Restriction fragment length polymorphism (RFLP) analysis and GISH (genomic in situ hybridization) were performed on euploid plants derived from crosses between Oryza sativa (2n = 24, AA) IRGC accession:02428 and two IRGC accessions, 105159 and 105163 of O. eichingeri (2n = 24, CC). The 164 RFLP markers used in this study cover all 12 rice chromosomes, with a marker interval of 0.4-46.3 cM. 60 of the 67 euploid plants were identified as introgression lines, each carrying 1-6 small O. eichinger segments integrated on chromosomes 1, 2, 6, or 10, identified by markers RG236, R210, G275, C601, G89-2B, RG752. In the somatic chromosome preparations of F₁ hybrid, O. eichingeri chromosomes, fluorescing greenish-yellow in the sequential GISH, appeared to be longer and to contain more heterochromatin than O. sativa ones. In addition, GISH identification presented direct evidence for the transfer of small segments from O. eichingeri to Oryza sativa chromosome(s) which were subsequently recognized according to their condensation pattern, arm ratio, and chromosome length.

The two donor O. eichingeri parents showed high level of resistance to brown planthopper, while the cultivated rice variety was susceptible (Heinrichs et al. 1985). Intergenomic F₁ hybrids obtained by embryo rescue were backcrossed to 02428 and, meanwhile, self-pollinated to produce BC₁ and F₂ plants; both were identified as allotriploids (2n = 36, AAC) due to the formation of reduced gametes in the F₁ plants (Yan et al. 1997). In this investigation, a total of 67 cytologically identified euploid plants, 64 from the backcross progeny of the above allotriploids and three from the BC₄ generation of a monosomic alien addition line, were subjected to RFLP analysis.