Effects of Foliar Application of Fe and Zn on Seed Yield and Mucilage Content of Psyllium (Plantago psyllium) at Different Stages of Maturity

Introduction

Plantago belongs to the Plantaginaceae family with two valuable medicinal species of Isabgol (Plantago ovata) and Psyllium (Plantago psyllium) (Naghdibadi et al. 2004). Psyllium is native to Mediterranean regions and is cultivated in a large scale in France and Spain (Javidtash 1997). Economic value of this species is related to mucilage content of the seed mainly used in medicine and industry (Ebrahim Zadeh Mabood et al. 1998). Mucilage content of psyllium has been reported to reach between 10-15 % (Blumental et al. 2000). Some reports suggest that the secondary metabolites of medicinal plants can be improved by foliar application of micronutrients (Zehtab-Salmasi et al. 2008; Nasiri et al. 2010). However, the effect of micronutrients on mucilage content of psyllium seeds is not investigated.

         Micronutrient deficiency can greatly disturb plant yield and quality, and the health of domestic animals and humans (Malakouti 2007). Foliar application of fertilizers is a particulary useful technique designed to meet plants specific needs for one or more micro or macro nutrients especially trace minerals.This enables us to correct deficiencies, strengthen weak or damaged crops, speed up growth and grow better and healthier plants (Naguib et al. 2005). Micro- elements as Fe, Zn, Mn and Cu are added to foliar fertilizers, in order to compensate their deficiency especially in arid and semi arid regions (Kaya et al. 2005).

    Zinc is an important micronutrient that is closely involved in the methabolism of RNA and ribosomal content in plant cells, leading to stimulation of carbohydrates, proteins and the DNA formation. It is also, required for the synthesis of tryptophan, a precursor of IAA which acts as a growth promoting substance (Amberger 1982). Zinc has three functions: catalytic, cocatalytic (coactive) and structural (Valle and Auld 1990; Valle and Falchuk 1993). Iron (Fe) is another micronutrient that is a cofactor for approximately 140 enzymes that catalyze unique biochemical reactions (Brittenham 1994). Hence, iron has many essential roles in plant growth and development including chlorophyll synthesis, thylakoid synthesis and chloroplast development (Miller et al. 1995). Said-Al Ahl and Mahmoud (2010) reported that basil plants sprayed with zinc and/or iron under normal and saline conditions were superior compared with non-sprayed plants. Also the highest plant height, branches per plant, fresh and dry biomass and essential oil yield obtained by foliar application of these elements in the normal soil. Foliar spraying with zinc (100 ppm) in blue sage (Salvia farinacea L.) enhanced the length of peduncle, length of main inflorescence, number of inflorescence and florets, and fresh and dry weight of inflorescences/plant (NahedAbd El-Aziz and Balbaa 2007). It was reported that flower yield, essential oil percentage and essential oil yield of chamomile (Matricaria chamomilla) increased by foliar application of Fe and Zn compared with the control (Nasiri et al. 2010). Foliar application of microelements increased fresh and dry mater, leaf area of plant, bush and leaf essential oil percentage and essential oil yield of peppermint (Mentha piperita) (Zehtab-Salmasi et al. 2008).

       Timing of the harvest is also important with respect to oil yield and composition (Clark and Menary 2006; Marcuni and Hanson 2006). Zheljazkow and Cervan (2009) reported that peppermint oil content and yields were higher at bud formation than at flowering. In addition, the concentration of menthone and eucayptol and the yields of mentlione, +mentholuran and eucalvptol were higher at bud formation than at flowering. The purpose of this study is to investigate the effect of foliar application of some micronutrients and harvesting time on yield and mucilage content of psyllium.

Materials and Methods

A field experiment was carried out in 2009 at the Research Farm of the Faculty of Agriculture, University of Tabriz, Tabriz (37º, 5´ N, 46º, 17´ E and 1360 m mean sea level), Iran. The physicochemical properties of soil are given in Table 1. The treatments were foliar application of Fe, Zn and Fe + Zn (using ferrous sulphate and zinc sulphate at the concentration of 0.35% for the both micronutrients) with the control and four harvesting times during seed filling. The experiment was arranged as split plot based on randomaized complete block design with four replications.The plots were 4 × 1.8 m with 6 rows, 30 cm row distance and 7.5cm seed distance. Soil moisture was kept at adequate levels to prevent water deficit and wilting. Weeds were controled by hand as required. Foliar spray was done according to experimental treatments at the flowering stage.

Table 1.  Physico-chemical properties of the soil characteristics

Plants were harvested four times (Augest 8, 15, 22 and September 5) from four central rows (0/9 m² each time) during seed filling. One-gram seeds of each sample was put into a beaker with 25 ml capacity. Then, 20ml distilled water was added to it. The swelling of seeds was calculated after 24h. Mucilage percentage in the seeds were also determined according to Sharma and Koul (1986). Data were analyzed using MSTAT-C statistical package (MSTAT-C 1993). Duncan’s Multiple Range Test was used to compare the treatment means of (Duncan 1955).

Results and Discussion

Seed yield, seed swelling and mucilage percentage significantly affected by foliar application of iron, zinc and iron+zinc (p≤0.05) and harvesting times (p≤0.01). Seed yield was significantly increased by foliar application of Fe+Zn. This improvement was 16.09, 17.47 and 31.04 %, compared with foliar application of Fe, Zn and control, respectively (Table 2). Similar effects of Fe+Zn supply on seed yield were reported in wheat (Pol Shekane Pahlevan et al. 2006; Soleimani 2006) and onion (Bybordi and Malakouti 1998).  Zeidan et al. (2010) reported that application of Fe, Mn and Zn significantly increased grain yield and yield components of wheat. Similarly, Maralian (2009) found that foliar application of Zn and Fe increased seed yield and quality of wheat compared with control. Zinc is a component of carbonic anhydrase, as well as several dehydrogenases and auxin production, which in turn enhance plant growth. However, iron is necessary for the biosynthesis of chlorophyll and cytochrome, leading to increase in the biosynthesis of materials and growth (Marschner 1995).Thus, effects of foliar application with micronutrients (Zn, Mn and Fe) might be due to their critical role in crop growth, involving in photosynthesis processes, respiration and other biochemical and physiological activities and their importance in achieving higher yields. The highest seed yield (1564 kgha^-1) was observed in the plants that harvested at maturity stage (51 days after flowering) (Table 3). This means that maximum seed weight was achieved at mass maturity (Ghassemi-Golezani and Hosseinzadeh-Mahootchy 2009).

Table 2. Effect of foliar application of Zn and Fe on yield and mucilage percentage of psyllium

                   Different letters shows significant difference at p≤0.05

Table 3. Effect of harvesting time on yield and mucilage percentage of psyllium

                   Different letters shows significant difference at p≤0.01