Abstract: A field study was carried out with twelve Central Research Institute for Dryland Agriculture (CRIDA) castor genotypes along with the check 48-1 to assess the variability in physiological parameters like photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr) and Water Use Efficency (WUE) along with seed yield during kharif, 2013. The results revealed that two CRIDA genotypes viz., CRC-2 and CRC-9 were found to be superior over the check for seed yield and have lower gs and Tr thereby recorded improved WUE. The Pn values of selected castor genotypes were not varied significantly and the WUE is mainly influenced by Tr. Among the physiological parameters, gs and Tr showed significant negative correlation with seed yield revealing that the gs and Tr values need to be low to improve the seed yield of castor under rainfed condition.
INTRODUCTION
Castor (Ricinus communis L.) belongs to Euphorbiaceace family which is found in both tropical and sub-tropical regions of the world (Weiss, 2000). Castor is indigenous to the southeastern Mediterranean Basin, Eastern Africa and India but is widespread throughout tropical regions. Castor seed is the source of castor oil, which has a wide variety of uses. Castor oil is one of the important raw materials for the chemical and polymer industries (Mutlu and Meier, 2010) are used as biodiesel stock (Hall et al., 2009; Da Silva Cesar and Batalha, 2010). With its unlimited applications, castor oil has a tremendous worldwide demand and it accounts for 0.15% of vegetable oils (Scholz and da Silva, 2008). India and Brazil together accounts for more than 80% of the castor oil supply. In India, castor is cultivated in an area of 8.4 lakh ha under both irrigated and rainfed conditions. Castor has the potential for its use in bioenergy and industrial feed stock due to its high oil content and has the adaptability to grow under drought and saline conditions (Severino et al., 2012). India is the first country in the world to exploit hybrid vigour of castor crop on commercial scale (Ramchandram and Rao, 2012).
Castor is considered to be a drought hardy crop and grows well under dry and warm regions receiving a rainfall of 500-750 mm. It has a wide range of adaptation and has the ability to grow on marginal sites subjected to drought and saline conditions. To produce higher yields, it requires a moderate temperature of 20-26°C and low humidity (Gangaiah, 2008). High temperature above 41°C at flowering time even for a short period results in blasting of flowers and poor seed set. The kharif season crop essentially grown as rainfed crop, require a minimum of 500-700 mm rainfall depending on the soil type and higher yield can be obtained with 1-2 supplemental irrigations (Sharma et al., 2010).
In India, Telangana and Gujarat are well known for castor production and productivity. To develop high yielding castor genotypes that get fit into the present cropping system, it is important to create the genetic variability for the selection of desirable variant (Sarwar and Chaudhry, 2008). However, as major cropped area is under rainfed, the physiological efficiency of the genotypes especially water use efficiency has become pivotal. Under limited water supply, it maintains efficient stomatal control with a high level of net CO2 fixation (Severino et al., 2012). In order to identify the variability in the physiological parameters which are indicative of moisture stress tolerance and towards this endeavour 12 varieties of castor from CRIDA were evaluated at field conditions along with the popular check to find out the best lines with better physiological efficiency coupled with higher seed yield. This identification of better lines would be helpful in the process of improving castor productivity and production.
MATERIALS AND METHODS
A field study was conducted during kharif with twelve CRIDA castor genotypes, viz., CRC-1, CRC-2, CRC-3, CRC-4, CRC-5, CRC-6, CRC-7, CRC-8, CRC-9, CRC-10, CRC-11, CRC-12 and a check 48-1 at Hayathnagar research farm, Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad. The trial was sown on June 23rd, 2013 in RBD with three replications and the crop was raised purely under rainfed conditions. The crop received 904.5 mm rainfall spreading in 60 rainy days during the crop growth period and the crop experienced 3 dry spells (<2.5 mm) of 10 days or more with the first dry spell during the vegetative stage, the second dry spell of 27 days during the maturation of secondary raceme and a no rainfall of 91 days during initiation to maturation of tertiary racemes. During the crop growth period, the average temperature was 23.4°C with minimum and maximum of 8.4 and 38.6°C, respectively. Each genotype was sown in 5 m length of three rows with plant to plant spacing of 30 cm and 1 m between rows. At 50% flowering of primaries (53 DAS), the physiological observations such as photosynthesis (Pn), stomatal conductance (gs), transpiration rate (Tr) were recorded with portable photosynthesis system (LICOR-6400, USA) and WUE was calculated as the ratio Pn to Tr. The capsules of first (primaries), second (secondaries) and third (tertiaries) order spikes were pooled and the seed yield and yield components were recorded on per plant basis.
