Influence of Plant Growth Regulators and Nitrogen on Leaf Area Index, Specific Leaf Area, Specific Leaf Weight and Yield of Black Gram (Vigna mungo L.)  

K. Krishna    Surendar 1 , S. Vincent 1 , Mallika  Vanagamudi 2 , H.  Vijayaraghavan 1
1. Department of Crop Physiology, TNAU, Coimbatore-3, India;
2. Professor of Crop Physiology, Department of ACRC, TNAU, Coimbatore-3, India;
Author    Correspondence author
Plant Gene and Trait, 2013, Vol. 4, No. 7   doi: 10.5376/pgt.2013.04.0007
Received: 02 Apr., 2013    Accepted: 11 Apr., 2013    Published: 22 Jul., 2013
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This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Surendar et al., 2013, Influence of Plant Growth Regulators and Nitrogen on Leaf Area Index, Specific Leaf Area, Specific Leaf Weight and Yield of Black Gram (Vigna mungo L.) , Plant Gene and Trait, Vol.4, No.7 pp.37-42 (doi: 10.5376/pgt.2013.04.0007)
Abstract

The field experiment were undertaken to study the effect of nitrogen in combination with foliar spray of bioregulators and micronutrients on growth and productivity of CO5 black gram. Photosynthetic pigments and foliage soluble protein content were estimated at different phenological phases of black gram. Seed yield were assessed at the time of harvest. Significant increase in the LAI (Leaf Area Index) and SLW (Specific Leaf Weight) due to basal application of nitrogen 25 kg per hectare with foliar spray of urea 2% and 0.1 ppm brassinolide. The SLA (Specific Leaf Area) was also greatly altered by the basal application of nitrogen 25 kg per hectare with foliar spray of urea 2% and 0.1 ppm brassinolide treatment.

Keywords
Black gram; PGR; LAI; SLA; SLW; Nitrogen and yield

1 Introduction

Pulses are the most important crops in India because of its low cost and high quality protein. They play a major role in providing a balanced protein component in the diet of the people. Pulses contain a higher level of quality protein, nearly three times as much as cereals; therefore they are the cheapest and rich source of protein and essential amino acids and thus share a major protein of the vegetarian diet. Besides, the crops enrich the soil fertility and health in terms of addition of nitrogen and organic matter. Among pulses, black gram (Vigna mungo L. Hepper), occupies a unique place for its use as vegetable, and it is grown both as pure and mixed crop along with maize, cotton, sorghum and other millets. It is also known as urd bean, and it is an important pulse crop grown all over the world. It is a major component of the daily Indian diet and serves as a rich protein source (23.9%) besides; it also contains 60.4 per cent carbohydrates. As per the World Health Organization every man needs 80 g of pulses per day and as per the Indian Council of Medical Research, every man needs minimum consumption of 47 g of protein per day to meet requirement of the body. But at present, the per capita availability of pulses is only 30~35 g/d. Therefore, there is a need for three fold increase in pulse production as that of current production. Black gram is indeterminate in its flowering and fruiting habits and there is a competition for available assimilates between vegetative and reproductive sinks. There is limitation of source (leaves) particularly at flowering and fruiting stage. Hence, there is a need to improve LAI and LAD. Being a C3 plant, CGR and RGR are relatively less than cereals and the major yield components are pods per plant, seeds per plant and test weight of seeds. Apart from this genetic makeup, the major physiological constraints limiting its production are flower drop and fruit drop (Ojeaga and Ojehomon, 1972). This performance of the crops can be overcome by foliar application of growth regulating chemicals at the crucial stages of the crop, which is one of the latest trends in agriculture. The growth regulating chemicals bioregulators can improve the LAI, SLW and SLA and play a significant role in improving the productive potential of the crop. With this above background, the present investigation was carried out.
 
