Physiological Growth and Yield of Two Groundnut Varieties as Influenced by Light and Boron

Light and boron play a significant role in the physiological growth and yield of crops such as groundnut. Even so, there has been little information on the application of boron in groundnut, while no information is available in Bangladesh regarding the imposition of light in groundnut. Therefore, two field experiments were conducted in order to evaluate the physiological growth and seed yield of groundnut. Treatments included two levels of light, viz., L0 = normal day length (≈12-h light) and L = normal day length + 6-h extended light at night (≈18-h light); three levels of boron, viz., 0-kg B ha (B0), 1-kg B ha(B1) and 2-kg B ha (B2), and two groundnut varieties, viz., V1 = ‘Dhaka-1’ and V2 = ‘BARI Chinabadam-8’. The results obtained from the experiment revealed that the highest LAI, LAR, LMR and RWR were recorded in L, B2 and V2 variants, while NAR was the highest in L0 and B0. Moreover, it was noted an inconsistent result for RGR found for boron application. Based on the results, it could be concluded that boron is one of the factors responsible for higher yield of groundnut; nevertheless, under the extended light, it is not possible to get the highest yield.


Introduction
Groundnut (Arachis hypogaea L.) is one of the major and crucial oilseed crop, as well as protein rich crop, in the world (Onemli, 2012), while boron is an important micronutrient that is essential for healthy growth and development of groundnut (Gascho and Davis, 1995).This micronutrient played a vital role in the different physiological functions and process of plants (Mengel and Kirkby, 1982).As a result, application of boron facilitated the vegetative growth and reproductive development of groundnut.A slight quantity of boron is required by plants (El-Wahab and Mohamed, 2008) but the application of this element in crops was limited in farmer's field (Nasreen et al., 2015).As a result, this nutrient was rapidly becoming deficient in soils (Tahir et al., 2009) and the boron deficiency problem had been identified in Bangladesh (Ahmed and Hossain, 1997).Therefore, more research was needed to find out the effect of the application of boron in the soil of Bangladesh.So, it was a principal issue to investigate the response of boron on physiological growth as well as the yield of groundnut.
Light also solely played a crucial role in the physiological process and reproductive development of legume crops, like groundnut.The three most important characteristics of light (quantity, quality and direction) were perceived by different photosensory systems of the plant that collectively regulate the plant development (Hangarter, 1997).Imposition of light positively influenced on the vegetative growth, but reduced the yield of groundnut (Nigam et al., 1998;Bagnall and King, 1991;Quamruzzaman et al., 2016a).It was noted with specific evidence that excessive light stress can lead to antioxidant enzymes activation as well as ROS (Reactive Oxygen Species) accumulation in the plant (Mittler, 2002).
Never the less, no light experiment was conducted in Bangladesh to evaluate the effect of artificial light on physiological growth as well as yield of groundnut.As for why the present study was carried out, in order to determine the exact duration of light and the optimum boron levels for an improved physiological growth and yield of groundnut.

Experimental site
Two trial experiments were conducted at the Central Experimental Farm, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh.The first trial duration was between 17th March to 10th July 2014 and the second trial HI = (Economic yield)/(Biological yield) groundnut varieties viz., 'Dhaka-1' (V1) and 'BARI Chinabadam-8' (V2).The artificial lightening was done by fluorescence bulb to ensure the extended day length.This lightening was started after seedling emergence (one month after seed sowing) from 18:00 h 24:00 h at 30-50,000 lux.

NAR = RGR/LAR
Where Economic yield (pod yield) biological yield were measured as t ha-1

Statistical analysis
Data collected in two cropping seasons (2014 and 2015) were mean together on account of the non-significant interaction.Then one-way ANOVA (analysis of variance) of means data of two trial experiments was analyzed by using IBM SPSS (Version 20.0) and mean separation was done at P ≤ 0.05 by using Tukey's test (Tukey, 1977).

