Dan Singh Jakhar1*, Rajesh Singh1 and Brijesh Singh2
1Department of Genetics & Plant Breeding, Banaras Hindu University, Varanasi – 221 005, India.
2Department of Genetics & Plant Breeding, Sri Murli Manhor Town PG College, Ballia – 277001, India.
The genetic analysis was carried out to determine mode of inheritance of yield and its contributing trait under two environments in irrigated and rainfed conditions. The study was undertaken with the help of six generations P1, P2, F1, F2, B1, and B2 in three crosses, viz, 863B x P 7-7 (1), 843B x P 7-4 (2), and 81B x ICMP 451 (3) of pearl millet in two environments Varanasi (Irrigated) (E1) and Mirzapur (Rainfed) (E2) using six generations. Simple additive-dominance model failed to explain the genetic variation of most of the characters. The estimates for mean and dominance were reduced in Rainfed environment of Mirzapur, though all type of digenic interactions were prevalent, the dominance x dominance gene effects with duplicate epistasis were pronounced. It is suggested that cyclic breeding particularly reciprocal recurrent selections should be practised to improve yield and its attribute traits in Pearl millet rather than going only for simple selections methods.
Keywords : Pearl millet, Rainfed, Irrigated, Generation Mean Analysis, Genetics.
Pearl millet (Pennisetum typhoides (Burn) Stapf and C.E. Hubbard) is one of the important crops of semi-arid tropical regions of Asia, Africa, and America supplying food and fodder under the most trying farming conditions. It is particularly adaptable to nutrient-poor soil and low rainfed conditions, yet it is capable of rapid and vigour growth under favourable conditions (Maiti and Bidinger, 1981). This is crop is grown primarily for grain production on 26 million ha in the arid tropical region of Asia and Africa (Rai et al. 2007) but in USA and Europe, it is mainly grown as fodder crop (Poehlman and Borthakur, 1969). In India, it is cultivated in 7.95 million hectare with an annual production of 8.80 million tonnes (Annual Report of Government of India, Ministry of Agriculture, 2013-14). Nevertheless, not only the productivity remained low (11.38 q/ha) but also there are wide year to year fluctuations in terms of production and productivity. Therefore, yield improvement of varieties particularly under rainfed situation is of paramount importance. Genetic variability for yield and its component traits is the key component of the breeding programme for broadening gene pool of crops. However, genetic variability for many traits is limited in germplasm (Sabu et al. 2009). The overall performance of a genotype may vary due to changes in the environment, and if the heritability for the traits is higher, the selection process will be simpler and response to selection will be greater (Govindaraj et al. 2010; Larik et al. 1997 & 2000; Singh and Sagar 1989 & 2001; Soomro et al. 2008).
The genetic improvement of crops for quantitative traits requires reliable estimates of genetic variability, heritability and genetic advancement of breeding materials (Dudely and Moll, 1969; Izge et al. 2006; Chand et al. 2008; Govindaraj et al. 2010). The information on variability and heritability of characters is essential for identifying characters amenable to genetic improvement through selection (Govindaraj et al. 2010). In the present study attempt has been made to study the genetics of important quantitative characters including yield using generation mean analysis. The generations mean analysis is one of the important methods to understand the nature and magnitude of genetic variance.The gene effects, variability parameters, heritability and genetic advance for yield and its important attributing traits have been estimated and results discussed.
Materials and Methods
The study was conducted involving six generations viz, P1, P2, F1, F2, B1 and B2 of three Pearl Millet crosses viz., 863B x P 7-7 (1), 843B x P 7-4 (2), and 81B x ICMP 451 (3) at two locations. The parents of the crosses were stable inbreds with good genetic-agronomic base and combining ability. The six generations of each cross were grown in randomized complete block design with three replications at two locations. The two locations were Agriculture Research Farm of Banaras Hindu University under irrigated conditions (E1) and Rajiv Gandhi South Campus under rainfed condition (E2) during Kharif 2011-12. Two rows for each parent (P1, P2), three for each of F1 and backcrosses (B1, B2) and eight for F2, were grown in each replication. The rows were 4 m long with 45 cm row to row and 20 cm plant to plant distance. Observations were recorded on five competitive plants on seven quantitative characters in each row. The means and variances of a population worked out in a replication were used to calculate the weighted mean and variance over the replication. The Joint Scaling Test (Cavalli, 1952) was performed using the weighted least squares. The estimates of various genetic parameter was obtained by Jinks and Jones (1958) model. The estimates of the components of genetic variance were obtained following Mather (1949). Heritability and Genetic Advance were estimated according to Allard (1960).
RESULTS AND DISCUSSION
The mean values for seven quantitative characters of six generations of the three crosses 863B x P 7-7 (1), 843B x P 7-4 (2), and 81B x ICMP 451 (3) in two environments, Agriculture Research Farm of Banaras Hindu University under irrigated conditions (E1) and Rajiv Gandhi South Campus under rainfed condition (E2) are presented in Table 1. In general, the performance of the three crosses of various characters over different generations was better in Varanasi (E1) than in Mirzapur (E2). The poor performance in Mirzapur (E2) was mainly due to poor fertility and low water holding capacity of the soil. All these characters exhibited reduced expression under water stress; however, this was less for such characters as plant height and ear length. These observations confirm earlier findings of Govindaraj et al. (2010); Van Oosterom et al. (2006); Singh and Sagar (1989 & 2001); Soomro et al. (2008). The F1s of all the crosses performed better than both the parents and mid-parents in both the environments for all the characters, except for days to maturity in crosses 843B x P 7-4 and 81B x ICMP 451 in Varanasi. This indicated prevalence of heterobeltosis, which could arise due to true over-dominance or dispersion of completely or incompletely dominant genes. Negative heterosis for days to maturity indicated dominance for earliness. Higher heterosis in case of pearl millet, an allogamous species, is expected. Virk (1986) has noted positive heterosis for quantitative characters including grain yield (-56.62 to 424.16%), but negative heterosis for days to flowering. The better performance of F1 than both the parents for grain yield and other attributes even under moisture stress shows that hybrids will withstand moisture stress. The F2 means, lesser than the F1 in both the environments for all the characters and crosses except for ear length for cross 843B x P 7-4 in Varanasi indicated high amount of inbreeding depression. Smaller F2 mean than F1 could be due to elimination of dominance effects, as in all the crosses the dominant exceeded the additive component and may be responsible for bringing reduction in F2 mean. The F2 mean exceeding all other generations for ear length could be due to transgression and fixable epistatic effects. Both the backcrosses exceeded the respective recurrent parents in most of the cases, indicating the prevalence of allelic and non-allelic interactions for genetic control of important traits in pearl millet. Govindaraj et al. (2010); Gupta and Phul (1981); Girgla et al. (1985); Singh and Sagar (2001) also reported similar results.
Table 1. Mean performance of six generations of seven quantitative traits in two environments.
|ICMP 451 ( P2)||E1||197.7||3.65||17.9||81.8||28.2||50.7||90.3|
Table 2. Gene effect of six-parameter model for seven yield and component traits of Pearl Millet in two environments