Peter Griffith

JB Diego has thrown some strange looking ears this year. The extra or supernumerary spikelets are common in some varieties such as Einstein or Welford but are unusual in JB Diego.

Supernumerary spikelets occur either as sessile spikelets at a rachis node or on an extended rachilla as three types:

1. Multiple sessile spikelets (MSS). Two, frequently three and rarely four or five, over-lapping, sessile spikelets at a rachis node.
2. Transitional sessile spikelets (TSS). Single sessile spikelets at a rachis node divided into two (or three) parts, resembling MSS but possessing only a single pair of outer glumes. These were counted as single spikelets and they appeared to be transitional between normal and supernumerary spikelet classes 1 and 3.
3. Indeterminate rachilla spikelets (IRS). Two to 13 spikelets (some undeveloped) on an extended rachilla usually occurring between two MSS at a rachis node.

It is the TSS form that seems to be the predominant in crops of JB Diego this year.

Long photo-period

Many genes are involved in the development stages and spike characteristics in wheat and the degree of supernumerary spikelet expression (ear branching) in wheat is strongly influenced by environmental conditions. Varieties with a strong vernalisation requirement are particularly prone to ear branching. Research has shown that wheat with a strong vernalization response under a long photoperiod outdoor (low temperature) environment developed more supernumerary spikelets than under other photo-periods and temperatures.

JB Diego has a strong vernalisation requirement with a safe sowing date of the end of January.  The long cold spring created a long photoperiod when ear development was happening and is the most likely reason why the extra spikelets have formed this year.

More spikelets more grain?

So does this mean more yield? There isn't much research data on the impact of yield from supernumerary spikelets but the plant breeders have looked at this characteristic as a means of increasing yield in new varieties. However, back in 1948 in Oklahoma the wheat yields exceeded all expectations. That year there were reports of many wheat fields showing plants with supernumerary spikelets. The agronomists at the State Experimental Station commented that "From the widespread occurrence of these conditions it is felt that they were the major factors in the discrepancy between predicted and actual yields". So let's hope for a happy end to the season with bumper yields from this popular variety.



Notes

Journal of Agricultural Science Vol. 4, No. 8; 2012
Annals of Botany 53, 821-831, 1984
Can.J.Bot. 62: 1687-1692
Agronomy Journal Vol. 41 No. 1, p. 46-47
NIAB Wheat Guide