Agriculture Western Australia, PMB 50 Esperance WA 6450
Research conducted in Western Australia has shown that kernel discolouration in barley can be related to mean 3pm relative humidity during the period from early dough formation to harvest. Southern high rainfall areas in Victoria are at a high risk of kernel discolouration due to high relative humidity late in the grain filling stage and a high incidence of rainy days until harvest. In the short term agronomic practices are likely to have only a limited effect on improving grain colour. In the longer term substantial improvements may be obtained through the use of Japanese malting barleys such as Kino Nijo 7 in local breeding programs. Genetic improvements may need to include tolerance to high temperatures during the grain filling period, to enable to take full advantage of seasons that offer the appropriate conditions for the production of bright grain.
The major barley growing area of Western Australia is situated along the south coast surrounding the Albany and Esperance Port Zones. This region produces around 1m tonnes of barley annually. Grain quality is often affected by kernel discolouration (KD) due to weather staining resulting from rain and prolonged periods of high relative humidity from grain filling to harvest. The most commonly grown malting variety, Stirling, is particularly susceptible and has been known to increase grain colour after heavy dews.
Research commenced in 1995 to identify useful sources of resistance to KD and gain an understanding of the stages of grain development most susceptible, and the type of climatic conditions most conducive, to KD. Sources of resistance and susceptible stages of development have been previously reported (Young 1996). This paper aims to presents a summary of the effect of environmental conditions on KD and the possible agronomic and genetic solutions.
In short there is little that can be done with changes in agronomic practices. The following is a summary of the effects of various agronomic treatments on grain colour.
When applied during grain filling to control fungi associated with KD, fungicides have little effect. There is little evidence of the use of fungicides overseas to control KD.
Very high levels of foliar diseases, such as scald, may effect grain colour. Naturally it can be expected that fungicides applied to control these diseases may improve grain colour.
High grain nitrogen/protein can be associated with a slight increase in grain colour. This trend reverses when nitrogen application is so high that it causes smaller grain and higher screenings.
Once again this has no effect unless the plant density is so high that there is an increase in screenings which will more than likely mean slightly brighter grain.
Because relative humidity is decreasing as summer progresses, later sown crops often give brighter grain. This is of little use if sowing is so late that it effects yield and/or screenings. It is important to recognise that there is an optimum flowering time for yield and quality in each region. Sowing unnecessarily early is only likely to increase the chances of weather staining.
Swathing itself has little effect on grain colour. In the moist coastal environments it can be used to bring the crop to a harvest ripe condition 5 to 15 days earlier than a standing crop and allow more harvesting hours per day. If this means that early harvest results in avoiding damaging rains then, and only then, will a swathed crop be brighter than a standing crop. This can be quite an advantage in some seasons especially when combined with the fact that swathing overcomes yield loss associated with head drop.
In a prolonged hot dry spell, a standing crop will bleach so it is entirely possible that a standing crop in some years will be brighter than a swathed crop.
In summary, any management practice on its own is likely to have little affect on grain colour. In combination the effect will be greater, especially if a grower is getting the basics wrong. Consider, for example, the amount of room for improvement if a grower sows too early with a disease susceptible variety and no fungicides at too high a nitrogen rate and leaves the crop standing too long prior to harvest!
A small number of lines have been identified as having some resistance to kernel discolouration. The best of these are the Japanese lines, notably a line originating from the Kirin breeding program known as Kino Nijo 7 (also referred to as WA5034). This line has been studied in detail along with the KD susceptible variety Stirling in sowing date experiments at Esperance for the past three seasons. In order to gauge just how useful this level of resistance may be in other parts of Australia where grain colour is a problem, it is first necessary to develop a relationship between grain colour and data that is routinely collected by the Bureau of Meteorology.
The relationship between grain colour and climatic conditions
From 1995 to 1998 Stirling barley was studied in field experiments at Esperance across nine sowing dates so as to measure the effect of a wide range of climatic conditions on grain colour. Half-hourly measurements of temperature, relative humidity, precipitation and solar radiation were taken for the period from ear emergence to harvest. The period of grain formation found to be most susceptible to kernel discolouration was considered to be the early dough stage through to harvest (Young 1996). Grain colour was measured with a Minolta ‘Chroma Meter CR310’ and is presented as the ‘L’ value. This is closely related to the ‘Infratec’ value that is used to measure grain colour in bulk barley deliveries in Western Australia. On this scale the higher the value the brighter the grain (the lower the colour).
Factors and combinations of various factors were related to grain colour with most showing little or no relationship. The best relationship was obtained simply by plotting grain colour against the mean 3pm relative humidity reading for the period from the early dough stage through to harvest (Figure 1).
Figure 1. Relationship between grain colour and mean 3pm Relative Humidity from the early dough stage to harvest for Stirling barley at Esperance WA in the 1995 to 1998 harvests.
