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COORDINATION OF APEX AND LEAF DEVELOPMENT IN OATS

M. Sonego1, P.D. Jamieson2, D.J. Moot1 and R.J. Martin2

1 Plant Science Department, Lincoln University, Lincoln, New Zealand
2
New Zealand Institute for Crop & Food Research Ltd, Lincoln, New Zealand.

Abstract

A challenge in modelling phenological development in cereals is to predict the rate of production of leaves, the final leaf number on the main culm, and intermediate apical states. Accordingly oats, cv Cashel, were planted at two month intervals through an annual cycle. At regular intervals mainstem leaf number, leaf length, primordium number and apical state were observed. In this paper we show how apical states were related to, and therefore can be predicted from, mainstem leaf number. Leaf stage at the occurrence of double ridges and the beginning of stem elongation were delayed by close to one phyllochron for each unit increase in the final leaf number.

Keywords: phenology, phyllochron, leaf scale.

The duration of development phases in the life cycle of oats varies in response to temperature and daylength (8). The mechanism is mostly through responses in the rate of leaf appearance to temperature, and of final mainstem leaf number to daylength (5, 6). However, most cereal models do not use these mechanisms, but simply define the duration of phases in thermal or photothermal time (7). These two approaches need to be unified, and in this paper we show that this is possible for oats. Our objective was to define the occurrence of specific apical states between emergence and anthesis in terms of the leaf stage of the mainstem when they occur, and the final mainstem leaf number (1).

Materials and methods

Oats, cv Cashel, were planted on six dates (23 April, 21 May, 8 August, 20 September, 25 November, 1996 and 22 January, 1997) on the Crop & Food Research Experiment Station at Lincoln (latitude 43E36'S) in a Templeton silt loam soil. Plots were sown to establish a population of 300 plants/m2 in a randomised complete block design with three replicates. Insecticides and fungicides were applied as required to control pests and diseases, but no herbicides or fertilisers were applied. The experiment was irrigated four times with applications of 50 mm in response to water budget calculations. Meteorological data were obtained from a weather station within 300 m of the experiment.

Observations of external morphological development of plants were made twice weekly on ten tagged plants within each replicate for each sowing date treatment. On each plant, the length of each leaf was measured as it grew. On the same day, 5 plants were removed randomly from each plot and dissected under a binocular microscope to determine the developmental stage of the apex, using the methodology of Kirby and Appleyard (4). The sampled plants, including the soil around their roots, were sealed in plastic bags and stored at 2-4EC until dissected. The phenological stages noted were (3): plant emergence (EM), double ridge (DR), beginning of stem elongation (SE) and flag leaf ligule appearance (FL).

Results and discussion

To compare the leaf stage and apical state, we required a finer scale than would be given by either the cumulative number of visible tips or ligules (5). Therefore we constructed a leaf scale similar to the Haun scale for wheat (2), based on the progress of expansion of leaves. This was to provide a continuous decimal leaf scale from 0.0 at emergence to n.0 at the appearance of the flag leaf ligule, where the flag leaf is leaf n. Leaf length plots against thermal time were extrapolated back to the x-axis, and the fractional leaf stage at any time was taken as the proportion of the thermal time between leaves that had occurred (Fig. 1).

There was a strong relationship between the leaf stage at occurrence of the apical stage and final leaf number (Fig 2). Leaf stage at DR (Lsdr) and SE (Lse) were related to final leaf number (FLN) by
LSdr = -5.17 + 1.07 FLN r2 = 0.97 (i)
Lsse = -1.94 + 0.955 FLN r2 = 0.97 (ii)

The coefficients mean that increases in FLN cause a delay of about 1 phyllochron per leaf in DR and SE. Also, when these stages occur, there is a near constant number of leaves left to appear.

Conclusions

Apex and leaf development are closely linked, and respond similarly to their environment. Therefore, any method that will account for the rate of leaf appearance and final leaf number will allow the prediction of apical stages. This means that the apical state should be predictable from leaf stage and sowing time, at least for Cashel oats, and probably for other cultivars.

Acknowledgement.

MS gratefully acknowledges funding from CNPQ and EPAGRI, Brazil.

References

1. Aitken, Y. 1976. J. Aust. Inst. Agric. Sci., March, 1976. pp 65-66.

2. Haun, J.R. 1973. Agron. J., 65, 116-119.

3. Hay, R.K.M. 1986. Field Crops Res., 14, 321-337.

4. Kirby, E.J.M and Appleyard, M., 1981. Cereal development guide. National Agricultural Centre, Cereal Unit, 79 pp.

5. Martin, R.J., Sinton, S.M., Jamieson, P.D. and Sonego, M. 1998a. Proc. 9th Aust. Agron. Conf. Wagga Wagga. This volume.

6. Martin, R.J., Sinton, S.M., Jamieson, P.D. and Sonego, M. 1998b. Proc. 9th Aust. Agron. Conf. Wagga Wagga. This volume.

7. Slafer, G.A. and Rawson, H.M. 1994. Aust. J. Plant Physiol., 21, 393-426.

8. Sonego, M., Jamieson, P.D., Moot, D.J. and Martin, R.J. 1997. Proc. Agron. Soc. NZ., 27, (In Press)

Figure 1. Relationship between leaf length and thermal time for oats sown on 22 January 1997. Vertical lines indicate the times of DR and SE.

Figure 2. The relationship of leaf stage at DR and SE to final leaf number for Cashel Oats.

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