Mg. Milgroom et Se. Lipari, SPATIAL-ANALYSIS OF NUCLEAR AND MITOCHONDRIAL RFLP GENOTYPES IN POPULATIONS OF THE CHESTNUT BLIGHT FUNGUS, CRYPHONECTRIA-PARASITICA, Molecular ecology, 4(5), 1995, pp. 633-642
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.