Postharvest application of ethylene and 1-methylcyclopropene either before or after curing affects onion (Allium cepa L.) bulb quality during long term cold storage

The storability of onion bulbs is dependent on the incidence and rate of sprout growth. Exogenous ethylene applied continuously has been demonstrated to act as a sprout suppressant in onion. However, the ethylene binding inhibitor, 1-methylcyclopropene (1-MCP), can also suppress sprouting in onion. Given this seemingly contradictory result, the precise role that ethylene plays during onion storage and the effect of curing on its efficacy is not understood.‘Sherpa’ and ‘Wellington’ onion bulbs were treated before or after curing (28 °C for 6 weeks) with a single dose of 10 μL L⁻¹ ethylene or 1 μL L⁻¹ 1-MCP for 24 h at 20 °C, or no treatment (control). Replicated out-turns were sampled during 38 weeks storage at 0–1 °C. Sprout growth (31 weeks after harvest) was reduced in ‘Sherpa’ treated before curing with ethylene or before or after curing with 1-MCP. However, sprout growth of ‘Wellington’ was not affected by any treatment. Following treatment, the cured, thick-skinned ‘Wellington’ released a lower concentration of treatment gas compared with the newly harvested, thin-skinned ‘Sherpa’. Onion bulb respiration rate increased immediately after being treated with ethylene but to a lesser extent or not at all when treated with 1-MCP. Fructose concentrations of onions treated with ethylene or 1-MCP before curing were not significantly different, however, after curing concentrations were about 2-fold higher compared with the control. Mean glucose and sucrose concentrations for both cultivars were higher immediately after being treated before curing with ethylene or 1-MCP than control bulbs. It appears that inhibition of sprout growth can be achieved using just a short 24 h treatment with ethylene or 1-MCP. However, skin thickness or permeability, which is dependent on cultivar and curing, may affect ethylene or 1-MCP influx and therefore efficacy of sprout suppressant action.     

Research on the inheritance of seed dormancy in lettuce (Lactuca sativa L.) and selection for non-dormancy

Summary Inheritance of dormancy and the results of selection of non-dormant genotypes in segregating populations of lettuce were investigated. Diallel crosses were therefore carried out between two dormant (DOR) and two non-dormant (NDOR) cultivars. F₁, F₂ and F₃ populations were analysed.Environmental variation for dormancy usually was large. The mean germination time (GT) of F₁ seeds from the NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses was often intermediate to the GT of the NDOR and DOR parent. The mean GT of F₁ seeds from DOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses equalled the mean GT of the parents; the same applies for the NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]NDOR crosses. No differences between reciprocals were observed and neither were such differences found for F₂ populations. F₂ populations from DOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses showed no significant segregation of rapidly germinating seeds and in F₂ populations from NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses no accumulation of genes for long GT occurred. In F₂ populations from NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses usually 40–60% of the seeds germinated as rapidly as the seeds of the NDOR parents. Only one gene (D) could be responsible for the difference in dormancy behaviour of the DOR and NDOR cultivars. The behaviour of the F₃ lines from various NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses supports this hypothesis. A regression of F₃ means on the value of F₂ seeds for GT of various NDOR % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaKaaafaafaqabeGaba% aajqgaa+FaaiaadIhaaeaacaWG4baaaaaa!3B90!\[\begin{array}{*{20}c}x \\x \\\end{array}\]DOR crosses showed that h²-narrow usually was rather high for most crosses implying that selection for non-dormancy can be carried out in F₂ populations.     

Competition, growth and yield of faba bean (Vicia faba L.)

