Synthesis and Preliminary Characterization of A New Species (Amphidiploid) in Cucumis

The first repeatable interspecific hybridization between cucumber (C.sativus L., 2n=14) and a wild Cucumis species,C.hystrix Chakr.(2n=24) was successfully made through embryo rescue.The hybrid plants were morphologically uniform.While the multiple branching habit,densely brown hairs (especially on corolla and pistil),orange-yellow corolla,and ovate fruit of F 1 hybrid plants were similar to that of the C.hystrix parent,appearance of the first pistillate flower was more similar to that of C.sativus parent.The diameter and internode length of stem,shape and size of leaves and flowers were intermediate when compared to that of the parents.Self-pollination and backcrossing of the F 1 hybrid plants to either parent indicated that the original hybrid was both male- and female-sterile,probably due to meiotic abnormalities caused by lack of homology and the odd chromosome number 2n=19 (including 7 from cucumber and 12 from C.hystrix).The chromosome number in the hybrid was doubled with somaclonal mutation to restore the fertility.Pollen grains were released from the synthetic amphidiploid and fruits set with viable seeds on the fertility-restored plants.The results from flow cytometry indicated that,on average,7.3% of the regenerants with unique morphology were chromosome-doubled F 1 hybrids.The 2C DNAcontent of the original F 1 hybrid was 1.17 pg,and the 4C DNA content was 2.35 pg.This new species was preliminarily characterized in growth and development,nutrition value,and disease resistance.The results suggested it a possible place to be a new Cucum is crop in future agriculture.Two types of fruits produced in our first season of crosses included a potential pickling variety that produces multiple uniform fruits at a single node with the 1∶3 length/width ratio for once over harvest.Asecond cross produces long slender fruits,nearly seedless with the ability to grow in partially shaded conditions,which may be the suitable varieties for greenhouse production.Results from nutrition analysis indicated that the synthetic species has higher protein (0.78%) and mineral (0.35%) content compared to the normal pickling cucumber (0.62% and 0.27%,respectively).Ascreen for root-knot nematode resistance revealed a high level of resistance existed in C.hystrix,and the resistance was partially transmitted to the F₁ and the chromosome-doubled F₁ when the reciprocal hybrid was made.