Plant Growth Substances in Crop Production: A Review

INTRODUCTION

Nutrients are important and crucial elements, which are required for the plant for its growth and development. The translocation of photosynthates from source to sink is very important for the development of economic part. Plant growth regulators are chemical substances and when applied in small amounts, they bring rapid changes in the phenotypes of the plant and also influence the plant growth, right from seed germination to senescence either by enhancing or by stimulating the natural growth regulatory system. Plant growth regulators are known to enhance the source-sink relationship and stimulate the translocation of photo-assimilates thereby helping in effective flower formation, fruit and seed development and ultimately enhance productivity of the crops.

Growth regulators can improve the physiological efficiency including photosynthetic ability and can enhance effective partitioning of the accumulates from source and sink in the field crops (Solaimalai et al., 2001). Foliar application of growth regulators and chemicals at the flowering stage may improve the physiological efficiency and may play a significant role in raising the productivity of the crop (Dashora and Jain, 1994).

Importance of Salicylic Acid (SA): Salicylic acid belongs to an extra-ordinary diverse group of plant phenolics. Salicylic acid is ubiquitously found in all plant species and the highest levels are observed in the inflorescence of thermogenic plants and in plants infected with necrotizing pathogen (Raskin, 1992).

Salicylic acid is ortho-hydroxybenzoic acid and is a secondary metabolite acting as analogues of growth regulating substances. It helps in protection of nucleic acids and prevention of protein degradation. The SA is also known to induce many genes coding for pathogenesis-related proteins in response to biotic and abiotic stresses (Enyedi et al., 1992; Yalpani et al., 1994).

Foliar application of SA increased the IAA content in broad bean leaves (Xin et al., 2000). Foliar application of SA exerted a significant effect on plant growth metabolism when applied at physiological concentration, and thus acted as one of the plant growth regulating substances (Kalarani et al., 2002).

Effect of salicylic acid on growth parameters: Jeyakumar et al. (2008) reported that application of salicylic acid (125 ppm) increased the dry matter production (21.6 g plant^-1) in black gram. Nagasubramaniam et al. (2007) reported that foliar application of salicylic acid (100 ppm) on baby corn increased the plant height, leaf area, crop growth rate and total dry matter production.

Khan et al. (2003) reported that application of salicylic acid, acetyl salicylic acid and geninic acid enhanced the photosynthetic rate, stomatal conductance and transpiration rate in soybean. Sujatha (2001) reported that foliar application of salicylic acid (100 ppm) on green gram at 75 DAS increased the plant height (50.4 cm), root length (16.9 cm), number of leaves (18.4) and LAI (1.30).

Effect of salicylic acid on yield and yield parameters: Jeyakumar et al. (2008) reported that application of salicylic acid (125 ppm) in black gram increased the seed yield (855 kg ha^-1). Salicylic acid sprayed on mungbean significantly increased the pod number plant^-1 and yield (Singh and Kaur, 1981). Nagasubramaniam et al. (2007) revealed that the cob yield of baby corn was the highest (7703.4 kg ha^-1) by the foliar application of salicylic acid (100 ppm).

Sujatha (2001) reported that foliar application of salicylic acid (100 ppm) on green gram at 75 DAS increased number of pods plant^-1, number of seeds pod^-1, seed weight plant^-1, 100 seed weight and grain yield (840 kg ha^-1). In green gram, foliar application of salicylic acid at branching, flower bud initiation stages increased the number of flowers, pods and seeds plant^-1 and seed yield (Singh et al., 1980).

Effect of salicylic acid on quality parameters: Jeyakumar et al. (2008) reported that the highest seed protein content in black gram was recorded (24.5%) by foliar application of salicylic acid (125 ppm). Hussein et al. (2007) indicated that in maize hybrid, all determinate amino acids concentration such as tyrosine (31.16%), lysine (22.30%), aginine (20.68%), alinine (2.65%), lucine (2.78%) except methionine were increased with the application of salicylic acid (200 ppm). Proline concentration increased when using salicylic acid as foliar application under salt stress condition. Sujatha (2001) revealed that foliar application of Salicylic acid (100 ppm) on green gram at 75 DAS increased seed protein (23.98%) and soluble protein (12.9%). Kalpana (1997) found that foliar spray of salicylic acid increased the soluble protein in rice.

