Atriplex Nummularia (Oldman Saltbush)

THE USE OF STEM CUTTINGS TO PROPAGATE ATRIPLEX NUMMULARIA L. (OLDMAN SALTBUSH) VEGETATIVELY

Atriplex nummularia (oldman saltbush) is a naturalised and well known fodder shrub in the arid and semi-arid parts of South Africa. Stock farmers establish plantations of A. nummularia, to be used as a fodderbank during dry periods when the grazing capacity of natural grazing land is very low (Barnard, 1986). Differences in palatability caused the need of propagating the more palatable plants, to obtain a more homogeneous stand of palatable plants, which will ensure more effective utilization of A. nummularia plantations. As the genus Atriplex is dioecious and openpollinated (Osmond, Björkman & Anderson, 1980), a vegetative propagation method was tested. It was decided to use stem cuttings for vegetative propagation.

According to the literature, similar trials were conducted on other Atriplex (Saltbush) species (Ellern, 1970; Everett, Meeuwig & Robbertson, 1978 and Richardson, Barker, Crofts & Van Epps, 1979). De Kock (1983) mentioned that it is possible to root stem cuttings of A. nummularia, but did not quantify the success rate.

In this case it can be assumed that the Atriplex species is an easy rooter, as there is some evidence in the literature (Ellern, 1970 and De Kock, 1983). The specific research objectives were to: identify the optimum season to collect stem cuttings of A. nummularia, see whether the age of the stems plays an important role, determine how the portion of stem used for cuttings affect the rooting and to study the response of A. nummularia to various concentrations of exogenously applied indole-3-butyric acid (IBA).

The cuttings were taken from an existing A. nummularia plantation. Two different plants: one with new growth, since it was cut down to 45 cm. the season before and one with old growth, since it was not cut down the previous season, were used. This was decided to find out whether the age of the growth would make any difference on the rooting ability of stem cuttings.

For each plant two cutting types were tested: terminal (tip) and subterminal. The terminal cuttings from the new growth plant were juvenile growth and more herbaceous, while the other cuttings were more semi-hardwood than herbaceous.

Each cutting type were treated with three hormonal regimes: 0 g.kg-¹, 3 g.kg-¹ and 8 g.kg-¹ IBA. For each plant, cutting type and hormonal regime, 10 cuttings were used. All the treatments were executed in four replicates and replicated over three seasons: summer, autumn and spring. Which means that for each season 480 cuttings were taken, 240 for each plant and 60 for each replicate, with each replicate consisting of 30 terminal and 30 subterminal cuttings, 10 for each hormonal treatment.

Average rooting of cuttings was higher in spring (47%) than in summer (37%), with the autumn (42%) intermediate, as illustrated in Table 1. During the summer, high temperatures inside the greenhouse together with the high humidity caused disease development in the mist-bench, which contaminated most of the cuttings. This may have contributed to the low rooting percentage the summer.

Table 1: The influence of season on the rooting percentage of Atriplex nummularia

Cutting type	Summer	Autumn	Spring
Average for terminal cuttings	46	69	75
Average for subterminal cuttings	29	15	18
Total average	37	42	47

The best results as averaged for all treatments, were in spring. Although 47% rooting seems low, it is only the average over all treatments and, within the treatments, rooting success of up to 75% was achieved for terminal cuttings (see Table 1) during spring. It could therefore be recommended that spring is a better season to propagate A. nummularia vegetatively than autumn.

Rooting of the new growth plant was higher than rooting of the old growth plant. These results are similar to Arya, Toky, Tomar, Singh and Harris (1993) whose study indicated that stem cuttings of juvenile material are the best to propagate Prosopis cineraria(L.) vegetatively.

For the old growth plant, the terminal cuttings showed acceptable rooting (35%), but not as good as the terminal cuttings of the new growth plant (49%). According to Table 2, the largest difference between the two plant types were in autumn. During autumn and winter the plants are in a stage of dormancy which may explain the poor (24%) rooting of the old growth plant in autumn. Rooting percentage of the new growth plant was the highest in autumn. It may be that the new growth reach dormancy at a later stage than the old growth, or that new growth contains higher levels of carbohydrates, nitrogenous compounds and auxins than old growth, as there is a strong relation between these compounds and root formation (Joshi, Sharma, Shamet & Dhiman, 1992).

Table 2: The influence of age of growth on the rooting percentage of Atriplex nummularia

Season	Old growth	New growth
Summer	39	35
Autumn	24	60
Spring	41	53
Average	35	49

In both plants the performance of the subterminal cuttings was not convincing. In all three seasons rooting of terminal cuttings were higher than rooting of subterminal cuttings. The largest overall average of 75% was in spring as can be seen in Table 3.

Table 3: The influence of cutting type on the rooting percentage of Atriplex nummularia

Season	Terminal cuttings	Subterminal cuttings
Summer	46	29
Autumn	69	15
Spring	75	18
Average	63	21

The 0 g.kg^-1 IBA showed an average root initiation of 36%, while the 3- and 8 g.kg^-1 IBA showed an average root initiation of 46% and 45% respectively (Table 4). However, when only the terminal cuttings are evaluated, 3 g.kg^-1 IBA gave the highest results in autumn (73%) and spring (81%), with the average of 81% in spring higher than that of any other treatment. The 0 g.kg^-1 IBA treatment gave a 70% rooting success for terminal cuttings, which is promising in the sense that it would be much more economical if A. nummularia can be propagated vegetatively without auxin treatment. It may be possible to find some A. nummularia plants with the genetic ability to give a rooting percentage above 70%. Ellern (1970) got a 77% rooting for A. halimus without any hormonal treatment.

Table 4: The influence of hormonal regime on the rooting percentage of Atriplex nummularia

Season	0 g.kg^-1 IBA	3 g.kg^-1 IBA	8 g.kg^-1 IBA
Summer	26	37	49
Autumn	39	46	42
Spring	44	54	43
Average	36	46	45

From the results of this experiment it is clear that vegetative propagation of A. nummularia, by stem cuttings, is possible. According to the Response Surface analysis that was done, as the statistical analysis, to find the optimum method for rooting stem cuttings of A. nummularia, the following procedure is recommended: use a plant with new growth (for instance one that was cut down recently and already started new shoot growth), use only terminal stem cuttings of 10 to 15 cm, treat the cuttings with 3 g.kg^-1 IBA and do all of this in the late autumn or spring. Rooted cuttings can be transplanted into pots containing a mixture of 40% soil, 40% compost and 20% sand.

More than one mother plant should be used. The reason being the genetic difference between plants within this species, which may result in different rooting abilities between different plants. Another reason is, to maintain genetic variability, to protect the progeny against pests. If all the new plants are from the same mother plant, they could be highly vulnerable to pests.

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