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Research Article

Legume Research, volume 43 issue 3 (june 2020) : 401-407

Source-sink optimization and morpho-physiological response of soybean [Glycine max] to detopping and mepiquat chloride application

Manpreet Jaidka2, J.S. Deol1, Ramanjit Kaur3,*, R. Sikka1
1Punjab Agricultural University, Ludhiana-141 004, Punjab, India.
2Krishi Vigyan Kendra Langroya-144 516, SBS Nagar, Punjab, India.
3ICAR-Indian Agricultural Research Institute, New Delhi-110 012, India.

  • Submitted01-12-2017|

  • Accepted19-05-2018|

  • First Online 20-08-2018|

  • doi 10.18805/LR-3971

Cite article:- Jaidka Manpreet, Deol J.S., Kaur Ramanjit, Sikka R. (2018). Source-sink optimization and morpho-physiological response of soybean [Glycine max] to detopping and mepiquat chloride application . Legume Research. 43(3): 401-407. doi: 10.18805/LR-3971.

ABSTRACT

Effect of detopping and mepiquat chloride on morphological, physiological and yield attributes of soybean cultivar ‘SL 544’ was studied. A two year investigation was conducted at Punjab Agricultural University, Ludhiana, during kharif seasons of 2014 and 2015. The experiment was laid-out in randomized complete block design (RCBD) with eight treatments viz. control, detopping (removal of 4-5 cm apical portion of main stem) at 50-55 days after sowing (DAS), mepiquat chloride @ 200 ppm (50-55 DAS), mepiquat chloride @ 200 ppm (50-55 + 65-70 DAS), mepiquat chloride 250 ppm (50-55 DAS), mepiquat chloride @ 250 ppm (50-55 + 65-70 DAS), mepiquat chloride @ 300 ppm (50-55 DAS) and mepiquat chloride @ 300 ppm (50-55 + 65-70 DAS) with four replications. Detopping had a non-significant effect on leaf area index, SPAD value, PAR interception, abscission of reproductive parts, seeds per pod, 100-seed weight, pod length and stover yield of soybean. It significantly decreased plant height, increased total dry matter accumulation/plant, number of flowers and pods/plant, pod setting percentage and seed yield over control during 2014 and 2015. At crop harvest, detopping developed optimized source-sink relationship by means of distribution of total dry matter between stem, foliage and pods by 20.4, 14.9 and 64.6 % during 2014 while 22.6, 20.1 and 57.4 % during 2015, respectively. Mepiquat chloride posed a non-significant effect on plant height, PAR interception, number of flowers/plant, number of seeds/pod, pod length and stover yield of soybean but it significantly decreased leaf area index, abscission of reproductive parts while increased the dry matter accumulation/plant, number of pods/plant, 100-seed weight and seed yield relative to control. At harvest, two foliar applications of mepiquat chloride @ 250 ppm resulted in optimized source-sink relationship by the distribution of total dry matter among stem, foliage and pods by 20.6, 10.9 and 68.5 % during 2014 while 19.5, 7.6 and 72.9 % during 2015, respectively. Occurrence of more rainfall during 2015 as compared to 2014 caused mepiquat chloride to hike seed yield as compared to detopping which is clearly witnessed by increase in pod dry weight per plant during 2015 than 2014. Conclusively, both detopping and mepiquat chloride resulted in enhancement in source-sink relationship and seed yield of soybean.     

