Search

Genomic selection ( GS) is a powerful method for exploitation of DNA sequence polymorphisms in breeding improvement, through the prediction of breeding values based on all markers distributed genome-wide. Forage grasses and legumes provide important targets for GS implementation, as many key traits are difficult or expensive to assess, and are measured late in the breeding cycle. Generic attributes of forage breeding programmes are described, along with status of genomic resources for a representative species group (ryegrasses). Two schemes for implementing GS in ryegrass breeding are described. The first requires relatively little modification of current schemes, but could lead to significant reductions in operating cost. The second scheme would allow two rounds of selection for key agronomic traits within a time period previously required for a single round, potentially leading to doubling of genetic gain rate, but requires a purpose-designed reference population. In both schemes, the limited extent of linkage disequilibrium ( LD), which is the major challenge for GS implementation in ryegrass breeding, is addressed. The strategies also incorporate recent advances in DNA sequencing technology to minimize costs. [ABSTRACT FROM AUTHOR]

The suitability of different protocols was compared for entire plant regeneration by somatic embryo-genesis, of the forage plants Lolium multiflorum Lam. (Italian ryegrass) and Festuca arundinacea Schreb. (tall fescue). In the first protocol, immature embryos were used as starting material, while mature seeds were retained in the other two. Whichever the considered protocol, undifferentiated calli were produced on MURASHIGE and SKOOG MS medium supplemented with 2,4-D. The calli were subcultured in the dark on solid MS agar medium, containing 5 mg/l 2,4-D (protocol 2) or on solid MS medium followed by transfer to a rotated liquid MS medium with 2 mg/I 2,4-D (protocol 1). In these conditions, induction of somatic embryogenesis occurred, and whole plants were regenerated during a limited lapse of time, upon transfer in the light, to MS medium supplemented with BAP but devoid of 2,4-D. The simultaneous elimination of 2,4-D and transfer to light appeared essential for full regeneration of the plants. Using this characteristic, an additional step was added to a new protocol (protocol 3) in which microcalli, cultured on liquid MS medium containing 5 mg/l 2,4-D, were transferred to the same medium with 2 mg/l 2,4-D, in the dark. In these conditions, the suspensions kept their embryogenic potential for months. In all cases, plantlets were successfully transferred into the soil. An evaluation of the somaclonal variation potential of the plants issued from each protocol is now underway. [ABSTRACT FROM AUTHOR]

From 22 genotypes, selfed (S1) and testcross progenies were investigated. The latter were generated by i) polycross (PX) and ii) 2 topcrosses (TC) using cms-inbred lines as a tester. Progenies were tested for annual dry matter yield in 3 successive years, the 3-year average was 76.7 dt/ha for S2 and 76.9, 80.1 and 74.5 for PX, TC 1 and TC 2, respectively. Genetic variance was highest for S11 (20.42), while the average of the 3 testcrosses was 12.22. However, the genotype-year interaction variance of S: Was 52.21, being 2--3 times greater than for the 2 topcrosses. PX progenies were the most stable across years. Predicted response to selection was highest for S1 (10.4 %). Genetic correlation (rg) between S1 and the testcrosses was highest with TC 2 (rg = 0.593+ +). [ABSTRACT FROM AUTHOR]