It was obvious that the most important inter-specific barrier ofthe cross between C. baccatum L. accession no. KKU-P34021 (cv. B)and C. chinense Jacq. accession no. KKU-P11176 (cv. C) occurredduring the development of the embryo. The pollen germination posed no barriers for hybridization because pollen of both cultivars was able to germinate well in the germination medium, although pollen germination was higher for those collected on the blooming day than one day before blooming and the pollen should be germinated immediately after collection. The most suitable germination medium was the one supplemented with 5% sucrose. The ‘cv.C’ pollen tended to give a slightly higher germination percentagethan ‘cv. B’. The flowering stage at which the pollen was collected(day −1 or day 0) had variable effects on the pollen tube lengthof ‘cv. C’, but for ‘cv. B’ the pollen collected on day 0 in most casescould grow a longer pollen tube than those collected on day −1. Thegermination medium supplemented with 5% sucrose also inducedthe best pollen tube growth for ‘cv. C’ in addition to giving the high-est percent germination. It is well-established that sucrose is themost common energy source utilized during pollen germinationand pollen tube growth for synthesis of cell wall materials includingpectins, cellulose and callose (Mascarenhas, 1993) and optimumsucrose concentrations for different plant species varied greatly.Similar to this study, Mercado et al. (1994) found that pepperpollen (C. annuum L.) required relatively low sucrose concentration(5–10%) for germination and gave rise to comparable maximumpercentage of pollen germination. However, media with sucroseconcentration higher than 30% gave the low pollen germinationand pollen tube growth due to their imbalance between water andsugar, and resulted in loss of pollen germination (Chaengkrachanget al., 2006; Mascarenhas and Bell, 1969). It appeared that pollenof ‘cv. C’ could develop as much as 2–3 times longer pollen tubes