This blog post was by Allan Booth, a barley researcher at the James Hutton Institute who, the next few months, is working in Brisbane, Australia.
What is ‘Stay Green’ you may well be asking? Does this pertain to waste management or recycling? Of course not but perhaps sustainability is more appropriate.
The global challenges of climate change and the increasing occurrences of droughts (water and heat stresses) in various parts of the world have led to adverse effects in plant growth, grain development and crop productivity. Australia, of course, comes into this category and perhaps not such an issue with our more temperate Scottish climate and Northern Europe.
Earlier successes with Sorghum have encouraged researchers to look for the ‘Stay Green’-like trait in other cereals, particularly barley (whoopee!) and wheat (groan!).
Here at QAAFI (Hickey Lab) a number of phenotyping tools have been used by the students for their project outcomes in relation to ‘Stay Green’.
GreenSeeker® is an integrated optical sensing and application system that measures crop status and variably applies the crop’s nitrogen requirements. Yield potential for a crop is identified using a vegetative index known as NDVI (Normalized Difference Vegetative Index) and an environmental factor.
The plants want to be as green as possible for as long as possible to optimise grain fill and subsequently the plot yield or Harvest Index. Drought and Pathogen pressure will accelerate the senescence rate and have an impact on grain quality and yield.
Barley and wheat population trials were screened with this 1-2 times per week post flowering to determine the senescence rates of individual plots (2015, with thanks to Dr. Lee Hickey for the photographs).
In 2016 the GreenSeeker® was used from initial planting to monitor early vigour and beyond and again screened at least once a week.
In this series of photographs Hannah Robinson (3rd Year PhD Student), top left, is using the GreenSeeker® to screen her 600 plots of barley (2 treatments; irrigated (wetland) and non-irrigated (dryland)).
Dilani Gamaralalage (PhD student, top right) is using the GreenSeeker® equipment to monitor treated and untreated leaf/yellow rust (Puccinia striiformis f.sp. tritici) wheat population trials.
In the bottom 2 shots Samir Alahmad (2nd Year PhD Student) is screening his wheat populations at Wellcamp (Toowoomba). These plots are about 10 days from harvest and almost completely senesced. In the photograph on the left he appears to be using the equipment as some sort of virtual reality headset. Perhaps something for the future!
As part of his Honour’s project Cameron Van-Lane is researching early vigour and the role that it may play in the Stay Green trait. He has identified 56 plots in Hannah’s barley trial in the ‘Dryland’ only. In those 56 plots he has tagged 10 plants distributed throughout the plot. The GreenSeeker® has been used in this trial from the day of sowing. Early vigour is desirable to create a screen for the soil to prevent evaporation and retain the moisture for the plants. Combining NDVI data and tracking plant growth will give a greater understanding of canopy development. He has also harvested 3 of the plants from each plot and partitioned them for leaf area (Leaf Area Index Machine) and dry matter.
In these photographs; top left, Cameron measuring growth stage; top right, Cameron looking for his individual plants in the dense undergrowth; bottom left, Cameron harvesting plants for partitioning; bottom right, Cameron and Allan Booth collecting plants for partitioning and discussing what we are having for lunch.
Hazards of Greenseeking
The GreenSeeker® presents the user with a number of challenges; a steady hand, be sure of foot, be able to walk at a consistent pace, have a good sense of timing and of course to be able to screen 2×600 plots of barley in 30oC of heat requires a moderate standard of fitness.
Due to the unseasonably wet winter (2016) the genotypes in the barley trial have accumulated a great deal of biomass, so much so that some of the plots are lodging at growth stage 45 (GS45), an obvious tripping hazard tripping hazard.
The widening cracks in the wheel tracks which are as wide as your foot and up to 1 metre deep could cause a nasty ankle injury or indeed worse.
In these pictures lodging can be seen in the crop at a more mature stage.
Also secondary growth can record a misleading reading for the Stay Green trait.
And, of course, beware of the wriggly sticks (not that I’ve seen one yet)!
Another method used to measure senescence is the SPAD Meter which measures leaf chlorophyll content. This is not used in the field but in glasshouse experiments. After flowering date a pre-determined area of the flag leaf is marked and measured once or twice per week until senescence of that leaf is complete.
In the picture below are the SPAD team of Samir Alahmad, Ravinder Singh and Allan Booth in the glasshouse measuring a wheat trial which has been infected with crown rot.
This is set up in a glasshouse in root chambers. The plants are grown until flowering in these chambers which are then dismantled for root architecture analysis. The desirable root type for the heavy black clay soils in Queensland are the narrow deep seeking roots which will supply water at the critical grain filling development and allow the plant to stay green longer.
In the pictures below are; top, barley plants set up in the chambers in the glasshouse; bottom left, chambers have been dismantled and each one is photographed. Also in the picture are Dr Stephen Mudge and Andreas Stahl (Justus Liebig University, Giessen, Germany) who are sampling the roots for RNA extraction and further analysis; bottom right, a picture of root architecture in one of the chambers.