Two collection years from the same region
Peniocereus greggii invests much of its biomass below ground in a substantial storage organ. Above the soil remain slender stems, while nocturnal flowers form a distinctive feature of its desert habitat. The establishment of another such plant nevertheless begins with a small seed and an early period of susceptibility to environmental conditions. Fernando Loweree-Rivera and colleagues examined this stage, concentrating on factors that can be controlled during propagation. They published the results in 2026, although the experiment itself was conducted during the summer of 2023. [Loweree-Rivera et al. 2026a]
The material came from a natural population at San Onofre in the municipality of Satevó, Chihuahua, Mexico. Seeds collected in 2016 and 2022 were compared. Both lots were cleaned of pulp and mucilage, dried, and stored in darkness at room temperature. Retaining their collection years gives an accurate account of the material's history. Calling the newer lot fresh would overlook the interval between collection and the experiment. Comparing two collection years also differs from following the same seed lot repeatedly through successive years. [Loweree-Rivera et al. 2026a]
Seed age and physiological state
A seed that remains alive can stay dormant for a time. The embryo's readiness to begin growing then depends on physiological processes and the conditions experienced by the seed. After-ripening refers to changes occurring after harvest that can increase germinability in some plants. The authors consider this mechanism in Peniocereus greggii. Their interpretation rests on the older lot's greater germination after storage, together with responses to temperature and seed-coat treatments. The molecular mechanism of after-ripening was not measured in this experiment. [Loweree-Rivera et al. 2026a]
Dormancy, viability and germination describe related but distinct properties. Viability concerns the persistence of living tissues and developmental capacity. Germination is the response observed under particular conditions, while dormancy can limit that response despite continuing viability. In this study, germination was recorded when the radicle and hypocotyl, the seedling axis below the cotyledons, emerged through the seed coat. Ungerminated seeds were not subjected to a separate viability test. They could therefore include both dormant seeds and seeds no longer capable of further development. [Loweree-Rivera et al. 2026a]
An experiment with three factors
The design combined two collection years, four seed-coat treatments and two thermal regimes. Each combination had five replicates of ten seeds, giving 800 seeds in total. A container holding the germination substrate served as the replicate unit. The control retained an intact seed coat. The remaining treatments comprised two sulfuric acid treatments and one mechanical incision treatment. This comparison tests whether modifying the seed's outer covering actually improves germination relative to seeds receiving the less intrusive control treatment. [Loweree-Rivera et al. 2026a]
The moderate conditions were maintained in a chamber near 24°C, with an approximate range of ±2°C stated in the methods. The other treatment used room temperatures fluctuating between 30 and 37°C. Seeds were sown on the surface of a substrate containing tezontle, silica sand and commercial soil. Containers had drainage and gas-exchange openings. The researchers kept the substrate moist and monitored germination for 61 days. The outcome should therefore be interpreted alongside the stated storage history, seed preparation and growing conditions. [Loweree-Rivera et al. 2026a]
The older lot germinated more successfully
In the intact-coat control, the 2016 material reached a clearly higher germination percentage than the 2022 material. In the figure pooling both thermal regimes, the older lot's control reaches approximately 32%. This value refers to a particular combination of collection year and seed-coat treatment, averaged across temperatures. It should not be presented as the expected germination percentage for every sowing of the species. The newer lot germinated poorly across the treatments compared, and the interventions did not provide a clear advantage over its control. [Loweree-Rivera et al. 2026a]
The interaction between collection year and seed treatment was an important part of the analysis. This means that a treatment response must be interpreted in the context of the seed lot. In the older seeds, modifying the coat reduced germination relative to the control. The 2022 lot did not display the same pattern of differences. The authors propose that dormancy diminished during storage, leaving the older seeds more ready to grow. This is a biologically coherent explanation of the observation, bounded by the comparison of two independently collected lots. [Loweree-Rivera et al. 2026a]
What modifying the seed coat reveals
The seed coat separates the embryo from its surroundings and contributes to water uptake and gas exchange. Its hard appearance alone does not identify the process limiting germination. In the experiment, incision and chemical treatment of the covering did not improve the older lot's performance. Such interventions can injure internal tissues or alter their exposure to the environment, although those processes were not followed directly here. The results show that the tested ways of damaging the coat were not useful steps in handling these particular seed lots. [Loweree-Rivera et al. 2026a]
