Studies On Physiological And Genetic Analysis And Molecular Markers Of Parthenocarpy In Cucumber

Cucumber (Cucumis sativus L.) is an important vegetable in China, parthenocarpy is an important yield-related economic trait in cucumber, and it is one of the breeding objective traits of cucumber varieties special for protected cultivation. To evaluate correctly the parthenocarpy of germlasm, to realize the mechanism of physiology and inheritance of the parthenocarpy and to screen the molecular markers related to the parthenocarpy is the basis of genetic improvement in cucumber. In this disseration, based on the evaluation of parthenocarpy of 75 cucumber germplasm under different condition, using mixed major gene plus polygenes genetic models of quantitative traits, a joint analysis of multi-generations from crossing a highly parthenocarpic gynoecious line'6401'and a monoecious lines'6457'with two non-parthenocarpic inbred lines'6429'and'6426'was carried out to investigate the inheritance of the parthenocarpy in cucumber. The development and endogenous hormone of super ovaries and molecular markers of related to parthenocarpy were studied for genetic improvement to the parthenocarpy in cucumber. The main results are as following:1 Evaluation of parthenocarpy in cucumber germplasmParthenocarpy of 75 cucumber germplasm and cultivars was evaluated under greenhouse condition in spring season. The results showed that the parthenocarpy percentage was continuously distributed from 0 to 100%, and there were significant differences on parthenocarpy among accessions. While 40 accessions were found strongly parthenocarpic (53.3%),24 were medium (32%) and 11 were weakly parthenocarpic (14.7%).20 out of the 24 cultivars were found as strong parthenocarpic (83.3%), and the rest was mid-parthenocarpic. The degree of parthenocarpy was expressed by the fruit set capability,. The cucumber plants get stronger parthenocarpic with the nodes increase and the best evaluation should be done under 20th nodes. Parthenocarpy of 55 germplasms was evaluated in spring under the plastic tunnel in Najing. There were 4 accessions which parthenocarpic fruit set were more than 70%, while 28 accessions with 40%-70%, and 23 accessions with less than 40%. The parthenocarpy of 4 accessions performed relatively unvariable, these germplasms are elite for the purpose of breeding and genetic analysis.2 Study on development and endogenous hormone of super ovaries in cucumberThe development and endogenous hormone levels in the super ovaries of the strongly parthenocarpic inbred line'6457'under greenhouse in spring season were studied. The results showed that the length of the super ovaries at anthesis was much more than 9cm, accounted for 74.6%, the average length was 14.4cm, and concentrated at 13.0～17.0cm typically; While that of the normal ovaries is less than 9cm, accounted for 25.4%, the average length was 5.8cm, and concentrated at 5.0～7.0cm typically. The length of the super ovaries at anthesis was 3 times as that of the normal ovaries. The percentage of the plants with super ovary was 64%. The development of the pistil and fruit with super ovary present a good similarity with that of the normal, but the blooming time of the super ovary was four or five days later than that of the normal. The physiological mechanism of the super ovaries was concerned with the higher GA3 content as well as the ZT/ABA and GA3 /ABA.The super ovary could be induced by all kinds of concentrations of TDZ (10mg/L, 5mg/L,2.5mg/L,1.25mg/L, Omg/L). The best concentration for super ovary was 2.5mg/L. The blooming time of the treatment was four or five days later than that of the control. The average length of the ovary at anthesis was 11.2cm, and the super ovary percentage was 75%. While the treatment of 2.5mg/L TDZ could accelerate the fruit development rapidly. The average length of the fruit was 23.6cm at the 11 days after treatment, while that of the control was only 13.2cm.3 Inheritance of parthenocarpy in cucumberA joint analysis of six-generations from crossing a highly parthenocarpic gynoecious line'6401'with two non-parthenocarpic inbred lines'6429'and'6426'was carried out to investigate the inheritance of the parthenocarpy in cucumber. Results showed that the inheritance of gynoecious parthenocarpy was fitted the same genetic model in different