Molecular analysis of introgressive breeding in coffee (Coffea arabica L.)

Nineteen arabica coffee introgression lines (BC1F4) and two accessions derived from a spontaneous interspecific cross (i.e. Timor Hybrid) between #Coffea arabica (2n=4x=44) and #C. canephora (2n=2x=22) were analysed for the introgression of #C. canephora genetic material. The Timor Hybrid-derived genotypes were evaluated by AFLP, using 42 different primer combinations, and compared to 23 accessions of #C. arabica and 8 accessions of #C. canephora. A total of 1062 polymorphic fragments were scored among the 52 accessions analysed. One hundred and seventy-eight markers consisting of 109 additional bands (i.e. introgressed markers) and 69 missing bands distinguished the group composed of the Timor Hybrid-derived genotypes from the accessions of #C. arabica. AFLP therefore seemed to be an extremely efficient technique for DNA marker generation in coffee as well as for the detection of introgression in #C. arabica. The genetic diversity observed in the Timor Hybrid-derived genotypes appeared to be approximately double that in #C. arabica. Although representing only a small proportion of the genetic diversity available in #C. canephora$, the Timor Hybrid obviously constitutes a considerable source of genetic diversity for arabica breeding. Analysis of genetic relationships among the Timor Hybrid-derived genotypes suggested that introgression was not restricted to chromosome substitution but also involved chromosome recombinations. Furthermore, the Timor Hybrid-derived genotypes varied considerably in the number of AFLP markers attributable to introgression. In this way, the introgressed markers identified in the analysed arabica coffee introgressed gentotypes were estimated to represent from 9$ genome. Nevertheless, the amount of alien genetic material in the introgression arabica lines remains substantial and should justify the development of adapted breeding strategies. (Résumé d'auteur

Architectural analysis of root system of sexually vs. vegetatively propagated yam (Dioscorea rotundata Poir.), a tuber monocot

A-09-11International audienceArchitectural descriptors were used to understand root system structure and development in white yam (Dioscorea rotundata Poir., Dioscoreaceae), a tuber monocot. Observations were made on seedlings and plant derived from tuber fragments, cultivated in greenhouses over a developmental cycle. This study demonstrated that both seedlings and plants derived from tubers have two distinct root systems that are highly organized. The first (seminal or tubercular) has been called the temporary root system which is small and short lived. The architectural unit here is made up of two root axis categories. The second (adventitious in both cases) has been called the definitive root system. It is larger and has a far longer lifespan than temporary root systems. The architectural unit here is made up of three root axis categories. Adventitious root systems are formed by structural repetitions of their own architectural unit. The temporary and definitive root systems possess the same structural and functional properties and become established and succeed one another in time following an identical developmental sequence. Neo tuber development is coupled with the root system development. Our results highlight to what extent it is important to study simultaneously the different parts of a root system in order to understand its development. This study confirms how architectural tools can be used to understand root system structure and development and prove accurate informations on root system development for use in agricultural management