## 3 Factors Influencing the Genetic Transformation of Cucumber
### Pre-Culture Period  
Pre-culture refers to the process of culturing explants in differentiation medium before _Agrobacteriumium_ infection. Generally, pre-culture promotes cell division and adjusts the physiological condition of explants, which is conducive to the integration of exogenous T-DNA into explants. If the pre-culture time is too short, it is difficult for the explants to reach the optimal physiological state, and it may even be difficult to differentiate into regenerated plants [53]. However, the pre-incubation time should not be too long, otherwise a protective layer will be formed outside the wound, which will reduce the infection efficiency, or untransformed cells will form cell clusters, which will increase the resistance to the selection agent and inhibit the differentiation of transformed cells [23]. [PERSON] et al. [39] found that explants pre-cultured for 1 day grew more resistant shoots than explants used for direct infection, and the rate of resistant shoots increased from 11.1% to 27.3%; however, as the pre-culture time was prolonged, the cell division ability was weakened, and the transformation rate also began to decline. Similar conclusions were obtained by [PERSON] et al. [41]: with the progress of pre-culture, the bud induction rate first increased and then decreased, and 2 days was very effective in producing the highest cucumber regeneration frequency and \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Genotypes** & **Explant** & \
\begin{tabular}{c} _Agrobacteriumium_ \\ **Strains** \\ \end{tabular} & **Plasmil Vectors** & **Transgene Constructs** &
\begin{tabular}{c} **Transformation** \\ **Efficiency (\%)** \\ \end{tabular} & **References** \\ \hline cv. Cengelkioy & Cottyledon & EHA101 & PGAA48 XG & pHII + CUS & 16 & [26] \\ cv. Poinset76 & Cottyledon & EHA105 & pME504 & CaMV355:brz + sdr + GUS & 1.6 & [33] \\ cv. Spinhokuse1 & Cottyledon & EHA105 & pME508 & CaMV355:brz + sgr -TVG & 21 & [6] \\ cv. Shinhokuse1 & Cottyledon & EHA105 & pLG121-HN & NosP:mplt CaMV355:GUS + HPT & [40] \\  & & pLG5-sgr & NoS:mplt CaMV355:GUS +sgr & & \\  & & pGF-sgc & NoS:mplt CaMV355:sgr + HPT & & \\ cv. M8 & Cottyledon & EHA105 & pCAM481300- & 2A11:INH & 2 & [47] \\ cv. CU2 & Cottyledon & EHA105 & pKG420 & 1 & [48] \\ cv. CU2 & Cottyledon & EHA105 & pHCG401/pKGC401- & CsU6-1:gRNA d35:SzmCas9 + & 0.89 & [49] \\  & & & cSIFP1 & eGFP + Hgy & & \\  & & & pHCG401/pKGC401- & & 0.87 & \\  & & & pHCG401/pKGC401- & & & \\  & & & pHCG401/pKGC401- & & & \\  & & & CsMLO8 & & & \\  & & pHCG401/pKGC401- & & 0.83 & \\ cv. Nongneby No. 3 & Cottyledon & GV3101 & Partyk-2 & & 3.9 & [50] \\ cv. Xintimatic & Cottyledon & GV3101 & pCAMBIA2301s & & 2.89 & [8] \\ cv. 9930 & & & & & 4.13 & \\ cv. Xintimatic & Cottyledon node & GV3101 & pCAMBIA2300s & CaMV355:mplt & 8.1 & [7] \\ cv. Si1 & Cottyledon node & GV3101 & pCAMBIA2301- & GUS + nptl & 2.33 & [51] \\ cv. Cs0601 & Cottyledon node & GV3101 & pCAMBIA-1301 & p358:HCG & 2.4 & [41] \\  & & & LBA4404 & & & \\ cv. Xintimatic & Cottyledon node & LBA4404 & pBI121 & 358:mplt + s35:gusA & 4.8 & [30] \\ cv. Xintimatic & Cottyledon node & LBA4404 & pBI121 & NOS:mplt & 4.8 & [45] \\ cv. Smital & Leaf & LBA4404 & pBI121 & CaMV358:CUS + NOS:mplt & [9] \\ cv. poinset76 & Cottyledon & AGL1 & & & & 358:GUS + 358:mplt & 0.5 & [18] \\ cv. Changchun-mic & Cottyledon node & CS8 & pGreen0029 & & 1 & [52] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Details of some successful reports on _Agrobacteriumium_-mediated transformation of cucumber. number of shoots per explant (90.01% and 1.5, respectively). [PERSON] et al. [54] reported that compared with 1-2 d of pre-cultivation, a higher number of regenerated buds and resistant buds could be obtained in 3-7 d, considering that an excessive pre-culture time will lead to difficulties in later positive screening. A duration of 3 d was finally selected as the best pre-culture time.