Effect of salicylic acid on nutrient uptake: Gunes et al. (2007) at Turkey demonstrated that exogenously applied salicylic acid increased the plant growth in maize significantly both in saline and non-saline conditions. This may be related to its inhibiting effect on Cl^-1 and Na⁺¹ and improving the uptake of N, Mg, Fe, Mn and Cu due to its effect on lipid peroxidation.

Importance of boron: Boron is one of the important micronutrients, which has basic role in stabilizing certain constituents of cell wall and plasma membrane, enhancement of cell division, tissue differentiation and metabolism of nucleic acid, carbohydrate, protein, auxin and phenols (Marschner, 1997). Though the symptoms of boron are very striking, its role in plant metabolism is uncertain. Boron has been found to be involved in the carbohydrate transport system within the plant. Boron deficiency causes delay in tassel formation, decrease in pollen size, pollen germination and pollen production capacity of maize (Agarwala et al., 1981). Among the micro nutrients, boron is stated to influence many growth parameters and filling up of seeds (Blamey, 1976).

Effect of boron on growth parameters: Vishwakarma et al. (2008) revealed that in groundnut maximum plant height (60.33 cm) and number of branches (5.83 plant^-1) were recorded with application of borax as soil application. Dixit and Elamathi (2007) reported that foliar application of boron (0.2%) in green gram increased the plant height (32.26 cm), number of nodules plant^-1 (30.8) and dry weight plant^-1 (12.9 g).

Garg et al. (1979) found that germination capability, size and fertility of pollen grains of rice were considerably improved as a result of boron application at 2.5 ppm concentration. They also reported that inclusion of boron in the nutrient solution with optimum level induced some stimulatory effects on the pollen vitality and there by improved the grain yield of rice.

Effect of boron on yield and yield parameters: The highest number of pods plant^-1 (26.66), pod and kernel yield (25.46 and 16.34 q ha^-1, respectively) were recorded with application of borax as soil application in groundnut (Vishwakarma et al., 2008). The maize crop sprayed with boric acid @ 0.3% produced higher grain yield (6444 kg ha^-1) than no spray treatment (Sekar et al., 2009).

Dixit and Elamathi (2007) reported that foliar application of boron (0.2%) in green gram increased the number of pods plant^-1 (18.1), 1000 seed weight (28.7 g), grain yield (7.53 q ha^-1) and haulm yield (30.0 q ha^-1). Susheela (1996) revealed that foliar spraying of borax at 0.2% increased percentage of filled seeds in sunflower. This might be due to better pollen germination, increased pollen viability and fertilizing capacity.

Khan et al. (1990) found that dusting of borax at 2 kg ha^-1 on sunflower heads during seed filling stage significantly increased the seed yield by 87%, test weight by 60%, seed filling by 25% and head diameter by 21% compared to control. They also found dusting borax on ear heads gave the highest germination per cent of 96 and vigour index of 2162 compared to control (84% germination and 1263 vigour index, respectively).

Fernandez (1990) reported that the requirement of boron was maximum during flowering and the plant was therefore most susceptible to limitations and so the content of the 5th and 6th leaves under the flowering head should be maintained at 20 and 40 ppm, respectively. Sarkar and Sasmal (1989) found that applying 0.5 kg ha^-1 boron to sunflower grown in rabi (winter) season increased the capitulum diameter, number of filled seeds head^-1, 1000 seed weight and seed yield.

Randhawa and Nayyar (1982) reported that application of boron was found to be beneficial in increasing the yield of wheat and paddy. Satyanaryana et al. (1997) reported that application of boron at 2 and 4 kg ha^-1 increased the yield of sunflower by 38 and 59%, respectively over control. Rao and Vidyasagar (1981a) reported that foliar application of boron increased the plant height, stem girth, dry matter accumulation, total seed number per head, number and weight of filled seed per head, test weight and seed oil content.

Effect of boron on quality parameters: Application of boron either alone or in combination with FYM and sulphur helped in improving the quality of groundnut (Dongale and Zende, 1976; Survase et al., 1986; Patil et al., 1987). Sekar et al. (2009) recorded higher starch content in hybrid maize sprayed with boric acid @ 0.3%.

Effect of boron on nutrient uptake: Jain et al. (2007) revealed that Rhizobium inoculation along with zinc and boron in green gram gave better response in terms of N uptake as compared to Rhizobium alone. Ateeque and Malewar (1992) reported that uptake of N, P and boron was the highest when fertilized with boronated super phosphate as compared to SSP and DAP.

