Enhancing morpho-physiological vigour of sesame seedlings for improving productivity and weed competitiveness

Abstract

Sesame is one of the oldest oilseed crops grown in summer rice fallows of Kerala. Weed infestation is a major biotic stress affecting the yield of sesame. Seedling growth of sesame is slow during the first four weeks, making it a poor competitor during this period. Weed suppression during the early stages of crop establishment (10 to 30 DAS) is important for improving the productivity of the crop. The present study was initiated to enhance the early vigour of sesame plants by suitable seed priming treatments and also to assess the effect of early vigour on weed competitiveness and analyse the carry over effect of these treatments on the productivity of the crop. The variation in varietal response to these priming treatments were also studied. A laboratory study was conducted with five popular varieties of sesame viz., Surya, Thilak, Kayamkulam 1, Thilarani and Thilathara, released from Kerala Agricultural University. Ten priming treatments with plant growth regulators (IAA, GA), micronutrients (MnSO4, borax), mixture of MnSO4 and borax with GA (Tank mix), biofertilizers (phosphobacteria, azospirillum, PGPR mix-1) and water were tried. Results on observations showed that seed priming improved the germination and vigour of all the five varieties tested. Among the treatments, priming with micronutrients and hormones gave the best results. Based on the vigour index, five priming treatments were selected for the field trial and the variety Thilak, which gave maximum response to these treatments, was used as the test variety in the field. The experiment was laid out in split plot design at ORARS, Kayamkulam. Weeded and unweeded treatments formed the main plots and five selected treatments along with control (unprimed seeds) were the sub-plot treatments. Observations on morphological characters were studied at 20 days interval and yield characters were recorded at the time of harvest. Physiological and biochemical effects of the priming treatments were studied at vegetative and reproductive stages of the crop. Weed count and weed dry matter were recorded at 10 DAS and at the time of harvest in the unweeded plots. Weed control efficiency of the priming treatments was computed at the time of harvest. The biochemical parameters such as contents of chlorophyll, total soluble protein and GA were higher during the reproductive phase as compared to the vegetative phase. Chlorophyll including chlorophyll a and chlorophyll b, and soluble protein content showed greatest improvement in MnSO4 primed plants. The nitrate reductase enzyme plays a major role in nitrogen metabolism of the plant. In the present study, the nitrate reductase enzyme activity was found to be higher during the reproductive phase of the crop in all the treatments except for control (unprimed seeds) and water priming. The IAA content was also higher in the reproductive phase in all the treatments. Major improvement in IAA content was observed with borax priming. The growth indices such as crop growth rate, relative growth rate, net assimilation rate and leaf area index were improved with priming treatments in both unweeded and weeded plots. Yield and yield attributes such as number of branches, number of capsules and seeds per capsule improved significantly with MnSO4 and tank mix treatments, which contributed to higher yield. The improvement in vigour of sesame plants with seed priming treatments reduced the weed count and weed dry matter production in the unweeded plots as compared to the control (unprimed seeds) due to the higher competitiveness of the primed seeds. The study revealed that seed priming with MnSO4 or Tank mix of GA, borax and MnSO4 can be an effective component in the integrated management of weeds in sesame as it can contribute to 30 per cent control of weed growth.