Wheat. Peter R. Shewry

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1.4; Figure 1.7). Growth stage scores are used extensively to interpret the effects of the environment on crop growth and yield, and to optimize the timings of agronomic treatments including irrigation and the application of fertilizers, growth regulators, and crop protection agrochemicals (Barber et al. 2015). They can also be used to define safe grazing periods for dual‐purpose crops (Gooding et al. 1998). The most widely used growth stage scoring method for wheat, and that used throughout this book, is the decimal growth stage (DGS) system of Zadoks et al. (1974). Equivalents between the Feekes and Zadoks scales are given in Table 1.4. Equivalents with lesser‐used scoring systems are provided by Landes and Porter (1989) and Harrell et al. (1993, 1998).

Table 1.3 Mega‐Environments (ME) for wheat.

      Source: Adapted from Rajaram et al. (1993) and Gbegbelegbe et al. (2017).

ME	Wheat type	Agro‐climatic conditions
1	Spring	Irrigated. Temperate in winter to late heat stress.
2	Spring	High rainfall (> 500 mm during cropping season). Temperate.
3	Spring	High rainfall. Temperate. Acid soils.
4A	Spring	Low rainfall. Winter rain followed by drought. Temperate.
4B	Spring	Low rainfall. Early drought preceding summer rain. Temperate.
4C	Spring	Low rainfall. Soil water stored from monsoon. Temperate.
5A	Spring	High rainfall. Hot (coolest month > 17.5 °C).
5B	Spring	Irrigated. Hot.
6	Spring	Moderate rainfall. Winter would kill wheat. Coolest month < –10 °C.
7	Facultative	Irrigated. Cool.
8A	Facultative, daylength sensitive	High rainfall. Cool.
8B	Facultative, daylength insensitive	High rainfall. Cool.
9	Facultative	Low rainfall (< 500 mm available to crop). Cool.
10A	Winter	Irrigated. Cold winter.
10B	Winter	Rainfall + irrigation. Cold winter.
11A	Winter, daylength sensitive	High rainfall. Cold winter.
11B	Winter, daylength insensitive	High rainfall. Cold winter.
12	Winter	Low rainfall. Cold winter, hot summer.

The growth of wheat can be broadly divided into two phases: the vegetative phase and the reproductive phase. The distinction between the two phases depends on events in the bud tip, or stem apex (i.e. the apical meristem if referring to the main stem) of the plant. The vegetative phase encompasses germination, and then a period during which growth from the stem apex gives rise only to vegetative tissues: leaves, tillers (i.e. the branches or side stems of grass plants), and adventitious roots.

Table 1.4 Growth stage scores of wheat plants.

	Decimal growth stages (DGS) according to Zadoks et al. (1974)	The scale of Feekes (1941)
Major growth phases	Major division	Minor divisions described by n	Score	Description	Equivalent DGS score
Germination	0n	n indicates development before leaf emergence i.e. from dry seed (n = 0) to first leaf at coleoptile tip (n = 9)
Leaf production	1n	n is the number of unfolded leaves on the main stem to a max. n = 9	1	Seedling emergence to three leaf stage	10–13
Tiller production	2n	n is the number of tillers with their own unfolded leaf to a max. n = 9	2	Start of tillering	21–25
			3	End of tillering	26–29
Stem extension	3n	n is the number of nodes to a max. of 6, then n = 7 for flag leaf just visible, and n = 9 flag leaf unfolded	4	Leaf sheaths lengthen	30
			5	Leaf sheaths strongly erect	30
			6	One node detectable	31
			7	Two nodes detectable	32
			8	Flag leaf just visible	37
			9	Flag leaf emerged	39
Booting	4n	n indicates degree of swelling of Скачать книгу В начало < 9 10 11 12 13 14 15 16 17 18 > В конец e-mail: [email protected]