Abstract: [Objective] In this study, we investigated effects of continuous drought stress on growth and physiological characteristics of Masson pine (Pinus massoniana) and compared drought-resistances of 3 Masson pine families, to elucidate the mechanisms of drought resistance and their genetic effects, and to provide a theoretical basis for breeding drought-resistant families.[Method] Pot experiment with random block design in greenhouse was conducted to investigate the effect of drought stress on growth, osmoregulation and antioxidants of 2-year-old Masson pine seedlings, respectively from Guizhou and Guangxi provinces.[Result] With the increase of drought stress intensity, the activities of protective enzyme SOD of the three Masson pine families displayed an increase in the beginning and followed by a decrease, and significant difference in SOD activity among the three families was found (P<0. 05) during 0–10 days of stress; the activities of protective enzyme POD was found in the same tendency of SOD activities, but the difference in POD activity among the three families was not significant during the whole period of drought treatment ( P>0. 05); MDA content displayed a trend of increase followed by a decrease in GX01 but a reversed trend in GX02 and GZ01, and significant differences were found in MDA content among the three families (P<0. 05) from the 5^th to the 20^th day of drought stress and on the 30^th day of drought stress; the proline content of GZ01 was increased constantly, while the proline contents of GX02 and GX01 displayed a pattern of increase-decrease-increase, and proline contents were found significantly differences among the three families (P<0. 05) from the 20^th to the 30^th day of drought stress. Moreover, continuous drought restricts the growth of seedlings, the growth of height,and ground diameter and the accumulation of dry matters of the 3 families of Masson pine were all inhibited by the drought stress and varied significantly ( P<0. 05 ) among the three families. Continuous drought led to a significantly larger root to shoot ratio of GX01 and GX02 compared to the control. The ratio of GZ01 was also larger than that of the control, but not to a significant level. In addition, subordinate function was used to rank their drought resistance and the order was GX01>GX02>GZ01. Root to shoot ratio, height, MDA and Pro were as the key indicators to evaluate the drought resistance of Masson pine.[Conclusion] These results indicated that activities of antioxidant enzymes of Masson pine seedlings was increased to resist the damage of mild drought stress; and then, the content of osmotic substance was increased to prevent the damage of dehydration from moderate and severe drought stresses; at last, the membrane was seriously damaged with increasing of MDA contents under aggravation drought stress. Obviously, Masson pine seedlings adapted to drought stress by increasing underground growth and decreasing aboveground growth. We conclude that drought resistance of Masson pine was mainly controlled by genetic factors, and differences of its drought resistance maybe caused by the genetic difference which was formed by long-term domestication under different geographical and ecological environment.

Key words: Pinus massoniana, drought stress, growth characteristics, physiological response, drought resistance, hereditary