Leaf area index (LAI)
Leaf area index varied significantly by different light treatment (Table 3).Results revealed that LAI increased in L compared to L0.Data showed that the LAI ranged from 6.13 (L0) to 9.41 (Ll).Higher LAI is one of the most important criteria that help to produce higher metabolites of plants.Increased LAI has been found to increase the capability of the plants to intercept more light (Prieto et al., duration was between 15th March until 08th July 2015, respectively.Both experiments were conducted in the same field and soil samples of the experimental field werew analyzed in the laboratory of Soil Resource Development Institute (SRDI) before the experiment set up (Table 1).The experimental field was located at the Madhupur Tract, which is the name of the Agro-ecological Zone "AEZ-28" (BBS 2014-15).The average air temperature, relative humidity and rainfall of the two cropping seasons (2014 & 2015 cropping season) of the experimental site were also recorded (Table 2).

Experimental design and treatment details
Both of the experiments were laid out in a 2×3×2 factorial design with three replications.Spacing was maintained 30 cm x 15 cm and seed rate was of 110 kg seeds ha -1 (with shell).The first factor was duration of light, e.g., normal day length + 6 -h extended light at night (≈18-h light) (L) and normal day length (≈12-h light) (L0); the second factor was represented by the three levels of boron (source: Boric Acid) viz., 0 kg B ha -1 (B0), 1 kg B ha -1 (B1) and 2 kg B ha -1 (B2); the third factor was represented by two 281  ).The highest LAI was found due to the supplementation of L that may have the ability to produce higher metabolites in groundnut.
Leaf area index was increased significantly up to 90 DAP and then decreased at harvest in boron application area (Table 3).Due to different doses of boron, the variation of LAI was observed, and it ranged from 0.64 (B0) to 10.74 (B2).Probably, application of boron increased the vegetative growth of plant up to the certain period and then started to work on the reproductive unit.It had evidence that the application of boron increased the vegetative growth and yield of groundnut (Singaravel et al., 2006;Kabir et al., 2013), which is in consequence of the increased LAI and the resultant increased light interception (Prieto et al., 2007).The higher LAI was found due to the application of B2 that may have the ability to produce higher metabolites in groundnut.Geethanjali et al. (2015) stated that application of boron increased the leaf area and LAI of groundnut.

Leaf area ratio (LAR)
Table 3 showed that the highest leaf area ratio was recorded from L0 at 60 DAP (276.97 cm 2 g -1 ) and 90 DAP (139.98 cm 2 g -1 ), but at harvest the highest LAR was found from L (82.29 2 g -1 ).Variation in LAR due to the imposition of light produced the highest leaf area and plant dry weight compared with control at 60 DAP and 90 DAP.It was observed that leaf shedding started after 90 DAP and got the maximum at harvest in L treatment area.Probably this leaf shedding was responsible for the highest LAR in light treatment plots.Therefore, it can be concluded that the supplementation of light facilitated vegetative growth (Ketring, 1979), as given by the results with the highest leaf area and plant dry weight as well as LAR.
Due to the application of boron, the highest LAR was recorded from boron at 1-kg ha -1 at all sampling dates and the lowest were from control treatment (Table 3).Data also represented that LAR is showing an increasing trend up to 60 DAP and then started to gradual decrease up to the harvest, because boron was responsible for the vegetative growth of groundnut plant (Kabir, 2013).Harris and Brolmann (1996) also reported that plant dry weight increased with the application of boron in groundnut.The addition of B was also responsible for the leaf expansion of groundnut (Dell and Huang, 1997).Thus, a higher value of LAR was found in boron application area.

Leaf mass ratio (LMR)
For the supplementation of additional light, the leaf mass ratio showed variation result at all sampling dates (Table 4).The highest LMR was recorded as 0.875 g g -1 and the lowest as 0.280 g g -1 .Though, the light was responsible for the highest plant dry weight (Ketring, 1979) and leaf dry weight (Acock et al., 1996), it did not produce the highest LMR at 60 DAP.Data showed that light treatment produced maximum LMR at 90 DAP and at harvest.Probably, at 60 DAP plants did not get enough light to produce high LMR, where as in the present study light was imposed just after 30 DAP.
Boron at 2 kg ha -1 produced significantly (p≤0.001) higher LMR at all growth stage (Table 4) where the lowest LMR was found from control treatment.The highest number of leaf, plant dry weight and leaf dry weight, as well as LMR, were recorded from boron at 2-kg ha -1 .It was reported that vegetative growth, as well as plant dry weight of groundnut, were the highest for application of boron (Kabir et al., 2013).So, the fact that LMR was significantly higher for the application of boron.Prieto et al. (2007) stated that increased LMR gave a higher capability of the plants to intercept more light.The highest LMR was found due to the application of B2 that may have the highest capability to produce more elevated metabolites in groundnut.