2 Materials and methods
The present investigation was undertaken under field condition to study the effect of nutrients and plant growth regulators on growth and productivity of black gram variety CO 5. The research experiment was carried out at Millet Breeding Station, Tamil Nadu Agricultural University, Coimbatore during July to October, 2007. Growth regulators like Naphthalene Acetic Acid (NAA), Salicylic Acid (SA), Cycocel (CCC), Brassinosteriod (BR), Humic Acid and the nutrients such as Nitrogen, DAP, Boric Acid, Ferrous Sulphate, Zinc Sulphate were used.  The data were statistically analyzed with the Design of Randomized Block Design with three replication and the Plot size of 4  x 3 m with Spacing of 30  x 10 cm.  in this research study having nine treatments and the details are, T1 - Control , T2 - N 25 Kg / ha + Urea 2 % + NAA 40 ppm, T3 - N 50 Kg/ha + CCC 200 ppm, T4 - N 25 Kg/ha + Urea 2% + CCC 200 ppm, T5 - N 25 Kg/ha + Urea 2% + Humic acid 0.1%, T6 - N 25 Kg/ha + Urea 2% + Salicylic acid 100 ppm, T7 - N 25 Kg/ha + Urea 2 % + Brassinosteriod 0.1 ppm, T8 - N 25 Kg/ha + Urea 2% + ZnSO4 0.5% + FeSO4 0.5 + Borax 0.2%, T9 - N 25 Kg/ha + Water spray. The LAI was calculated by employing the formula of Williams (1946). Specific leaf weight (SLW) was calculated by using the formula of Pearce et al. (1968) and expressed as mg/cm2. Employing the formula of Kvet et al. (1971), the SLA was calcu¬lated by using leaf area and leaf dry weight and expressed as cm2/g.
 
3 Result
3.1 Leaf area index
The time trend of leaf area index exhibited the pattern similar to that of leaf area of the plant (Table 1). The leaf area index at various stages of crop growth viz., vegetative, (30 DAS), flowering (45 DAS), pod filling (60 DAS) and harvest stages ranged from 0.283 to 0.343, 0.607 to 0.820, 1.345 to 1.890 and 1.179 to 1.648, respectively. At pod filling stage, the treatment T7 (N 25 kg/ha + Urea 2% + BR 0.1 ppm) recorded the highest leaf area index of 1.890 followed by T3 (1.867) and T4 (1.803) over control. The treatment T3 and T7 recorded statistically equivalent values with T4.

 
Table 1 ffect of nitrogen nutrition nutritions and growth regulators on leaf area index in blackgram at different growth stages

 
3.2 Specific leaf weight (SLW)
The data on SLW (mg/cm2) of black gram CO 5 at various crop growth stages is presented in Table 2. The results revealed that the specific leaf weight increased up to pod filling stage and declined thereafter. The treatment T7 (N 25 kg/ha + Urea 2% + BR 0.1 ppm) registered more specific leaf weight of 13.68 at pod filling stage and the lowest value was recorded in treatment T1 (control) at vegetative stage with a value of 4.76. 

 
Table 2 Effect of nitrogen nutrition and growth regulators on specific leaf  weight (mg/cm2) in black gram at different growth stages

 
3.3 Specific leaf area (SLA) 
The values of SLA (cm2/g) of black gram CO 5 decreased at flowering stage and thereafter showed a steady increase up to harvest stage (Table 3). The flowering stage recorded the lowest values while the vegetative stage recorded the highest values, irrespective of the treatments. The treatment T7 (N 25 kg/ha + Urea 2% + BR 0.1 ppm) registered lowest SLA (cm2/g) ranged from 125.06 cm2/g, 77.06 cm2/g, 87.90 cm2/g and 103.72 cm2/g at all the growth stages followed by T3 (128.72, 83.37, 97.61 and 109.84 cm2/g) and T4 (131.88, 86.06, 101.31 and 113.92 cm2/g) respectively.

 
Table 3 Effect of nitrogen nutrition and growth regulators on specific leaf area (cm2/g) in black gram at different growth stages

