Browsing by Author "Archana, Devadas"

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    Crop growth regulation in african marigold
    (Department of Floriculture and Landscaping, College of Agriculture,Vellanikkara, 2024-03-13) Archana, Devadas; Shajma Nafeesa Basheer
    The study entitled “Crop growth regulation in African marigold” was carried out in the Department of Floriculture and Landscaping, College of Agriculture, Vellanikkara during 2021-2023. The objective of the study was to control seedling height in protrays and to induce compactness in potted African marigold plants. The study consisted of two experiments. The first experiment was focused on standardization of the concentration and soaking time of hybrid marigold seeds with paclobutrazol (PBZ). Hybrid marigold seeds ‘Royal orange’ were subjected to various concentrations of paclobutrazol (C1: 750 ppm, C2: 1000 ppm, C3: 1250 ppm, C4: 1500 ppm and C5: 2000 ppm) and distilled water (C0). The seeds were soaked for different durations (D1: 2 hours, D2: 4 hours and D3: 6 hours). Additionally, an untreated control group was also included in the experiment. Significant variations were observed in various seedling and physiological characters due to the influence of the different concentrations, soaking duration and their interactions. The length and weight of shoots of seedlings (10 DAS) were observed to be minimum in C5 (2000 ppm PBZ) and soaking duration of D3 (6 hours) whereas the length and weight of roots were maximum for the same concentration and duration of soaking. The height of seedlings and height upto the first node (30 DAS) was the shortest in C5 (2000 ppm PBZ) and D3 (6 hours). However, the minimum germination percentage (33.50 %) was recorded at higher concentration (2000 ppm) and longer soaking time (6 hours) of paclobutrazol. Significantly lower shoot length (1.83 cm), height up to the first node (0.52 cm), and overall seedling height (13.04 cm) was noticed in C5 x D3 (2000 ppm PBZ + 6 hours). Further, the shoot weight was lowest (24.60 mg) for C5 x D3 which was on par with C4 x D3 (33.60 mg). The root length was highest for the treatment C5 x D2 (3.19 cm) which was on par with C5 x D1 (3.18 cm) and C4 x D3 (3.18 cm). The root weight was recorded highest in C5 x D3 (32.00 mg). The curving of stems was absent in seedlings treated with C4 x D1, C4 x D2, C4 x D3, C5 x D1, C5 x D2 and C5 x D3. The physiological parameters like chlorophyll, carotenoid, IAA and GA content, catalase and peroxidase activity were superior for the concentration C5 (2000 ppm PBZ) and soaking duration D3 (6 hours). The maximum photosynthetic pigments and antioxidant activity and minimum IAA and GA contents were recorded for C5 x D3 (2000 ppm PBZ +6 hours).¬ The second experiment was standardisation of the concentration of paclobutrazol for drenching. Potted African marigold plants were drenched with various concentrations of PBZ (A1: 60 ppm, A2: 90 ppm, A3: 120 ppm, A4: 150 ppm and A5: 200 ppm at different stages (S1;15 and 30 DAP, S2: 30 and 45 DAP). Paclobutrazol treatment A5 (200 ppm PBZ) produced the shortest plants with maximum plant spread, number of branches and leaves. The first stage of application S1¬(15 and 30 DAP) recorded the shortest plant height, larger plant spread and greater number of branches. The stage of application had no significant effect on the number of leaves per branch. Among the interaction effects, the shortest plants (25.33 cm) with maximum plant spread (25.88 cm) were recorded in A5 x S1(200 ppm PBZ +15 and 30 DAP). The number of branches per plant was recorded as maximum (8.67) for A5 x S1 on par with A4 x S1 (8.47) and A5 x S1 (8.33). The maximum number of leaves per branch (33.00) in A5 x S2 which is on par with A5 x S1 (31.60). Among the floral characters, the days taken for flower bud emergence, fifty per cent flowering, were recorded as minimum in A1 (60 ppm PBZ). The number of days taken for flower bud initiation to flower opening was recorded to be minimum for all concentrations except A5 and A4. Flowers with larger diameter and greater longevity of flowers were observed in A5 (200 ppm PBZ). The number of flowers were maximum in A4 (150 ppm PBZ) which was on par with A5. Flowers with larger diameter and greater longevity of flowers were observed in A5 (200 ppm PBZ). The flower duration was prolonged for the treatment with A4 (150 ppm PBZ) which is on par with A5 (200 ppm PBZ). The minimum number of days taken for flower bud emergence, flower bud initiation to flower opening and fifty percent flowering and maximum number of flowers were recorded in S1(15 and 30 DAP). The diameter of flowers, longevity of flowers and duration of flowering was maximum in S2 (30 and 45 DAP). The minimum number of days for flower bud emergence (35.80) and days for fifty percent flowering (35.56) was recorded in A1 x S1¬ (60 ppm PBZ + 15 and 30 DAP. The minimum days taken for flower bud initiation to flower opening (21.20) was in A1 x S1 (60 ppm PBZ+ 15 and 30 DAP) which was on par with A2 x S1, A3 x S1, A1 x S2, A2 x S2 and A4 x S1 (21.47, 21.93, 22.00, 22.07, 22.40 and 22.53 days respectively). The maximum number of flowers (11.07) was recorded for the treatment A4 x S1 which is on par with A5 x S1 (10.87) and A5 x S2 (10.53). The maximum diameter of flowers was recorded (4.70 cm) for the treatment A5 x S2 on par with A5 x S1 (4.65 cm). The greater longevity (8.33) of flowers was recorded for the treatment A5 x S2. The photosynthetic pigments and antioxidant activity were highest in the concentration A5 (200 ppm) and in the stage S1(15 and 30 DAP). The IAA as well as GA content was lowest in A5. Among the interactions, the treatment A4 x S1¬ (150 ppm +15 and 30 DAS) recorded the highest chlorophyll a content (1.643 mg/g) which was on par with A5 x S1 (1.637). The maximum chlorophyll b (0.663 mg/g) was obtained for the treatment A5 x S1 (200 ppm PBZ+ 15 and 30 DAP) and total chlorophyll (2.930 mg/g) for the treatment A5 x S1 which was on par with the treatment A4 x S1 (2.883 mg/g). The maximum carotenoid (0.310 mg/g) was obtained for the treatment A5 x S1 which was on par with A5 x S2 (0.293 mg/g). The minimum IAA (1.26 µg/g) and GA content ((0.71 ng/g) was in A5 x S2 (200 ppm PBZ+ 30 and 45 DAP). The maximum catalase activity (17.14 µg of H2O2 /mg/ minute) and peroxidase activity (121.30 units/min/mg) was recorded for the treatment A5 x S1. From the present study it can be concluded that the marigold seeds treated with 2000 ppm paclobutrazol for a duration 6 hours produced desirable results such as shortest shoot length, overall height of seedlings, least curvature of stem and highest length of roots. However, the germination percentage was lowest in this treatment. The seed treatment with 1000 ppm PBZ for 6 hours produced a better germination percentage of 61% and lower seedling height (22.5 cm). Thus, a paclobutrazol concentration of 1000 and 2000 ppm PBZ for a duration of 6 hours can be recommended for seed treatment. Paclobutrazol concentration of 200 ppm PBZ applied at 15 and 30 DAP resulted in superior characters like shortest plant height, more plant spread, number of branches per plant, number of leaves per branch. Therefore, 200 ppm PBZ at 15 and 30 DAP can be recommended for media drenching for producing compact potted marigold plants.