The 3pm RH reading is low on hot days that reduce discolouration and high when cold fronts pass through and cause the conditions that increase discolouration, so it is not surprising that this one measurement can reasonably be related to grain colour. The advantage of using the 3pm RH reading is that this data is readily available for a wide range of sites across the barley growing areas of Australia.
As the mean 3pm RH reading increases from 50% to 60% for the period prior to harvest the grain colour of Stirling barley deteriorates rapidly (Figure 1). On this basis the barley growing areas of Victoria such as Birchip and Horsham, are likely to have few problems with grain colour. However the southern areas from Colac through to Ballarat and Geelong are likely to have problems similar to those experienced on the south coast of Western Australia (Figure 2).
Figure 2. Mean monthly relative humidity for a selection of barley growing areas in Victoria compared to Esperance WA. Approximate periods from late grain filling through until harvest (D. Moody pers. comm.) represented as a dotted line for each site.
While the relative humidity in the Geelong and Colac regions is slightly lower than those for Esperance, there could be an increased risk of discolouration due to the higher mean number of rainy days in those regions near the harvest period than observed in Esperance (Figure 3).
Figure 3. Number of rain days per month for a selection of barley growing areas in Victoria compared to Esperance, WA. Approximate periods from late grain filling through until harvest (D. Moody pers. comm.) represented as a dotted line for each site.
Genotypes with improved grain colour
The screening trials conducted in Esperance have shown that most Australian cultivars are equally susceptible to KD when compared under the same environmental conditions. The exceptions are Schooner, which is generally slightly brighter than Stirling (in the order of one Minolta ‘L’ unit), and the early indication is that Sloop is slightly brighter again. The largest advances however, are likely to come from the use in breeding programs of Japanese lines such as Kino Nijo 7 which is significantly brighter than Stirling at 3pm RH readings of >50% (Figure 4).
Figure 4. Relationship between grain colour and mean Relative Humidity from the early dough stage to harvest for Stirling barley and the Japanese line Kino Nijo 7 at Esperance WA 1997 and 1998 harvests.
Fortunately this Japanese barley also has the advantage of having very large plump grain of high malting quality. It does however have a few unfortunate characteristics such as very early maturity, tall weak straw, disease susceptibility and the tendency to drop heads at a rate rarely seen. The challenge clearly lies ahead for Australian barley breeders.
Delayed flowering, temperature and grain filling
There may be a suggestion that delayed flowering in an area such as Colac will push grain filling into a time of lower relative humidity and so reduce the risk of kernel discolouration (figure 2). Apart from the risk of reduced grain size due to moisture stress there is a real possibility that high temperatures will slow grain filling.
A detailed study of rates of grain filling in Western Australia (K.J.Young and B.H.Paynter, in preparation) has shown that the optimum temperatures for grain filling are in the range 14°C to 16°C as a mean daily temperature. Furthermore the rate of grain filling in most varieties is markedly reduced as mean daily temperatures climb above 16°C. This means that while moisture stress may be increasing with late flowering, the problem is accentuated by rates of grain filling that are slowing at the same time.
The southern higher rainfall sites in Victoria such as Geelong and Colac (Figure 5) are completing grain filling under high temperatures in an ‘average’ season. It will therefore be preferable to breed varieties for this region with improved tolerance to high temperatures. This will enable them to successfully complete grain filling in the warm dry seasons that are likely to provide ideal conditions for the production of bright grain.
Figure 5. Mean monthly temperatures for a selection of barley growing areas in Victoria compared to Esperance, WA. Approximate periods from late grain filling through until harvest (D. Moody pers. comm.) represented as a dotted line for each site.
Small improvements in grain colour can be achieved in the short term through attention to the finer details of agronomic packages. In the longer term it should be possible to breed locally adapted varieties with significant improvements in resistance to kernel discolouration using Japanese malting lines.
It must be remembered that resistance by the industry to the purchase of discoloured grain is because it has for a long time been associated with a high level of fungal activity and subsequently the risk of associated problems in both the malthouse and the brewery. It is pointless breeding for resistance to weather staining unless such resistance is linked to reduced populations of microflora on the surface of the grain. It would, however be a definite advantage to the barley growers of the higher rainfall areas of southern Australia to have access to varieties that did not discolour quite so readily.
Agriculture Western Australia and the Grains Research and Development Corporation support this research. David Dodge and Vanessa Dooley provided technical assistance.
Young, K.J. (1996) An assessment of effect of genotype and environment on kernel discolouration of barley in Western Australia. In Proc. 7th Int. Barley Genet. Symp., (Eds. A. Slinkard, G. Scoles and B. Rossnagel) Poster Sessions Vol 2, pp. 688-690.