Enhancing the germination of three fodder shrubs (Atriplex amnicola, A. nummularia, A. undulata; Chenopodiaceae): implications for the optimisation of field establishment

Abstract

Saltbush (Atriplex) species are widely grown in Australia as saltland pastures. Direct seeding practices for saltbush currently result in asynchronous and unreliable seedling establishment (5% successful establishment is not uncommon from field-sown seed). In part this may stem from a limited understanding of Atriplex seed germination requirements. This paper presents findings with 3 Atriplex species, A. amnicola (Paul G. Wilson.), A. nummularia (Lindl.), and A. undulata (D. Dietr), each of which differs in germination characteristics. For A. amnicola, the presence of light (and artificial substitution of light by 1000 ppm gibberellic acid) improved germination under controlled conditions and resulted in a 4-fold increase (70% total emergence) in field emergence of seedlings. For A. undulata, removing bracteoles increased germination under controlled conditions (~15%), with a 1.5-fold improvement in field seedling emergence (55% final emergence); however, seed priming or gibberellic acid application had no significant effect. In contrast, for A. nummularia, bracteole removal and light had minor positive effects on germination under controlled conditions, but this did not translate into improved emergence in soil or in the field. Under –0.5 MPa NaCl stress, application of gibberellic acid, salicylic acid, or kinetin to the germination medium significantly increased the final germination percentage of A. amnicola seeds (58, 16, and 14%, respectively) and improved the rate at which seeds germinated. All plant signalling compounds significantly increased final germination percentage and germination rate of A. undulata, albeit with a <10% increase at –0.5 MPa NaCl. Priming seeds with plant signalling compounds had similar effects on seed germination under low water potentials compared to direct treatment of the germination media. The effects of seed priming on Atriplex seedling emergence from saline soils varied among species. Priming with water significantly increased emergence percentage of A. amnicola but had no effect on A. nummularia and A. undulata. Gibberellic acid improved A. amnicola germination parameters only, whereas salicylic acid and kinetin improved the rate of emergence in all 3 species at various levels of salinity. This study suggests that a basic understanding of seed dormancy and germination requirements has the potential to substantially improve field emergence of saltbush species.