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A total of 1,110 decamer primers were screened for RAPD markers linked to a dominant allele in hazelnut ( Corylus avellana) that confers resistance to eastern filbert blight caused by Anisogramma anomala. Twenty RAPD markers linked in coupling, and five markers linked in repulsion, were found. A seedling population was used to construct a linkage map of the region flanking the resistance locus. The map spans 46.6 cM, with 14 markers on one side of the resistance locus and eight on the other side. Eleven markers showed less than 3% recombination with resistance, including three that showed no recombination. Seven of these 11 markers are sufficiently robust to allow their use in marker-assisted selection. These include AA12(850) which shows no recombination, and six markers on one side of the resistance locus: 173(500), 152(800), 122(825), 275(1130), H19(650) and O16(1250). Marker 268(580), which flanks the resistance locus on the other side, is also suitable for use in marker-assisted selection, but shows 5.8% recombination with resistance. Other markers are less suitable for marker-assisted selection because of sensitivity to changes in primer or MgCl(2) concentration, or the long time required for electrophoresis to separate bands of similar size. The 16 markers closest to the resistance locus were cloned and sequenced. The W07(365) marker, which showed no recombination with the resistance locus but is difficult to score, includes a CT microsatellite repeat. The sequence information will allow the design of SCAR primers and eventual map-based cloning of the resistance allele.

Anonymous DNA fragments from the genome of cultivated avocado (Persea americana Mill.) were cloned into a plasmid vector and used to screen a total of 36 cultivars. There is a high level of polymorphism among cultivars allowing all cultivars to be assigned a unique genotype based on 14 genetic loci. A cluster analysis of genetic similarities among cultivars revealed three major clusters that correspond to the three major racial groupings of cultivated avocado. Additional clusters appear to reflect cultivars derived through interracial hybridization.

Plants native to boreal, temperate, and subtropical regions are subjected to large seasonal variations in temperature. In these regions, woody perennial plants have evolved annual growth cycles that promote long-term survival and growth. These annual growth cycles involve alternations between active shoot growth and vegetative dormancy (endodormancy) that are closely timed with seasonal changes in the local climate. Dormancy, in general, is defined as the temporary suspension of visible growth of any plant structure containing a meristem (Lang, 1987). Endodormancy, which develops in the fall, is characterized by a requirement for sustained exposure to low, near-