Pre-harvest sprouting (PHS) is a common threat to cereal crops in which the grain maturation phase takes place under rainy, moist conditions. Susceptibility to PHS is higher in sorghum genotypes displaying low levels of seed dormancy before harvest maturity. Other attributes such as glume or panicle morphology may also affect susceptibility to PHS. Breeding for resistance to PHS in grain sorghum requires the identification of grain physiological and morphological attributes affecting this trait, and a protocol for phenotyping and rating genotypes according to their susceptibility to PHS. In this work, we tested germination under laboratory conditions using detached grains and intact panicles for a panel of 20 sorghum genotypes including 11 parental lines, 6 hybrids and 3 reference inbred lines with contrasting PHS response. Records for natural sprouting in the field for these genotypes were also included in the analysis. Multivariate analyses of germination data allowed separation of genotypes into two major categories (resistant and susceptible to PHS). Laboratory germination data correlated significantly with PHS in the field. In most genotypes, the glumes had a significant, inhibitory effect on germination. The low levels of grain dormancy were observed among high tannin backgrounds, and vice versa, indicating that a pigmented testa alone does not provide resistance to PHS. Altogether, the phenotyping protocol allowed the classification of sorghum genotypes according to their susceptibility to PHS and the identification of different attributes useful for breeding for PHS resistance in this crop.

Reactions leading to dormancy release (DR) in ‘dry’, orthodox seeds are still poorly understood, as well as their dependence on moisture content (MC) and temperature. In this study, sunflower achenes were used to explore the effects of MC combined with a wide range of storage temperatures (ST°) on DR dynamics, tested at 10 °C and 25 °C. Embryo sensitivity to abscisic acid and oxygen uptake were determined and ageing indicators were assessed and complemented with dynamics for predicted viability loss. Water status was examined using sorption isotherms and the glass transition temperature (Tg). The results showed that small variations in MC and ST° had profound effects on achene dormancy and embryo responsiveness to ABA. Using a ‘temperature-by-humidity’ coordinate system we mapped three regions allowing DR during the glassy, rubbery, and fluid states of the achenes. Full DR (allowing germination at 10 °C and 25 °C) occurred only in the rubbery state (above Tg), and the optimal ST° for full DR dropped from 30 °C to −18 °C with MC increasing from 0.045 gH2O g−1 DW to 0.10 gH2O g−1 DW. In contrast, under both glassy and fluid states, DR was incomplete (allowing germination at 25 °C but not at 10 °C) and required warm ST° that promoted ageing.

In dormant sunflower achenes, several structures—the pericarp, seed coat and embryo—contribute to the repression of germination. Achene dormancy varies widely among cultivated sunflower genotypes, and understanding its transmission to hybrid progeny is important both for hybrid seed production and for clarifying the role of these structures. This study examined the inheritance of dormancy in the F1 progeny, with particular emphasis on thermo-inhibition (inhibition of germination at warm temperatures). Reciprocal crosses were performed using three oilseed inbred lines with contrasting dormancy phenotypes. Germination of achenes, seeds, and embryos was tested at 10 and 30 °C at harvest and during postharvest, together with hormonal responses (abscisic acid, ethylene and gibberellins) and measurements of endogenous ABA levels. Results show that maternally inherited, pericarp-imposed thermo-inhibition depends on the dormancy level of the hybrid embryo, which follows a zygotic pattern with incomplete dominance. While embryo sensitivity to ABA related positively with thermo-inhibition, surprisingly, embryonic ABA content was inversely related to dormancy level across genotypes. These findings provide new insight into physiological control of achene dormancy in sunflower and contribute to improved breeding strategies for high-quality hybrid seed.