The interpretation of physiological dormancy derives from the combined pattern of responses rather than simply the number of ungerminated seeds. The authors did not measure seed-coat permeability, hormonal changes in the embryo or expression of dormancy-regulating genes. Those mechanistic levels remain distinct from the germination measurements. The experiment does, however, provide practical information about the effects of particular interventions. It supports omitting a procedure that worsened the outcome here and concentrating on seed history and an appropriate environment for the beginning of growth. [Loweree-Rivera et al. 2026a]
Temperature contributes separately to the outcome
Germination was greater under the moderate regime than at temperatures between 30 and 37°C. The analysis detected no significant interactions of temperature with collection year or treatment, so the authors presented its main effect after pooling those conditions. The result displayed in this way describes the average response across the experimental set. Reduced germination in the hotter conditions points to the importance of the thermal environment even before seedling emergence, when seeds can be simultaneously moist and strongly heated. [Loweree-Rivera et al. 2026a]
The comparison changed both the mean temperature and the degree of fluctuation. It therefore supports a better outcome under the particular moderate regime tested. It does not separately determine how much of the response reflects fluctuation itself and how much reflects high values reaching 37°C. The authors consider exposure to high temperature a likely explanation. For practical interpretation, the relevant measurement is consequently temperature at the seeds. A location name, season or general description of a warm place does not fully characterize conditions at the substrate surface. [Loweree-Rivera et al. 2026a]
Factors that still need to be distinguished
Two lots collected in different years can differ in initial quality, the growing conditions of maternal plants and the proportion of fully developed seeds. This study lacks a germination measurement made immediately after the 2016 harvest. It also lacks an independent viability test of seeds remaining at the end of the experiment. Greater germination in the older lot therefore supports the after-ripening hypothesis without independently establishing the trajectory followed by every seed during storage. A subsequent experiment could follow one lot at several time points. [Loweree-Rivera et al. 2026a]
Seeds stored in a jar likewise experience a different environment from those lying in soil at a desert site. Soil adds fluctuating moisture, seed consumers, microorganisms and movement across the surface. The retention of germinability in the stored lot provides a reason to investigate seed persistence. A long-lived natural soil seed bank of Peniocereus greggii nevertheless remains a separate question. Establishing that requires observations or experiments in the habitat that follow the fate of seeds after dispersal. [Loweree-Rivera et al. 2026a]
Sowing records as part of biological understanding
The study suggests which records make a sowing result more informative. Collection year, storage conditions, seed preparation and substrate temperature allow successive trials to be compared. A germination percentage without these data combines many possible causes into a single number. Keeping separate records for each lot preserves the biological history of the material. A result obtained after extended storage can then be compared with an earlier measurement of the same lot, rather than assigning the difference entirely to age from two independent collections. [Loweree-Rivera et al. 2026a]
For the seeds examined by Loweree-Rivera and colleagues, retaining the coat and providing moderate temperatures proved favourable. The older collection demonstrated that stored material could still initiate growth after several years. Each finding has its own evidential scope. Together they provide a detailed account of the beginning of life in Peniocereus greggii, involving embryo physiology, seed-lot history and the germination environment. Recording these elements makes further improvements in propagation possible through observations that can be meaningfully compared. [Loweree-Rivera et al. 2026a]
Germination of Peniocereus greggii (Engelm.) Britton & Rose is regulated by seed age and temperature, not scarification
Loweree-Rivera F. D., Villavicencio-Gutiérrez E. E., Morales-Nieto C. R., Corrales-Lerma R., Vega-Mares J. H., Aguilar-Palma G. N., Villarreal-Guerrero F., Germination of Peniocereus greggii (Engelm.) Britton & Rose is regulated by seed age and temperature, not scarification, Journal of the Professional Association for Cactus Development, 2026, 28:168-181, doi: 10.56890/jpacd.v28i.618
The study compares germination in two Peniocereus greggii seed lots collected in 2016 and 2022. It evaluates temperature and chemical and mechanical modification of the seed coat. Differences between lots are interpreted in relation to after-ripening, with limitations arising from the absence of initial viability measurements.