Impact of Lipo-Chito-Oligosaccharides (LCO) as Foliar Spray on Soybean ( Glycine max (L.) Merr.) Yield

The bacterium to plant signal, lipo-chito-oligosaccharides (LCOs) or Nod factors induce cell division and enhance plant growth. In the present study LCO has been applied through foliar spray at two different stages (V 2 ), 20-25 DAS and 40-45 DAS (V 4 ). All the yield contributing parameters were increased by the foliar spray of LCO in soybean and the maximum yield was recorded in LCO @ 300 ml ha -1 at 20-25 DAS. The yield increased by 10.6 per cent at kharif and 14.3 per cent during rabi 2012. Correlation studies indicated that seed yield per hectare exhibited stable positive association vis-a vis number of flowers, pods per plant, fertility coefficient, 100 grains weight and harvest index at different stages and seasons.

Lipo-chito-oligosacchrides (LCO) in general are capable of influencing plant growth and development.They are mainly secreted by Rhizobia spp and play a key role in the stimulation of nodules in legumes by activating signaling events of certain growth hormones, nutrients and important plant metabolism.LCO have both direct and indirect effects on various physiological processes.They provide minerals, biochemical substances and nutrients to the rhizosphere microbial population, carry the trace elements and growth regulators for stimulating plant growth.
LCO signal molecules are composed of three to five, 1-4 â linked acetylglucosamine residues with the N-acetyl group of terminal non-reducing sugar replaced by an acyl chain.However, various modifications of the basic structure are possible and these, at least in part, determine the host specificity of rhizobia (Schultze et al., 1992).
LCOs at very low concentration, initiate cell division at distinct sites in the root (Lerouge et al., 1990;Truchet et al., 1991).Possibly, these signals affect the regulation of the plant cell cycle and evidence is accumulating that LCOs play a general role as plant growth regulators (Schmidt et al., 1999).LCOs enhance photosynthesis and plant growth, and help to ensure that corn and soybean crops realize their performance potential.When applied on the foliar surface of corn or soybean, the LCO signal molecule provides an increase in photosynthesis and sugar production, which may enhance plant growth and improve overall crop performance.
Number of flowers produced, flowering duration and percentage of pod set are very important traits *Corresponding author email : suganagri@gmail.com in determining pod yield (Patel et al., 1988).Excessive flower production and long flowering duration appear to be a persisting phenomenon that would act as an insurance against climatic and biotic factors.Flower production is reduced by temperature below 20°C and above 40°C in soybean (Van Schaik and Probst, 1958).With these background, the present study has been taken up to elucidate the association of LCOs on yield and its parameters in soybean, over two different seasons.

Field trials
The field experiments were conducted during winter (January, 2012) and summer (April, 2012) in a randomized block design (RBD) with three replications at wet land farm of Tamil Nadu Agricultural University, Coimbatore.The plant density in the field was approximately 3,33,000 ha-1.Other agronomic practices were carried out as mentioned in crop production guide (CPG, 2005).Plants in the field received the foliar application of LCOs at a dosage of 150 ml ha-1, 300 ml ha-1 and 600 ml ha-1 at two different stages i.e.,V2 (20-25 DAS) and V4 (40-45 DAS).

Chemical composition of LCOs
RatchetTM is a LCO promoter compound, which is manufactured by EMD Crop Biosciences.It contains a minimum of 4 x 10-7 per cent lipo-chito oligosaccharide (LCO) in an aqueous carrier, which has been formulated for maize and soybean as foliar application.This product contains only components that are naturally occurring in soil and are biodegradable.Ratchet is compatible with most of the post emergence applied products such as agrochemicals to get an optimal result, it has to be applied between V2 (early vegetative stage -20 DAS) and V6 (late vegetative stage 50 DAS) of the crops.

Statistical analysis
The data collected on different characters from the field were statistically analysed as suggested by Gomez and Gomez (1992) and the least significant difference (LSD) test was used to detect critical differences at 5% level among treatment means.

Results and Discussion
Number of flowers and pods, fertility co-efficient and 100 grains weight were increased due to the application of LCO.In LCO treated plants, flower dropping was reduced consequently, and the number of pods per plant was found to be increased.Significant variation was observed among the seasons and the maximum number of flowers was found in summer, when compared to winter.LCO application showed significant effect on plant hormones such as GA3 and IAA, which are known to help in preventing flower abortion and increasing fruit set.The increase in yield over control was around 21 per cent in both the season and stages.Similar result was noticed by Atti et al. (2005) in soybean and Chen et al. (2007) in tomato.Application of LCO as foliar spray promoted pod setting.LCO application at V2 stage @ 300 ml ha-1 (T3) increased the pod number by 44.5 per cent during winter season and T4 (LCO @ 600 ml ha-1 during V4 stage) has increased pod number upto 56.9 per cent during summer (Table 1).
The optimum foliar application of LCO was found to be 150 to 600 ml ha-1.These dosages were   applied at two different stages of the crop for better result.The present studies indicated that the application of LCO at later stage (V4) had increased the yield of soybean crop upto 16 per cent (Table 2).LCO helps in maintaining the higher chlorophyll content of the leaf, inturn increasing the leaf area and duration.The enhancement in yield may be due to the increase in photosynthetic rate of the crop.
This results are also supported by the increase in root length, which might have helped the plants to uptake more nutrients, especially nitrogen resulting in the maintenance of greenness of the leaf, ultimately enhancing photosynthetic rate.LCO acts similar to that of cytokinin, which helps in translocation of photoassimilates from the source (leaf) to the sink (kernel/pod), by delaying the senescence of the leaves (stay green).The increase in yield due to the application of LCO was reported earlier by Atti et al. (2005) in soybean; Chen et al. (2007) in tomato and Khan (2003) in corn.Dry matter seems to be non significant even after the application of LCO (Table 3).
Pod number is a major yield determining factor in plants that belong to Fabaceae.Seasons had also showed significant influence on the number of pods per plant.Higher number of pods per plant was recorded in summer season in pigeon pea (Anil kumar et al., 2004) Sekhon, 2007).
Present findings are also in line with the earlier reports of Lalit Kumar et al. (2009) and Naeem et al. (2009).Enhancement in yield attributes ultimately might have culminated into pod yield as reported by Naeem et al. (2009).Correlation of yield and yield related parameters exhibited individual or combination effects over seasons.It was further observed that yield parameters such as number of flowers and pods, fertility co-efficient and 100 grains weight have showed positive and significant association with grain yield and harvest index in combination with seasons (Table 4).