Heterosis and Combining Ability in Cucumber ( Cucumis sativus L.)

The present study on heterosis and combining ability for fruit yield and its components was carried out in a set of 27 F 1 hybrids of cucumber obtained from a Line x Tester method involving twelve diverse parents at Navsari Agricultural University, Navsari 2009. The ratio of the genetic variance was less than unity, which indicated the predominance of the non-additive gene action in all the traits. The analysis revealed that none of the parents was found good general combiners for all the traits consistently, however parents CCP-9, Gujarat local and SPP-44 were good combiner for fruit yield and its contributing traits. The hybrids Pilibhit Local x K-90 followed by Sheetal x SPP-44 and Sheetal x CC-9 have exhibited higher heterobeltiosis for fruit yield and its components characters. These crosses involved poor x poor and poor x good combiner parents. Further improvement in fruit yield could be possible through the hybridization and selection in transgressive segregants.


Material and Methods
An experiment was conducted during Kharif 2009 at the Experimental farm, N. M. College of Agriculture, Navsari Agricultural University, Navsari.The experimental materials comprised of 3 lines (females) namely; Sheetal (L1), Gujarat Local (L2) and Pilibhit Local (L3) and nine testers (males) namely; SPP-44 (T1), K-90 (T2), CV-5 (T3), SPP-93 (T4), CC-9 (T5), SPP-63 (T6), DC-2 (T7), PCUC-8 (T8) and PCUC-28 (T9) and Gujarat Local-1 as an standard check.The complete set of 27 F1s and 12 parents were grown in randomized block design (RBD) with replications.Row to row and plant to plant spacing were maintained at 3 m and 2 m, respectively.All the recommended agronomic package of practices was followed to grow a healthy crop.In each replication, 5 plants and F1s were marked for observation.Observations were recorded on nine important characters, viz.node number on which first male flower appeared, node number on which first female flower appeared, average fruit length (cm), average fruit diameter (cm), number of lateral branches per vine, number of fruits per vine, length of vine and fruit yield per vine (kg).Combining ability analysis was done by using Model l and Method ll of Griffing (1956).Heterosis was calculated as the percentage of F1 performance in the favorable direction of its better parent as suggested by Hayes et al. (1955).

Results and Discussion
The mean sum of square due to gca and sca were highly significant for all nine characters except node number on which first male flower appeared, node number on which first female flower appeared, number of lateral branches and fruit diameter for gca variance (Table 1).It indicated that both additive and non-additive gene action were involved in the  expression of these traits.Similar results have been reported by Prajapati (2008) and Prasad and Singh, (1992) in cucumber.The estimates of sca variance (σ2 sca) was higher than gca variance (σ2 gca).The ratio of gca/sca variance (σ2 gca/σ2 sca) being lesser than unity for all the nine traits revealed preponderance of non additive gene effects in the inheritance of fruit yield and its components traits.The present findings are in congruence with the reports of Solanki and Shah (1990), Ananthan and Pappiah (1997), Sarkar and Sirohi (2006) in cucumber.
The estimates of gca effects (Table 2) revealed that the none of the parents exhibited good gca for all the characters so it was difficult to pick good combiners for all the characters together because the combining ability effects were not consistent for all the yield components, possibly because of negative association among of the characters (Solanki and Shah, 1990).This shows that genes for different desirable characters would have to be combined from different sources (Nehe et al. 2007).Among the twelve parents, CC-9, Gujarat local and SSP-44 were good general combiner for fruit yield and Sheetal x CC-9 produced the highest sca effect for the fruit yield per vine (Table 3).Thus, sca effect of these three crosses indicates the inclusion of atleast one good combining parent in producing superior hybrids.However, a former cross involved both of the parents with poor combining abilities.This suggests that high sca effect of any cross combination does not necessarily depend on the gca effects of the parental lines involved.This superiority of sca effects may be due to complementary type of gene action or involvement of non allelic interaction of fixable and non fixable genetic variance (Patel andDesai, 2008 andPurohit, 2007).
The hybrids varied in magnitude and direction of heterosis for most of the characters (Table 4).The significant heterobeltiosis observed for node number on which first male flower appeared in cross combination viz., Gujarat Local x PCUC-28 (-32.43) and Gujarat Local x SPP-44 (29.25), node number  -44(18.83) and Sheetal x CC-9 (18.61) showed higher heterosis.These reports are similarly Randhawa and Singh (1990) and Rao et al. (2000).
Fruit characters directly played important role in the enhancement of the yield.Cross combinations viz., Sheetal x SPP-44 (66.67),Sheetal x CC-9 (75.00) and Pilibhit Local x K-90 (33.33) exhibited the highest heterobeltiosis for the number of fruit per vine.The results are in close conformity with findings of Prajapati, (2008) and Prasad and Singh (1992).Number of fruit per vine had direct correlation with fruit yield per vine (Ananthan and Pappiah, 1997).The extent of heterosis for fruit yield per vine varied greatly.The highest value of heterosis was observed in Pilibhit Local x K-90 (57.96) followed by Sheetal x SPP-44 (56.60) and Sheetal x CC-9 (53.89).These crosses showing desirable heterosis for fruit yield per vine in addition to most of the yield contributing characters studied.Thus, total yield could be the result of combinational heterosis (Das and Rai, 1972).Similar results were reported by Prajapati, (2008), Bairagi, et al. (2002) and Hormuzidi and More (1989).
Considering the overall performance in respect of fruit yield per vine, most promising three hybrids viz., Pilibhit Local x K-90, Sheetal x SPP-44 and Sheetal x CC-9 exhibited high heterotic effects.These crosses have higher sca effects due to involvement of poor x poor and poor x good parents.The higher sca effect observed in poor x poor general combiners cross might be due to non-additive gene effects and such could be exploited through the hybridization, which is possible in the crop due to monocieous nature of flowers.The cross involved poor x good general combiners can produce good transgressive segregants in later generation.

NFM=
Node number on which first male flower appeared, NFF= Node number = Fruit diameter (cm), AFW = Average fruit weight (g), VL = Vine length (cm), on which first female flower appeared, NLB = Number of lateral branches per vine , F =Fruit length (cm), FD NFP = Number of fruit per vine, FYV = Fruit yield per vine (kg).

Table 2 . Estimation of general combining ability (gca) effects of parents for different characters in Cucumber
Niyaria and Bhalala (2001)se in breeding for yield and earliness.Similar results reported byNehe et al. (2007)in cucumber andNiyaria and Bhalala (2001)in ridge gourd.