India is the largest producer of chickpea in the world with annual production of 9.07 million tons from an area of 9.54 m ha. with productivity of 951.4 kgha
-1 (
FAO STAT, 2019). In India chickpea area is mainly distributed in six states
viz., Madhya Pradesh, Uttar Pradesh, Rajasthan, Maharashtra, Andhra Pradesh and Karnataka. In Andhra Pradesh, the area under chickpea has increased from less than one lakh ha (1993-94) to more than 6.0 lakh ha by 2007-08 registering the highest productivity of 1449 kg ha
-1. Introduction and widespread adaptation of short duration, wilt resistant varieties such as ‘JG 11’, ‘JAKI 9218’ and ‘KAK 2’ and mechanization of farming operations has contributed to witness the highest productivity. However, farmers are unable to go for machine harvesting operation, as the existing varieties have semi spreading growth habit and attain a short plant height of 35-40 cm in warm growing environments of Southern India. To enable complete mechanization (machine harvesting and threshing) of chickpea cultivation, development of chickpea cultivars with 30 to 40 per cent more height than the existing cultivars with semi-erect to erect growth habit and with branching starting from 25- 30 cm from ground level with yield potential equal to or more than existing popular cultivars is pressing need of current chickpea breeding programmes. Location specific breeding programmes at Regional Agricultural Research Station, Nandyal of Acharya N G Ranga Agricultural University in Andhra Pradesh state of India have led to development of a chickpea cultivar Dheera (NBeG 47) which is suited to mechanical harvesting
(Jayalakshmi et al., 2017).
In Southern India, drought stress particularly at the end of the growing season is a major constraint to chickpea production and yield stability. This problem is more serious in Andhra Pradesh where chickpea is traditionally planted towards the end of the rainy season and generally grown on progressively declined residual soil moisture. With predicted climate change scenarios and continuous population explosion, there is a great need to develop high-yielding chickpea varieties with improved drought tolerance
(Krishnamurthy et al., 2013). Therefore, breeding efforts are needed to develop chickpea varieties suitable for machine harvest and with inbuilt tolerance to drought conditions. Therefore, study of genetic variability utilising physiological traits to be utilised in breeding for drought along with seed yield and yield components and traits which make cultivar amenable to machine harvesting would be useful for planning suitable breeding strategies to develop new machine harvestable chickpea genotypes with increased drought tolerance.
The investigation was carried out during
rabi 2018-19 at Regional Agricultural Research Station, Nandyal, situated at 15°29’ North latitude and 78°29’ East longitude at an altitude of 211.76 m above mean sea level. The research station comes under scarce rainfall agro-climatic zone of Andhra Pradesh. The experimental material comprised of 25
desi chickpea genotypes and five checks
viz., NBeG 47, NBeG 49, JG 11, GBM 2 and HC 5 which were sown on 24
th October
rabi, 2018 in a Randomized Block Design (RBD) with three replications under rainfed and irrigated situations. Since very meagre rainfall was received during
rabi season, a pre sowing irrigation was given to take up the sowing of experiments. In rainfed condition genotypes were grown on receding soil moisture where as in irrigated condition two supplemental irrigations were given at 35 and 55 days after sowing through sprinklers. Each genotype was sown in two rows in a plot of 3m row length at spacing of 30 cm between rows and 10 cm between plants within the row. Observations were recorded on 19 traits
viz., angle of the primary branch (°), height of the first pod (cm), plant height (cm), days to 50 per cent flowering, days to maturity, duration of reproductive phase, number of primary branches per plant, number of secondary branches per plant, SPAD Chlorophyll Meter Reading (SCMR), number of pods per plant, biological yield (g), harvest index (%), seed yield (g), 100 seed weight (g), Specific leaf area (SLA) (cm
2 g
-1), Relative water content (RWC) (%) at 30 DAS and 60 DAS, proline (µ mole g
-1) and protein content (%). The measures of variability were categorized in to high, medium and low as reported by various researchers. PCV and GCV were classified as low (< 10 per cent), moderate (10-20 per cent) and high (> 20 per cent) as per
Subramanian and Menon (1973).
