Objective: To study the relationship between physiological indexes

photosynthetic efficiency and yield of tetraploid Scutellaria baicalensis

in order to provide the oreticalbasis for further development and utilization of tetraploid Scutellariae series D20. Method: The physiological and biochemical indexes were detected by routine methods; photosynthetic indexes were determined using LI-6400/XT portable photosynthesis measuring system; yield measurement was made by the single-factor completely randomized block designand repeated for 3 times in total; residential area covered 6 square meters (3 m×2 m)

with 10 transplanting lines in each area

line spacing of 20 cmand row spacing of 5 cm. Result: SOD and POD in tetraploid leaves of S. baicalensis and CAT enzyme activity were significantly higher by 28%

2% and 17%than those of diploid leaves

with significant difference except for POD (P<0.05); soluble sugar content was higher by 19%than that of diploid leaves

MDA content was significantly lower than that of diploid leaves

indicating a higher antioxidant ability in tetraploid Scutellariae Radix. The field trial showed significant differences between the lengths of tetraploid and diploid S. scutellaria roots

with an average of up to 34 cm

the root diameter of tetraploid Scutellariae Radix was less than that of diploid

but with more branch roots than diploid

which were up to 8 at most

andthe single root weight and total yield were also higher than those of diploid

withthe increase of production of up to 31.4%. Conclusion: Because of chromosome doubling

tetraploid of S. baicalensis showed enhanced growth and resistance against plant diseases and pests

which the refore indirectly affected the increase of yield of medicinal herbs. The enhanced photosynthetic capacity of tetraploid S. baicalensis could increase the accumulation of dry substances of plants

which directly affected its yield. This characteristic has a special application value and higher potential for increasing yield for medicinal plants.