Influence of salinity and boron on germination, seedling growth and transplanting mortality of guayule: A combined growth chamber and greenhouse study

Abstract

Guayule (Parthenium argentatum A. Gray), a drought tolerant plant, originating from southwestern United States and northern Mexico, is considered to be a promising rubber-producing plant for arid and semiarid areas. To evaluate the potential of guayule as an alternative crop for saline boron-laden soils in the West side of central California, four experiments were conducted to evaluate germination, seedling growth and transplanting mortality of six guayule lines (AZ-1, AZ-2, AZ-3, AZ-4, AZ-5, and AZ-6) at different levels of salinity (electrical conductivity (EC) of 5, 10, 15, and 20 dS/m) and boron (B) levels (5, 10, 20, 30, and 40mg/L) under both growth chamber and greenhouse conditions. Overall, increased salinity (especially at levels of EC>10 dS/m) inhibited both germination and seedling growth of all guayule lines. In contrast, B positively influenced (to varied degrees) germination and growth of specific guayule lines (AZ-1, AZ-2, and AZ-4) and had no significant negative influence on the other three lines. The combination of 5 mg B/L and salinity (EC) of 5 dS/m significantly (P<0.05) increased both germination percentage and speed of germination of AZ-4 and AZ-6, and the seedling vigor index (SVI) and length of AZ-1 and AZ-6, SVI of AZ-2, and length of AZ-5, respectively. There was no statistical difference on germination percentages for most guayule lines (except for AZ-3) grown in saline B-laden (EC of 10 dS/m, 10mg B/L) and control (EC of 0.4 dS/m, 0.12mg B/L) soils under greenhouse conditions. AZ-4 showed even a greater germination percentage in saline B-laden soil than in control soil, while AZ-6 showed very small difference between both types of soils. AZ-1 and AZ-6 showed greater germination percentage and speed of germination than the other lines, although greater mortality percentage was observed when AZ-1 and AZ-6 seedlings were transplanted into saline B-laden soils. Our results from both growth chamber and greenhouse experiments indicate that AZ-4 and AZ-6 can successfully germinate in typical saline B-laden soils present in the westside of central California.