Heteromorphic seeds of wheat wild relatives show germination niche differentiation

Abstract

Crop wild relatives are fundamental genetic resources for crop improvement. Wheat wild relatives often produce heteromorphic seeds that differ in morphological and physiological traits. Several Aegilops and Triticum species possess, within the same spikelet, a dimorphic seed pair, with one seed being larger than the other. A comprehensive analysis is needed to understand which traits are involved in seed dimorphism and if these aspects of variation in dimorphic pairs are functionally related. To this end, dispersal units of Triticum urartu and five Aegilops species were X‐rayed and the different seed morphs weighed. Germination tests were carried out on seeds, both dehulled and left in their dispersal units. Controlled ageing tests were performed to detect differences in seed longevity among seed morphs, and the antioxidant profile was assessed in terms of antioxidant compounds equipment and expression of selected antioxidant genes. We used PCA to group seed morphs sharing similar patterns of germination traits, longevity estimates and antioxidant profile. Different seed morphs differed significantly in terms of mass, final germination, germination timing, longevity estimates and antioxidant profile in most of the tested species. Small seeds germinated slower, had lower germination when left in their dispersal units, a higher antioxidant potential and were longer‐lived than large seeds. The antioxidant gene expression varied between morphs, with different patterns across species but not clearly reflecting the phenotypic observations. The results highlight different trait trade‐offs in dimorphic seeds of Aegilops and T. urartu, affecting their germination phenology and longevity, thereby resulting in recruitment niche differentiation.

Comparative seed longevity under genebank storage and artificial ageing: a case study in heteromorphic wheat wild relatives

“…aegilopoides showed variable behaviours in terms of heteromorphism when subjected to the two storage environments (AA, SB). In previous studies we demonstrated that different morphs of the same species respond differently to AA in several wheat wild relatives, with smaller seeds possessing higher longevity, dormancy and antioxidant profiles (Guzzon et al 2018;Gianella et al 2020). These seed traits are known as part of a bethedging evolutionary strategy that allow smaller seeds a longer persistence in the soil (Arshad et al 2019), thereby spreading the risk of germination failure over time.…”

“…Probit analysis was carried out using Genstat 9 to obtain the time for viability to fall by 50% (P 50 ), used then as measure for seed longevity by fitting the viability equation (Ellis & Roberts, 1980) as previously described by Gianella et al . (2020). P 50 s, estimated in triplicate, were compared between seed lots belonging to the same species and subjected to the same ageing conditions (AA or SB) using Student t‐ tests.…”

“…The fresh seeds used for AA are hereafter referred to as 0d. At the beginning of the experiment, both AA and SB seeds were extracted from the spikelets and sorted according to the morph, as previously described (Gianella et al 2020): the larger, basal morph 'A' and the smaller, apical morph 'B'. This was done at the beginning of 2019 for SB seeds of both species, at the end of 2019 and at beginning of 2021 for fresh (and therefore also AA) seeds of Ae.…”

Ecological, (epi)genetic and physiological aspects of bet-hedging in angiosperms

“…Similarly, when subjected to accelerated ageing, heteromorphic caryopses of Aegilops and of Triticum urartu Thum. ex Gandilyan (Poaceae) showed different lifespans and antioxidant activities: the shorter-lived, larger morphs possess lower antioxidant activities when compared to their smaller, darker and longer-lived counterparts (Gianella et al 2020).…”

“…From an ecological point of view, most of the studies on bet-hedging have focused on just one phenotypic trait, such as seed longevity (Guzzon et al 2018) or resistance to abiotic stresses during germination (Bhatt and Santo 2016). Further studies are needed to consider simultaneously the different traits influenced by bet-hedging in order to clarify the ecological trade-offs involved in this strategy in different plant species (Gianella et al 2020). Moreover, a more comprehensive phylogenetic analysis is needed to assess the presence of bet-hedging and its evolutionary significance in the whole phylum, considering taxa from all over the globe (Scholl et al 2020;Gioria et al 2020).…”