This paper reviews current knowledge regarding the influence of plant density on the growth and yield of the faba bean crop (Vicia faba L.). An analysis is also made of sowing rate and other factors that may modify optimum plant density, including environmental conditions; in this sense, should be made a differentiation between faba crops grown in temperate conditions and those grown in Mediterranean and semi-arid conditions. The genotype also prompts variations in optimum plant density, depending on the botanical type (mayor, equina or minor) and the growth habit (determinate versus indeterminate) of the cultivar selected. Sowing date also influences optimum seeding rate, which is lower for autumn–winter sowing under temperate and Mediterranean conditions and increases as the sowing date is delayed. For the spring-sown crops typical of temperate conditions, optimum plant density will be higher due to the shorter growing season. With a longer growing season and under optimum environmental conditions, there is normally no additional response to densities over 20 plants m⁻², while in suboptimal conditions, optimum plant density may increase to over 60 plants m⁻². Although the faba bean crop displays considerable plasticity in response to variations in plant density, mainly with regard to number of pods per square meter, it is not wholly clear to which component of yield this should really be ascribed. Number of stems per plant appears to be the most influential factor, although further research is required to confirm this.     

Effects of water deficit and plant interaction on morphological growth parameters and yield of white clover (Trifolium repens L.) and ryegrass (Lolium perenne L.) mixtures

The effects of soil water deficit and interspecific plant interaction were studied on the dry matter (DM) yield of white clover and ryegrass and on the morphogenesis of white clover. Plants were grown either: (1) individually (no interaction); or in a mixture of equal plant numbers with either (2) just shoot interaction, or (3) both shoot+root interaction. Plants were subjected to soil water deficits corresponding to no (0 MPa), moderate (−0.5 MPa) or severe (−1.0 MPa) water deficit. Ryegrass had higher above- and below-ground DM yields than white clover. The above- and below-ground DM yield for ryegrass, and the above-ground DM yield, stolon growth and relative growth rate (RGR), and leaf appearance rate (LAR) for white clover decreased as soil water deficit increased. In shoot+root interaction at no and moderate soil water deficit levels, white clover had the highest proportion of above-ground growth in the leaf form (69%) and had, respectively, 11% and 32% more above-ground DM yield than when grown in just shoot interaction; ryegrass had, respectively, 20% and 25% more above-ground DM yield than ryegrass grown in just shoot interaction. In shoot+root interaction at severe soil water deficit, ryegrass had twice as much above-ground DM yield as white clover (3.50 g per plant versus 1.59 g per plant, respectively) and white clover had 60% less above-ground DM yield than when grown in just shoot interaction. In a soil column of restricted depth (30 cm) at no and moderate soil water deficit levels, remarkable increases in shoot biomass yield were observed for both white clover and ryegrass grown in shoot+root interaction. The increased shoot biomass yield of ryegrass can be attributed to benefits from white clover's N fixing ability, whereas the causes for increased white clover biomass yield need to be studied further. However, at severe soil water deficit, ryegrass had a competitive advantage over white clover when grown in shoot+root interaction. This was due to the larger root system of ryegrass and its ability to control transpirational losses more efficiently, thus prolonging its growth period compared with white clover.     

Ultralow oxygen treatment for postharvest control of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), on iceberg lettuce: I. Effects of temperature, time, and oxygen level on insect mortality and lettuce quality

Ultralow oxygen (ULO) treatments with different oxygen levels, treatment times, and temperatures were studied to determine effects on western flower thrips mortality and postharvest quality of iceberg lettuce. Thrips mortality increased with reduced oxygen level and increased treatment time and temperature. At 0.003% oxygen, over 99.6% mortality rates of thrips were achieved in three ULO treatments of 2, 3, and 4 d at 10, 5, and 1 °C, respectively. No treatments caused injury to lettuce surface leaves and there was no reduction in visual quality for treated lettuce. However, about 9–33% of lettuce heads sustained injury to heartleaves. The 2 d ULO treatment with 0.003% oxygen had the lowest injury rate to heartleaves and the injury increased with increased treatment duration. The amount of injured leaves was small (<2 g per head). There were also some variations among the lettuce cultivars in susceptibility to heartleaf injury by ULO treatments. Four out of eight cultivars tested tolerated the 2 d ULO treatment at 10 °C without any injury. Therefore, ULO treatment has potential to be developed as an alternative postharvest treatment for western flower thrips on iceberg lettuce.     