INTRODUCTION

Soybean [Glycine max (L.) Merrill] belonging to family fabaceae, has been globally recognized as potential source of protein, edible oil and functional food (Kaur et al., 2006). Instability in the better realization of yield under irrigated conditions becomes one of the major reasons behind reluctance of farmers to adopt soybean. Ecologically, evolution of pulse crops including soybean occurred in response to their cultivation preferably under dryland areas. Concurrent drought events in dryland areas curb vegetative and reproductive growth in pulse crops but indeterminate growth habit acts as compensatory mechanism to the yield loss under moisture deficit. On renaissance of favourable moisture regime, regrowth of vegetative parts along with reproductive parts is prime source of photosynthates to the developing fruiting bodies. While in irrigated areas, owing to indeterminate growth, disturbance in source-sink relationship in terms of assimilate supply leads to abscission of flowers and young pods, which otherwise would develop into mature pods leading to enhanced productivity. So managing the balance between vegetative and reproductive growth is needed in order to effectively remove physiological flaws in soybean. Growth regulators are known to enhance the source-sink relationship and stimulate the translocation of photo-assimilates for effective pod formation, seed development and ultimately high productivity of soybean (Kaur et al., 2015). Growth retardants, like mepiquat chloride (MC) and cycocel (CCC) reduce internode length, thereby, reducing plant height and stimulating the translocation of photosynthates towards sink (Prakash and Prasad, 2000). Exogenous application of plant growth regulators has been exploited to cause favourable shifts in endogenous hormonal levels by increasing the retained flowers, fruit set, 100-seed weight and yield (Arora et al., 2005).  Sandhu et al., (2015) reported significant effect of mepiquat chloride on dry matter/plant, pod dry weight, number of pods/plant and seed yield of summer mungbean. Detopping (removing apical bud) overcomes the apical dominance, increases the number of lateral branches, pod setting and better source-sink relationship along with synchronous plant growth. Singh and Devi (2006) concluded that nipping of Pisum sativum at 30 DAS significantly increased number of branches/plant, pods/plant and seed yield. So keeping in view the importance of plant growth regulators, the present investigation was undertaken with the objectives to study the effect of detopping and mepiquat chloride on growth, dry matter distribution, yield and yield attributes of soybean.

MATERIALS AND METHODS

The investigation was carried out in Punjab Agricultural University, Ludhiana, during kharif season of 2014 and 2015. Ludhiana is located in Trans-Gangatic agro-climatic zone and represents the Indo-Gangatic alluvial plains. It is located in 30°56’ N latitude and 75°52’ E longitude at an altitude of 247 m above the mean sea level. Ludhiana is characterized by sub-tropical semi-arid type of climate with hot summer and cold winters. The soil of the experimental site was sandy loam with neutral soil reaction and electrical conductivity, low in organic carbon, available nitrogen and potassium while high in available phosphorus. The experiment was laid-out in randomized complete block design (RCBD) having eight treatments viz. control, detopping (removal of 4-5 cm apical portion of main stem) at 50-55 DAS, mepiquat chloride @ 200 ppm (50-55 DAS), mepiquat chloride @ 200 ppm (50-55 + 65-70 DAS), mepiquat chloride 250 ppm (50-55 DAS), mepiquat chloride @ 250 ppm (50-55 + 65-70 DAS), mepiquat chloride @ 300 ppm (50-55 DAS) and mepiquat chloride @ 300 ppm (50-55 + 65-70 DAS) with four replications. Sowing of  soybean cultivar ‘SL 744’ was done on 13-06-2014 during first year and on 08-06-2015 during second year through pora method using seed rate of 75 Kg/ha keeping row to row and plant to plant spacing of 45 cm and 5 cm, respectively. Gross and net plot size during both the years was 45 m2. The fertilizers were applied at the time of sowing @ 32 kg N/ha and 80 Kg P2O5/ha through urea and SSP, respectively. Stomp 30 EC (Pendimethalin) was applied @ 1500 ml ha-1 as a pre-emergence herbicide. Total 4 irrigations were applied as given below:



Crop was harvested and threshed with the schedule as given below:

     
 
Meteorological data
 
The meteorological data (Fig 1) recorded at meteorological observatory of the Punjab Agricultural University, Ludhiana describes that total rainfall received during the crop growing seasons of 2014 and 2015 was 447.7 mm and 541.7 mm, respectively, exhibiting a difference of 15.66 mm. During 2015, month of July, August and October received 102, 76.4 and 3.5 mm higher rainfall than July, August and October, 2014, respectively.
 

Fig 1: Monthly meteorological data during 2014 and 2015.


 
Growth and yield parameters
 
The periodic plant height was measured from the base of main stem to the base of top most fully opened leaf. The periodic leaf area index was recorded with the sun scan canopy analyzer between 12:00 noon to 12:30 pm. Specific leaf weight was determined as follow:
 
                                              

LW – Leaf Weight (g).
LA – Leaf area (cm2).
 
       
SPAD value was estimated by using hand held Minolta SPAD-502 chlorophyll meter. Line quantum sensor which has quantum response through wavelength range of 400-700 nm for PPFD (photosynthetic photon flux density) was used for PAR measurement. Photosynthetically active radiation interception (PARI) was calculated as per the following formula:
         
                                                                                               
       
For determining the plant dry matter accumulation, five randomly selected plants from each plot were uprooted. Sample plants were separated into stem, foliage and fruiting bodies. The plant parts were first dried in the sun followed by oven drying at 60°C till constant weight. Weight of oven dried plant parts was used to be expressed as dry matter accumulation (g/plant) as well as dry matter partitioning (g).
 