genetic backgrounds. Parthenocarpy is incompletely recessive and controlled by two additive-dominant-epistatic major genes and additive-dominant polygenes (E-1-1 model) in the two crosses. Dominant effect of the first major gene and dominant×dominant interaction between the two major genes as well as polygene effects were higher. The major gene heritabilities of B1, B2, and F2 were 0.6%～51.1%,59.6%～75.4%, and 41.3%～71.4% respectively. While the corresponding polygene heritabilities were 0.2%～19.9%, 0.0%～12.7%, and 3.2%～35.5% respectively.A joint analysis of six-generations from crossing a highly parthenocarpic monoecious lines'6457'with two non-parthenocarpic inbred lines'6429'and'6426'was carried out to investigate the inheritance of the parthenocarpy in cucumber in different backgrounds and seasons. The results showed that inheritance of parthenocarpy was controlled by two major genes and polygenes. The additive effects of the two major genes were great. The major gene heritabilities of B1, B2, and F2 were 72.2%～88.8%,52.5%～93.1%, and 88.6%～95.4% respectively. While the corresponding polygene heritabilities were 0.0%～11.2%, 0.0%～43.1%, and 0.0%～1.5% respectively.A joint analysis of four-generations from crossing a highly parthenocarpic gynoecious line'6401'and monoecious line'6457'with a non-parthenocarpic inbred line'6429'was carried out. The results showed that under the same genetic backgroud, inheritance of parthenocarpy in monoecious and gynoecious cucumber was controlled by two major genes and polygenes. The inheritance of parthenocarpy in gynoecious cucumber was controlled by two additive-dominant-epistatic major genes and additive-dominant-epistatic polygenes (E-1-0 model), the major gene heritability of F2 was 83.5%. While the inheritance of parthenocarpy in monoecious cucumber was controlled by two additive-dominant-epistatic major genes and additive-dominant polygenes (E-1-1 model), the major gene heritability of F2 was 42.1%.A joint analysis of four-generations from crossing two monoecious inbred lines were carried out to study inheritance of parthenocarpy in cucumber at Jiangning (Nanjing) and Changli (Hebei). The results showed that the interaction between genotype and environment was detected, and the inheritance of parthenocarpy in monoecious cucumber was fitted E-1-1 model, and controlled by two additive-dominant-epistatic major genes and additive-dominant polygenes under different eco-environments. While the F1 tendency and genetic parameters of the parthenocarpy were different, and the major gene heritabilities of F2 were 42.1%～97.5%.Parents that both are highly parthenocarpic should be chosen in breeding programs for cucumber with highly parthenocarpy. Selection of parthenocarpy can be carried out in the earlier generations of conventional crossing breeding.4 Studies on the molecular markers linked to parthenocarpy in cucurmberExtreme parthenocarpy and extreme non-parthenocarpy DNA pools, which came from F2 population between a highly parthenocarpic monoecious line '6457' and non-parthenocarpic line '6429', were developed separately according to the bulked segregant analysis (BSA). AFLP technique was employed to sreen molecular markers linked to the parthenocarpy. In extreme non-parthenocarpy DNA pool, a 325bp specific fragment was amplified with the primer E41/M47. This marker was testified with individual DNA of the F2 population. Linkage analysis using the software of MapMaker 3.0 indicated its genetic distance to the non-parthenocarpy was 9.7 cM, and this AFLP marker was designed as AGG/CAA325.In extreme parthenocarpy DNA pools from the same population, a 580bp specific fragment was amplified with the ISSR primer I-75, its genetic distance to the parthenocarpy was 27.5 cM, and this ISSR marker was designed as I75580. In addition, an SSR specific fragment CSWTA06350 was related to parthenocarpy in monoecious cucumber.Extreme parthenocarpy and extreme non-parthenocarpy DNA pools, which came from F2 population between a highly parthenocarpic gynoecious line'6401'and non-parthenocarpic line'6429', were developed separately according to the bulked segregant analysis (BSA). In extreme parthenocarpy DNA pool, a 580bp specific fragment was amplified with the ISSR primerⅠ-61, its genetic distance to the parthenocarpy was 22.5 cM, and this ISSR marker was designed asI6147o.