Regulation of seed germination by diurnally alternating temperatures in disturbance-adapted banana crop wild relatives (Musa acuminata)

Abstract

Seed conservation of banana crop wild relatives (Musa L. spp.) is limited because of lack of knowledge about their germination ecology. Musa acuminata Colla, the most important banana crop wild relative, is distributed in tropical and subtropical Asian and Pacific rainforests and colonizes disturbed sites. The role of temperature in stimulating/inhibiting germination to detect disturbance when canopy gaps are formed is not well known. We assessed seed germination thermal requirements of three subspecies of M. acuminata using nine seed accessions which had been stored in the Millennium Seed Bank. Diurnally alternating temperature cycles were almost completely essential for germination compared with constant temperatures. Germination was optimal when the upper temperature of a diurnal cycle was at 35°C; the lower temperature of the cycle was less important. Subspecies occurrence coordinates were used to extract climate temperature data which were then compared against the temperature requirements for germination from our experiment results. Maximum temperatures of the warmest month across subspecies ranges were close to but below optimal germination temperatures, as were diurnal ranges, suggesting soil-warming at the micro-climate level following gap creation is important for M. acuminata seed germination. Additionally, pre-treatment for 3 months at 60% relative humidity at constant 25°C improved germination from 14 ± 10 (mean, standard deviation) to 41 ± 29% suggesting a period in the soil seed bank under the canopy may increase sensitivity to alternating temperature cycles. Overall viability was low (49 ± 28%), and considerable variance was caused by the different accessions. Germination remained somewhat inconsistent.

Reproductive biology of wild and domesticated Ensete ventricosum: Further evidence for maintenance of sexual reproductive capacity in a vegetatively propagated perennial crop

“…It is difficult to ascertain whether this is functional, or more likely developmentally linked to another gene under selection. We found no evidence of differing seed viability rates between wild and domesticated enset, though we did find high variability in seed viability across accessions, consistent with previous reports in both enset (Karlsson et al 2013) and Musa (Kallow et al 2021). Internal and external seed morphology was also consistent between wild and domesticated accessions.…”

“…More broadly, we note that enset germination requirements appear consistent with reports from Musa (Stotzky et al 1962; Kallow et al 2021). Specifically, in enset, alternating temperatures elicit a stronger germination response than constant temperatures, though in Musa this is virtually an absolute requirement.…”

“…We exclude treatments involving sulphuric acid, sodium hydroxide, ammonium nitrate, sodium hypochlorite or hot water as Karlsson et al (2013) reported that these had no significant positive effect on germination; and indeed, scarification and 70% ethanol had significant negative effects. To mimic natural conditions we draw on germination ecology in Musa (Laliberté 2016), where alternating temperature regimes are known to be a key requirement in M. balbisiana due to exposure of the seeds on the soil surface to alternating day and night temperatures (Stotzky et al 1962; Kallow et al 2021) and similar behaviour reported by Tesfaye (1992) in enset. Exp 1: First, using RPS seed we screened a range of 15 constant and alternating temperature regimes to guide our experimental design for subsequent germination tests.…”

Using semi-natural and simulated habitats for seed germination ecology

“…The conditions for germination are not well understood and germination is notoriously inconsistent and often very low (Kallowet al 2020;Singh et al2021). LC experiments show a requirement for alternating temperatures (Stotzky & Cox 1962;Kallow et al 2021), but no NH experiments have been executed to interpret this. For instance, is this requirement a gap or depth detection mechanism affected by microclimates?…”

“…To assess dormancy and dormancy loss in the soil (stratification), seeds from the two M. balbisiana accessions (bal106 and bal115) were incubated at alternating 35°C in the light for 6 hours and 20°C in the dark for 18 hours (based on Stotzky, Cox & Goos 1961;Kallow et al 2021). Additionally, seeds were buried at two of the cooler Simulated-NHs (Spring/Exposed and Leuven/Exposed) in March 2019 and exhumed each month for a total of three months and placed in the incubator conditions described.…”