| Embryonic callus induction and somatic embryogenesis of watermelon have very important theoretical and practical significance in rapid multiplication, conservation of germplasma resources, exploiting of fine quality and optimization of genetic engineering receptor system. This paper use cotyledon, cotyledon node, hypocotyl and radicle of watermelon aseptic seedling as explants, studied the factors affecting embryonic callus induction and somatic embryogenesis and maturity and germination of somatic embryo, histological observation of somatic embryogenesis was also studied. The main results were as follow:1. The best culture condition of watermelon aseptic seedling is studied, the most suitable 0.1% HgCl2 solution disinfection time of hulled seed is 8 min, aseptic seedling is poisoned when more than 8 min, and the explant of aseptic seedling is easy polluted when less than 8 min.1/2MS medium is the best medium for aseptic seedling culture. Watermelon is dark seed, first incubated in dark 3 d, and then transfer to 16 h light/8 h dark photoperiod, aseptic seedling is stronger than which without dark treatment.2.4-5 d is the most suitable seedling age for somatic embryo indution. Curl is decreased when the facade of cotyledon is downward, and there are more embryonic callus and somatic embryo.1/2 cotyledon explant is more suitable for somatic embryo induction than integrated cotyledon. Culture in dark 1-2 weeks after inoculated is better than which without dark treatment, induction rate of somatic embryo is low and pass out after long time culture when whithout dark treatment.3. Induction rate of somatic embryo is significantly different among different genotypes, the highest induction rate is ’Kangbingjingxin’, and then ’Zaojia8424’, the lowest induction rate is ’Heimeiren’.4. Use cotyledon, cotyledon node, hypocotyl and radicle of 5d watermelon aseptic seedling as explants, the highest induction rate of embryonic callus and somatic embryo is radicle, and then is cotyledon and cotyledon node, hypocotyl cant to induct somatic embryo. However, somatic embryo induced by radicle can’t mature.5. Adding 2,4-D or NAA in medium, the induction rate of embryonic callus is low and hasn’t somatic embryogenesis. Adding 6-BA or TDZ could induce embryonic callus and somatic embryo well. The highest induction rate of embryonic callus and somatic embryo is 70% and 56.7% when adding 4.0 mg/L 6-BA. The most suitable concentration of TDZ for somatic embryo induction is 0.1-1.0 mg/L, the highest somatic embryo induction rate is 55.6% when adding 0.1 mg/L TDZ. Browning is serious when TDZ concentration is high, while adventitious bud is frequently when TDZ concentration is low.6. In combination of cytokinin and auxin, MS+6-BA 3.0 mg/L+NAA 0.1 mg/L gained the highest somatic embryo induction rate 54.7%. TDZ 0.5 mg/L with NAA 0.05-0.5 mg/L could also induce well somatic embryo.6-BA with 2,4-D induced less somatic embryo, most callus is non-embryonic callus.7. The development of somatic embryo is often stagnation or decline, adding TDZ or GA3 could promote maturation and germination of somatic embryo. Low concentration of inorganic salt is also conducive to maturation and germination of somatic embryo, germination rate of 1/2MS medium is highest (20%). As an important osmotic regulator,2% sucrose is suitable for somatic embryo germination.8. Histological observation indicated that non-embryonic callus were seen to consist of sparse cells with small nucleus and was lightly stained; Embryonic callus were seen to consist of small, dense cells with large nucleus and was deeply stained. Watermelon indirect somatic embryogenesis include both exogenous and endogenous origins, but msotly is unicellular endogenous origins. Somatic embryogenesis gradually go through globular, heart, torpedo and cotyledon embryo. |
PDF Full Text Request