Towards alfalfa free-hybrids. Comparison for pod fertility of 2S2Syn2 vs. the corresponding 4S2Syn2 and double hybrids vs. the corresponding 8S2Syn2.

P.Rotili*, C. Scotti*, S.Gnocchi*, D.Kertikova** and G.Gnocchi*

*Istituto Sperimentale per le Colture Foraggere, Lodi, Italy

**Forage Institute, Pleven, Bulgaria

Free – hybrid program

1) Four constituents

2) Eight constituents

A B C D

E F G H I L M N

Diallel cross

1997

Diallel cross

6 2S2Syn1(SH)

4S2Syn1

1998

16SH

8S2Syn1

6 2S2Syn2

4S2Syn2

1999

8DHF1

8S2Syn2

6 2S2Syn3

4S2Syn3

2000

8DHF2

8S2Syn3

Diallel cross

 

 

Diallel cross

 

15DH

4S2Syn4

2001

28OH(octuple)

8S2Syn4

 

 

 

 

 

Agronomic test

2002

Agronomic test

The same individual plants, selected for vigor (DMY at the 5th cut 1998) and simultaneous flowering among the respective Simple Hybrid (SH) families, were used to obtain the generations 2S2Syn2 (5 plants/combination), 4S2Syn2 (30 plants), Double Hybrid (3+3 plants), and 8S2Syn2 (84 plants)(Rotili et al., 1999). All the crossings are made by hand without emasculation.

The main results on pod fertility (average seed number per pod) can be summarized as follows:

  1. Four - constituent program - Two groups, A and B were constituted by crossing S2 plants coming each from different sources. For the two groups A and B: a) average pod fertility in 4S2Syn2 is significantly higher (P<0,1%) than in 2S2Syn2. b) The maximum values of pod fertility found among the six 2S2Syn2 never exceed the corresponding 4S2Syn2. c) Average pod fertility is stable going from 2S2Syn1 to 2S2Syn2 even if inbreeding coefficient is expected to increase. Pod fertility strongly increases passing from 4S2Syn1 to 4S2Syn2.

  2. Eight - constituent program - Three groups with different levels of genetic diversity were constituted: group C with the 8 S2 constituents coming each from different sources, group E with the 8 S2 constituents coming from two different sources (50% each), and group D with all the constituents originating from a single variety. a) For the three groups, average pod fertility in DH F1 and 8S2Syn2 is not significantly different. b) The maximum values found among the 16 Simple Hybrids crossed to obtain the 8 Double Hybrids always exceed the corresponding 8S2Syn2. c) Group D, with the lowest genetic diversity, shows pod fertility values, both in DH F1 and in 8S2Syn2, significantly lower than groups E and C. d) In all the three groups pod fertility increases going from SH to DH F1. The same is true for the 1st and 2nd generation of 8S2Syn. In both cases group C, with the maximum genetic diversity, shows the highest increases in pod fertility.

Reference

Rotili, P., Gnocchi,G. Scotti,C. Zannone,L. 1999.Some aspects of breeding methodology in alfalfa. www.naaic.org/TAG/TAGpapers/rotili/rotili.html

 

 

Previous Page