Combining ability and heterosis analysis over two environments in a diallel cross of three families of the clam Meretrix meretrix

A 3×3 complete diallel cross comprising three families of the clam Meretrix meretrix（P1, P2 and P3） was used to determine the combining ability of parental families and heterosis of F1 under indoor and openair environments for growth traits. Analysis of variance for shell length and whole body weight indicated highly significant cross effects, environment effects and the interaction of cross by environment. General combining ability（GCA） and specific combing ability exhibited great variation among crosses and between two environments. Pooled over environments, P2 was the top combiner among the three parental families for both traits studied. The cross of P1 and P3 had the highest SCA. Additionally, significant reciprocal effects were observed. For individual environment, about half of the crossbred combinations showed favorable Mid-parent heterosis（MPH）（〉1%） for the shell length and whole body weight. Our data has shown that non-additive genetic and reciprocal effects constituted the major sources of genetic variation for both shell length and whole body weight, which indicates that crossbreeding among selective families could further explore the heterotic effects.

Diallel Crossing Analyses of Resistance to Main Diseases in Pepper(Capsicum annuum L.)

Fifteen capsicum combinations were made with 6 parents by （1/2）n（n-1） diallel crossing. Genetic parameters in the resistance to TMV, CMV, phytophthora blight, bacterial spot of these combinations were studied by Hayman. The results indicated that the resistance to TMV, CMV and bacterial spot conformed genetically to the “additive-dominant” model but the resistance to phytophthora blight did not and significant epistatic dominance effect existed in it. F1 hybrid＇s resistance to CMV was controlled by homozygous dominant gene （s）, but resistance to bacterial spot by heterozygous one （s）. There were little, or no sum of dominant effect and genomes controlling the dominant expression of F1 hybrids in its phytophthora blight resistance.

Combining Ability and Parent-Offspring Correlation of Maize(Zea may L.) Grain β-Carotene Content with a Complete Diallel

Vitamin A deficiency has become a worldwide problem.Biofortified foods can potentially be an inexpensive,locally adaptable,and long-term solution to dietary-nutrient deficiency.In order to improve the β-carotene content in maize grain by breeding and minimize vitamin A deficiency,a complete diallel cross was designed with eight inbred lines of maize,and 64 combinations were obtained in this study.The experimental combinations were planted in Yunnan and Sichuan provinces,respectively,with a random complete block design.The β-carotene contents in the grains of the experimental materials were analyzed by high-performance liquid chromatography.Among the tested materials,the effect difference of general combining ability of the β-carotene content was significant;however,the effect difference of the special combining ability and the reciprocal effect were not significant.The β-carotene content of maize grain was not influenced significantly by the cross and the reciprocal cross.There was a significant correlation about the β-carotene content in the maize grains between the F 1 and their parents.The combinations with high β-carotene content were obviously influenced by the environment,and the mean value of β-carotene content for the experimental materials planted in Ya＇an of Sichuan was higher than that planted in Yuanjiang of Yunnan,with the results being significant at the 0.01 level.

Estimates of genetic and phenotypic parameters for weight and length in Paralichthys olivaceus(Temminck et Schlegel)

The complete diallel cross design was employed to estimate the genetic parameters of the growth of Japanese flounder （Paralichthys olivaceus）. A total of 60 full-sib families were cultivated and two growth-related traits, body weight （BW） and body length （BL）, were examined at average 2, 3 and 8 months of age respectively, with 1 800 individuals measured in each age group （30 per family）. Based on the additive-dominance-maternal-effect genetic analysis model, the restricted maximum likelihood approach was used to estimate various （co）variance components. The results showed that narrow-sense heritability estimates of BW and BL were respectively： 0.29 ± 0.01 and 0.22 ± 0.02 at 2 months of age, 0.32 ± 0.02 and 0.30 ± 0.04 at 3 months of age, 0.48 ± 0.04 and 0.40 ± 0.05 at 8 months of age; broad-sense heritability estimates were respectively： 0.44 ± 0.02 and 0.54 ± 0.04 at 2 months of age, 0.35 ± 0.01 and 0.36 ± 0.03 at 3 months of age, 0.49 ± 0.03 and 0.45 ± 0.04. All heritabilities were statistically significant （P 0.05）. Additive genetic correlations between BW and BL at 2, 3 and 8 months of age were consistently positive and highly significant （P 0.01）： 0.93 ± 0.02, 0.95 ± 0.03 and 0.92 ± 0.03 respectively. Maternal effect was significant （P 0.05） only at 2 months of age, and was not detected at 3 and 8 months of age. According to the heritability estimates, the mass selection strategy should be efficient for the breeding of Japanese flounder.