Root weight ratio (RWR)
Root weight ratio differed significantly due to the imposition of light (Table 4).The highest RWR was found at harvest in L (0.080 g g -1 ) and the lowest at 90 DAP in L0 (0.045 g g -1 ).The RWR showed a decreasing trend up to 90 DAP, but at harvest it suddenly increased for both treatments.This might be due to leaf shedding, since leaf shedding started after 90 DAP and it was maximum at harvest.Even so, root dry weight was almost the same as 90 DAP data.The longer roots, as well as the highest root weight, might be responsible for the highest nutrient uptake from soil.And the highest RWR could be responsible for the highest vegetative growth of plants, as concluded by Nigam et al., 1994, who noted that light facilitated the highest vegetative growth in peanut plants.
Root weight ratio was significant in boron application area (Table 4).The highest significant RWR was recorded from 2-kg boron ha -1 at all sampling dates (0.198 g g -1 , 0.089 g g -1 , 0.063 g g -1 and 0.083 g g -1 , respectively).Harris and Brolman (1966) stated that due to the application of boron root weight increased and Kabir et al. (2013) found that groundnut plants' dry weight was highest for boron fertilization.Therefore, RWR in the present study might also be the highest for the application of boron.

Relative growth rate (RGR)
The relative growth rate was the highest at 60 DAP in L, but the rest of sampling dates it was highest in L0 (5).Due to the light treatment, the significantly decline trend of RGR towards physiological maturity could be a result of leaf shedding.There is also evidence that the upper leaves when in dense condition caused shedding effect on the lower leaves reducing the photosynthetic capability and imposing them to more pest attack (Banik et al., 2009).
Boron produced inconsistent, but significant, relative growth rate at all growth stage (Table 5).The highest plant dry weight was found from boron at 2-kg ha -1 , but in the case of RGR it was not consistent among the boron treatments, because initial plants dry weight was not similar for different treatments.Cikili et al. (2015) found that application of boron increased plant growth and biomass production up to a certain growth stage, but when more boron doses were applied soil toxicity occurred, that reduced plant growth and biomass production.In the current study, it was not observed boron toxicity effect.Since plant dry weight was significantly higher for the addition of boron, RGR also might be significant for boron application.RGR was not showing the similar trend as others parameter studied hereby, as why further study is continuing to find out the inconsistent result of RGR.

Net assimilation rate (NAR)
Net assimilation rate was found with a significantly increasing trend up to 90 DAP due to light treatment (Table 5).The highest NAR was recorded from light treatment compared with control treatment, at 60 DAP and 90 DAP, but at harvest, it showed a decreasing trend.The decreased trends of net assimilation rate in groundnut may be due to mutual shading at physiological maturity stage of plants, which affects the lower leaves and thus reduce the photosynthetic capability of the older leaves (Banik et al., 2009).This mutual shading is also responsible for pest attack that reduced leaf area of groundnut (Banik et al., 2009).Data revealed that light helped to produce the highest vegetative unit in a plant that was most relevant to higher NAR.Quamruzzaman et al. (2016a) reported that light helped to produce the highest vegetative growth, thus the current data consisted with their finding.
Although at 30 DAP the highest NAR was recorded from 2-kg ha -1 boron application area, at the rest of sampling dates control treatment produced the highest NAR (Table 5).It had evidence that shading reduced the NAR, but had  no effect on yield (Watson and Wilson, 1956) and the highest number of leaves was observed fr ha -1 .The highest leaf area was found from B2 that might be created excessive shading and maximum numbers of new leaves could have the highest shading effect on older leaves.Thus, NAR decreased due to the application of boron, but B probably helped to increase the uptake of nutrients, that ultimately resulted in the highest yield of groundnut (Naiknware et al trend like other parameters investigated, as why further study is continuing to find out th NAR.

