Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/20/2003
Publication Date: 4/15/2004
Citation: Chen, J., Luo, X., Qian, C., Jahn, M.M., Staub, J.E., Zhuang, F., Luo, Q., Re, G. 2004. Cucumis monosomic alien addition lines: morphological, cytological, and genotypic analyses. Theoretical and Applied Genetics. 108:1343-1348. Interpretive Summary: Cucumber is susceptible to many fungal and bacteria pathogens as well as insect pests. This is partially due to the narrow genetic diversity in cucumber (all cultivars are genetically very similar). One way to increase the genetic diversity and introduce new genes into cucumber by way of conventional crossing and plant breeding is to make crosses between cucumber and exotic wild species from India and China. Unitil recently this has been impossible since wild species do not cross with cucumber. One such cross was made with cucumber using a wild species, Cucumis hystrix, originating from southern China. This wild species has genes for disease and pest resistances not present in cucumber. Although the offspring of this cross were sterile, new biotechnological techniques allow for us to restore fertility so that the progeny from this cross could be crossed to cucumber repeatedly to develop individuals that possessed disease and pest resistant genes present in Cucumis hystrix. In order to do this, the chromosome number of the offspring of the original cross needed to be changed. This was done by conventionial genetic manipulation resulting in lines that would be used for further crossing to cucumber and for genetic studies to better understand the genetics of the disease and pest resistance that was transferred in the original cross. The results of these experiments resulted in plants that will lead to the improvement of commercial cucumber by private and public breeders, and thus will enhance the competitiveness of the U.S. cucumber grower in the global marker place.
Technical Abstract: Cucumis hystrix Chakr. (HH, 2n=24), a wild relative of the cultivated cucumber, possesses several potentially valuable disease-resistance and abiotic stress-tolerance traits for cucumber (C. sativus L., CC, 2n=14) improvement. Numerous attempts have been made to transfer desirable traits since the successful interspecific hybridization between C. hystrix and C. sativus, one of which resulted in the production of an allotriploid (HCC, 2n=26: one genome of C. hystrix and two of C. sativus). When this genotype was treated with colchicines to induce polyploidy, two monosomic alien addition lines (MAALs) (plant nos. 87 and 517: 14CC+1H, 2n=15) were recovered among 252 viable plants. Each of these plants was morphologically distinct from allotriploids and cultivated cucumbers. Cytogentic and molecular marker analyses were performed to confirm the genetic constitution and futher characterize these two MAALs. Chromosome counts made from at least 30 meristematic cells from each plant confirmed 15 nuclear chromosomes. In pollen mother cells of plant nos. 87 and 517, seven bivalents and one trivalent were observed at diakinesis, and metaphase I; the frequency of trivalent formation was low (about 4-5%). At anaphase I and II , stochastic and asymeteric division led to the formation of two gamete classes:n=7 and n=8; however, pollen fertility was relatively high. Pollen stainability in plant no. 87 was 86% and in plant no. 517 was 93.2%. Random amplified polymorphic DNA analysis was performed using 100 random 10-base primers. Genotypes obtained with eight primers (A-9, A-11, AH-13, AL-19, Aj-18, AJ-20, E-19, and N-20) showed a band common to the two MAAL plants and C. hystrix that was absent in C. sativus, confirming that the alien chromosomes present in the MAALs were derived from C. hystrix. Morphological differences and differences in banding patterns were also observed between plants nos. 87 and 517 after amplification with primers AI-5, AJ-13, N-12, and N-20, suggesting that these plants may contain different C. hystrix chromosomes.