Effects of previous cropping on seed yield and yield components of oil-seed rape (Brassica napus L.)

Information about the effect of the preceding crop or crop combination on the seed yield of oil-seed rape is extremely scarce. Experiments were carried out in northwest Germany to investigate the effect of different preceding crops on the growth, seed yield and yield components of oil-seed rape. The two directly preceding crops, wheat and oil-seed rape, had only a negligible and non-significant effect on the seed yield of the following oil-seed rape crop. Oil-seed rape grown after wheat had more pods per plant, due to an increase in the number of pods on the higher category branches. In contrast, the seed yield and yield components were more affected by the cropping sequence, i.e. the crops 2 years before. Averaged over two experimental years, the greatest yields were observed in oil-seed rape following the sequence peas-wheat (694 g m⁻²), whereas the smallest seed yield occurred after 2 years of oil-seed rape cropping (371 g m⁻²). The differences in the seed yield were again associated with more pods per plant, which compensated for the lower number of plants m⁻², whereas the number of seeds per pod and the mean seed weight were almost unaffected by the previous cropping. It was not possible to relate the described differences to the crop development, since differences in the biomass caused by the previous cropping were only significant at maturity. Oil-seed rape grown after 2 years of oil-seed rape had the highest ratings of stem canker (Leptosphaeria maculans) as well as verticillium wilt (Verticillium dahliae). But the general level of the diseases was low, and therefore other causes for the effects described must be considered.     

The Influence of Plant Water Stress on Net Photosynthesis and Yield of Sunflower (Helianthus annuus L.)

The effect of plant water stress on net photosynthesis, leaf growth, yield and yield-related components were investigated in a single experiment in order to determine in which way water deficits affect sunflower yields.
Sunflower plants, grown under controlled temperature regimes, were stressed during budding, anthesis and seed filling by withholding water until the leaf water potential reached -1600 and -2000 kPa. Leaf area of unstressed plants significantly exceeded that of plants under severe stress during all growth stages investigated. The CO₂ uptake rate per unit leaf area as well as the total uptake rate per plant, significantly diminished with stress, while this effect drastically increased during the reproductive phase of the plant. Although this resulted in significantly smaller heads and kernels, it did not affect the number of seeds borne in the inflorescence. Severe stress during anthesis and seed filling resulted in more empty kernels. Moderate and severe stress during budding significantly lowered both grain and oil yields while plants that experienced moderate stress during anthesis and seed filling significantly outyielded those under severe stress.     

Effect of preceding crop combination and N fertilization on yield of six oil-seed rape cultivars (Brassica napus L.)

Information about the effect of the cropping history on the seed yield of oil-seed rape is extremely scarce. In 1992/93 and 1994/95, the effects of different preceding crop combinations (winter barley and winter wheat as preceding crops, oil-seed rape and wheat as pre-preceding crops) on the yield of six double low oil-seed rape cultivars were examined in a field trial at Hohenschulen Experimental Farm, north-west Germany. In addition, eight nitrogen treatments (different amounts and distribution patterns) were tested for their potential to reduce negative effects of the preceding crops. Following the cropping sequence of oil-seed rape then wheat, oil-seed rape yielded only 3.12 t ha⁻¹; after oil-seed rape then barley, the yield was 3.43 t ha⁻¹ compared with 3.77 t ha⁻¹ following wheat then barley and 3.71 t ha⁻¹ following wheat then wheat. The number of seeds per m² showed a similar pattern, whereas the thousand-seed weight partly compensated for the reduced seed number. It was highest if oil-seed rape was grown 2 years previously. The cultivars differed significantly in their yield potential. Express (3.79 t ha⁻¹) yielded 0.6 t ha⁻¹ more than Falcon (3.18 t ha⁻¹). Increasing amounts of fertilizer-N (80–200 kg N ha⁻¹) increased the seed yield from 3.21 t ha⁻¹ to 3.84 t ha⁻¹. Changes in the distribution pattern within one fertilizer amount had no effect on seed yield. In addition, no interactions between preceding crop combination and the different cultivars or N treatments occurred. It is concluded that crop management cannot totally eliminate the negative effects of an unfavourable cropping history on the seed yield of oil-seed rape.     

