Improving dual purpose wheat cropping in Tasmania by evaluating defoliation strategies and new genotypes

Wheat cultivated for forage plus grain is commonly termed as dual-purpose (DP) crops. The climate in Tasmania fulfils the requirement of winter wheat vernalisation therefore winter types are preferred for DP cropping. To extend our understanding about wheat defoliation management and identification of potential varieties for Tasmania, three experiments were conducted at Tasmanian Institute of Agriculture, Mount Pleasant Laboratories, Launceston, Tasmania from 2015-16. Experiment 1 (Chapter 3) was conducted in a glasshouse to study the relationship between defoliation, plant morphology and crop recovery. Four wheat varieties (Tenant, Revenue, Chara and Bolac) were defoliated using Clip and Crash strategies at four different plant anatomical cut points (LL75%, LL50%, LL100% and LS50%) at mid-tillering (GS25). Clipping at 50% and 75% of leaf length had positive effects on regrowth and increased crop height by 15%. Crash treatments were cut at the end or half way along the leaf sheath and produced more forage but affected plant regrowth at the start of stem elongation (GS30). Experiment 2 (Chapter 4) was established in a field to study the effect of cutting height on forage yield and crop regrowth of three wheat varieties (Bolac, Revenue and CS170). Five cutting heights at were imposed at mid-tillering (GS25) to estimate forage yield. Treatments included Clipping (cutting at ground level, 3 and 5 cm) and Crash (cutting at 8 and 10 cm above ground level). Clipping treatments did not affect plant height or biomass compared with the uncut control whereas the Crash treatment significantly affected plant height at the start of stem elongation (GS30). Moreover, forage production at mid-tillering (GS25) was significantly influenced by cutting. The Biomass yield of Clipped plot was 50% less than control, whereas, defoliating above 5 cm resulted plant height similar to uncut. Tall and medium statured varieties produced 50% more forage yield than prostrate. Defoliation below 5 cm affected plant regrowth and biomass. The findings from both experiments above were applied in Experiment 3 (Chapter 5) to evaluate 99 genotypes including landraces and commercial from China and Australia to identify the new varieties suitable for DP production under Tasmanian conditions. Evaluation of two levels of cutting treatments (control and cut at 5 cm) at the start of stem elongation (GS30) showed differences among genotypes in calendar days, forage yield, plant height and GDD (Growing Degree Days). Genotype H-051 had the greatest height (46.6 cm), higher forage yield (2.23 t ha\(^{-1}\)) and biomass yield (3.39 t ha\(^{-1}\)). Genotypes H-061 and Mackellar showed the best potential regrowth capacity by attaining height (60 and 64 cm respectively) after cutting at GS30. The genotypes accumulating less days to reach GS45 had less height than genotypes accumulating maximum GDD to GS45. The regrowth of the genotypes after defoliation was related to the number of leaves on main stem and tillers plant\(^{-1}\). the genotypes reaching stem elongation stage late had higher forage and biomass yield. The genotypes producing higher forage yield and recovering height similar to uncut are recommended to be evaluated at other location across Tasmania for further screening