 
4 Discussion
4.1 Leaf area index
Leaf area index is one of the principle factors influencing canopy net photosynthesis of the crop plants (Hansen, 1972). Patra et al. (1995) stated that total dry matter production and pod yield of groundnut were attributed to higher LAI through facilitating efficient interception of light. As observed from the results of leaf area, leaf area index was also greatly influenced by nitrogen and hormonal treatments. The normal recommended dose of nitrogen along with foliar spray of Urea (2%) and BR (0.1 ppm) resulted in a remarkable improvement in LAI with 35 and 40 per cent increase during flowering and pod filling stages of the crop. This finding was in close conformity with the results of Nithila (2007) in groundnut. In this crop BR application resulted in a 31 per cent increased in LAI. As per the report of Braun and Wild (1984), high LAI at the time of pod formation stage of mustard was associated with high rate of current photosynthesis with better translocating efficiency of the crop, which intimately reflected on pod yield. Kelaiya et al. (1991) further explained that brassinolide promoted the leaf area development in crop plants due to increase in leaf number. The significant role of nitrogen in improving the LAI was also revealed in the present study. High dose of nitrogen in combination with foliar spray of CCC resulted in about 30 and 40 per cent enhancement in LAI at the time of flowering and pod filling stages of the crop. Parihar et al. (1996) also observed similar findings in cowpea. Better foliage retention with delayed senescence was attributed to maintenance of higher LAI of this crop subjected to the treatment with high N dose. In rice also increased N application led to greater leaf area index as reported by Rammohan et al. (1999). The favourable effect of CCC in improving LAI, as observed in the present study, was also reported by Jeyakumar and Thangaraj (1996).
 
4.2 Specific leaf weight (SLW)
Specific leaf weight, a measure of leaf thickness, has been reported to have a strong positive correlation with leaf photosynthesis of several crops as reported by Bowes et al. (1972). Thicker leaves would have more number of mesophyll cells with high density of chlorophyll and, therefore, have a greater photosynthetic capacity than thinner leaves (Craufurd et al., 1999). SLW is highly correlated with the development of reproductive organs (Arnon, 1975).  The results of the present investigation revealed that the specific leaf weight of black gram increased very steeply from vegetative to flowering stage of the crop, maintained the same weight till pod filling stage and slightly decreased at maturity. This trend indicated that the developmental processes at cellular and tissue levels of shoot system completed almost before flowering. Therefore, nutritional and hormonal manipulation of the crop during this rapid developmental stage, would ensure the regulation of the metabolic processes for the enhancement of growth and productivity. In the present study, the two treatmental combinations, N (25 kg/ha) foliar spray of BR (0.1 ppm) + Urea (2%) and high dose of N (50 kg/ha) + foliar spray of CCC (200 ppm) were equally effective in increasing the SLW of the crop by 12 and 11.6 per cent over control. The beneficial effect of BR in improving the thickness of the leaf was revealed by Bindu Joseph (2000) in cotton. As per the result Braun and Wild (1984), BR application increased the thickness of the 3rd leaf of wheat. Dornhoff and Shibles (1970) presumed that higher SLW might be associated with higher cell surface to volume ratio and hence lower mesophyll resistance to CO2 entry and increase in photoassimilates accumulation in soybean. Krizek and Mandaya (1983) also quoted the favourable effect of BR on increasing the specific leaf weight of primary leaves in bean plants. Besides these findings, Reddy et al. (1988) observed an increase in specific leaf weight due to spray of CCC in cotton. This finding strongly supported the results of the present study.
 
4.3 Specific leaf area (SLA) 
The specific leaf area is a measure of leaf area for unit leaf dry weight and it varies with cultivar, leaf position growth stage and environmental conditions (Murata, 1975). SLA was found to have inverse relationship with SLW (Thandapani, 1985). SLA was high at vegetative stage, declined drastically at the time of flowering, and again increased towards maturity. The high specific leaf area at early stage may be due to the fact that the biomass added to the leaf is minimum. The decreased SLA at rapid vegetative growth as well as flowering stage may be due to increased leaf weight. The increase in SLA at later period may be attributed to the transport of assimilated from the leaf to the reproductive sink for its development. The results of the present study indicated that nutrients and plant hormones played their effectives role in reducing the specific leaf area. Accordingly, the treatment N (25 kg/ha) + Urea (2%) + BR (0.1 ppm) reduced the specific leaf area by 19 per cent over control and N (50 kg/ha) + CCC (200 ppm) by 13 per cent over control at flowering stage. All the other treatments showed comparatively lesser effect on the reduction of SLA. The reduced SLA by the application of BR in green gram was also observed by Sujatha (2001). This negative effect of BR on SLA was related to enhancement of phloem transport towards the newly developed photosynthetic assimilatory surfaces and utilization of carbohydrates for the developmental process of photosynthetic organs.

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