Controlling seedling height of cowpea (Vigna unguiculata (L.) Walp.) transplants using plant growth regulators

Abstract

Cowpea (Vigna unguiculata (L.) Walp) is an annual leguminous vegetable crop. It is grown throughout india for its tender green pods used as vegetable. Green cowpea seeds are boiled as a fresh vegetable or may be canned or frozen. The beans are nutritious and provide complementary proteins to cereals diets. Seedlings like cowpea, cucurbits having lanky growth growing in polyhouses is an undesirable quality, especially in plugs intended for mechanized planting and long distance transport. Seed treatment with growth retardants is an effective method for controlling seedling height .However limited studies have been conducted in vegetable crops The present study was undertaken with the objectives of controlling seedling height of vegetable cowpea and to assess the field performance of treated seedlings. The experiment was conducted at the Centre for Hi-Tech Horticulture and Precision farming, Vellanikkara KAU, Thrissur during the year 2020-2021 In seedling stage, highest germination was recorded in control treatment on 5th and 10th days after sowing (89%) and (91%) respectively in Vellayani Jyothika. Minimum germination percentage was recorded in Paclobutrazol @ 200 ppm on 5th and 10th day after sowing (64.3%) and (66.0%) respectively in cowpea genotype Vellayani Jyothika. Significantly lower germination percentage was recorded in treatments receiving Paclobutrazol @ 200 ppm on 5th and 10th day after sowing (70.0%) (72%) in the genotype Kashi Kanchan. In both the genotypes there were no significant difference between the treatments on 15th days after sowing. Paclobutrazol treatment took more number of days for emergence of seedling up to the first node compared to control treatment ie Paclobutrazol @ 200 ppm (8.13) and (8.00) respectively in both the genotypes. Highest shoot length was recorded in control treatment on 5th, 10th and 15 th days after germination in both the genotypes. Significantly lower shoot length was recorded in treatments receiving Paclobutrazol @ 200 ppm irrespective of the number of days after germination. Growth retardants in general reduce root growth, shoot weight and root weight of the seedlings. In both the genotypes (Vellayani Jyothika and Kashi Kanchan) significantly lower root length, shoot weight and root weight was obtained in Paclobutrazol treatments compared to non-treated control. Height of seedling up to the first node was directly linked to shoot length. In both the genotypes of the cowpea significantly lower shoot length was recorded in treatments receiving Paclobutrazol @ 200 ppm (4.09) and (4.03) respectively. Paclobutrazol treated seedlings had dark green leaves when compared to other growth regulator and control treatments on 5th ,10th and 15th days after germination. In both the cowpea genotypes, when compared to other growth retardant and control treatments highest stem girth of the seedlings was recorded in treatments receiving Paclobutrazol @ 200 ppm on 5th (3.19 mm) 10th (3.45mm) and 15th (3.7mm) in Vellayani Jyothika and on 5th (3.3mm ) 10th (3.4mm) and 15th (3.8mm) in Kashi Kanchan. There were no significant difference between the treatments on 5th (2) and 15th days (7-8) after germination in both the genotypes. The total chlorophyll content and carotenoid content was recorded highest in treatments receiving Paclobutrazol treatments on seedling stage. Minimum auxin content and gibberellic acid contents were observed in Paclobutrazol treatments. In the field experiment, in both the cowpea genotypes, plant growth regulator Ethrel recorded maximum plant height where as in Vellayani Jyothika minimum plant height was recorded in Cycocel@ 50 ppm (112.40 cm) .In Kashi Kanchan lowest plant height was recorded in Paclobutrazol @ 200 ppm (33.06 cm) in Kashi Kanchan. In vellayani Jyothika highest internodal length was recorded in Ethrel @100 ppm (3.13 cm) and Ethrel @50 ppm (3.04 cm). Minimum was recorded in Paclobutrazol@ 200 ppm (2.63 cm). In the genotype Kashi Kanchan maximum internodal length was recorded in Ethrel@ 200 ppm (3.34 cm) and minimum was recorded in Cycocel @ 100 ppm (2.53cm). Highest number of primary branches was recorded in treatments receiving Paclobutrazol @ 200 ppm which was on par with Paclobutrazol @ 100 ppm compared to control in Vellayani Jyothika. In Kashi Kanchan there were no significant differences found between the treatments. Growth retardants had significant effect on the viz days to first flowering, days to first harvest and crop duration. Early flowering results in early harvesting of pods. Plant growth retardant Cycocel @ 200 ppm (41day) and Cycocel @ 25 ppm (36.80 days) recorded earliest flowering in the field in both the genotypes. In both the genotypes delayed flowering and maximum crop duration was recorded in Paclobutrazol treatments. Pod length and pod girth are related with pod weight. Ethrel treatment had highest pod length and pod girth compared to control .The higher number of flowers, pod girth and pod length contributed to production of more number of pods which in turn resulted in higher yield per plant. In both the cowpea genotypes, highest number of pods per plant and yield per plant was recorded in Ethrel treatments (Ethrel 100 ppm) in Vellayani Jyothika followed by Paclobutrazol treatment (Paclobutrazol 100 ppm) where as in Kashi Kanchan Paclobutrazol 100 ppm was on par with Ethrel 100 ppm. From the above study it could be concluded that, Paclobutrazol 100 ppm seed treatment was effective in controlling seedling height as well to obtain good yield in vegetable cowpea.