The Australian wheat production environments are typically water-limited, and both temperature and vapour pressure deficit increase as the season progresses. As a result, high incidences of small or shriveled wheat kernels (screenings) are commonly generated and can substantially reduce grain value. Previous studies suggest the incorporation of the tiller inhibition (tin) gene can reduce the production of infertile tillers and increase kernel weight (KW). It was hypothesised that the incorporation of the tin gene into wheat germplasm may a) contribute to the maintenance of large KW and reduction in screenings (SCR) in terminal water deficit environments; and b) not be associated with a grain yield (GY) penalty in terminal water deficit environments. Thus, the major objective of this thesis was to evaluate the expression and performance of tin gene in terms of GY and SCR: 1) in different genetic backgrounds and across Australian production environments; 2) in various northern production environments which are particularly prone to terminal water deficit conditions; and 3) to determine the mechanisms that contribute to the maintenance of large KW of tin lines in terminal stress conditions. To address the overall objective, populations of lines were genotyped for the presence/absence of the tin gene and were field tested. Line differences in GY, yield components, SCR and general growth and development attributes were determined in 22 field experiments conducted between 2005-2007. The experiments were grouped into those that evaluated: a large number of sister lines from four genetic backgrounds in multi-location experiments; selected lines from Silverstar population in multi-location experiments; and selected sister lines in detailed agronomic experiments examining the effect of plant density and controlled levels of water supply through the use of a rainout shelter facility. The effect of tin on GY and SCR varied with environment and genetic background. In the Brookton, Wyalkatchem and Chara background, there was no reduction in GY associated with tin in southern production environments. However, a 31% and 10%, advantage of free-tillering over reduced tillering Silverstar lines existed in the 2005 western and 2006 northern experiments respectively, and led to an average 12% reduction in GY of Silverstar tin lines. In northern experiments, tin lines in a Silverstar background produced up to 50% fewer SCR than Silverstar free-tillering lines. Averaged across experiments, KW of Silverstar tin lines was 10% greater than free-tillering lines. Based on stem number per plant, Silverstar lines were classified into three groups; the restricted (R) and semi-restricted (SR) tin and free-tillering lines attained 2.9, 3.4 and 4.8 stems per plant respectively. Expression of tin in terms of maximum stem number production was genetic background and genotype dependent, and unlike free-tillering lines, R tin lines in particular, were not as responsive to plant density. Head number per unit area rather than kernel number per head was strongly associated with KW determination. Therefore, to maximize KW under water limiting conditions it is more beneficial if high kernel number can be achieved via the production of low head number with more kernels per head, as can be achieved with the use of tin lines. The KW advantage of Silverstar R tin was associated with greater anthesis total dry matter, stem water soluble carbohydrate and nitrogen available per head relative to free-tillering lines, and thus R tin lines had more assimilate for translocation during the grain filling period. In a terminal water deficit experiment, individual KW data collected for Silverstar tin and free-tillering lines revealed that KW of tin lines (≈ 25 mg per kernel) was maintained for main stem to fourth tiller heads and across floret positions 1-4 within spikelets. In contrast, free-tillering lines (≈ 18 mg per kernel) generated small kernels across the entire plant, with the largest proportion originating from floret positions 3 and 4. Lines containing the tin gene had a greater mean KW and kernel width, and a higher frequency of wider kernels than free-tillering lines. The high frequency of large kernel widths was associated with significantly less SCR in tin lines. A strong positive association between maturity head number per plant and SCR indicated, for every fertile head produced, SCR increased by 11% in the terminal water deficit experiment. Reduction in SCR in the Silverstar tin material in the north, was associated with high KW and a tendency for lower GY, although tin lines with equivalent GY to Silverstar could be identified in each environment. The incorporation of the tin gene has the potential to significantly reduce the incidence of SCR in commercial wheat crops. The reduction in GY associated with the tin gene was dependent on genetic background, suggesting the potential for selection of higher-yielding tin progeny in commercial line development. However, a tailored agronomic package to optimize yield potential of tin lines needs to be developed for different target environments. With the incorporation of the tin gene into genetic material adapted to the northern wheat belt and optimisation of head density, there exists scope for simultaneous improvements in GY and KW and subsequent reduction in SCR for terminal water deficit environments.
| Identifer | oai:union.ndltd.org:ADTP/291182 |
| Creators | Jaqueline Mitchell |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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