Effects of Planting Date and Plant Density on Morphology and Yield of Indigo (Indigofera tinctoria L.) as a Medicinal Plant

Medicinal plants are valuable sources in Iranian natural resources whose understanding and scientific cultivation can play an important role in people’s health, job creation and preventing genetic erosion of invaluable medicinal herbs due to their improper harvest from natural habitats and non-oil exports. Indigo (Indigofera tinctoria L.) belongs to the Fabaceae family which popularly known as Neeli in Tamil and found throughout India. The roots, stems, and leaves of indigo are bitter, thermogenic, laxative, tchronic bronchitis, asthma, ulcers, skin diseases, diuretic and are useful for promoting the growth of hair. It has been reported that appropriate planting date and plant density will improve crop yield and secondary metabolite component. Yield loss due to undesirable planting date and plant density has been reported in many plants. Amin Ghafouri (2014) reported that delaying in planting date (from October to March) caused a significant reduction in plant height, canopy diameter, inflorescence number per branch, dry weight of shoots, and seed yield of Ziziphora and as density increased from 6 to 10 plants.m-2 plant height, canopy diameter, inflorescence No. per branch, dry weight of shoots, and seed yield were enhanced. In another study, was examined planting date in Achillea millefolium L. yield was reported, higher plant height, total dry matter production, Biomass yield, were observed during January planting. Ghorbani et al. (2010) evaluated the effect of planting date on yield of Cuminum cyminum reported that earlier sowing date was followed by higher seed yield. They also reported that 1000-seed weight and harvest index were not affected by planting date. Koocheki et al. (2004) showed that plant density had a significant effect on plant height and dry weight of shoots of Thymus )Zataria multiflora L.  (and Hyssop) Hyssopus officinalis L.  (Nadjafi and Rezvani Moghadam (2002) and Rahimi et al. (2009) reported the increase in P. ovata seed yield with the increase in plant density. Therefore, the objective of the present study was to determine the quantitative yield of affected by planting date and plant density. An experiment was conducted as a split-plot based on a randomized complete block design (RCBD) with three replications at the Bam, Iran, during growing seasons of 2012-2013. Four sowing dates (4 April, 19 April, 4 May, and 19 May) and four plant densities (15, 25, 35 and 45 plants.m-2) were allocated to main and subplots, respectively. Plant height, canopy diameter, number of branches, dry weight of leaf, dry weight of shoots and total dry yield of above ground matter of indigo at the first and the second cuttings were measured and calculated accordingly. For statistical analysis, analysis of variance (ANOVA) and the least significant test (LSD) at 0.05 level, were performed using SAS ver 9.1. The results showed that the simple effects of sowing date and plant density were significant (p≤0.05) on plant height, canopy diameter, number of branches, dry weight of leaf, dry weight of shoots and fresh weight of flower of indigo at the first and second cuts. The highest dry weight of leaf and dry weight of shoots was observed at the first and second cuts in the 4 April (with 464.79 g.m-2, 463.54 g.m-2, and399.75 g.m-2 and 404.04 g.m-2, respectively). However, the dry yield of above ground matter at the first and the second cuts were decreased up to 32.76 and 78.57%, respectively with the delay in sowing date from 4 April to 19 May. Generally, early sowing date because of providing a longer growing period, optimum relative humidity and also cooler weather is suitable for indigo leaf production. Based on the results of this study it can be concluded that the planting date has a meaningful effect on vegetative and reproductive characteristics of indigo. Overall, Because of the benefits of longer growing season and more soil moisture content, early planting (early spring) and highest plant density (45 plants.m-2) were the best date and density for indigo production in the climatic conditions of Bam region