%R:30%B, 50%B:50%R, and 70%B:30%R stood out in the number of leaves (7.44 – 8.00), and the last two, along with green, white, and red lights, accumulated higher protein contents (6.18 - 7.90 mg g⁻¹). Shoot length was superior under blue, red, and green lights (6.63 - 6.96 cm). White light promoted greater leaf dry mass (20.21 mg), while blue stimulated stem (47.92 mg) and total (77.16 mg) dry mass, and green and yellow lights provided higher starch content (22.24 - 23.78 mg g⁻¹). Among the natural ventilation systems, the NVS2 and NVS4 treatments excelled in the number of leaves (1.45 - 1.62) and in leaf dry mass accumulation (17.83 - 19.82 mg). The greatest shoot lengths (4.92 - 5.22 cm) occurred in NVS1, NVS2, and NVSA. Furthermore, the NVS4 system accumulated, isolatedly, the highest stem (3.13 mg), root (5.97 mg), and total (28.92 mg) dry mass, as well as the highest protein (12.77 mg g⁻¹) and starch (10.13 mg g⁻¹) contents. Light intensity, light quality, and natural ventilation influence the growth, dry matter, and metabolism of sweet potato plantlets, impacting their development for the subsequent stages of acclimatization and cultivation. It is concluded that the association of the 69 µmol m⁻² s⁻¹ intensity, the 70%B:30%R light combination, and the NVS4 ventilation system positively influences the growth and metabolism of the plantlets, configuring an efficient management to optimize plant development for the acclimatization stages.