The transfer of brown planthopper resistance from Oryza eichingeri to O. sativa

Oryza eichingeri, a distantly-related diploid wild species of cultivated rice with CC genome, is an important source of resistance to brown planthopper (BPH). Interspecific hybrids between Oryza sativa cv. 02428 and two accessions of O. eichingeri from Uganda were therefore produced through embryo rescue to transfer the BPH resistance, and the crossability was only 0.36% and 1.62%. The F₁ hybrids were vigorious and profuse in tillering but highly male sterile, the mean frequency of bivalents at MI was 1.33 to 1.37 with a range of 0-4. The infertile BC₁F₁ and F₂ progenies, derived from backcrossing to 02428 and selfing of F₁ hybrids, were similar in plant appearance and . were further cytologically ascertained to have identical genomic constitution of AAC. These allotriploids had a chromosome configuration of (12.02∼12.08)I+(11.67∼11.89)II + (0.04∼0.19)III at MI of PMCs. The chromosome number of 42 BC₁F₂ plants and 9 BC₂F₁ plants varied from 24 to 38, from which 21 plants with 2n = 25 and 21 diploid plants with 2n = 24 were isolated. Five out of the 21 diploid plants tested were resistant to BPH. This indicated the successful transfer of chromosome segment carrying BPH resistant gene(s) from the two accessions of O. eichingeri to cultivated rice. Moreover, traits absent in both parents, such as tall plant height and large panicle, were also observed in some introgression lines, presumably resulted from the interaction of genes in genomes A and C.