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THE EFFECT OF DAYLENGTH ON FINAL LEAF NUMBER IN DRUMMOND OATS

R.J. Martin, S.M. Sinton, P.D. Jamieson and M. Snego

New Zealand Institute for Crop & Food Research Ltd.

Abstract

The influence of daylength on final leaf number (FLN) was determined for oats cv. Drummond sown on six dates in the 1994-95 season. The emergence dates of the tip and ligule were recorded for each leaf on the main stem of six tagged plants. FLN varied from 7.7 to 11.3, and was related directly to the photoperiod at the time of emergence of the sixth leaf tip or fourth leaf ligule. A hysteresis plot was obtained when FLN was related to photoperiod at the emergence of all other leaf tips and ligules. Thus, in this oat cultivar, FLN is easily predictable from the daylength at the appearance of the sixth leaf tip or fourth leaf ligule. This, together with knowledge of the relationship of leaf emergence and grain growth to temperature, could be used to construct a simple model of oat development..

Key words: Oats, Avena sativa L., leaves, photoperiod, sowing date.

In wheat, most developmental events until anthesis can be related to the appearance of main stem leaves (1, 2). Duration of growth depends on the number of leaves produced sequentially on the main stem and the rate at which they are produced. In wheat the final leaf number (FLN) is often related to photoperiod at a certain stage of development (1). This aspect of plant development has not been researched in oats (Avena sativa L.). To develop a model of oat growth to predict its performance in different environments requires knowledge of FLN, the rate at which these leaves appear, the rate of biomass accumulation during leaf production, and its partition-ing.

The objective of this study was to determine the response of FLN to photoperiod using data from a time of sowing trial with Drummond, a semidwarf milling oat grown in New Zealand.

Materials and methods

The experiment was carried out on a Templeton silt loam at Lincoln, New Zealand (latitude 43o39'S, long-itude 172o30'E). Oats cv. Drummond were sown at 167 kg/ha, with the aim of establishing 300 plants/m2. Sowing dates were 16 September, 2 November and 21 December 1994 and 7 February, 3 April and 16 May 1995. A randomized block design was used with four replicates. Plot size was 15 m long by 2.7 m wide. Herbicide, insecticide and fungicide were applied as required to minimize restrictions to crop growth, but no fertiliser was applied in order to avoid lodging. For the same reason, irrigation was applied only when soils were close to wilting point.

After plant emergence, six plants in the middle of each plot were tagged and subsequently monitored at fre-quencies ranging from twice a week in summer to once every three weeks in winter until the panicle emerged. Each time the number of leaf tips and ligules on the main stem were counted. For this study, the means of leaf numbers from the four replicates were used for regress-ion analysis.

Results

FLN varied from 7.7 for the November sowing to 11.3 for the May sowing. When plotted against photoperiod at the time a certain number of leaf tips or ligules had emerged, a hysteresis response was obtained (Fig. 1). This hysteresis loop closed to produce a straight line for the cases when the sixth leaf tip and the fourth leaf ligule emerged (Fig. 1b, 1d). The regression equations were:

FLN = 17.0 (0.06) - 0.561(0.0118) PLT6
(r2=0.998, d.f. 4) ; (i)
FLN = 17.0 (0.06) - 0.563(0.0118) PLL4
(r2=0.998, d.f. 4)&nbs p; (ii)

where: PLT6 = photoperiod at sixth leaf tip appear-ance and PLL4 = photoperiod at fourth leaf ligule appearance.

Discussion

The very close relationship between photoperiod at the time when the sixth leaf tip emerged and FLN means that, in this oat cultivar at least, FLN is easily predict-able, and this relationship could be easily incorporated into a simple model of oat development.

With long days, only one to two more leaves appear after the sixth leaf, so the response to photoperiod occurs very late in development when plants are sown in late spring. Similar late commitment of a primordium to become either a leaf or a spikelet also occurs in some wheat cultivars (1).

In many wheat cultivars, the number of leaves produced also depends on daylength, but the timing and magnitude of the response varies between cultivars (1). Work is currently under way to determine the variation of this response among oat cultivars.

Conclusions

In Drummond oats, FLN is determined by the photoperiod at the time when the sixth leaf tip or fourth leaf ligule emerges.

References

1. Brooking, I.R., Jamieson, P.D. and Porter, J.R. 1995. Field Crops Res. 41, 155-165.

2. Jamieson, P.D., Brooking, I.R. and Porter, J.R. 1996. Proc. 8th Aust. Agron. Conf. Toowoomba, 337-340.

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