Summary

Barley head loss remains a risk when harvest is delayed, particularly where lodging is also a concern. Trials at Tarlee and Cooke Plains found that plant growth regulators (PGR) consistently shortened the peduncle, the section of the barley stem that supports the head. A two-stage application of PGR at GS31 and GS37 provided the most consistent yield protection in 2023-24, while a single application at GS37 shortened peduncles in most susceptible cultivars. Newer Compass-type barley cultivars did not show clear improvements in head retention, although environmental conditions were not conducive to major head loss events across the two years of trials. Genetic screening identified substantial variation in peduncle structure and candidate genes for future breeding.

Background

Barley head loss costs South Australian growers millions annually in lost yield. The strength and structure of the barley peduncle can influence whether heads remain attached. The project examined both agronomic and genetic approaches to improve barley head retention without relying on whole-plant dwarfing. This included investigating head retention and peduncle architecture of recently released barley varieties, and also the diversity in peduncle structure across a diverse range of barley cultivars.

Research Aims

The core objectives of the project were to:

• Determine whether recently released barley cultivars have improved head retention and peduncle architecture.
• Measure variation in peduncle structure across a diverse collection of barley cultivars.
• Identify genes that could be targeted to control peduncle growth and strength.

In The Field

Ten barley cultivars were tested over two seasons at Tarlee in the Mid North and Cooke Plains in the Murray Mallee. Trials compared untreated crops with those treated with Moddus Evo® at GS37 (200mL/ha), or at GS31 (200mL/ha) and GS37 (200mL/ha). Plant height, peduncle length, lodging, brackling (stem bending or breaking), head loss and grain yield were recorded.

The project also examined approximately 240 cultivars in the OzBarley diversity panel in trials at Roseworthy. Researchers measured plant and peduncle characteristics and used X-ray CT to assess barley stem dimensions and density. Genetic mapping was then used to identify DNA regions associated with favourable peduncle architecture.

RNA sequencing was used to investigate which genes were active in Compass peduncles and how gene activity changed after PGR treatment.

Results

Head loss was low in both seasons. The previously identified threshold of 26 detached heads/m² was not reached at either trial site, limiting the ability to rank cultivars for head retention under severe head loss conditions.

PGR treatments consistently reduced peduncle length. In 2023-24, early season rainfall was confounded by a dry finish. A single 200mL/ha application at GS37 was enough to significantly shorten the peduncle in Schooner, Beast, Compass and Commodus CL at one or both sites. The two-stage treatment reduced plant height and peduncle length further. At Tarlee, the two-stage treatment produced the best or equal-best yield in 16 of 20 cultivar and treatment combinations, mainly because it reduced lodging.

The 2024-25 season start was dry with some in season rainfall, but this was below average. Plant heights were significantly reduced compared to typical seasons. Lodging was recorded in Beast, Compass, Commodus CL and Schooner at Tarlee, which confounded head loss scores and yield comparisons. PGR treatments still shortened peduncles, but did not produce significant yield differences, indicating that effectiveness of PGRs is likely dependent on seasonal conditions.

Newer Compass-type cultivars Beast and Commodus CL recorded similar head loss susceptibility and PGR response to Compass, indicating no obvious differences in head retention in seasons with below-average rainfall.

Peduncle architecture varied substantially among the approximately 240 cultivars in the OzBarley panel. Genetic analysis identified regions of the barley genome associated with peduncle traits, providing potential targets for future breeding, without making the whole plant semi-dwarf.

RNA sequencing identified 764 genes with expression specific to the peduncle and about 76 genes that responded to PGR treatment, providing further potential targets for future breeding work.