毕研胜ꎬ郑莉娜ꎬ张璐ꎬ王瑜晖ꎬ钱春桃∗.

[Objectives]The paper aimed to obtain double haploids of the melon (2n=2x=24) inbred line BPC-4 by distant hybridization, and analyse botanical traits and genomic changes. [Methods]The melon inbred line BPC-4 was used as the maternal parent to cross with eight different materials of the genus Cucumis. F1 generation of the obtained cross was selfed to obtain F2 and F3,which were used for chromosome number observation, SSR molecular marker analysis and plant traits consistency in the same generation to identify their double haploid feature; F2 and F3 were genome resequenced and then purified site distribution and stability of double haploid genome SNP were analyzed. [Results]Among the eight hybrid combinations, three seeds were obtained from the combination of (BPC-4×cucumber inbred line YPJ-6) (2n=2x=14),among which one seed was planted and 50 self-crossing progenies were obtained. The chromosome number of the F2 generation were identified to be 2n=2x=24. SSR identification showed that the PCR bands by 27 SSR markers in F2 generation were the same as those of the maternal parent. The PCR bands of F2 was consistent among single plants and F3 was not separated, indicating that the F2 gene loci were homozygous. Statistical analysis of botanical traits showed that the main changes in F2 were compact and dwarf compared with BPC-4. The average values of internode spacing, stem diameter, leaf length and width, and petiole length in F2 were all lower than those of BPC-4,and F2 individual plants were consistent. The above results proved that the progenies obtained from the distant crosses were double haploid, and thus F1,F2 and F3 were named as DH0,DH1 and DH2,respectively. The data of seed number and seed setting rate of dihaploid showed that fertility of DH0 was low, while fertility of DH1 and DH2 had recovered up to that of BPC-4 and could be used for seed propagation and preserved through self-crossing. The genome resequencing revealed that the double haploid SNP loci were further purified by 0.26% compared with BPC-4,and the new purified loci were distributed on all 12 chromosomes. The difference of purified loci between DH1 and DH2 of the double haploid selfing progeny was 1 016,accounting for only 0.05%,which was smaller than the heterozygosity difference of 3.13% from Mendelian theory conventional self-crossing S4 to S5,indicating that the double haploid genome had been stabilized. [Conclusions]Genome resequencing and botanical trait variation demonstrated that it was still necessary to create a double haploid in melon after four generations of self-crossing, and that the double haploids obtained could be saved by seed for further breeding and theoretical studies.  [ABSTRACT FROM AUTHOR]