Rao and Vidyasagar (1981b) reported that boron when applied to soil resulted in increased N content of leaf, K content of stem and P content of petiole during early vegetative stage, N and P contents of leaves during flowering stage and P contents of leaves and stems, and N and K contents of petioles at harvest. Boron when sprayed on foliage helped to increase the mineral composition of leaves, stems and petioles during different growth stages of sunflower. They also noticed that foliar sprayed boron influenced the absorption and preferential translocation of mineral elements into different parts of the plant.

Effect of boron on economics: Dixit and Elamathi (2007) reported that foliar application of boron (0.2%) in green gram increased the B: C ratio (1.54). Susheela (1996) revealed that net return and B: C ratio was higher with 60 kg P₂O₅ ha ^-1 combined with of 2% DAP and 0.2% borax spray in sunflower.

Importance of panchagavya: In 1950, James F. Martin of USA made a liquid catalyst (living water) from milking cow, using dung, sea water and yeast and it was claimed that it was capable of greening degraded land (Vivekanandan et al., 1998). Cows ghee had been used in ancient and medieval times (Kautilya 321-296 BC and Someshwara Deve 1126 AD) for managing seedling health. The ghee contains vitamin A, vitamin B, calcium, fat and also glycosides, which protects cut wounds from infection. Cows curd is rich in microbes (Lactobacillus) that are responsible for fermentation (Chandha, 1996).

Panchagavya has got reference in the scripts of Vedas (divine scripts of Indian wisdom) and Vrkshayurveda (Vrskha means plant and ayurveda means health system). The texts on Vrskhayurveda as systematization of the practices that the farmers followed at field level, placed in a theoretical frame work and it defined certain plant growth stimulants; among them Panchagavya was an important one that enhanced the biological efficiency of crop plants and quality of fruits and vegetables (Natarajan, 2002). The positive effect of panchagavya on growth and productivity of crops has been reviewed and documented by Somasundaram and Amanullah (2007).

Effect of panchagavya spray on growth parameters: Mohanalakshmi and Vadivel (2008) revealed that ashwagandha plant sprayed with panchagavya (3%) produced higher number of leaves plant^-1 (670). Vennila and Jayanthi (2008) revealed that application of 100% recommended dose of fertilizer along with panchagavya spray (2%) significantly increased the okra plant height (131.7 cm) and dry matter production (5.90 g plant^-1).

Biogas slurry with panchagavya combination is adjudged as the best organic nutrition practice for sustainability of maize-sunflower-green gram system by its overall performance on growth, productivity, quality of crops, soil health and economics (Somasundaram et al., 2007).

Panchagavya was tested for different crops such as turmeric, paddy, onion, gingely, sugarcane, banana, vegetables and curry leaf and it was found that it enhanced the growth, vigour of crops, resistance to pest and diseases and improvement of keeping quality of vegetables and fruits (Natarajan, 2002).

Xu (2001) reported that Effective Micro Organism (EMO) cultures could synthesize phytohormones i.e., auxins and other growth regulators that stimulated maize plant growth and they contained proactive substances that could significantly affect leaf stomatal response in maize. Leaf stomata of the EMO treated maize opened more rapidly than water treated control plants and when leaves were subjected to dehydration, the stomata closed more slowly (i.e., remained open longer) thus showed that, EMO contained bioactive substances that could have significantly affected leaf stomata response and led to increased LAI.

Effect of panchagavya spray on yield and yield attributes: Mohanalakshmi and Vadivel (2008) revealed that application of poultry manure (5 t ha^-1) + panchgavya (3%) in aswagandha exhibited significantly superior performance by registering the highest root yield of 1354.50 kg ha^-1. Vennila and Jayanthi (2008) revealed that application of 100 per cent recommended dose of fertilizer along with panchagavya spray (2%) significantly increased the number of fruits plant^-1 (21.8), fruit weight g fruit^-1 (13.9) and fruit yield q ha^-1 (12.7) of okra.

Swaminathan et al. (2007) concluded that application of panchagavya at 3% as foliar spray on 15, 25, and 40 DAS on black gram recorded the highest grain yield of 1195 kg ha^-1. Kanimozhi (2003) revealed that application of panchagavya at 4 per cent spray was found to be superior in respect of root yield (12.4 kg/plot) compared to control (5.23 kg plot^-1) in Coleus forskohili.

