The variability of the ribosomal DNA intergenic spacer (IGS) was analy
sed in 58 cultivars from a worldwide collection and 14 Spanish landrac
es of hexaploid oats. IGS sequences were amplified by the polymerase c
hain reaction using primers complementary to conserved sequences of th
e ribosomal genes. Twelve IGS length variants ranging from 4090 to 321
0 bp were observed; some are frequent and distributed worldwide wherea
s others seem to be restricted to Spanish landraces. Variability in le
ngth variant patterns among cultivars and landraces was extensive: a t
otal of 28 different patterns was observed, which included two to six
length variants. No variation was detected within cultivars except in
six Spanish landraces. Length variants and patterns were unevenly dist
ributed between bred cultivars, in which the longest were frequent, an
d landraces, in which some of the shortest were observed. No different
iation was found between spring and winter sown material. The possible
relationship between IGS length variants and breeding and environment
al adaptive responses, other than those related to the spring or winte
r habit, are discussed.