| Cordyceps militaris, is an important medicinal fungus and a nutritious edible fungus. In this study, molecular markers were used to investigate the genetic analysis of different Cordyceps militaris strains at molecular level and to construct the genetic maps of Cordyceps militaris to analyze the diversities of germplasm resources. Based on these results, a dominant strain was screened out of optimizating cultivation conditions and exploring the degradation mechanism. The main results were as followed.The genetic relationships of Cordyceps militaris were analyzed base on the RAPD and SRAP molecular makers. Ten RAPD primers were screened out and choosen for identifying strains, total 101 clear bands were produce by PCR, sixty-nine bands of clear bands by PCR were polymorphism bands, the average rate of diversity was 68.3%. Eleven SRAP primers were screened out and used for identifying strains, total 83 clear bands were produced, fifty bands of them were polymorphism bands, the average polymorphism rate was 60.2%. The UPGMA cluster analysis which was based on RAPD and SRAP markers indicated that 17 Cordyceps militaris strains could be divided into three categories under similarity coefficient of 0.78, the first category included cm-14, cm-15 and cm-16, the second one included cm-10 and cm-13, the rest were the third category. When the similarity coefficient was 0.83, the third one could be divided into two subcategories. One subcategory included cm-2, cm-3, cm-4, cm-5, cm-6, cm-7, cm-9, cm-11, cm-12 and cm-17, the other subcategory included cm-1 and cm-8. The results showed that strains from same area had closer genetic relationships, the strains from different regions had the distant genetic relationships. There were large of genetic differences between Cordyceps militaris samples, and the genetic diversity was rich. Also, those genetic differences showed geographical differences in the distribution and increased with the increase of the geographical span.The optimal cultivation conditions of Cordyceps militaris were:the solid-liquid ratio of 1:1.5, liquid spawn was 4 d, inoculums volume was 1:1.2, cultured 6 d in the dark. When Cordyceps militaris mycelia covered full of cultivation media, added scattering of light illumination cultivated mycelia from white change into a golden yellow or orange and stimulated the formation of primordia by scratching mycelia. During the fruiting bodies growth, the fresh air of cultivation bottles was maintained and the air humidity levels kept between 80% and 90%. In these cultivation conditions, the wet weight of Cordyceps militaris was 24.71 g/(12 g cereal), dry weight reached 3.29 g/(12 g cereal). Also, Cordyceps militaris fruiting bodies was golden and yellow, uniform and better quality. Compare with Lin (2006) of fruiting bodies 19.96 g/(20 g rice) and Liu (2009) of the dry weight 3.23 g/(30 g rice), the effective utilizatio rates of raw materials increase 17%.In this study, the experiments some nutrition indexs of the degradation strains and normal strains were measured. The results showed the carotenoid content of degradation strains was significantly lower than normal strains, and the activities of cellulase and amylase of degradation strains were slight lower, but intracellular polysaccharide content was higher than normal strains, and the extracellular polysaccharide was lower than normal strains. Carotenoids content can be used as a judgment indicator of Cordycepd militaris strain degradation. The results based on RAPD and SRAP molecular markers technology on the degradation of strains and normal strains showed that the two types of strains at the DNA level were no difference. The combination of the results of molecular marker and indexs measured showed that the degradation of Cordyceps militaris was caused by the inhibition or synthesis uncoordinated of metabolic, but this conclusion should be further verified. |
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