Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

 

Poster Abstract - 4.40

 

TOWARDS ALFALFA FREE-HYBRIDS. DIALLEL CROSSES AMONG THE FREE-HYBRID PARENTAL CONSTITUENTS: POD FERTILITY

 

ROTILI P.*, SCOTTI C.*, GNOCCHI S.*, KERTIKOVA D.**, GNOCCHI G.*

 

*) Istituto Sperimentale Colture Foraggere, Lodi, Italy

**) Institute of Forage Crops, Pleven, Bulgaria

 

 

alfalfa, diallel cross, free-hybrid, pod fertility

 

General objectives: a)Construction of free-hybrids in alfalfa(Medicago sativa L.),using partially inbred (S2) parental plants (Rotili et al., 1999). b)Experimental evaluation of free-hybrids and synthetics derived from the same parental plants (Table 1).

 

Table 1. Free-hybrid program

 

4 - constituents

8 - constituents

 

A B C D

E F G H I L M N

1997

Diallel cross

Diallel cross

1998

6 2S2Syn1 (SH)

4S2Syn1

16 2S2Syn1 (SH)

8S2Syn1

1999

6 2S2Syn2

4S2Syn2

8 S2DHF1

8S2Syn2

2000

6 2S2Syn3

4S2Syn3

8 S2DHF2

8S2Syn3

2001

Diallel cross

 

Diallel cross

 

 

15 S2DH

4S2Syn4

28 S2OH

8S2Syn4

2002-03

Agronomic Test

SH: Simple Hybrid; DH: Double Hybrid; OH: Octuple Hybrid

 

4-constituents program: Partly inbred constituents originating each from different sources (groups A and B). Diallel crossing among 6 2S2Syn3 parents to obtain Double Hybrids (DH).

 

8-constituents program: Partly inbred constituents originating each from different sources (group C), each from two different sources (group E) and each from a single variety (group D). Diallel crossing among 8 S2DHF2 parents to obtain Octuple Hybrids (OH).

 

The individual plants crossed at each generation derived from selection for vigor (DMY/plant) within the respective families. All the crossings were made by hand without emasculation. The variance analysis was made by Method III Model I of Griffing ; since data on pod fertility concern the mother plant and not their progenies, general and specific abilities to give seeds are dealt with in the analysis.

 

I. For both the variety models (free-hybrids and synthetics) pod fertility significantly increased going from 4 to 8 constituents. Irrespective of the number of constituents, pod fertility was significantly higher in the synthetics than in free-hybrids. In 8-constituents program, diallelic crossings in group D, with the minimum genetic diversity, showed pod fertility values significantly lower than in group E (50% of genetic diversity); group C (100% of genetic diversity) was intermediate between E and D. Comparing the diallel crossings at the beginning and at the end of the program (Table 1), pod fertility of the 2S2Syn3 parents (4-constituents program) was not significantly different from that of S2 parental plants used at the beginning; the S2DHF2 parents (8-costituents program) showed a significant increase in pod fertility compared to the initial S2 parents.

 

II. The analysis of variance showed that the general ability (GA) to give seeds was always highly significant in the 5 diallel groups; the same was true for the specific ability (SA) except for group B. The GA/SA ratio was positive, ranging from 2.25 to 9.09, in groups A, B  and E ; it nearly equaled the unity in groups C and D. Comparing the GA/SA ratio in diallel crossings at the beginning and at the end of the program, an increase of the ratio was observed for both the groups A and B (4-constituents program) and a decrease for the groups C, D and E (8-constituents program).