Sweetpotato cultivar “Xushul 8”（ I. batatas （ L. ） Lam. ， 2n = 6x = 90） as maternal， were pollinated with pollen from two related wild species， I. grandifolia （2n = 2x = 30） and I. purpurea （2n = 2x = 30）. To overcome interspecific cross-incompatible barrier， we implied a certain content of plant growth regula- tors to the stalk of the pollinated flower，followed as 100mg/1 GA3 +50rag/1 6-BAo It should be trea- ted at least 7 days consecutively for good fruits and seed sets.
For mitotic chromosome counting，the F. hybrids stem was cut and put in water to obtain roots. Grown about 1 cm in length，young root tips were pre-treated with 8-hybroxyquinoline for 2 h at 20C and fixed in 3 1 ethanol-acetic acid for 24 h. Root tips were squashed in Carbol fuchsin and chromo- some counting was carried out. For meiotic study， the F1 hybrids young floral buds of different sizes were collected and also fixed in 3 1 ethanol-acetic acid for 24 h，then were transferred to 70 % alcohol and stored under refrigeration until use. The anthers were dissected out from floral buds. And micros- porocytes were squashed in Carbol fuchsin. Photomicrographs were made with a Leica DM2500 micro- scope. Pollen viability was assessed with 2 % acetocarmine in freshly ripened pollen grains.
For inter-simple sequence repeat（ISSR）analysis， genomic DNA was extracted from freeze-dried leaves from plants grown in field. The leaf tissue was ground to a fine powder and DNA extracted u- sing the improved CTAB method. The PCR amplification conditions adopted were similar to those of Huang et al. （2000）. The 30-mer primes（UBC setNo. 9）were synthesized and were finally selected for use in this study. Amplifications were carried out in 1.5 mM MgC12，2%formamide，200 nM primer， 1 U of Taq polymerase，and 10 ng of genomic DNA per 20 1 reaction. PCR amplification was performed using the following cycle profile：l cycle at 94C for 5 min followed by 45 cycles at 94C for 45 s，50- 55C （depending on primers used）for 45 s，72C for 1.5 rain；and a final 7-min extension at 72C. Theamplified products were electrophoresed on 1.5 % agarose gels and detected by staining with ethidiumbromide.Results and AnalysisI. Interspecies hybridityWith Xushu18 as material，it was pollinated with 68 and 59 flowers of two related species， ， grandi-folia and I. purpurea，respectively. To overcome the ovary development barrier， the complex of plantgrowth regulators were applied to stalk of flowers. 2 and 11 fruits were obtained from each cross. Andeach set 3 and 5 satiation seeds（Table 1）. Owing to seeds weak germination and growth， only oneseedling of each cross grew into adult plant. By somatic chromosome preparation， two plant were both60 chromosomes which verify the two hybrids maybe come from the true hybridity of cultivars（2n=90）and two wild species（2n=30）. Both hybrids（/， batatas X I. grandi f olia and I. batatas X I. pur-purea） were morphologically different in leaf shape and leaf color（Fig， l a-b）， and intermediate betweentheir respective parents in tube root morphology（Fig. 1c-e）The F1 hybrid I. batatasX I. grandifolia was characterized by fast-growing， muti-branching and slim tube root（Fig， l d）， while the hybrid I. batatas X I. purpurea was medium-growing，short-branching and medium tube root（Fig， le）.