| Cassava is the staple food in the tropical area of the Africa, the South America and the Oceania for its starchy root. It’s the important source of starch in China. The main cultivar in China is cassava south China (SC205). It has the characteristics of medium maturation, well adaptive, et al. As the typical tropical plant, cassava is vulnerary to low temperature. Thus limit the planting in northern areas of China. The traditional methods of breeding such as hybridization don’t work efficiently due to the high heterozygosis and offspring separation easily. The biotechnology will provide effective methods in novel cassava cultivar breeding.Cassava cultivar South China205(SC205) was employed in this experiment. We established the tissue culture system first for this is the most important fundamental technology in breeding via biotechnology. Then the chilling tolerant capacity was assayed by measuring the characteristics related to chilling of cassava under low temperature. We established the methods of combined usage of principal component analysis and cluster analysis to select the sensitive factors under low temperature so that we can use in the following research in chilling-tolerance cassava breeding. The results were listed as follow.1. The best sterilizing method of explants of cassava stem is that75%of ethanol for20seconds followed by0.1%of mercuric chloride for6minutes. The survival of explants was high as83.3%. The suitable initiative medium is MS containing2uM of copper and2%of sucrose, named as MSII. The number of bud using this method was5.7buds per explant. The favorite adventitious bud induction medium was MSII containing0.5mg/L BAP which could get the biggest regeneration coefficiency of5.3. The suitable root induction medium was MSII containing0.5mg/L of NAA which led to1.11millimeter of the diameter of the root and the average number of the root was12per explant.2. The suitable somatic embryonic callus induction medium from young leaves and shoot tips was MS II containing8mg/L of2,4-D and MSII containing9mg/L picloram, respectively and the induction rate was50.0%and53.3%, respectively. The maturation medium of somatic embryonic callus from young leaves was MSII containing0.4mg/L of BAP and its induction rate was66.7%and the plant generation rate was46.6%. While the maturation medium of somatic embryonic callus from shoot tips was MSII containing0.3mg/L of BAP, the induction rate was86.7%and the plant regeneration rate was70.0%.3. After24h treatment of a range of low temperature, young leaves of cassava SC205seedlings were collected to measure the biophysical and biochemical characters and to select the sensitive factors by the principal component analysis and cluster analysis. The results show that the content of chlorophyll a, b and caroteinoid were reduced for a certain degree. The content of superoxide and the hydrogen dioxide was increased. The content of MDA (Malondialdehyde) was increased, either. This showed that low temperature lead the production of active oxygen species and make the membrane injury. The osmotic substances such as proline, soluble sugar (SS), soluble protein (SP) were increased during low temperature stress. The activity of superoxide dismutase (SOD) and catalase (CAT) was improved and that of the peroxidase was improved and then decreased during low temperature stress. This indicated that cassava could modulate the inner status to protect against low temperature induced oxidative stress. The activity of ascorbate-dependent peroxidase (APX) was decreased during the low temperature indicated that this enzyme was sensitive to low temperature and doesn’t work due to chilling.4. The thirteen characters were changed to two independent classes of index with the principal component analysis. The first principal component is the soluble substance, the photosynthetic pigments, activity of SOD and the characters related to cell memberane. In these characters, the content of MDA, Chla, Chlb and the activity of SOD are the more important. The correlation co-efficiency factor were0.996,0.993,-0.984,-0.988, respectively. The second principal component identified as the activity of POD and the content of caroteinoid, the correlation coefficients were0.956,0.695respectively. We analyzed the characters by using the cluster analysis method then. The results showed that the following character such as H2O2, O2-, CAT, SOD, Pro, MDA, SS, SP were gathered to one class and then were gathered with POD. The characters such as APX, Chla and Chlb were gathered to one class and then were gathered with Car. In each class, the characters had the same trends. Then one character could be measured in later experiments to evaluate the trends. We selected the four characters as MDA, Chla, Car and POD as the sensitive characters to evaluate the effect of low temperature in cassava cultivar205. |
