Synthetic auxins concentration and application time modulates seed yield and quality of carrot by altering the umbel order

Abstract

Quality seed is an essential prerequisite to achieve good yield of a crop. Carrot (Daucus carota) seed quality is affected due to uneven maturation of seeds produced in different umbel orders. Seed quality can be improved by altering the umbel order. Auxins play role in apical dominance and thus can be tested to suppress tertiary umbels in carrot seed crop. A study was conducted to explore the potential of synthetic auxins on alteration of umbel order in carrot seed crop. Significant differences were recorded among different concentrations (0, 100, 200 or 300 mg L−1) of plant growth regulators for growth, yield and seed quality. All growth related traits were improved when Indole acetic acid (IAA) was applied three times at 300 mg L−1. Naphthalene acetic acid (NAA) at 200 mg L−1 or IAA at 100 mg L−1 applied at three times, viz. planting of stecklings (PoS) + 15 days after PoS + 30 days after PoS significantly enhanced number of secondary umbels by suppressing the tertiary umbels. Seed yield and 1000-seed weight of primary, secondary and tertiary umbels was maximum for NAA or IAA at 100 mg L-1 applied three times. Seed quality attributes, viz., final germination, vigour index, enzymatic activity i.e. Superoxide dismutase (SOD), Peroxidase (POD), Catalase (CAT), total antioxidants and total phenolic contents from seeds of primary, secondary and tertiary umbels were increased when three applications of IAA or NAA were done at 200 mg L−1. Moreover, three times application of IAA or NAA at 200 mg L−1 not only minimized the conductivity of seed leachates and malondialdehyde contents from seeds of primary and secondary umbels but also in tertiary umbels seeds. It was concluded that three times foliar application of IAA or NAA at 100 or 200 mg L−1, till 30 days after planting of stecklings, can be effectively used to modify umbel order and hence to increase yield and seed quality. Therefore, seed companies and growers may apply IAA or NAA at 200 mg L−1 for obtaining higher yield of good quality carrot seed.