The perennial legume Bituminaria bituminosa (L.) C.H. Stirt. var. albomarginata (tedera) has been identified as a promising fodder plant for the southern Australian wheatbelt, but little is known about its drought resistance as a seedling. This study was conducted to (i) examine physiological and morphological responses to water stress of seedlings of tedera, in comparison with lucerne (Medicago sativa L.), biserrula (Biserrula pelecinus L.) and Afghan melon (Citrullus lanatus Thunb.), and (ii) investigate drought adaptation mechanisms of tedera seedlings.

Seedlings were grown in a reconstructed field soil profile in pots in a glasshouse. By 25 days after sowing (DAS), plants of all species in the drought-stressed (DS) treatment had experienced water stress, with an average leaf relative water content (RWC) of 66% in DS compared with 79% in well-watered (WW) plants. Tedera, biserrula and Afghan melon maintained a higher RWC than lucerne. At 25 DAS, reductions in shoot dry matter in the DS treatment differed between species: 52% for Afghan melon, 36% for biserrula, 27% for lucerne, and no significant reduction for tedera. Paraheliotropic leaf angles of biserrula, lucerne and tedera were all higher in the DS treatment than in the WW treatment at 25, 32 and 52 DAS.

This study revealed significant differences in rooting depth and stomatal conductance between the three legume species when under water stress, with tedera being the most drought-resistant. Traits that may allow tedera to survive a dry period following opening rains include vigorous seedling growth, early taproot elongation, effective stomatal control and paraheliotropic leaf movements.