New development scales for cereals created

The initiative aimed to improve Agricultural Production Systems sIMulator (APSIM) Next Gen so that it can "accurately predict cultivar phenology classification and optimal sowing dates across Australia at point of release".

Dr Celestina said for the initiative, they needed "repeatable, reproducible protocols" and existing scales were "inadequate".

"I needed to be able to hand members of the initiative the same protocol, so that we would all get the same answer and that same answer repeatedly when assessing the same plants," she said.

"We were assessing the development of 96 wheat and barley cultivars, all with different phenology and different times of heading.

"We also had field experiments, with a population of plants, and also controlled environment experiments for single plants.

"We also had people rotating in and out and diverse expertise, ranging from agronomists, modelers, geneticists, statisticians, so we needed to make sure we were all speaking the same language with the scales that we're using.

"And because of the project, we needed our scale to be compatible with APSIM.

"So in our paper published last year, we presented our new scales and highlighted its benefits."

Dr Celestina acknowledged the question - why change already well-known scales, such as Zadoks or Feekes or BBCH, widely used by agronomists and grain researchers to describe the stages of crop growth and development.

Other than the fact that most of the papers were quite old - with the original Zadoks paper published in 1974 with about 7000 citations online - they also outline 'growth scales', "when really we should be talking about development", she said.

"For a lot of applications, that's not a big issue, but for precision of scientific accuracy and reporting, that can be a problem," she said.

"With growth specifically - the assimulation of carbohydrates - we're getting bigger, either in biomass, leaf area, tiller number, that sort of thing.

"With development however, which is what we're actually measuring, with scales like Zadoks, it is the progression through the crop life cycle over time - the phenology.

"You can think of it as getting older versus getting fatter.

"Growth and development are two distinct concepts and a lot of existing scales conflate the two."

Dr Celestina said another issue was the confusion of 'phase' and 'stage'.

"A phase, in terms of thinking about crop life cycle, crop development, progresses over time," she said.

"Whereas a stage is a point within a phase or it marks the transition between phases. So sowing is a stage - that's the start of the vegetative phase. And the vegetative phase technically ends at the floral initiation, when that developing apex has started making spikelets.

"So there's a definition difference there between phase and stage that often also gets confused."

Dr Celestina said existing scales were also "poorly defined".

"Descriptions of development tend to be ambiguous and subjective, and quite qualitative," she said.

"Good examples would be when looking at grain filling. We're talking about watery or milky soft dough or hard dough can be quite hard to understand.

"There's classic issues with things like Z55, Z65. I think if I asked attendees what their definition of Z55 was, we would probably get many different answers.

"And an extension of that is the scales don't always apply to both single plants and populations of plants.

"So Zadoks decimal code up to booting in the original paper, technically refers to the main stem of the plant, but then when they talk about heading, they sort of flip to talking about populations of plants, and if the population is non-synchronous or synchronous?

"So Z55 in a synchronous crop - all plants have half their heads out.

"Definitions in these original papers and then subsequent papers, it can be confusing and that's a big issue."

Dr Celestina said the newly-published 'Scales of development of wheat and barley specific to either single culms or a population of culms' in the European Journal of Agronomy "clearly defined growth and development and phase and stage".

"We have endeavoured to describe development in terms that are unambiguous, subjective and quantitative," she said.

"We have two scales, because we needed to distinguish between plant level and crop level developments with a single plant or the population.

"And we've taken many previously published scales and merged them together so we could fill gaps in existing scales and then also extend it to cover all phases of development.

"And we have designed these so that they're compatible with our analytical, computational technologies.

"We have used it with APSIM and we've got some researchers who are interested in using it for automated image analysis to take a picture of canopy, count how many heads etc."

Dr Celestina implored conference attendees to consider using the new scales of development.

"We've used them and they've worked for us," she said.

"The Zadoks scale has been around since 1974. We know that it's not perfect, but we also know enacting change is a massive hurdle.

"But if you are in the business of research or you need to give precise recommendations or precise communication of what stages and phases you're talking about, we recommend using these new scales of development.

"I know a lot of growers and agronomists won't go out immediately and use them, but it really did work for what we needed to do for our project."

Dr Celestina said after the scales were published, she received an email from Dr Zadoks himself, calling the new scales a "great achievement".

"That gave us a vote of confidence about what we had done," Dr Celestina said.

The European Journal of Agronomy's 'Scales of development for wheat and barley' paper is available free online at https://doi.org/10.1016/j.eja.2023.126824