Anthracnose, one of the most important diseases of common bean (Phaseolus vulgaris), is caused by the fungus Colletotrichum lindemuthianum. A "candidate gene" approach was used to map anthracnose resistance quantitative trait loci (QTL). Candidate genes included genes for both pathogen recognition (resistance genes and resistance gene analogs [RGAs]) and general plant defense (defense response genes). Two strains of C. lindemuthianum, identified in a world collection of 177 strains, displayed a reproducible and differential aggressiveness toward BAT93 and JaloEEP558, two parental lines of P. vulgaris representing the two major gene pools of this crop. A reliable test was developed to score partial resistance in aerial organs of the plant (stem, leaf, petiole) under controlled growth chamber conditions. BAT93 was more resistant than JaloEEP558 regardless of the organ or strain tested. With a recombinant inbred line (RIL) population derived from a cross between these two parental lines, 10 QTL were located on a genetic map harboring 143 markers, including known defense response genes, anthracnose-specific resistance genes, and RGAs. Eight of the QTL displayed isolate specificity. Two were co-localized with known defense genes (phenylalanine ammonia-lyase and hydroxyproline-rich glycoprotein) and three with anthracnose-specific resistance genes and/or RGAs. Interestingly, two QTL, with different allelic contribution, mapped on linkage group B4 in a 5.0 cM interval containing Andean and Mesoamerican specific resistance genes against C. lindemuthianum and 11 polymorphic fragments revealed with a RGA probe. The possible relationship between genes underlying specific and partial resistance is discussed.

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The effects of thidiazuron, benzyladenine and zeatin were tested with respect to bud regeneration of different flax explants from hypocotyls, cotyledons and apices of two fibre varieties (Ariane, Viking) and one linseed variety (Antarès). These three cytokinins were tested either alone or in combination with naphthalene acetic acid, indole acetic acid or 2,4-dichlorophenoxyacetic acid.Hypocotyls were the most responsive explants. Thidiazuron was significantly the most effective followed by benzyladenine, and then zeatin, in inducing organogenesis from hypocotyl segments. The optimal thidiazuron concentration for bud regeneration from hypocotyls was 0.1-0.3 μM in combination with 0.01 μM of naphthalene acetic acid. Six days after plating, shoot initials began to appear on hypocotyl sections compared with ten to fifteen days when using benzyladenine or zeatin.

complement an experimental study of the possible interest for plant breeders of an allele increasing recombination rates. In the first simulation study, 4 populations of 10 individuals were simulated in the case of high (45%), medium (19.6%) and low (6.9%) recombination frequencies. Ten-plant populations were derived by one generation, either from selfing or from crossing in a circular mating design, from each of the 4 populations. For each initial population, the distribution of the genetic variances in the populations obtained by one mating system overlapped widely in the 3 cases of recombination rates considered, whether the initial population presented an excess of coupling phase, or an excess of repulsion phase. An experimental assessment of the effect of recombination rate differences on genetic variability of quantitative traits is therefore likely to be difficult. The second study simulated a recurrent selection program in the case of high (45%), medium (19.6%) and low (9%) recombination rates. The mean genetic value increased somewhat more slowly and reached a slightly lower value for low recombination rates, whereas the genetic variance remained the highest after the second selection cycle. The evolutions in genetic mean values and genetic variances were almost identical for medium and high recombination frequencies. Thus, an allele which increases recombination rates will only be of interest in the case of close linkage or difficult crossing. Otherwise, a circular