Johnson et al., (1955) classified heritability as low (< 30 per cent), medium (30 to 60 per cent) and high (> 60 per cent) and; genetic advance as per cent of mean as low (< 10 per cent), medium (10 to 20 per cent) and high (> 20 per cent).
In crop improvement program, the efficiency of selection largely depends upon the magnitude of genetic variability present in the working germplasm. Hence, an insight into the magnitude of variability present in the working germplasm is of paramount importance to a plant breeder for starting a sensible plant breeding programme. Quantifying the extent of genetic variability, heritability of traits and the expected gains through selection are fundamental parameters that help in choosing a breeding programme. Chickpea is highly self-pollinated crop and limited variability has been reported for various traits of importance. Terminal drought is the major constraint limiting the productivity of chickpea since the crop is predominantly cultivated under residual and receding soil moisture conditions of rainfed environments. Under rainfed, residual soil moisture conditions, seed yield in chickpea can be increased by accumulation of genes for modified phenology, resistance to major biotic and abiotic stresses for maximum expression of yield potential and those traits that increase biomass and harvest index
(Hegde et al., 2010). In view of increased demand for machine harvestable genotypes, there is also need to look for variability in the germplasm to incorporate these traits in new varieties that are being developed. In the present study the extent of genetic variability and the heritable portion of variability for yield attributing traits and traits amenable to mechanical harvesting and drought tolerance attributes under rainfed and irrigated conditions were studied and presented in Table 1.
Genetic variability for traits related to yield
High PCV and high GCV was recorded for seed yield per plot (rainfed : PCV = 31.6%, GCV = 30.1% and irrigated : PCV = 25.3%, GCV = 21.8%) under both rainfed and irrigated conditions; number of secondary branches per plant, number of pods per plant and harvest index recorded high PCV and high GCV under rainfed alone. High PCV and GCV values for number of pods per plant, harvest index and seed yield were reported earlier by
Swarup and Holkar (2014).
High PCV coupled with moderate GCV was exhibited by number of primary branches per plant under rainfed and number of pods per plant under irrigated condition which was in accordance in with
Parameshwarappa et al., (2012), Parhe et al., (2014) and
Warkad et al., (2018).
Moderate PCV coupled with moderate GCV was recorded for days to 50% flowering, 100 seed weight and biological yield per plot under both rainfed and irrigated conditions. Moderate GCV and PCV for days to 50% flowering were reported earlier by
Parhe et al., (2014), Singh et al., (2014) and
Thakur et al., (2018). Under irrigated conditions, number of primary branches per plant, number of secondary branches per plant, harvest index and protein exhibited PCV and moderate GCV.
Protein content exhibited moderate PCV coupled with low GCV (PCV = 12.2%, GCV = 7.4%) under rainfed condition.
Parhe et al., (2014), Singh et al., (2014) and
Kumar et al., (2018) also reported low GCV for protein content.
Low PCV coupled with low GCV was observed for days to maturity (rainfed : PCV = 6.1%, GCV = 5.9% and irrigated : PCV = 5.9%, GCV = 5.8%) and duration of reproductive phase (rainfed : PCV = 6.6%, GCV = 5.3% and irrigated : PCV = 8.0%, GCV = 6.5%) under both the conditions. Low PCV and GCV for days to maturity were also reported by
Kanouni et al., (2012) and
Kumar et al., (2016).
Heritability estimates along with genetic advance are normally more helpful in predicting the gain under selection
(Johnson et al., 1955). Under both the tested environments, high heritability coupled with high genetic advance as percentage of mean was exhibited by days to 50% flowering (rainfed : h
2 b = 95.4%, GAM = 29.7% and irrigated : h
2 b = 92.6%, GAM = 30.6%), harvest index (rainfed : h
2 b = 92.3%, GAM = 47.1% and irrigated : h
2 b = 90.6%, GAM = 30.8%), 100 seed weight (rainfed : h
2 b = 97.2%, GAM = 37.6% and irrigated : h
2 b = 96.7%, GAM = 34.0%) and seed yield (rainfed : h
2 b = 90.9%, GAM = 59.1% and irrigated : h
2 b = 74.7%, GAM = 38.9%).