Statistical analysis
 
The various data were subjected to statistical analysis by general linear model (GLM) procedure (SAS Software 9.2, SAS Institute Ltd., U.S.A.) by applying Duncan Multiple Range Test (DMRT) and Least Significant Difference (LSD) method.

RESULTS AND DISCUSSION

Growth parameters
 
Investigation of data revealed a significant decrease in plant height (Table 1) with detopping but non-significant effect of mepiquat chloride application, as compared to control. Results regarding effect of detopping on plant height are in line with Sandhu et al., (2015) who also reported a significant decrease in plant height of summer mungbean at 60 DAS and at harvest. Decrease in plant height in detopping can be attributed to removal of stem apex which acts as a potential source of auxins and cessation of apical dominance. Detopping had a non-significant effect on leaf area index as compared to control. Rather an increase in leaf area index was reported in detopping treatment which can be attributed to stimulation of lateral buds and foliage. In 2015, more occurrence of rainfall led to enhanced leaf area in detopping relative to 2014. Foliar application of mepiquat chloride led to significant decrease in leaf area index in comparison to control at 110 DAS during 2014 and 2015. Maximum decrease in leaf area index was resulted by foliar application of mepiquat chloride @ 300 ppm at two growth stages, which was found 26.4 and 27.2% lesser than control in 2014 and 2015, respectively. Although more rainfall occurred during 2015 yet mepiquat chloride application resulted in decrease in leaf area index relative to contrast. Results regarding effect of mepiquat chloride on leaf area index are in accordance with Shyam (2016). Decreased leaf area index can be attributed to decreased cell expansion as a result of low level of gibberellins. During 2014 and 2015, mepiquat chloride application significantly enhanced the SPAD value over control and detopping treatment. However, SPAD value of control and detopping was statistically at par with each other. Sandhu et al., (2015) also reported a non-significant effect of detopping on chlorophyll content of summer mungbean. Shyam (2016) also observed significant increase in chlorophyll content index (CCI) with foliar application of mepiquat chloride @ 250ppm at 35 DAS in greengram. Enhancement in SPAD value by mepiquat chloride applications can be attributed to enhanced activity of nitrate reductase which further led to increased assimilation of nitrogen for synthesis of chlorophyll. Furthermore, a non-significant effect of detopping and mepiquat chloride application on PAR interception (Table 2) was recorded as compared to control at all growth stages during 2014 and 2015. Results of mepiquat chloride were in accordance with Ananthi and Vanangamudi (2013). Although there was decrease in leaf area index due to application of mepiquat chloride even then PAR interception was statistically at par with control. It could be attributed to increase in SPAD value, leaf thickness and specific leaf weight by mepiquat chloride which further led to decreased diffusion of incident radiation through crop canopy and decreased amount of radiation reaching at ground level. Thus efficient utilization of incident radiation by thickened leaves and high specific leaf weight led to non-significant variation in PAR interception over control even under low leaf area index. Furthermore, detopping as well as mepiquat chloride application resulted in significantly higher specific leaf weight (SLW) at 80 and 110 DAS as compared to control during both the years. Increase in SLW with detopping can be due to cessation of apical dominance which leads to promotion of axillary bud growth, more number of leaves and enhanced foliage weight.
 

Table 1: Effect of detopping and mepiquat chloride application on growth parameters of soybean.


 

Table 2: Effect of detopping and mepiquat chloride on growth parameters of soybean.


