CGA, SCA, GRE and SRE are estimated in 5 diallel crosses derived from 8 parental S2 families. In the first diallel cross (2.21 and 54 mean values for pod fertility and seed setting respectively) the 8 parental families have the same genetic origin (cv Lodi); in the second diallel cross (2.95 and 63 mean values) they have the 50% of the genetic diversity (cvs Lodi and La Rocca). The last 3 diallel crosses have 100% of the genetic diversity, and precisely: the third diallel cross (3.03 and 63 mean values) derived from the cvs La Rocca, Sprinter, Selene, Shell, Birouk, Robot, Romea, Siwa; the fourth diallel cross (2.81 and 64 mean values) derived from the cvs Oro, Prosementi,Odessa, Supreme, Estival, Natsuwa, Amiral, Tunetana; the fifth diallel cross (2.88 and 57 mean values) derived from the cvs Cimarron, Vitroculture, Gilboa, Delta, Boreal, Diablo verde, Kara, Lodi. This study is the first phase of a program concerning the construction of semi-hybrid varieties. Seed-setting (percentage of pod per tripped flowers) and pod fertility of the parental plants are measured. In the diallel cross progenies the following characters are studied: height, number of stems, flowering degree, dry weight.

On this paper only the seed-setting and pod fertility results are reported. The crosses were made by hand in the greenhouse without emasculation. The variance analysis was made by Method III Model I of Griffing. The results for seed-setting and for pod fertility show:

1) the importance of parental genetic diversity. Notice that a diversity of 50% gives the same results of a diversity of 100%. 2) General Combining Ability (GCA) was much larger than Specific Combining Ability (SCA) in both characters. Some cases of SCA could be utilized for the choice of single crosses for the construction of double hybrids. At the same time we can observe some negative cases of SCA. 3) General Reciprocal Effects (GRE) were much larger than Specific Reciprocal Effects (SRE). This means that in the selection of single crosses the direction of the crossing is very important (Rotili and Zannone, 1977). 4) The positive correlation between pod fertility and seed-setting will allow us to utilize these two parameters in the selection for seed production. These results suggest that the polycross method in the construction of synthetic varieties could give negative results or results of little efficiency for the seed production and for the forage production. This method, even without the selective effect of pollinators, does not permit to know the reproductive possibilities of an individual plant of the polycross group. The real situation is very far from panmictic conditions because it is very frequent to have a high variability among parental plants for the quantity and quality of pollen that influence the pollen competition. Therefore even in the construction of synthetic varieties a better solution is to utilize the diallel cross method realized by hand without emasculation.

Reference

Rotili, P.,Zannone, L., 1977. Quantitative analysis of fertility in lucerne at different levels of selfing. Ann. Amélior. Plantes, 27,(3), 341-354.