RESULTS AND DISCUSSION
Seed yield: The seed yield of all the 13 genotypes ranged from 32 g per plant (CRC-7) to 73.6 g per plant (CRC-2) with an average of 46.8 g per plant. Among the 12 CRIDA genotypes, CRC-2 (73.6 g per plant) CRC-11 (57.6 g per plant) and CRC-9 (55.3 g/plant) were superior over the check, 48-1 (53.2 g/plant). Ahmed et al. (2012) reported higher seed yield in two castor mutants CBM-7 and CBM-17 over the check DS-30.
The seed yield from three spike orders varied in different selected castor genotypes. In majority of the genotypes the contribution of third order spike was higher than other two orders. However, in genotypes CRC-5 and 48-1 all the three spike orders contributed equally to final seed yield. The seed yield of primaries ranged from 7.5 (CRC-12) to 17.0 g per plant (CRC-2), for secondaries it ranged from 6.6 g per plant (CRC-4) to 21.9 g per plant (CRC-11) and for tertiaries the range was from 11.1 g per plant (CRC-5) to 39.3 g per plant (CRC-2).
| Table 1: | Physiological parameters and seed yield in castor genotypes during kharif, 2013 |
| Pn: Photosynthesis rate, gs: Stomatal conductance, WUE: Water use efficiency, Tr: Transpiration rate | |
| Table 2: | ANOVA for physiological parameters in castor genotypes during kharif, 2013 |
| *p<0.05 level, **p<0.01, Pn: Photosynthesis rate, gs: Stomatal conductance, WUE: Water use efficiency, Tr: Transpiration rate, DF: Degree of freedom | |
The impact of first, second and third orders of castor crop vary the final seed yield due to the genotype, environmental (Fanan et al., 2009; Neto et al., 2009; Zuchi et al., 2010a, b; Vallejos et al., 2011) and location factors (Abimiku et al., 2012). In the present trial, the crop was affected by the infection of Botrytis during maturity of primaries and this also influenced the yield of secondaries of susceptible genotypes. From the overall seed yield of three spike orders it was observed that three CRIDA genotypes CRC-2, CRC-11 and CRC-9 superior over the check 48-1. The genotype CRC-2 was also found to be resistant to Botrytis disease as check 48-1.
Physiological parameters: The ANOVA of physiological characteristics of castor genotypes were presented in Table 1 and highly significant (p≤0.01) variation for the physiological parameters gs, Tr and WUE was observed (Table 2) whereas photosynthetic rate was non-significant.
Photosynthetic rate (Pn-μmol CO2 m–2 sec–1): The Pn values of selected castor genotypes was not varying significantly and it ranged from 30.72 (CRC-2) to 37 μmol CO2 m–2 sec–1 (CRC-6) and check 48-1 with 30.80 μmol CO2 m–2 sec–1. The high yielding genotypes CRC-2 30.72 and CRC-9 (31.94 μmol CO2 m–2 sec–1) recorded lower Pn values whereas CRC-11 (35.80 μmol CO2 m–2 sec–1) was with moderate values. Dai et al. (1992) reported that decrease in photosynthesis and increase in photorespiration under high VPD can be accounted for closure of stomata and Bindumadhava et al. (2005) opined that stable isotope ratios of 13C/18O provide a powerful option in identifying the desirable genotypes with superior photosynthetic capacity which can be used in crop improvement.
