Assessing plant and crop development – from DC29

Within the manual Protocols for experimental plot sampling, handling and processing of cereals in field experiments by G.J. Rebetzke (Greg.Rebetzke@csiro.au), A. van Herwaarden, B. Biddulph, C. Moeller, R. Richards, A. Rattey and K. Chenu.

Plant growth can be divided into growth stages associated with the timing of different vegetative and reproductive growth processes. Understanding how growth varies with prevailing environmental conditions, primarily temperature and daylength, can be very important in assessing factors contributing to yield differences between genotypes and/or environments.

Method

Crop development can be thought simply in terms of six key phases: 1. Vegetative (where the apical meristem produces leaves); 2. Floral initiation (where the apical meristem transitions from vegetative to reproductive development); 3. Growth of reproductive structures; 4. Flowering; 5. Grain development; and 6. Physiological maturity. The methodology described below is for wheat and triticale – similar methodology may be obtained for other cereals from the literature.

1. Vegetative growth: plants are growing vegetatively developing leaves, tillers and accumulating biomass. Using a simple compound microscope, the plant apex can be dissected and the vegetative whorls are seen as discrete single bands or -ridges’ (Fig 13 (a) 1 and 2).
2. Floral initiation: plants remain vegetative until adequate environmental stimulus is provided (i.e. daylength and temperature). Plants commence floral initiation whereby the apical meristem commences the transition from ‘vegetative’ to the ‘floral’ or reproductive growth. Using a simple compound binocular microscope, the dissected apex shows pairs of rings or a -double-ridge’ commencing at the centre of the apex (Fig. 13 (a) 3). These ridges represent the commencement of growth of the floral bud primordium as they begin to grow out. Leaves are no longer being produced with the apical apex now committed to producing reproductive parts only. The culmination of floral development occurs with the production of the terminal spikelet (TS in Fig. 13 (b)). This stage (also scored as DC31 or Z31) coincides with the commencement of stem elongation and the production of the first node (known as -jointing’). This node can be felt as a swelling at or near the soil surface. The detection of this swelling is commonly used as a quick and non-destructive surrogate for determination of TS under a microscope.
3. Growth of reproductive structures: following terminal spikelet, ears grow rapidly contained within the leaf whorls until emerging above the ligule of the flag leaf (DC51+)(Appendix 1 and 2). The ear is fully emerged above the ligule for all spikes at DC60.
4. Flowering: fertilisation commences with dehiscence of anthers at flowering (or anthesis). Flowering is commonly scored as DC65 when 50% of spikes contain one or more dehisced anthers (observed as yellow anthers emerge from the spikelet). In some cases and particularly under drought, anthers may not emerge from the spikelet requiring the spikelets to be opened to confidently determine anther dehiscence.
5. Grain development: grain development commences with fertilisation and is finished at physiological maturity with the completion of grain dry matter accumulation.
6. Physiological maturity: maturity defines the time when grains have ceased accumulating carbon and commence drying-down. Typically at this stage most or all the chlorophyll has been lost from the plant and remains only in the stem nodes.

a)

b)

Figure 13. Various stages toward floral initiation in wheat: (a) apex development from vegetative (1) to double-ridge (3); (b) apex at terminal spikelet (ref: Moncur 1981)

Other resources

Appendix 1. Text description of phenological scale, Zadoks decimal code (DC).
Appendix 2. Picture description of phenological scale, Zadoks decimal code (DC).
Zadoks JC, Chang TT, Konzak CF (1974) A decimal code for the growth stages of cereals. Weed Research 14(6),415-421. doi: 10.1111/j.1365-3180.1974.tb01084.x

Notes and troubleshooting tips

Literature

Moncur MW (1981) Floral initiation in field crops: an atlas of scanning electron micrographs (CSIRO Publishing)

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