Seed yield (t ha
Light treatment was responsible for the significant (p≤0.001)reduction of seed yield.Data showed that the highest significant seed yield was recorded from control treatment (L0 (L=1.23 t ha -1 responsible only for vegetative growth and dry matter produced.Probably this limited time light duration was not responsible for better seed yield.Quamruzzaman (2016b) also stated that the low yield of groundnut was found due to the extended light.
Boron was highly responsible for better yield of groundnut and a significant positive seed yield was recorded from application of boron (Fig. 1).The highest groundnut seed yield (1.53 t ha and the lowest from control.Because boron was highly responsible for the reproductive development of groundnut (Ansari et al., 2013) and highest yield was recorded in boron treatment area.The finding supported the present finding.

Harvest index (HI)
Harvest index treatment.The additional artificial light was sensible for better vegetative growth.As for why supplementation of produced the lowest HI (31.75) compared to control (37.457) (Fig. 2).The highest economic yield was found in L highest biological yield in L. Probably photoperiod limited the reproductive development of groundnut, but increased 1979).Quamruzzaman findings.
Boron treatment also caused a significant increasing result of HI.The highest HI (38.323) was significantly no effect on yield (Watson and Wilson, 1956) and the highest number of leaves was observed fr .The highest leaf area was found from B2 that might be created excessive shading and maximum numbers of new leaves could have the highest shading effect on older leaves.Thus, NAR decreased due to the application of boron, but bly helped to increase the uptake of nutrients, that ultimately resulted in the highest yield of groundnut et al., 2015).NAR was not showing the similar trend like other parameters investigated, as why further study is continuing to find out th Seed yield (t ha -1 ) Light treatment was responsible for the significant ≤0.001) reduction of seed yield.Data showed that the highest significant seed yield was recorded from control 0=1.37 t ha -1 ) compared than 1 ) (Fig. 1).So, the 6 responsible only for vegetative growth and dry matter produced.Probably this limited time light duration was not responsible for better seed yield.Quamruzzaman ) also stated that the low yield of groundnut was found due to the extended light.
Boron was highly responsible for better yield of groundnut and a significant positive seed yield was recorded from application of boron (Fig. 1).The highest groundnut yield (1.53 t ha -1 ) was found from boron at 2 and the lowest from control.Because boron was highly responsible for the reproductive development of groundnut ., 2013) and highest yield was recorded in boron treatment area.The finding supported the present finding.Quamruzzaman no effect on yield (Watson and Wilson, 1956) and the highest number of leaves was observed fr .The highest leaf area was found from B2 that might be created excessive shading and maximum numbers of new leaves could have the highest shading effect on older leaves.Thus, NAR decreased due to the application of boron, but bly helped to increase the uptake of nutrients, that ultimately resulted in the highest yield of groundnut ., 2015).NAR was not showing the similar trend like other parameters investigated, as why further study is continuing to find out the inconsistent result of Light treatment was responsible for the significant ≤0.001) reduction of seed yield.Data showed that the highest significant seed yield was recorded from control ) compared than ) (Fig. 1).So, the 6-hr extended light might be responsible only for vegetative growth and dry matter produced.Probably this limited time light duration was not responsible for better seed yield.Quamruzzaman ) also stated that the low yield of groundnut was found due to the extended light.
