An F2 population of pea (Pisum sativum L.) consisting of 174 plants was analysed by restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) techniques. Ascochyta pisi race C resistance, plant height, flowering earliness and number of nodes were measured in order to map the genes responsible for their variation. We have constructed a partial linkage map including 3 morphological character genes, 4 disease resistance genes, 56 RFLP loci, 4 microsatellite loci and 2 RAPD loci. Molecular markers linked to each resistance gene were found: Fusarium wilt (6 cM from Fw), powdery mildew (11 cM from er) and pea common Mosaic virus (15 cM from mo). QTLs (quantitative traits loci) for Ascochyta pisi race C resistance were mapped, with most of the variation explained by only three chromosomal regions. The QTL with the largest effect, on chromosome 4, was also mapped using a qualitative, Mendelian approach. Another QTL displayed a transgressive segregation, i.e. the parental line that was susceptible to Ascochyta blight had a resistance allele at this QTL. Analysis of correlations between developmental traits in terms of QTL effects and positions suggested a common genetic control of the number of nodes and earliness, and a loose relationship between these traits and height.

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Breeding for resistance to extremes of temperature and moisture in cool season food legumes is limited by the lack of adequate screening techniques . The success of each technique depends upon the representativeness and reproducibility of the type of stress created . Descriptions of successful techniques are presented for frost and terminal drought . Development of new screening tests designed to select for specific adaptive traits require a better knowledge of the mechanisms of resistance in these crops, especially to drought . Rooting depth, early vigor, reduced branching, and osmotic adjustment are discussed . Other mechanisms of resistance to drought, heat, freezing, or chilling have been proposed but need to be studied jointly by crop physiologists and plant breeders .

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