Selection and propagation of elite Atriplex material

Abstract

The aims of this study were to compare 16 Atriplex accessions as fodder shrubs; to find a method of vegetative propagation for A. nummularia and A. canescens; and to find a non destructive way of monitoring dry matter (DM) production and structure. Characteristics evaluated included DM yield, structure, nutritive value and adaptation to different ecological conditions. The accessions were also compared for palatability using grazing sheep in a cafeteria system. Two methods of vegetative propagation were evaluated, namely in vitro tissue culture propagation (A. canescens and A. nummularia) and stem cuttings (A. nummularia). With all accessions the percentage leaves decreased and percentage twigs increased as the plants matured. Leaves were more nutritious than edible twigs. At an age of 15 months edible DM yield ranged from 0.71 t.ha-1 (A. canescens Rincon) to 5.78 t.ha-1 (A. rhagadioides). For most accessions crude protein (CP) content, neutral detergent fibre (NDF), in vitro DM digestibility (IVDMD) and ash contents were acceptable for livestock. The two most promising accessions were A. nummularia (CP content 15%, NDF 48%, IVDMD 60% and ash 20%) and A. canescens cultivar Santa Rita (CP content 13%, NDF 49%, IVDMD 58% and ash 18%). The two least promising accessions as fodder shrubs were A.glauca (CP content 8%, NDF 61%, IVDMD 42% and ash 16%) and A. canescens Rincon (CP content 10%, NDF 58%, IVDMD 44% and ash 15%). Survival at different locations were not only influenced by ecological and climatological conditions, but also by different management practices. Average survival ranged from 41% to 87%. Sampling for nutritive value varied between locations and had a stronger influence on the nutritive values than location. Accessions with the broadest adaption were A. amnicola, A. canescens (S.R.), A. halimus and A. nummularia. According to visual observation and utilization, A. amnicola, A. canescens (S.R.), A. cinerea, A. rhagadioides and A. semibaccata were the most palatable accessions. The sheep, contrary to expectations, were able to select equally nutritious diets over time. In vitro propagation of A. nummularia was more successful than A. canescens. The best medium for shoot multiplication and elongation for A. canescens was the Murashige and Skoog (MS) basal medium with 0.20 mg.1-l 6-benzylaminopurine (BA) and 1.0 mg.1-l naphthalene acetic acid (NAA), while a medium with 0.05 mg.1-l BA and 0.05 mg.1-l NAA was best for elongation and rooting. For multiplication of A. nummularia the MS basal medium with 0.20 mg.1-l BA and 0.05 mg.1-l NAA was the best, while the MS basal medium without any hormones was the best for elongation and rooting. Atriplex nummularia was successfully acclimatized. Vegetative propagation using stem cuttings was also possible for A. nummularia. The best results (up to 95% rooting) were obtained using terminal cuttings of new growth in the autumn or spring, treated with 3 g.kg-l indole-3 buteric acid (IBA). Suitable models for the prediction ofDM yield, using non-destructive measurements were found. The model: DM = 553.24X + 129.47, where, DM = dry matter yield (g.plant-l) and X = shrub volume (m3), gave very good predictions (r2 = 0.72; P = 0.0001). Other models, which were species specific, included: DM yield in relation to volume; height and diameter in relation to DM yield; and shrub volume related to DM yield, where each accession has its own intercept while, the slope were the same for all. Acceptable models were found for all accessions with the exception of A. semibaccata. Another model should be tested for this accession with its creeping growth form.