The effect of temperature and other factors on chlorophyll a fluorescence and the lower oxygen limit in apples (Malus domestica)

The effects of temperature, scan interval and rate of oxygen (O₂) decline on pulse frequency modulation (PFM)-based minimum fluorescence (F_α) and the F_α-based lower oxygen limit (LOL) were investigated using ‘Honeycrisp’ apples (Malus × domestica Borkh). The effects of temperature and hypoxic stress on pulse amplitude modulation (PAM) fluorescence parameters were also investigated. The PFM scan interval had no effect on the F_α baseline, but increases in the scan interval decreased the low-O₂-induced fluorescence spike intensity (ΔF_α). Temperature negatively correlated with the F_α baseline while ΔF_α °C⁻¹ was greater at lower than at higher temperatures. When using a PAM fluorometer, the minimum fluorescence (F_o), and to a lesser extent the maximum fluorescence (F_m), were similarly affected by temperature as was F_α. Temperature altered the LOL in fruit. Apples stored at 20, 10, 3.5 and 0 °C spiked at 0.72, 0.33, 0.22 and 0.08 kPa O₂, respectively, under a rapid O₂ decline (i.e., 20.9 to <1 kPa O₂ in ≈5–6 h). Although the low-O₂ F_α spike apex values did not change with temperature, the spike intensity increased with temperature due to a reduced fluorescence baseline. A slower O₂ decline rate produced slightly higher LOL and lower spike intensity values. In conclusion, temperature and rate of O₂ decline affected the low-O₂-induced PFM fluorescence spike intensity as well as the LOL, while the PFM scan interval affected the spike intensity.     

Influence of aqueous 1-methylcyclopropene concentration, immersion duration, and solution longevity on the postharvest ripening of breaker-turning tomato (Solanum lycopersicum L.) fruit

The influence of aqueous 1-methylcyclopropene (1-MCP) concentration, immersion duration, and solution longevity on the ripening of early ripening-stage tomato (Solanum lycopersicum L.) has been investigated. Tomato fruit at the breaker-turning stage were fully immersed in aqueous 1-MCP at 50, 200, 400 and 600 μg L⁻¹ for 1 min, quickly dried, and then stored at 20 °C. Ethylene production, respiration, surface color development, and rate of accumulation of lycopene and polygalacturonase (PG) activity were suppressed and/or delayed in fruit exposed to aqueous 1-MCP. Suppression of ripening was concentration dependent, with maximum inhibition in response to 1 min immersion occurring at concentrations of 400 and 600 μg L⁻¹. Climacteric ethylene peaks were delayed approximately 6, 7, and 9 d and respiration was strongly suppressed in fruit treated with aqueous 1-MCP at 200, 400, and 600 μg L⁻¹, respectively, compared with control fruit. Fruit firmness, lycopene content, PG activity, and surface hue of fruit treated at the three higher levels remained strongly suppressed compared with control. Skin hue values and pericarp lycopene content in response to treatment at the subthreshold 50 μg L⁻¹ provided evidence for differential ripening suppression in external versus internal tissues. Maximum delay of softening and surface color development in response to 50 μg L⁻¹ aqueous 1-MCP occurred following immersion periods of between 6 and 12 min. Factors affecting fruit penetration by aqueous 1-MCP and mechanisms contributing to recovery from 1-MCP-induced ripening inhibition are discussed.     