Foliar spray of Panchagavya @ 3 per cent on 15, 25, 40 and 50 DAS with no fertilizers was the most effective low cost technology in terms of grain yield of greengram (Somasundaram et al., 2003). Panchagavya and vermicompost combination has given the highest pod yield of french bean variety Ooty 2, which was 36 per cent higher than the conventional method (Selvaraj, 2003). The treatment combinations of poultry manure + neem cake + panchagavya along with increased dose of fertilizers increased the stick yield of moringa (Beaulah et al., 2002). Balasubramanian et al. (2001) reported that dipping of rice seedlings in panchagavya before transplanting enhanced the growth and yield.

In panchagavya, Effective Micro Organisms (EMO) were the mixed culture of naturally occurring, beneficial microbes (mostly lactic acid bacteria (Lactobacillus), yeast (Saccharomyces), actinomyces (Streptomyces), photosynthetic bacteria (Rhodopsuedomonas) and certain fungi (Aspergillus)) and that improved the soil quality and growth and yield of sweet corn, which was equal to or higher than what was obtained from chemical fertilizers (Xu, 2001).

In jasmine, spraying two rounds of panchagavya, one before the flower initiation and another during bud setting phase ensured continuous flowering and in annual moringa sprayings doubled the stick yield besides giving resistance to pests and diseases (Vivekanandan, 1999). Panchagavya sprayed on 25 and 40 DAS advanced the paddy harvest by 10 days (Vivekanandan, 1999).

Effect of panchagavya spray on quality parameters: Vennila and Jayanthi (2008) revealed that application of 100% recommended dose of fertilizer along with panchagavya spray (2%) in okra resulted in higher crude protein, ascorbic acid and Barletts index. The presence of auxin in panchagavya controls the water regulation in developing fruits. Regular and uniform water supply to the developing fruits resulted in increased ascorbic acid content, Barletts index and crude protein content.

Yadav and Lourduraj (2006b) revealed that foliar spray of panchagavya and organic manures recorded better cooking qualities and physical characteristics of rice as well as higher sensory score as compared to recommended N, P and K through fertilizers.

Effect of panchagavya spray on nutrient uptake: Presence of macro (N. P, K and Ca) and micro (Zn, Fe, Cu, Mn) nutrients besides total reducing sugars (glucose) were observed in panchagavya. Chemolithotrops and autotropic nitrifiers (ammonifers and nitrifers) present in panchagavya which colonize in the leaves increase the ammonia uptake and enhance the total N supply (Papen et al., 2002).

Beaulah (2001) reported that the secondary and micronutrients (Ca, S and Fe) and macronutrients (NPK) contents of leaves and pods of annual moringa were superior under poultry manure + neem cake + panchagavya treatments. Higher nutrient uptake and nutrient use efficiency in both main and ratoon crops of annual moringa were also observed. Similarly, the quality parameters viz., crude fibers, protein, ascorbic acid, carotene content and shelf life were also higher under organic manure applied with panchagavya spray (Beaulah et al., 2002).

Influence of panchagavya spray on soil fertility: Microbial flora of soil play an important role in soil health. The microorganisms present in the rhizospheres environment around the roots influence the plant growth and crop yield. The beneficial microorganisms from panchagavya and their establishment in the soil improved the sustainability of agriculture.

Effect of panchagavya spray on economics: Swaminathan et al. (2007) reported that application of panchagavya at 3% as foliar spray on 15, 25, and 40 DAS on black gram under irrigated condition recorded the highest net return (Rs. 28544 ha^-1) and B:C ratio (4.91).

Application of 50 per cent N through composted poultry manure + 50 per cent N through green leaf manure along with panchagavya spray recorded higher net returns (Rs. 17822 ha^-1), followed by recommended NPK through panchagavya spray (Rs. 15586 ha^-1) in rice (Yadav and Lourduraj, 2006a).

Importance of Pink Pigmented Facultative Methylotroophic bacteria (PPFMs): Pink Pigmented Facultative Methylotrophs (PPFMs) belonging to the genus Methylobacterium are persistently present in the rhizosphere and phyllosphere regions of plants and even on the surface of the seeds of various plants. They were revealed on leaves of almost all plants (Corpe and Rheem, 1989).