Purushothaman et al., (2017) observed high heritability values for days to 50% flowering under drought stress conditions compared to irrigated treatments. He also observed high heritability for grain yield under drought treatments.
Effective selection for superior genotypes would be possible in chickpea by considering seed yield, harvest index, 100 seed weight and days to 50 per cent flowering under both rainfed and irrigated conditions where they exhibited moderate to high variability estimates as well as high heritability coupled with high genetic advance. Due to predominant additive gene effects in the inheritance of these traits, simple breeding procedures such as pure line selection, mass selection and progeny selection can be followed. Exclusively under rainfed condition, number of secondary branches per plant, number of primary branches per plant, number of pods per plant and biological yield per plot associated with moderate variability, high heritability coupled with high genetic advance as percentage of mean can also be used as target traits as they exhibited sizeable genetic advance expected from simple selection. Under irrigated condition, protein with moderate variability, high heritability coupled with high genetic advance as percentage of mean can also be considered as a target trait.
Genetic variability for traits related to drought tolerance
Though breeding for high yield under drought tolerance through drought escape mechanism by early maturity is being practised, trait based breeding utilising physiological and shoots traits such as photosynthetic efficiency, chlorophyll content, chlorophyll refraction, ABA content, proline accumulation, stomatal conductance etc. has been proposed by several researchers for increasing the efficiency in selecting drought tolerant genotypes
(Purushothaman et al., 2016).
High PCV and high GCV was exhibited by proline (rainfed : PCV = 33.4%, GCV = 30.6% and irrigated : PCV = 34.9%, GCV = 30.6%) under both rainfed and irrigated conditions. High PCV coupled with moderate GCV was recorded by SLA under both the tested conditions.
Under both the tested environments, high heritability coupled with high genetic advance as percentage of mean was exhibited by SLA (rainfed: h
2 b = 78.2%, GAM = 35.5% and irrigated : h
2 b = 87.1%, GAM = 37.0%) and proline (rainfed: h
2 b = 84.0%, GAM = 57.8 % and irrigated : h
2 b = 76.8%, GAM = 55.2%). High heritability accompanied with moderate genetic advance was observed for SCMR under both rainfed and irrigated conditions. High heritability of SCMR was reported earlier by
Jayalakshmi et al., (2011). Under irrigated condition, RWC at 30 DAS exhibited high heritability combined with moderate genetic advance as percentage of mean whereas under rainfed condition, it exhibited moderate heritability combined with low GAM. RWC at 60 DAS recorded moderate to low heritability together with low genetic advance which indicates that this trait is highly influenced by environmental effects and selection would be ineffective considering this trait.
Genetic variability for traits related to mechanical harvest
Under both rainfed and irrigated conditions, moderate GCV coupled with moderate PCV was recorded by height of the first pod and plant height.
Mannur et al., (2017) reported moderate PCV for height of the first pod. Low GCV coupled with low PCV was observed for angle of primary branch under both rainfed and irrigated conditions.
High heritability coupled with high genetic advance as percentage of mean was exhibited by height of the first pod (rainfed: h
2 b = 92.6%, GAM = 32.4 % and irrigated: h
2 b = 89.6%, GAM = 25.9%) under both rainfed and irrigated conditions. Plant height also exhibited high heritability combined with high genetic advance as percentage of mean under rainfed condition in accordance to
Akthar et al., (2011) and
Babbar et al., (2012) whereas under irrigated condition it showed high heritability combined with moderate genetic advance as percentage of mean. High heritability combined with low genetic advance as percentage of mean was exhibited by angle of primary branch under both rainfed and irrigated conditions.
Vishnu et al., (2018) also reported that height of the first pod under rainfed and irrigated conditions and plant height under irrigated condition exhibited moderate variability combined with high heritability and high genetic gain under selection. Among traits related to mechanical harvesting, height of the first pod and plant height exhibited moderate variability, high heritability and high genetic advance as percentage of mean under both environments.