Stomatal conductance (gs cm sec–1): The gs of the 13 selected castor genotypes recorded a significant difference and it ranged from 0.471(CRC-2) to 1.073 cm sec–1 (CRC-5). The two high yielding CRIDA genotypes, CRC-2 (0.471) and CRC-9 (0.481 cm sec–1) recorded the lower values than the check 48-1 (0.764 cm sec–1) for gs. Earlier reports of Sausen and Rosa (2010) showed that castor bean plants combine an efficient stomatal control with high levels of net CO2 fixation.
Transpiration rate (mmol H2O m–2 sec–1): The transpiration rate of the genotypes ranged from 6.73 (CRC-2) to 13.58 mmol H2O m–2 sec–1 (CRC-4) with a significant difference among the genotypes. The Tr values of the high yielding CRIDA genotypes CRC-2 (6.73) and CRC-9 (7.49 mmol H2O m–2 sec–1) were lower than the check 48-1 (10 mmol H2O m–2sec–1). Earlier reports by Sheshshayee et al. (2005) revealed that transpiration rate can increase either because of increased stomatal conductance or when the vapour pressure difference between the leaf and air is increased. The reports of Sausen and Rosa (2010) revealed that the water loss by transpiration was minimized by an early closure of stomata in castor.
| Fig. 1(a-d): | Relationships between the selected physiological parameters of castor genotypes (a) gs and WUE, (b) Tr and WUE, (c) gs and Tr and (d) gs and Pn selected physiological parameters of castor genotypes |
| Table 3: | Correlation of physiological parameters with the seed yield in castor genotypes |
| *p<0.05, **p<0.01, Pn: Photosynthesis rate, gs: Stomatal conductance, WUE: Water use efficiency, Tr: Transpiration rate | |
Water Use Efficiency (WUE) (μmol CO2 mmol–1 H2O m–2 sec–1): The WUE of the genotypes was calculated as the ratio of Pn and Tr and it ranged from 2.29 (CRC-4) to 4.92 μmol CO2 mmol–1 H2O m–2sec–1 (CRC-6) and better yielding genotypes CRC-2 and CRC-9 recorded higher WUE over check 48-1. Lakshmamma et al. (2010) observed WUE was strongly correlated with the root traits. Through enhanced WUE, significant improvement in productivity was demonstrated in crops like groundnut by Condon et al. (2004).
The regression equation between gs has significant positive relation with Tr (r2 = 0.9773) whereas WUE has significant negative relation with gs (r2 = 0.8972) and Tr (r2 = 0.9128) revealing that the WUE of castor is mainly dictated by Tr and which in turn by gs and not Pn (Fig. 1). The correlation studies (Table 3) also revealed that gs was significantly and positively correlated with Tr (0.988**) and significantly and negatively correlated with WUE (-0.947**) and seed yield (-0.500*). Significant negative correlation was observed for Tr with WUE (-0.955**) and seed yield (-0.492*). Hence for identifying or developing genotype for better water use and higher seed yield, lower gs and Tr need to be considered. The WUE is strongly correlated in C3 plants with stomatal conductance (Medrano et al., 2002). Jatoi et al. (2012) experiments with wheat showed that there was a negative correlation of gs with yield and its traits. Bindumadhava et al. (1999) opined that 18O acts as surrogate for transpiration efficiency and gs and high 18O shows high transpiration rate which is related to yield directly. Seed yield and its traits of castor are useful to bring the crop improvement (Udayabhanu et al., 2013; Najan et al., 2010; Patel et al., 2010).
CONCLUSION
Based on the physiological and yield performance of selected castor genotypes, it can be concluded that there was significant variability in these parameters. Among the physiological parameters, gs and Tr are found to be significantly negatively correlated with seed yield. Two CRIDA genotypes CRC-2 and CRC-9 recorded lower gs and Tr with higher WUE and seed yield than check 48-1. It can be summarized that for rainfed condition, the castor genotypes need to have not only high seed yield but also low gs and Tr for high WUE values.
ACKNOWLEDGMENTS
The present work is part of Ph.D thesis work. We acknowledge the Director, CRIDA and Head, Division of Crop Sciences for providing both field and lab facilities to conduct experiments.