Mature and immature axes of Theobroma cacao (cocoa) seeds tolerated desiccation under a rapid-drying regime to critical water contents of 1.0 and 1.7 g g-1 dw, respectively. These critical water contents corresponded to water contents below which activities of free radical-scavenging enzymes (ascorbate peroxidase, peroxidase and superoxide dismutase) decreased rapidly during desiccation. The decline in axis viability below the critical water content was correlated with sharp increases in lipid peroxidation and cellular leakage. Cotyledon tissues were more desiccation-tolerant than axes, with a low critical water content of 0.24 g g–1dw. Desiccation sensitivity in cotyledon tissues was also correlated with the decrease in superoxide dismutase activity and increased lipid peroxidation products. However, in the cotyledons, no ascorbate peroxidase activity was detected at any water content, and peroxidase activity was gradually reduced as desiccation proceeded. Cocoa embryonic axes contained large amounts of sucrose, raffinose and stachyose but only traces of reducing monosaccharides. Desiccation sensitivity of recalcitrant cocoa axes did not appear to be due to the lack of sugar-related protective mechanisms during desiccation, and it was more likely related to the decrease of enzymic protection against desiccation-induced oxidative stresses.

Grain production of two wheat cultivars (Triticum aestivum L. cv Recital and Scipion), known for their different germination behaviour, was studied at two different temperatures. The study of dormancy onset during grain development showed that in both cultivars, dormancy developed on the mother plant. In Recital grain, after a period of high germinability, dormancy developed for a transient period. However, full germination was obtained on medium supplemented with fluridone, showing that dormancy was associated with abscisic acid (ABA) biosynthesis inside the grain. Dormancy progressively disappeared during natural drying, at a slower rate for grains developing at 15°C than for grains developing at 25°C. However, at both temperatures, the release from dormancy was complete at maturity. In Scipion grain, dormancy was almost total throughout grain development irrespective of the temperature. However, grains could germinate in the presence of fluridone: changes in sensitivity to fluridone were observed during grain development, showing an increase in dormancy during the first half of development, followed by a progressive decrease during the second half. This decrease occurred later for grains developing at 15°C than for those developing at 25°C. In Scipion grain, unlike the cultivar Recital, release from dormancy was not completed before the end of development on the mother plant. An additional dry storage period was necessary which was shorter for grains developed at 25°C than for grains produced at 15°C. A comparison of embryo ABA levels after a 24-h culture in the presence or absence of fluridone, allowed the ABA synthesis to be estimated. It appears that the depth of dormancy was related to the estimated ABA synthesis capacity of the embryos.

Internal cracks caused by high temperature or excessive moisture during maize (Zea mays L.) kernel development were characterized, and their effects on kernel quality were assessed. Pre-harvest stress cracks are often located near the middle of the kernel along the embryo axis, but they were also detected in other positions, irrespective of the shape of the kernel. X-ray analysis enabled visualisation of stress cracks that are invisible to the human eye and, therefore, gave a better estimate of the percentage of cracks. However, low temperature scanning electron microscopy of the surface of milled kernels revealed small cracks not noticed by visual or X-ray inspection. All kernels tested in this way had a crack of some sort in the endosperm tissue. Cracks were also frequent in the scutellum, but rare in the embryo axis. Endosperm cracks followed the boundary of the starch granules, but did not extend into the pericarp tissue. In contrast to external cracks caused by mechanical impact, pre-harvest internal stress cracks generally are not detrimental to germination and vigour. However, if the crack is located inside or perpendicular to the embryo axis, it may affect the quality of the kernel, probably by impeding nutrient translocation to the embryo.

Fourteen seedlots of five species of Rhus were surveyed for presence/absence of physiological dormancy and/or for germination requirements of non-dormant seeds. Physiological dormancy was present in the four seedlots of R. aromatica studied, but not in either of the two seedlots of its close relative R. trilobata, which is in contrast to previous reports. Neither were seeds of R. glabra, R. typhina, nor R. virens physiologically dormant. Stratification at 5oC for 1 week or incubation in 500 or 1000 mg/l solutions of gibberellic acid broke physiological dormancy in > 90% of the R. aromaticaseeds. Maturation desiccation acted as a switch from a developmental to a germinative mode in R. aromatica embryos, whereas it was not required for germination of R. glabra or R. virens (R. trilobata and R. typhinanot tested). Seeds of all five species incubated on a moist substrate became fully imbibed in 2 d, at which time moisture content was approx. 70–80%of their initial weight. In general, germination of non-dormant seeds was rather insensitive to temperature and light. Seeds germinated equally well in light and in darkness over a daily (12 h/12 h) temperature range of 15/6–35/20oC. Over a 4 week period, the best germination percentages were obtained at 25/15 and 20/10oC, whereas 35/20oC appeared to be supraoptimal, though not always significantly so. If the incubation period was extended to 30 weeks, germination percentages were as high at 15/6oC as at 25/15 and 20/10oC.

Seed (= seed plus endocarp) morphology and physical dormancy were studied in seven North American Rhus species: R. copallina, R. glabra, R. typhina, R. aromatica (var. aromatica), R. microphylla, R. trilobata, and R. virens (var. virens). Seeds of Rhus glabra and R. typhina, of subgenus Rhus, were gray, approx. 3 mm long, 2 mm wide, and weighed approx. 7 mg, whereas those of R. aromatica, R. trilobata, and R. virens, of subgenus Lobadium, were brown, >4 mm long, approx. 4 mm wide, and weighed approx. 14.5 mg (R. trilobata) to approx. 23 mg (R. aromaticaand R. virens). Dormancy in all seeds was due to a water-impermeable endocarp, but depth of dormancy varied greatly among species and seedlots. After 4 weeks, 29–34% of the seeds from all five seedlots of R. trilobata, R. microphylla, and R. virens incubated on moist substrate had imbibed, compared to 0–14% of the seeds of all 16 seedlots of R. aromatica, R. copallina, R. glabra, and R. typhina. After 1 yr, imbibition among seedlots of R. aromaticavaried from 28 ± 2% to 69 ± 5%, whereas 93 ±2% to 100 ± 0% of the seeds from all seedlots of R. microphylla, R. trilobata, and R. virens did so. Neither dry laboratory storage for up to 4 yr (even 29 yr in R. aromatica) nor dry heating at 100oC or at 120oC effectively broke dormancy in any of the species tested (R. aromatica, R. glabra, R. trilobata, R. virens). Immersion in boiling water was the best method to render seeds of R. glabra and R. typhinapermeable, yet it was ineffective for those of R. aromatica, R. trilobata, and R. virens. In contrast, a 1 h-soaking in concentrated H2SO4 led to complete loss of endocarp impermeability in the latter three species, but mostly was ineffective in R. glabra and R. typhina. Thus, there seems to be a tendency for seeds of subgenus Rhusto respond well to boiling in water, but not to soaking in H2SO4, whereas the opposite is true for those of subgenus Lobadium.

Seeds of watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai var. Congo) were subjected to mild accelerated ageing treatments of 30 and 60 d at 30°C at a moisture content of 7.2%. In comparison to a cold-stored control, normal germination and viability were slightly (but not significantly) decreased by these treatments. Subsequent construction of survival curves during storage at 40°C, at seed moisture contents ranging from 10–18%, revealed that the prior 30°C ageing treatments prolonged survival under these conditions.