 
Dry matter accumulation and partitioning
 
During both the years, at all growth stages, detopping and mepiquat chloride applications significantly increased the dry matter accumulation and distribution among different plant parts by efficient translocation towards foliage and reproductive parts as compared to control (Table 3, 4 & 5). For instance, at crop harvest, detopping resulted in 45.2 and 43.0% higher dry matter accumulation per plant than control, during 2014 and 2015, respectively. At the same time, foliar application of mepiquat chloride @ 250 ppm at two growth stages resulted in 25.7 and 19.6% increase in dry matter accumulation per plant as compared to control during 2014 and 2015, respectively. Detopping as well as foliar application of mepiquat chloride @ 200 and 250 ppm at two growth stages significantly increased the dry weight of pods per plant which could be attributed to decreased leaf area index, vegetative growth, more efficient translocation of assimilates towards reproductive organs. Extent of optimization between source-sink can be judged from the percent distribution of dry matter among different plant parts and final seed yield. At crop harvest, detopping developed optimized source-sink relationship by means of distribution of total dry matter between stem, foliage and pods by 20.4, 14.9 and 64.6% during 2014 while 22.6, 20.1 and 57.4% during 2015, respectively. Two foliar applications of mepiquat chloride @ 250 ppm resulted in optimized source-sink relationship by the distribution of total dry matter among stem, foliage and pods by 20.6, 10.9 and 68.5% during 2014 while 19.5, 7.6 and 72.9% during 2015, respectively. Occurrence of higher rainfall during 2015 led to more stem and foliage dry weight plant in detopping treatment as compared to 2014. This effect of rainfall is revealed at crop harvest by higher translocation of total dry matter towards stem and foliage than pods during 2015 than 2014. Increase in dry matter accumulation with detopping can be due to cessation of apical dominance, stimulation of lateral dormant buds. Increase in dry matter accumulation by mepiquat chloride could be attributed to increased RuBP activity, chlorophyll content, leaf thickness, specific leaf weight. Results of mepiquat chloride were in consonance with Shyam (2016) and Sharma et al., (2013).
 

Table 3: Dry matter accumulation and partitioning (g) in soybean at 80 DAS under the influence of detopping and mepiquat chloride application.


 

Table 4: Dry matter accumulation and partitioning (g) in soybean at 110 DAS as affected by detopping and mepiquat chloride application


 

Table 5: Dry matter accumulation and partitioning (g) in soybean at harvest under the influence of detopping and mepiquat chloride application.


 
Yield and yield attributes
 
Detopping resulted in significantly higher number of flowers/plant (Table 6) as compared to control and mepiquat chloride application during both the crop seasons. A significant decrease in abscission of reproductive parts was resulted by all the mepiquat chloride application treatments as compared to control during 2014 and 2015. During both the years, detopping and mepiquat chloride application, registered significantly higher number of pods/plant as compared to control. Results of detopping on pods/plant were in accordance with Singh and Devi (2006) while that of mepiquat chloride were in conformity with Kumar et al., (2006), Sandhu et al., (2015) and Godara et al., (2017). Detopping and mepiquat chloride applications significantly enhanced pod setting percentage during both the years. All the treatments were statistically at par with respect to number of seeds/pod and pod length during 2014 and 2015. Foliar applications of mepiquat chloride significantly increased the 100-seed weight than control and detopping (Table 7). Results of 100-seed weight from mepiquat chloride application were in line with Reddy et al., (2009) and that with detopping were in consonance with Sandhu et al., (2015). Detopping as well as foliar applications of mepiquat chloride resulted in significantly higher seed yield than contrast. Results of detopping were in accordance with Singh and Devi (2006) and that of mepiquat chloride were in conformity with Sandhu et al., (2015), Kaur et al., (2015) and Godara et al., (2017). A non-significant effect of detopping and mepiquat chloride applications was also observed in terms of stover yield of soybean during both the years. Effects of detopping on seed yield and yield attributes could be attributed to cessation of apical dominance, stimulation of lateral buds. Effect of mepiquat chloride could be attributed to decreased leaf area index, increase in the SPAD value, specific leaf weight. Thus, decreased vegetative growth and hiked photosynthetic rate of the crop resulted in better availability of assimilates and more efficient translocation.
 

Table 6: Effect of detopping and mepiquat chloride on yield attributes of soybean.


 

Table 7: Effect of detopping and mepiquat chloride on yield attributes and yield of soybean.

CONCLUSION

Cessation of apical dominance by detopping put favourable effect on plant growth and development which was clearly reflected in terms of decreased plant height, optimized source-sink relationship, enhanced yield attributes and seed yield. Mepiquat chloride posed a favourably impact on soybean in terms of decreased leaf area index, enhanced SPAD value, high specific leaf weight, dry matter accumulation, optimized source-sink relationship resulting into better seed yield and yield attributes.

FUTURE THRUST

There is need to study the effect of mepiquat chloride on soybean through seed priming. Mepiquat chloride is growth retardant which needs to be studied along with the use of defoliants which stimulate the crop senescence to decrease in crop duration bringing flexibility in soybean crop to fit in cropping system.

ACKNOWLEDGEMENT

The authors are thankful to the Ministry of Science and Technology, Department of Science and Technology (DST), Govt. of India for providing financial assistance in the form of JRF (INSPIRE Fellowship) during the course of study. Special thanks to Head, Department of Agronomy, Punjab Agricultural University, Ludhiana for providing required research facilities.

REFERENCES


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