Heterosis and Combining Ability for Major Yield Traits of a New Wheat Germplasm Shannong 0095 Derived from Thinopyrum intermedium

The wheatgrass, Thinopyrum intermedium （Host） Barkworth ＆ DR Dewey, shows many beneficial characteristics, such as big spikes and high resistance to many diseases. To transfer the beneficial genes of this species, many wheat- Thinopyrum intermedium alien chromosome lines were developed. Of them, Shannong 0095 （SN0095）, a disomic substitution, has long spikes and flag-leaves, and thus may be an important genetic resource for wheat yield improvement. In order to realize its heterosis and combining ability on major yield traits, a 7 ×7 complete diallel design was made according to Griffing＇s Method-1. The results showed that heterosis for spike length （SPL）, flag-leaf area （FLA）, number of spikes per plant （NSP）, number of spikelets per spike （NSL）, kernels per spike （KPS）, 1 000-kernel weight （TKW） and grain yield per plant （GYP） existed in all the crosses by SN0095, but heterobeltiosis occurred only for KPS, TKW, and GYP. The relative mid-parent heterosis （RMH） and relative high-parent heterosis （RHH） for GYP, which valued as high as 35.32 and 29.92% respectively, were the highest among all the traits mearsured. Though additive and non-additive gene effects and cytoplasmic effects （or cytoplasmic-nuclear interaction effects） were found in governing all the traits measured above, additive gene action played a predominant role. The results also showed that SN0095 was the best-general combiner for SPL and FLA, and high-general combiner for NSP amongst all the parents. Estimates of specific combining ability （SCA） showed that SN0095 could also make high-SCA combinations for GYP, such as SN0095 × Jimai 19 （JMI9）. SN0095 could be a unique and important parent in hybrid wheat breeding programs.

Combining Ability and Genetic Effects of Germination Traits of Brassica napus L.Under Waterlogging Stress Condition

Cross combinations from six rapeseed cultivars and lines were evaluated under waterlogging stress condition in order to understand the genetic mechanism of waterlogging tolerance of Brassica napus L.and provide reasonable improvement programs.There were six germination traits investigated on combining ability and heritability using complete diallel crossing method designed for 30 combinations from those six cultivars and lines.The traits included relative root length,stem length,fresh weight per plant,survival rate,electrical conductivity,and vigor index.After flooding treatment,the six traits of parents and F1 were analyzed.The general combining ability（GCA） and special combining ability（SCA） of germination traits were analyzed using Griffing I method.Among 30 cross combinations,the GCA was significantly different among six waterlogging resistance traits.The SCA of these traits was significantly different except the SCA of electrical conductivity.As a representative trait of waterlogging tolerance in rapeseed,relative vigor index had the highest narrow heritability and relatively low broad heritability.The cultivars Zhongshuang 9 and P79 had higher tolerance potential to waterlogging stress.It can be concluded that combining ability and genetic effects of relative vigor index during germination stage could be used to identify the waterlogging tolerance of rapeseed in breeding program.

Heterosis and Inbreeding Depression in Sunflower

Information on heterosis and inbreeding depression for yield and agronomic characters is essential for sunflower （Helianthus annuus L.） breeding programs. This research was conducted to evaluate heterosis and inbreeding depression for yield and agronomic characters of hybrids involving eight sunflower inbred lines. These inbred lines were crossed in 8×8 half diallel to obtain 28 F The 28 hybrids were self-pollinated to produce the F2 generation. The 8 parents, 28 F1 hybrids and 28 F2 populations hybrids were evaluated using a randomized complete block design with three replications at two locations in Nakhon Ratchasima （SUT Farm and National Corn and Sorghum Research Center） in 2009. Mid-parent heterosis and inbreeding depression were estimated for yield, head diamete oil content, 1,000-seed weight and plant height. Significant differences were found among the parents, F1 hybrids and F2 populations for all traits. F1 hybrid means were significantly higher than the parental means for all traits. In addition, F1 hybrids considerable heterosis and heterobeltiosis when compared with the mid-parent and better parents, respectively. Yield, showed oil content and plant height showed highly positive heterosis in F1 hybrids, ranging from 14.48 to 49.45%, 8.88 to 33.22% and 9.51 to 29 respectively. Similarly, heterobeltiosis were positive significant for yield （19.22 to 49.04%）, oil content （8.65 to 28.30%） and height （2,83 to 27.61%）. However, 1,000-seed weight showed a low level of heterosis in F1 hybrids （-9.36 to 8,07%） oil content, 1,000-seed weight and plant height in F2 populations were lower than their respective Fi hybrids the F2 populations was comparatively high for yield, oil content and plant height. The cross of lines 5A×for yield （49.45%） and 1,000 seed-weight （8.07%） but low 25%, plant Means for yield, Inbreeding depression in 2A gave the highest heterosis inbreeding depression for yield （10.06%）. Based on the mean performance and heterotic effects for seed yield, 1,000-seed weight and oil content, the inbred lines 2A and 5A are suggested for the development o hybrids,

Heterosis and combining ability in cucumber(Cucumis sativus L.)

The objective of this work was to evaluate four parental lines of cucumber which included:‘Zeina’(Zna),‘Beit Alpha’(BA),‘Straight 8’(Strght 8)and‘Calypso’(Capso)and six F1s generated by diallel cross,using randomized complete block design with three replications to study heterosis and combining ability for yield and yield component traits.Estimated heterosis showed that cross‘Zna
Capso’had the highest Better Parent(BP)heterosis in total fruit yield/ha while‘BA
Capso’had the highest Mid Parent(MP)heterosis in the same trait.Significant general(GCA)and specific(SCA)combining ability variances were obtained in all the traits implying that both the additive and non-additive gene effects operated in the genetic expression of the traits.Relative magnitude of GCA and SCA variances indicated preponderance of additive gene action for all the traits.‘Beit Alpha’and‘Straight 8’are best general combiners while‘BA
Capso’and‘Capso
Strght 8’were the best specific combiners for total fruit yield.