| Cucumber (Cucumis sativus L.) is one of the most important vegetables in China, and also the most popular vegetables all over the world. As a member of Cucurbitaceae, the abundant sexual types of cucumber enable it to be one of the model plants for the sex expression research. Meanwhile, the sex differentiation and the sex expression are directly related to yield and quality of cucumber. The gynoecious lines can make the hybrid seed production easier. At present, the introduced cucumber varieties of high yields in protected cultivation are mainly gynoecious lines. The varieties of stable and good fruit-set subgynoecious type, multi-pistillate type and monoeciou type are popular in the cucumber production for the fresh/pickling market. However, the sex expression of cucumber is complicated and diverse. The sexual types and their stability of cucumber germplasm resources have not been identified, and the existing researches cannot explain the genetic mechanisms of all cucumber sexual types completely. Using the traditional method for sex breeding is very inefficient. Therefore, it is necessary to evaluate the sexual types and their stability of cucumber core collection and study the inheritance of typical cucumber sexual types and the molecular mechanism related to the sex determination. All of these researches will not only be useful for thorough understanding the regulation mechanism of cucumber sex expression, but also have theoretical and practical significance in speeding up the sex breeding in cucumber.In this paper, the identification and evaluation of sexual types and their stability of cucumber core collection were carried out, and the inheritance of the node rate of multiple female flowers (NRMFF) to single female flower per pistillate flower node was analyzed using the F2 segregation population derived from the cross combination between the inbred line with multiple female flowers per pistillate flower node ('1613EF') and the inbred line with single female flowers per pistillate flower node ('YX05-3-10'). Further, QTLs related to NRMFF were located based on the construction of a cucumber molecular genetics map. The main results are as follows:1. The sexual type identification of the cucumber core collection in Spring and Autumn (total 322 germplasm) showed that there had single female flower, multiple female flowers, hermaphroditic flowers and male flowers in terms of the flower type in one node. According to the node rate of the pistillate flowers (including single female flower / multiple female flowers / hermaphroditic flower, ab. NRPF), the NRPF ranged from 2.43% to 100% among all accessions in Spring. 88.82% of accessions had the NRPF of 10%～60%. In Autumn, the NRPF, which decreased significantly for most germplasm, was distributed from 0 to 100%. 91.93% of accessions displayed the NRPF of 10%～30%. Based on the sex expression of core collection in Spring and Autunm, the classification of cucumber exsual types had been modified into ten types as gynoecious, subgynoecious, common monoecious, subandroecious, androecious, multi-pistillate, hermaphroditic, gynomonoeciou, monoecious-hermaphroditic, andromonoecious types. Most of germplasm presented as the common monoecious type and the subandroecious type, which accounted for 94.41% in Spring. There were 10 accessions of the gynoecious type without any male flowers. About 93.48% accessions were subandroecious types in Autumn, even eight of the ten germplasm being gynoecious types in Spring had a few male flowers in Autumn. There were 4 accessions belonging to androecious type in Autumn. Meanwhile, 2 accessions of multi-pistillate type and 2 andromonoecious type had been discovered in the cucumber core collection. The flower type of multi-pistillate flowers and hermaphroditic flower showed stable whenever Spring or Autumn, but the NRPF in this two special sexual types also showed the downtrend in Autumn.Identification on the sex stability of the cucumber core collection showed that the single flower type of one germplasm had less change between Spring and Autumn; but the maximum difference in NRPF of the same germplasm between Spring and Autumn was 63.07% (DF280), and the minimum difference was 0 (DF301, DF308). In Autumn, the NRPFs of most germplasm had dropped 10%～40% compared to the NRPF in Spring. According to the difference significance of the NRPF of the same germplasm in different seasons by T-test, all germplasm were classified into three groups. The first one was the stable type, which included 25 accessions. The second one was the sensitive type containing 61 accessions and the third one was the highly sensitive type of 236 accessions. By analyzing the relation between the change of temperature and sunshine duration and the change of sexual types in the cucumber germplasm during the plant growth in Spring and Autumn, it was found that the type of single flower was less affected and showed stable. But no matter single female flower, multi-pistillate flowers or hermaphroditic flower, NRPFs of most germplasms was affected by the temperature and sunshine hours to some extent.2. F1, BC1P1, BC1P2 and F2 populations were derived from the cross between the inbred line with multiple female flowers per pistillate flower node ('1613EF') and the inbred line with single female flower per pistillate flower node ('YX05-3-10'). The inheritance of the NRMFF was studied by joint analysis of six generations based on major genes plus poly genes mixed inheritance model. The main results showed that the fittest genetic model for the target character was two major genes plus poly genes mixed inheritance model (E-0-0). It meant that this trait was controlled by 2 major genes, the polygene effect also existed, and high NRMFF was recessive or partially recessive to low NRMFF. The major genes had synergistic action to the node of multiple female flowers, because the additive effects of the major genes and the additive×additive effects between two major genes was positive. But the dominant×dominant interaction effects between poly genes was -43.73, the high negative-effect enable the NRMFF decreased. In the F2 population, the heritability of major genes was 90.44%. In the BC1P1 and BC1P2 populations, the heritability of major genes was 90.16% and 58.42% respectively. In the BC1P1 and F2 generation, the heritability of poly genes was 5.87% and 4.91% respectively, the heritability of poly genes in BC1P2 was 0. The environment played certain role in the NRMFF and the environment variance was 3.97% ~ 41.58%.3. The F2 segregation population of 287 individuals was derived from the cross between the inbred line with multiple female flowers per pistillate flower node and the inbred line with single female flower per pistillate flower node ('1613EF'×'YX05-3-10'). 129 SSR makers were selected showing polymorphism between the parents from 1632 SSRs which were developed based on the whole genome sequencing in cucumber and 47 SSRs which were published. According to the linkage analysis of the 129 SSR makers by using the JoinMap 4.0, a SSR genetic map of seven linkage groups and 128 SSR makers was constructed. Three markers showed segregation distortion. This map span in total 775.8cM, and the average distance was 6.06cM between adjacent makers.4. The QTLs and their genetic effects for NRMFF were analyzed on the basis of the cucumber molecular genetics linkage map constructed by the method of QTL IciMaping. 5 target QTLs was found. They were qMP-1-1, qMP-3-1, qMP-6-1, qMP-6-2 and qMP-6-3. Among them, qMP-6-1 displayed the maximum contribution of 27.71%, which was located on the LG 6. The flanking markers were SSR16020 and SSR07198, a=19.06, d=-6.53. The major QTL(qMP-6-2)was located on the LG 6 too, The flanking markers were SSR02763 and SSR20852, and the contribution was 10.26%, a=4.36, d=-17.9. The additive effects of the rest of QTLs were positive too. But only the qMP-3-1 of the contribution rate 9.59%possessed the positive additive effect and dominant effect, and showed the synergistic action to the node of multiple female flowers. The interval of all the five QTLs located in this study arranged from 1.5cM to 4.5cM, the distance to one flanking maker was completely less than 5cM. The distance of qMP-3-1 to the left flanking maker SSR06210 was only 0.2cM, which was equal to the distance of qMP-6-3 to the left flanking maker SSR07248. These markers could be used for improving the NRMFF by MAS (marker assisted selection) as needed.
|
PDF Full Text Request