SPATIAL-ANALYSIS OF NUCLEAR AND MITOCHONDRIAL RFLP GENOTYPES IN POPULATIONS OF THE CHESTNUT BLIGHT FUNGUS, CRYPHONECTRIA-PARASITICA

Spatial structure of both nuclear and mitochondrial RFLPs were studied in several populations of the chestnut blight fungus, Cryphonectria p arasitica, using a variety of spatial autocorrelation tests designed t o detect nonrandom patterns. Fungal individuals were sampled from cank ers on infected chestnut trees, and the location of each tree was mapp ed. Single-locus nuclear RFLPs, nuclear fingerprints, and mitochondria l DNA haplotypes were determined for each individual. Individuals with the same DNA fingerprint genotypes occurred closer together than woul d be expected at random in four of the five plots, while mitochondrial DNA haplotypes were aggregated in all five plots. Genetic distances b etween individuals, expressed as one minus the proportion of shared re striction fragment size classes for fingerprints and mitochondrial hap lotypes, were significantly correlated with Euclidean distances betwee n individuals in four of the five populations, but these correlations were very weak (r < 0.18). The same DNA fingerprint and single-copy nu clear RFLP alleles occurred on the same trees or immediately neighbour ing trees more often than would be expected at random. Most of the agg regation for all three genetic markers occurred among individuals with in the same cluster of chestnut stems or on neighbouring trees. Lack o f spatial autocorrelation in one population was probably due to sampli ng on a larger scale that was too coarse to detect any patterns. Signi ficant aggregation of genotypes in C. parasitica is most likely caused by some degree of restricted dispersal within populations. The implic ations of restricted dispersal are discussed in relation to the breedi ng system and isolation by distance in populations of C. parasitica.