Speaker
Description
Introduction:
The use of subterranean clover (Trifolium subteranneum L.), an annual pasture legume, combined with correction of soil phosphorus (P) deficiency has led to major improvements in the productivity of both livestock and crop production systems in southern Australia. The climate across this region ranges from Mediterranean through to temperate. Under these conditions, annual plants need to flower at an optimal time in spring to minimise the exposure of flowers and young seeds to frost, whilst also ensuring that seed development and maturation has occurred prior to the onset of the hot, dry conditions of summer. Subterranean clover cultivars with appropriate flowering times have been selected to fit the range in growing season lengths (~5-9 months) across this large agricultural zone. Serradella species (Ornithopus spp.) are viable alternatives to subterranean clover and offer an opportunity to diversify the legume base of these pastures, but there are gaps in the availability of cultivars with flowering times that will fill all climatic niches. Certain serradella cultivars also lack stable flowering dates (Boschma et al. 2019) and this is a problem for species persistence in self-regenerating pastures. Flowering responses to low (vernalising) temperatures and photoperiod essentially determine flowering date. The aim of this study was to characterise the nature of the interaction between a cultivar’s flowering time response to photoperiod and its response to vernalisation and to understand how this interplay influences the time of flowering by each cultivar.
Key words:
Phenology, adaptation, persistence, temperate, climate
Materials and methods:
Two cultivars of yellow serradella (O. compressus L., ‘Yellotas’ and ‘Avila’), French serradella (O. sativus Brot., ‘Erica’ and ‘Serratas’) and subterranean clover (‘Coolamon’ and ‘Goulburn’) were subjected, in controlled-environment plant growth chambers, to ‘vernalised’ (9 weeks at 5 oC), or ‘unvernalised’ treatments (0 weeks at 5 oC) followed by five photoperiod treatments (11, 12, 13, 14 or 15 h with a weighted mean daily temperature of 18 oC). Appearance of the first flower was measured using thermal time from sowing to first flower (oC d). Critical photoperiods were defined for each cultivar by identifying the minimum photoperiod at which there was no additional decrease in time to flower for unvernalised plants when grown under longer photoperiods. A reverse sigmoidal function was fitted to the data from this experiment and data from a historic dataset (Goward et al. 2023). This model described how time to flower by unvernalised plants was modified by growth in photoperiods from 8 to 20 h.
Results:
Differences were observed between the cultivars in the time to flower when unvernalised and grown in short photoperiods. Under relatively short photoperiods, the ‘vernalised’ treatment was sufficient to reduce time to flower to a minimum, reflecting the intrinsic earliness of each cultivar. Growth in photoperiods ≥12 h reduced the need for vernalisation to promote earlier flowering. This interaction between responses to photoperiod and to vernalisation differed among the cultivars with some cultivars expressing different critical photoperiods (13 or 15 h). The reverse sigmoidal model described the interaction of photoperiod and vernalisation responses reasonably well and indicated differences among cultivars in the rate at which the response to photoperiod would override the need for vernalisation.
Discussion:
This study showed that if plants are not fully vernalised after a mild winter, increasing photoperiods during spring (>12 h) will override the need for vernalisation. This should permit the plant to still flower in a timely manner. As such the interaction of a cultivar’s responses to photoperiod and vernalisation provides a safeguard mechanism that protects flowering and seed production. The cultivar-specific responses observed in this experiment indicate there may be significant challenges for modelling flowering time of individual genotypes because of the considerable time and resources required to parameterise factors such as the critical photoperiod of each genotype/cultivar.
References:
Boschma S, Kidd D, Newell M, Stefanski A, Haling R, Hayes R, Ryan M, Simpson R (2019) Flowering time responses of serradella cultivars. In ‘Proceedings of the 2019 Agronomy Australia Conference’, Wagga Wagga, Australia.
Goward LE, Haling RE, Smith RW, Penrose B, Simpson RJ (2023) Flowering responses of serradella (Ornithopus spp.) and subterranean clover (Trifolium subterraneum L.) to vernalisation and photoperiod and their role in maturity type determination and flowering date stability. Crop and Pasture Science 74, 769–782. doi:10.1071/CP22366.
| Keywords | Phenology; adaptation; persistence; breeding; climate |
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