Studies on genetic variability and heterosis in vegetable pea ( Pisum sativum L . ) under high hills condition of Uttarakhand , India

The estimates of genetic parameters of 39 (11 parents and 28 crosses) genotypes of garden pea (Pisum sativum L.) indicated a good amount of genetic variation in the experimental materials under investigation. Characters like plant height, days to first picking, 100 green pod weight, green pod yield and days to 50% flowering revealed higher values of heritability in broad sense and genetic gain indicating that the additive gene actions are important in determining these characters. Therefore, selection programme based on these characters would be more effective in improving yield parameters of garden pea. The cross VRP-5 x Pusa Pragati manifested maximum significant heterosis for days to 50% flowering, DVP-2 x VL-7 for days to first picking and PMR-32 x snow pea for number of green pods per plant and green pod yield per plant, respectively.


INTRODUCTION
Garden pea (Pisum sativum L.) is an important vegetable crop due to its high nutritive value.It is a leading offseason vegetable grown in hilly regions of Uttarakhand.Its improvement is based mainly on exploiting the natural sources of germplasm by means of selection or hybridization followed by selection.An insight into the magnitude of variability present in a crop provides the basis for effective selection.Heritability is the portion of phenotypic variation which is transmitted from parent to progeny.The higher the heritable variation, the greater will be the possibility of fixing the characters by selection methods.The present investigation was therefore undertaken to predict the traits with high heritability and to create variation through hybridization so as to identify superior plants in the segregating generation.

Recording of observation
The data were recorded on five randomly selected plants on the traits viz., days to 50% flowering (1), days taken to first picking (2), pod length in cm (3), number of green pods per plant (4), green pod yield per plant in g (5), number of primary branches per plant (6), 100 green pod weight in g (7), shelling percentage in percent (8) and plant height in cm (9).The data were analyzed as per Gomez and Gomez (1983).The parameters of variability were estimated by the formula given by Burton and Devane (1953).Heritability in broad sense was calculated as per formula given by Burton and Devane (1953) and Allard (1960).Heterosis was calculated as the increase or decrease over better parent and standard check by the following formulae as suggested by Hayes et al. (1955) (Table 3): (1) Heterosis over better parent Where, F1 is the mean of particular individual (F1); BP is the mean of better parent in the cross and SP is the mean of standard/check parent.

Perse performance
The mean sums of squares due to genotypes were found highly significant for all the characters under study indicating the presence of substantial amount of variation between the genotypes for the characters studied (Table 1).Average number of days taken to 50% flowering was found to be 34.46 ranging from 29.33 (VRP-5 x Arkel, VRP-6 x snow pea) to 46.33 days (DVP-2), while average number of days to first green pod picking was recorded to be 62.66 with a range of 56 days (VRP-6 x VL-7) to 87 days (DVP-2).The average pod length recorded was 8.83 cm (Table 1).The average number of green pods per plant was recorded as 8.78 with a range of mean values from 5.33 (VRP-6 and DVP-1) to 15 (PMR-32 x snow pea).The green pod yield per plant showed a range of 25.00 (DVP-1) to 129.66 g (PMR-32 x snow pea) with a average of 66.74 g.The maximum number of primary branches per plant was recorded in DVP-2 x Pusa Pragati (9.80) and minimum in VRP-6 x Arkel (5.03) with general mean of 7.05 (Table 1).The cross combination PMR-32 x Pusa Pragati exhibited highest average value for 100 green pod weight (941.00 g) followed by VRP-6 x Arkel (911.66 g), PMR-32 x snow pea (894.33 g) and VRP-6 x Pusa Pragati (880.0 g), while lowest 100 green pod weight was recorded in DVP-1 x Arkel (516.66 g) with average of 713.09 g.The average value for shelling percentage was recorded as 41.02% with a range of 52.86% (PMR-32 x snow pea) to 21.83% (snow pea).The average for plant height was found to be 59.97 ranging from 38 cm (VRP-5) to 90.56 cm (PMR-32 x Pusa Pragati).

Genotypic coefficient of variation (GCV), phenotypic coefficient of variation (PCV), heritability and genetic advance
The results of coefficient of variation analysis (Table 2) showed that the PCV was higher than the GCV for all the characters under study.The genotypic coefficient of variances (GCA) varied from 8.14 (pod length) to 33.35 (green pod yield per plant).The estimates of GCA were found highest for green pod yield per plant (33.35), followed by plant height (26.82) and number of green pod per plant (21.02), respectively.The remaining characters revealed medium to lower estimates of GCA.Kumaran et al. (1995), Vikas and Singh (1999), Singh et al. (1996), Sureja and Sharma (2000) and Kalloo et al. (2005) also reported high estimates of genotypic variability for yield and its contributing traits.High estimates of broad sense heritability were recorded for plant height (97.84%), days to first green pod picking (95.80), 100 green pod weights (94.69%), green pod yield per plant (93.10), and days to 50% flowering (92.25%), whereas remaining characters revealed moderate heritability.Heritability estimate provides guide for the selection procedure to be followed by the breeder for improvement of these traits under a given environment.The high genetic advance as percent of mean along with high heritability was obtained for green pod yield per plant (66.28), plant height (54.67), number of green pod per plant (38.28), 100 green pod weight (32.07), while lowest for pod length indicating that these characters are least affected by environment.High heritability along with high genetic advance reveals that additive type of heritability is there.Therefore, these traits can be improved by selection and genotypic variability so realized can be maintained in subsequent generation.Similar findings were also reported by Kumar et al. (2000), Mahanta et al. (2001) and Chaudhary and Sharma (2003).

Morphological traits
Out of 28 crosses, 27 and 25 crosses revealed significant negative heterosis for days to 50% flowering over better parent and standard check, respectively.The cross combination VRP-5 x Pusa Pragati manifested maximum significant negative heterosis for days to 50% flowering (-36.69) and DVP-2 x VL-7 showed highest negative heterosis for days to first green pod picking.The

Table 1 .
Perse performance of parents and F1 crosses of garden pea.

Table 2 .
Mean, range, genotypic and PCV, heritability and genetic advance in the population.

Table 3 .
Estimates of heterosis for different trais of garden pea.