Response of Different Explants for Callus Induction in Cucumber

In vitro regeneration of cucumber is relatively difficult for genetic improvement. In this regard, different concentrations of growth regulators and three types of explants (cotyledon, hypocotyl and leaf disc) were investigated for their efficiency on callus induction potential. Among different explants explored for callus induction with different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D), leaf disc responded earlier (4.67 days) and showed higher percentage of callus induction (91.50%) with 2 mg/l 2,4-D supplemented Murashige and Skoog (MS) media. The same concentration of 2,4-D resulted in the maximum callus fresh (0.56 g) and dry weight (0.39 g) from leaf disc explant. Then the callus was transferred to untreated, 2.0 mg/l BAP + 0.2 mg/l NAA + 1.0 mg/l Kn, 2.0 mg/l BAP + 1.0 mg/l NAA + 1.0 mg/l Kn and 2.0 mg/l BAP + 1.5 mg/l NAA + 1.0 mg/l Kn fortified MS medium. After transferring the callus of different explants to shoot regeneration media containing different concentrations of 6-benzylaminopurine (BAP), 1-naphthaleneacetic acid (NAA) and Kinetin (Kn), only cotyledon callus started to regenerate shoot. The combination of BAP (2 mg/l) + NAA (0.2 mg/l) + Kn (1 mg/l) showed highest shoot regeneration percentage (67.77%) and the maximum number of shoots (5.12) per explant were recorded in the treatment combination of 2 mg/l BAP + 0.2 mg/l NAA + 1 mg/l Kn. These results provided a basis for the optimization of the callus induction protocol of cucumber for genetic transformation.

Use of Forcing Solution Techniques to Improve Chestnut Micropropagation

Chestnut (Castanea spp.) is considered difficult to micropropagate. The timing for harvesting explant materials from forced stems is critical, although many factors need to be considered for successful micropropagation. Previous research with spirea and five-leaf aralia demonstrated that forcing solution techniques extended the availability of high-quality explant material, thus expediting micropropagation. However, preliminary research illustrated that chestnut is very difficult to force and the new forced softwood growth is very short-lived, which made micropropagation difficult. It was found that, at about 7 days from budbreak, the forced chestnut softwood growth (about 2 cm long) served as the best explant material. If longer than this timing window, the new growth would die. If shorter, the explants had a high contamination rate, exudation of purported phenolic compounds, and explants would not regenerate. Shoot proliferation and callus regeneration were achieved by culturing good-quality explants on Woody Plant Medium supplemented with 0.1 mg BA/liter. The new shoots grew vigorously in vitro with apparent normal morphology.