Optimizing propagation techniques in neelayamari (Indigofera tinctoria L.)

Abstract

India is acknowledged as one of the world’s richest treasure trove of medicinal plants. Neelayamari (Indigofera tinctoria L.) commonly known as ‘Indian indigo’, is a commercially grown leguminous plant of medicinal importance. The extract of the leaves is reported to have remarkable effect on hair growth and in preventing juvenile greying of hair. Due to the presence of many worthy phytochemicals, the crop is being documented in ‘Ashtangahridaya’ and is being cultivated by several pharmaceutical entrepreneurs, both in public and private sector. Like most of the medicinal plants, the cheapest method of propagation of this crop is through seeds. However, poor germination and vigour of seeds is a major problem in Neelayamari. In addition, heavy loss in seed yield occurs due to the splitting of pods at maturity. The study ‘Optimizing propagation techniques in Neelayamari (Indigofera tinctoria L.)’ was conducted in the Department of Plantation crops and Spices, with the objectives of standardizing the physiological maturity stage in Indigofera tinctoria L. for seed harvest, presowing seed treatments to enhance seed quality and longevity and vegetative propagation technique in Indigofera tinctoria L. through stem cuttings. In order to assess the stage of attainment of physiological maturity for seed harvest in Neelayamari, flowers were tagged on the day of anthesis and the pods were harvested at five days interval from 30 days of anthesis up to the pod splitting stage (63 days after anthesis). It was observed that the values of pod, seed and seedling characters increased up to 45 days after anthesis to reach their highest and thereafter declined till the pod splitting stage (63 days after anthesis). Germination and vigour indices at 45 days after anthesis were 73.80 per cent, 485 and 294 respectively and those at the pod splitting stage were found to be 31.33 per cent, 132 and 65 respectively. Hence, it was inferred that the seeds of Neelayamari reached physiological maturity stage by 45 days after anthesis. The seeds harvested at physiological maturity were dried to 8 per cent moisture content and subjected to various seed treatments before being packed in 700 gauge polyethylene bags. Untreated seeds served as the control. The seeds were stored under ambient conditions upto six months. The scarification treatments included treatment with Conc. H2SO4 for 5, 10 and 15 minutes, mechanical scarification with sand, hot water treatment at 80oC for 20 minutes and 60oC for 30 minutes and hydration for 24 hours. The quality parameters of the stored seeds were recorded at monthly intervals during the storage period and were put for germination test in sterilized sand media. Results pointed out that most of the seed treatments were effective in enhancing germination. High initial germination was recorded in mechanically scarified (95.83 %) and hydrated seeds (93.27%), while the untreated seeds showed a germination of 74.33 per cent. Vigour index I (703 and 698 respectively) and II (430 and 428 respectively) were also the highest in these treatments. Seed treatment with sulphuric acid, however, proved to be detrimental. Seed treatment also helped in extending the viability of the seeds. Mechanically scarified and hydrated seeds retained their germination above 60 per cent for six months during storage (65.67% and 63.67% respectively), while, in untreated seeds, germination reached 61.33 per cent at four months of storage and declined to 44.34 per cent by six months of storage. Seeds treated with sulphuric acid never attained the germination of sixty per cent throughout the storage period and those treated with sulphuric acid for 15 minutes failed to germinate at sixth month of storage. EC was found to be the lowest in hydrated seeds (0.0011 dSm-1) and mechanically scarified seeds (0.0012 dSm-1). The results thus indicated that mechanical scarification of seeds or hydropriming for 24 h can not only improve seed germination and seed quality but also prolong the longevity of the seeds. It was also noticed that all the seed quality parameters declined along the storage period. Attempt to assess the possibility of vegetative propagation in Neelayamari was carried out using hardwood, semi-hardwood and softwood cuttings, exposed to varying doses of IBA (250 ppm, 500 ppm, 750 ppm, 1000 ppm, 1500 ppm, 2000 ppm and 2500 ppm) and charcoal slurry dip. The cuttings were planted in polythene bags and were maintained in a mist chamber. Initially, the experiment was conducted during summer season and only the softwood cuttings treated with 2000 (8.89%) and 1500 ppm IBA (5.53%) survived after 60 days of planting, while all others withered and dried off. The experiment was then repeated during rainy season and the best results were obtained in the season. Softwood cuttings treated with 2000 ppm IBA during rainy season exhibited early sprouting (7.18 days) and a field establishment of 70.67 per cent. In comparison, the semi-hardwood and hardwood cuttings exhibited very low establishment rates of 21.77 per cent and 17.90 per cent respectively. Hence, it was evident that vegetative propagation using softwood cuttings treated with 2000 ppm IBA during rainy season can be relied upon as an alternative propagation method in Neelayamari.