Methylotrophs have received a great deal recently due to their importance in the biosphere and their potential commercial applications. Holland (1997) reported that the invention provided a method for increasing productivity of a plant by spraying PPFM on a plant. The invention also related to increasing productivity of a plant under stress by applying PPFM to a plant and subsequently applying an aqueous solution-containing methanol to the plant.

Methylobacterium have some sort of beneficial interaction with plants (Holland and Polacco, 1992, 1994). Pink pigmented facultative methylotrophs (PPFMs) isolated from the liverwort stimulated growth of the liverwort (Scapania nemorosa) and Streptocarpus prolixus (flowering plant) in tissue cultures and a positive commensal interaction was proposed (Corpe and Basile, 1982). Effect of PPFMs on germinating seeds has been suggested to be mediated by cytokinin or other plant growth promoting substances (Holland and Polacco, 1994) and a possible connection between bacterial and plant metabolism has also been suggested (Holland and Polacco, 1992).

Effect of PPFM spray on growth attributes: Under the pot culture condition in blackgram variety CO₂, the plant height was significantly increased (37.28 cm) by foliar application of urea and phyllosphere spraying of Methylotrophs extorquees PPFMs-Vm-11, which was superior to uninoculated control (30.28 cm plant^-1) (Madhaiyan, 2003).

Madhaiyan, 2003 reported that inoculation of Methylobacterium and methanol spray significantly increased the plant height and dry matter production of cotton than uninoculated control. The inoculation of M. extorquens PPFM-GO-71 by phyllosphere spray with methonal had significantly increased the plant height (84.3 cm plant^-1) and dry matter production (15.12 g hill^-1) than all the other treatments.

Sundaram et al. (2002) stated that PPFMs influenced seed germination and seedling growth by producing plant growth regulators zeatin and related cytokinin. Due to the production of plant hormone and vitamins by pink pigmented facultative methylotrophic bacteria colonizing on the phyllosphere regions of maize, PPFM enhanced the seedling vigour in maize. Inoculation of Methylobacterium sp. PPFMs-Ah recorded maximum plant growth of groundnut at harvest (57.0 cm) which was followed by Methylobacterium sp. PPFMs-Os (52.7 cm) and M. extorquens AMI (51.1 cm) (Reddy, 2002).

Effect of ppfm spray on yield and yield attributes: Radhika et al. (2008a) revealed that the highest maize cob yield (7785 kg ha^-1) was obtained from foliar application of PPFMs at 5 L ha^-1. The highest cob yield was due to significant increase in length, diameter and weight of cob and corn. Exogenous methanol of plant stimulated the growth of methylobacterium sp, which provided plants with cytokinins and auxin which in turn enhanced plant development and ultimately increased the yield (Lidstrom and Chistoserdova, 2002). This might be due to supply of cytokinin by PPFMs. Cytokinin helps in promotion of cell division, delaying of senescence, counteracting apical bud dominance, translocation of assimilates and thereby improve the yield potential of plants (Madhaiyan et al., 2005).

Madhaiyan, 2003 observed that application of PPFMs as foliar spray significantly increased the boll numbers, boll weight and kapas yield of cotton. Foliar application of urea and phyllosphere spraying of M. extorquens PPFMs-Vm-11 significantly increased the seed weight of black gram (7.52 g plant^-1) over uninoculated control (5.12 g plant^-1) (Madhaiyan, 2003).

The highest boll and seed weight of cotton was obtained with phyllosphere spraying M. extorquens AMI with methanol spray followed by seed imbibitions of M. extorquens, PPFMS-GO-71 reported by (Madhaiyan, 2003). Reddy (2002) revealed that the inoculation of PPFMs isolate Methylobacterium sp. PPFMs-Ah recorded higher number of nodules at 60 (30.33), 90 (52.32) and 120 DAS (61.22) than other treatments in groundnut. Reddy (2002) revealed that Methylobacterium sp. PPFMs-Ah recorded maximum pod weight of groundnut (10.60 g) by seed imbibition method, where as Methylobacterium sp. PPFMs-Os recorded 8.98 g and M. extorquenes AMI 8.86 g.

Effect of PPFM spray on quality of crops: Radhika et al. (2008b) concluded that application of pink pigmented facultative methylotrophs at 5 L ha^-1 increased the productivity as well as quality parameters of baby corn. Madhaiyan et al. (2005) revealed that inoculation of PPFM resulted in significant increase in sugar cane plant growth, cane yield and sugar quality.