New pointer to better leaf disease management

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Alan Bowring who is researching the role of head and flag leaf development in contributing to wheat yield.

Alan Bowring who is researching the role of head and flag leaf development in contributing to wheat yield.

By Bob Freebairn
Agricultural Consultant, Coonabarabran NSW

New research is suggesting lower leaves contribute more to wheat yield than is currently the “accepted norm” – under which protection of the flag leaf is the principal determinant of grain yield.

These preliminary findings by Industry and Investment (I&I) NSW technical officer Alan Bowring could have considerable ramifications for the management of leaf diseases such as stripe rust, yellow leaf spot and leaf rust – all diseases that can dramatically reduce grain yield and grain quality.

The research was Alan Bowring’s honours project for his Bachelor of Rural Science at the University of New England (UNE). The research also involved Primary Industries Innovation Centre head Bob Martin, Guy McMullen from I&I NSW in Tamworth, UNE’s Chris Guppy, Neil Fettell from I&I NSW in Condobolin, Tamworth district agronomist Loretta Serafin and research pathologist at I&I NSW at Tamworth, Steve Simpfendorfer.

Australia, for what may be largely historic reasons, has tended to accept the UK view of which parts of a wheat plant contribute most to grain yield and quality. But the UK environment, clearly, is very different to northern NSW, where Alan Bowring and his colleagues conducted their three years of research into leaf influences.

The UK belief is that the flag leaf (the last leaf formed and on top of the extended stem) contributes almost 45 per cent towards grain yield, with the head/awns and the second last leaf (flag leaf -1) each contributing about 20 to 23 per cent.

In similar cool long season conditions in Australia this also seems to be the case, however in more difficult hot, dry seasons in northern Australia, Alan Bowring’s results suggest that the importance of the flag leaf is about half of what is accepted in the UK. His data indicates that in these dry conditions the earlier leaves preceding the flag leaf (especially the preceding two; flag leaf -1 and -2) have a similar overall contribution to yield as the flag leaf, at least in environments such as northern NSW.
Contribution to yield of pre-flowering stem reserves was assessed in the research and is believed to contribute between 16 and 21 per cent by remobilisation of sugars and proteins to the grain. It also appears that the contribution to grain yield from the head and awns is more than that indicated by the UK standards.

Adult resistance often does not fully ‘cut in’ until plants begin heading. For example, some wheat varieties are rated moderately resistant (MR) to stripe rust, which commonly means good adult resistance but some susceptibility during the seedling stage. Alan Bowring’s research suggests that in dry northern cropping conditions the leaves prior to flag leaf need more diligent protection. An earlier control spray may be appropriate in this situation.

Differences between the northern NSW research and the UK approach are believed to be largely related to the different environment and possibly different genetics. Average temperatures are much lower in the UK and the growing season is longer. The shorter, and often heat and moisture-stressed, northern NSW environment probably relates to the greater importance of earlier leaves and sugar and protein storage within the plant.

The Australian research is now extending over several popular commercial varieties, including durum wheat. Findings overall suggest they all have a similar behavioural response as far as what parts of the plant contribute most to yield.

More information: Alan Bowring, 0427 236 847,

Region North