| The watermelon cultivation area and total production in China rank first in the world. Triploid watermelons [Citrullus lanatus (Thunb.) Matsum & Nakai] are an attractive vegetable for people, which is high quality and nice taste. Triploid watermelons are gaining market prominence. Due to strong resistance to nematodes and storage, plant production is always increasing. However, the worse germination rate and inconsistent emergence are the major limitis to develop the industry quickly. This study mainly focused on the germination barriers mechanism and methods of improving germination of triploid watermelon seeds. The main results were as follows:(1) Germination Barrier of triploid watermelon seed causes by a variety of factors on the basis of analysis of experimental results. When seed morphological components were measured for each cultivar of triploid and diploid, triploid seeds had a thick seedcoat, especially difference of mesosperm thickness. There was a sclerotic tissue in mesosperm that cell arrangement was very dense. The thick and hard seedcoat of triploid watermelon played an important role of certain mechanical constraints on its germination. At the same time the seedcoat of triploid watermelon wasn’t impermeability to gas. The size of embryo of triploid is very small. Triploid seeds had a larger and highly variable air space.Triploid seed had a thicker seedcoat with a dense endotesta layer and a larger and highly variable air space surrounding the embryonic axis as compared to the diploid seed. The rapid imbibitions and excess water collected in the seedcoat and air space surrounding the embryo, which could reduce oxygen diffusion and impaire metabolic pathways leading to poor germination. (2) The LC-MS analysis indicated that changes of endogenous hormone in triploid watermelon were caused by different treatment during seed germination. On the whole, there was low ABA content. As well as it gradually reduced during germination. There was high ABA content in the initial stage of germination because of seed imbibition in CaO2. It indicated that the synthesis of ABA was promoted by enhanced-oxygen. The content of GA3 increased in initial stage of germination, but reduced after 36h. The content of ZR rose at first, and then decreased. The content of IAA didn’t change obviously except for drum-primming. GA/ABA rose during germination. The changes of ZR/ABA and (GA+ZR)/ABA were like GA/ABA.(3) The content of protein and starch decreased. The content of soluble sugar rose at first, and then decreased. The content of fat didn’t change obviously.(4) The activity of POD decreased rose at first, and then decreased. The joint activity of G-6-PDH AND 6-P-GDH rose at first, and then decreased. Both the peak activity of them and germination increased to maximum were simlutanous. The GS activities of CaO2 and shell broken were coincident, increased and then decreased. The GS activity of seed priming was higher, and the GS activity of no-broken treatment was lower than other treatments.The GDH activity was inceased gradually and was not influenced obviously by treatments of seeds. The ICDH changes were increased and then decreased. The peak activity and germination increased to maximum were simlutanous. The AcPA was increased gradually.(5) The germination barriers of triploid watermelon seeds were caused by the bigger space in the seed cavity resulted from the smaller embryo. The cavity led to moisture imbalance and oxygen deficit for embryo to germinate. It proved that the germination barriers wre not mainly caused by the mechanical force by epispern and faulty embryogenesis.(6) The experiments’results showed that the four methods of improving germination, the mechanical shell broken, manual shell broken, drum priming and CaO2 and H2O2 oxygenation, improved the germination of triploid watermelon seeds obviously. The germination rate reached 90.64%by the improvement rate 66.36% compared to common germinating. The best improving germination method was 1.5% CaO2 and 2%H2O2 to oxygenate 6 hours based on synthesis analysis. |