Boron was highly responsible for better yield of groundnut and a significant positive seed yield was recorded from application of boron (Fig. 1).The highest groundnut ) was found from boron at 2 and the lowest from control.Because boron was highly responsible for the reproductive development of groundnut ., 2013) and highest yield was recorded in boron treatment area.The finding of Naiknaware supported the present finding.significantly influenced by the light treatment.The additional artificial light was sensible for better vegetative growth.As for why supplementation of lowest HI (31.75) compared to control (37.457)The highest economic yield was found in L highest biological yield in L. Probably photoperiod limited the reproductive development of the vegetative growth (Ketring, et al. (2016a) also reported similar Boron treatment also caused a significant increasing result of HI.The highest HI (38.323) was significantly no effect on yield (Watson and Wilson, 1956) and the highest number of leaves was observed from boron at 2 .The highest leaf area was found from B2 that might be created excessive shading and maximum numbers of new leaves could have the highest shading effect on older leaves.Thus, NAR decreased due to the application of boron, but bly helped to increase the uptake of nutrients, that ultimately resulted in the highest yield of groundnut ., 2015).NAR was not showing the similar trend like other parameters investigated, as why further e inconsistent result of Light treatment was responsible for the significant ≤0.001) reduction of seed yield.Data showed that the highest significant seed yield was recorded from control ) compared than additional light hr extended light might be responsible only for vegetative growth and dry matter produced.Probably this limited time light duration was not responsible for better seed yield.Quamruzzaman ) also stated that the low yield of groundnut was Boron was highly responsible for better yield of groundnut and a significant positive seed yield was recorded from application of boron (Fig. 1).The highest groundnut ) was found from boron at 2-kg ha and the lowest from control.Because boron was highly responsible for the reproductive development of groundnut .et al / Not Sci Biol, 2017, 9(2 no effect on yield (Watson and Wilson, 1956) and the om boron at 2-kg .The highest leaf area was found from B2 that might be created excessive shading and maximum numbers of new leaves could have the highest shading effect on older leaves.Thus, NAR decreased due to the application of boron, but bly helped to increase the uptake of nutrients, that ultimately resulted in the highest yield of groundnut ., 2015).NAR was not showing the similar trend like other parameters investigated, as why further e inconsistent result of Light treatment was responsible for the significant ≤0.001) reduction of seed yield.Data showed that the highest significant seed yield was recorded from control additional light hr extended light might be responsible only for vegetative growth and dry matter produced.Probably this limited time light duration was not responsible for better seed yield.Quamruzzaman et al.
) also stated that the low yield of groundnut was Boron was highly responsible for better yield of groundnut and a significant positive seed yield was recorded from application of boron (Fig. 1).The highest groundnut kg ha -1 and the lowest from control.Because boron was highly responsible for the reproductive development of groundnut ., 2013) and highest yield was recorded in boron .( 2015) also significantly influenced by the light treatment.The additional artificial light was sensible for better vegetative growth.As for why supplementation of light lowest HI (31.75) compared to control (37.457) and the extended photoperiod limited the reproductive development of the vegetative growth (Ketring, . (2016a) also reported similar Boron treatment also caused a significant increasing result of HI.The highest HI (38.323) was significantly observed treatments (Fig. 2), but control and 1 showed statistically similar results.The reason behind these findings might be that the number of pods and pod dry weight increased after the application of boron.Literature revealed can be influenced by boron, which significantly produced higher seed yield in groundnut (Jena Significance (P)   Not Sci Biol, 2017, 9(2):280 observed from boron at 2 treatments (Fig. 2), but control and 1 showed statistically similar results.The reason behind these findings might be that the number of pods and pod dry weight increased after the application of boron.Literature revealed that the reproductive development of groundnut can be influenced by boron, which significantly produced higher seed yield in groundnut (Jena

