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Heterochromatin distribution in barley chromosomes was investigated by analyzing the C- and N-banding patterns of four cultivars. Enzymatic maceration and air drying were employed for the preparation of the chromosome slides. Although the two banding patterns were generally similar to each other, a clear difference was observed between them at the centromeric sites on all chromosomes. Every centromeric site consisted of N-banding positive and C-banding negative (N(+) C(-)) heterochromatin in every cultivar examined. An intervarietal polymorphism of heterochromatin distribution was confirmed in each of the banding techniques. The appearance frequencies of some bands were different between the two banding techniques and among the cultivars. The heterochromatic differentiation observed is discussed with respect to cause.

The Chinese native rice cultivar 'Maowangu' expresses a high level of resistance to many races of rice blast (Pyricularia grisea) collected from North China and Japan. 'Maowangu' was crossed with 10 Japanese differential cultivars and the susceptible Chinese cultivar 'Lijiangxintuanheigu' (LTH). AUelism tests were conducted in the Fj populations with rice blast races. The resistance of 'Maowangu' was governed by two dominant genes which were non-allelic to the resistance genes at seven loci: Pi-a, Pi-i, Pi-k, Pi-z, Pi-ta, Pi-b, and Pi-t. To identify the two resistance genes, two F3 Unes of'Shin 2/Maowangu' segregating 3R:1S were selected for linkage tests in 1994. One was linked to marker genes C and Amp-3 on chromosome 6 with recombination frequencies of 35.8 + 6.4% and 42.1 +6.2%, respectively, and the other to Amp-1 on chromosome 2 with a recombination frequency of 37.6 + 6.0%. To confirm these results, two F3 lines of 'LTH/Maowangu' were selected for linkage tests in 1995. The one was linked to Amp-3, and other was linked to Amp-1, with recombination frequencies of 36.9 + 3.1% and 34.3 + 3.2%, respectively. The two genes on chromosomes 6 and 2 were designated Pil3{t) and Pil4(t), respectively.

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