Abstract
The possibility of obtaining sorghum grains with quality to match the standards for a diversity of end-uses is frequently hampered by the susceptibility to pre-harvest sprouting (PHS) displayed by many elite genotypes. For these reasons, obtaining resistance to PHS is considered in sorghum breeding programs, particularly when the crop is expected to approach harvest maturity under rainy or damp conditions prevalence. As in other cereals, the primary cause for sprouting susceptibility is a low dormancy prior to crop harvest; in consequence, most research has focused in understanding the mechanisms through which the duration of dormancy is differentially controlled in genotypes with contrasting sprouting behavior. With this aim two tannin-less, red-grained inbred lines were used as a model system: IS9530 (sprouting resistant) and Redland B2 (sprouting susceptible). Redland B2 grains are able to germinate well before reaching physiological maturity (PM) while IS9530 ones can start to germinate at 40–45 days after pollination, well after PM. Results show that the anticipated dormancy loss displayed by Redland B2 grains is related reduced embryo sensitivity to abscisic acid (ABA) and increased levels of GA upon imbibition. In turn, transcriptional data showed that ABA signal transduction is impaired in Redland B2, which appears to have an impact on GA catabolism, thus affecting the overall GA/ABA balance that regulates germination. QTL analyses were conducted to test whether previous candidate genes were located in a dormancy QTL, but also to identify new genes involved in dormancy. These analyses yielded several dormancy QTL and one of them located in chromosome 9 (qGI-9) was consistently detected even across environments. Fine mapping is already in progress to narrow down the number of candidate genes in qGI-9.
Highlights
Grain sorghum [Sorghum bicolor (L.) Moench] is a grass species cultivated for its grain which is used for feeding both humans and animals
The possibility of obtaining grains with quality to match the standards for these end-uses is frequently hampered by the susceptibility to pre-harvest sprouting (PHS) displayed by many elite genotypes
We discuss the current understanding of the mechanisms that impose dormancy to the sorghum grain, and mention on-going work directed toward breeding for PHS tolerance
Summary
Grain sorghum [Sorghum bicolor (L.) Moench] is a grass species cultivated for its grain which is used for feeding both humans and animals. Pre-harvest Sprouting in Sorghum and subtropical environments to the point that it has become the fifth most important cereal of the world after rice, wheat, maize, and barley. The possibility of obtaining grains with quality to match the standards for these end-uses is frequently hampered by the susceptibility to pre-harvest sprouting (PHS) displayed by many elite genotypes. Sorghum sprouts accumulate toxic amounts of cyanide (Ikediobi et al, 1988). For these reasons, obtaining resistance to PHS is one of the main objectives in sorghum breeding programs, when the crop is expected to approach harvest maturity under rainy or damp conditions prevalence. We discuss the current understanding of the mechanisms that impose dormancy to the sorghum grain, and mention on-going work directed toward breeding for PHS tolerance
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