280-286
from boron at 2-kg ha treatments (Fig. 2), but control and 1 showed statistically similar results.The reason behind these findings might be that the number of pods and pod dry weight increased after the application of boron.Literature that the reproductive development of groundnut can be influenced by boron, which significantly produced higher seed yield in groundnut (Jena kg ha -1 compared to other treatments (Fig. 2), but control and 1-kg boron ha showed statistically similar results.The reason behind these findings might be that the number of pods and pod dry weight increased after the application of boron.Literature that the reproductive development of groundnut can be influenced by boron, which significantly produced higher seed yield in groundnut (Jena et al., 2009), whereas Therefore, light and born have a special importance on the vegetative growth and yield of groundnut, whereas both of the factors were highly responsible for the highest result of LAI, LAR, LMR and RWR.But in the case of RGR and NAR, an inconsistent result was found between the boron and light treatment.

Conclusions
In conclusion, boron application in groundnut field had a significantly positive impact that helped to produce higher physiological growth and yield of groundnut.But, due to the imposition of artificial light, it had both positive and negative effect on the physiological growth, whereas light reduced the seed yield.Thus, it is recommended to use boron, but not impose light, to get a better yield of groundnut.Boron helped to increase the physiological growth, pollen grain viability and stigma receptivity.That ultimately increased the number of pods, as well as pod yield.Supplementation of light increased the physiological growth and the number of flowers of groundnut.Therefore, light could increase the pod yield, but the duration of light was not enough for partitioning of dry matter towards the reproductive unit. 2007 Planting, B= Boron; L= light; V= Variety; P= Probability.Means were separated by B2= 2 Kg B ha -1 , L= normal day light + 6 ndex (HI) Harvest index was significantly influenced by the light treatment.The additional artificial light was sensible for better vegetative growth.As for why supplementation of lowest HI (31.75) compared to control (37.457)The highest economic yield was found in L highest biological yield in L. Probably photoperiod limited the reproductive development of but increased Quamruzzaman et al Boron treatment also caused a significant increasing result of HI.The highest HI (38.323) was significantly -Planting, B= Boron; L= light; V= Variety; P= Probability.Means were separated by , L= normal day light + 6 Planting, B= Boron; L= light; V= Variety; P= Probability.Means were separated by , L= normal day light + 6-h extended light at night ( Quamruzzaman M et al , 2013) and highest yield was recorded in boron of Naiknaware et al. (2015) also significantly influenced by the light treatment.The additional artificial light was sensible for better vegetative growth.As for why supplementation of lowest HI (31.75) compared to control (37.457)The highest economic yield was found in L0 and highest biological yield in L. Probably the extended photoperiod limited the reproductive development of the vegetative growth (Ketring, .(2016a) also reported similar Boron treatment also caused a significant increasing result of HI.The highest HI (38.323) was significantly Planting, B= Boron; L= light; V= Variety; P= Probability.Means were separated by h extended light at night (≈18-h light), L Fig. groundnut varieties B= Boron; L=Light; V= Variety; B L= normal day light + 6 day light ( separated by Tukey's test at P the means. Planting, B= Boron; L= light; V= Variety; P= Probability.Means were separated by Tukey's test at P = normal day light (≈12-h light), V 1.Effect of boron and light on seed yield (t ha groundnut varieties B= Boron; L=Light; V= Variety; B L= normal day light + 6day light (≈12-h light), V separated by Tukey's test at P the means.

2.
Effect of boron and light on harvest index of two groundnut varieties B= Boron; L=Light; V= Variety; B L= normal day light + 6day light (≈12-h light), V separated by Tukey's test at P the means.

,
of boron and light on seed yield (t ha = 0 kg B ha -1 , B1= 1 kg B ha h extended red light at night (≈18-h light), L = 'BARI Chinabadam ≤ 0.05.Vertical bars represent the standard error of Effect of boron and light on harvest index of two = 0 kg B ha -1 , B1= 1 kg B ha h extended red light at night (≈18-h light), L = 'BARI Chinabadam ≤ 0.05.Vertical bars represent the standard error of compared to other kg boron ha-1 showed statistically similar results.The reason behind these findings might be that the number of pods and pod dry weight increased after the application of boron.Literature that the reproductive development of groundnut can be influenced by boron, which significantly produced ., 2009), whereas of boron and light on seed yield (t ha -1 ) of two = 1 kg B ha -1 , B2= 2 kg B ha - h light), L0= normal BARI Chinabadam-8'.Means were ≤ 0.05.Vertical bars represent the standard error of Effect of boron and light on harvest index of two = 1 kg B ha -1 , B2= 2 kg B ha - h light), L0= normal BARI Chinabadam-8'.Means were ≤ 0.05.Vertical bars represent the standard error of compared to other 1 showed statistically similar results.The reason behind these findings might be that the number of pods and pod dry weight increased after the application of boron.Literature that the reproductive development of groundnut can be influenced by boron, which significantly produced ., 2009), whereas 1 05.Vertical bars represent the standard error of Effect of boron and light on harvest index of two -1 , = normal .Means were ≤ 0.05.Vertical bars represent the standard error of harvest index might be higher in boron application area.

Table 1 .
Composition of soil elements of the experimental field

Table 2 .
Monthly record of air temperature, relative humidity and rainfall of the experimental site during the period of March to July 2014 and 2015 (Mean of two years)

Table 4 .
Effect of light and boron on leaf mass ratio and root weight ratio of two groundnut varieties (Mean of two trails)

Table 5 .
Effect of light and boron on relative growth rate and net assimilation rate of two groundnut varieties (mean of two trails)