The Translocation of 14C-Sucrose and 14C-Benzyl Adenine in Winter Wheat (Tritkum aestivum L.) in the Period of Kernel Formation

The transport and distribution of ^14C-sucrose and ^14C-BA were studied in internode segments with ear of two winter wheat cultivars with a different mass of kernels in the period of kernel formation. While ^MC-sucrose was transported and accumulated intensively in the developing ear, ^14C-BA was transported much less and only a small part of it was found in the ear. With the ear development the accumulation of both ¹⁴C-sucrose and ¹⁴C-BA in the ear increased but the ¹⁴C-BA distribution pattern (ratio of the internode/kernel and the rest of the ear) did not change significantly. In the period of one to two weeks after anthesis the accumulation of ¹⁴C-sucrose and ¹⁴C-BA was higher in the kernels of the Slavia cv., i.e. in the cultivar with a higher mass of kernels.     

Effect of shading and nitrogen application on yield, grain size distribution and concentrations of nitrogen and water soluble carbohydrates in malting spring barley (Hordeum vulgare L.)

Experiments to investigate the effects of periods of low radiation, combined with different rates of nitrogen fertilization, on growth, grain yield, mean grain weight, grain size distribution and concentrations of nitrogen and water soluble carbohydrates (WSC) were carried out in 1991 and 1993. The low radiation (60% of ambient radiation) was achieved by placing shading nets in fields of barley (cv. Prisma). There was an unshaded control (S1), plus three shading period treatments during the main phenological phases, with three rates of nitrogen fertilization (unfertilized control, 90 kg ha⁻¹ minus soil nitrogen and this rate plus 60 kg ha⁻¹ at the flag leaf stage). It was found that total grain yield was 5% lower after shading during tillering (S2), 35% lower after shading during stem elongation (S3) and 45% lower after shading during grain filling (S4). Treatments S2 and S3 considerably reduced the concentration of WSC in plant organs and increased the nitrogen concentration and, in general, the concentrations returned to the values of the control after the shading period. The S3 treatment markedly reduced the number of grains m⁻², mainly because there were 35% fewer grains per spike. This treatment resulted in a mean grain weight 14% above that of the control, but only in 1991. Weather was probably responsible for this disparity: in 1991, the spring was cold and wet and the summer was warm and dry, but in 1993 the spring was warm and dry and the summer was cool and wet. The S4 treatment reduced mean grain weight by 40% in 1991 and by 25% in 1993 and shifted the median of the size distribution towards smaller grains in both years. In S4, the N concentration in the grains was markedly increased, resulting in unacceptably high protein concentrations (14–21%) for malting quality. Higher rates of nitrogen fertilization increased leaf area index (LAI), total dry matter production and grain N concentration. Nitrogen had a positive effect in establishing yield potential because it increased grain number per unit area; however, it did not improve assimilate supply during grain filling, and hence grain number and mean grain weight were negatively correlated. Only in 1993 did nitrogen increase grain yield. It is concluded that shading during the growing period and high rates of nitrogen fertilization adversely affect the quality (in terms of grain size, size distribution and grain nitrogen concentration) of malting barley.     

The Effect of Chilling Temperature on the Permeability of Membranes to K+, Mg2+, Ca2+ ions and on the Electric Potential of Leaves in the Seedlings of Maize (Zea mays L.)

The relations between the extent of injuries in seedlings caused by a few day-long exposures to chill (5°C) and the leakage of K⁺, Mg²⁺ and Ca²⁺ ions from the leaves as well as the electric potential in seven maize hybrids, were investigated. The permeability of cells to ions was defined based on their absolute concentration in a water diffusate (C_t) and concentration expressed in relation to the total ion content in the leaves (IL index).
At lowered temperature the hybrids of higher resistance to chilling temperature were characterized by a lower value of the IL index for K⁺ and Mg²⁺ ions than the chill-sensitive hybrids. On the other hand, absolute concentration of the ions (C_t) Mg²⁺ and Ca²⁺ leaking from the leaves before chill exposure of the seedlings was positively and highly correlated with the extent of injuries in hybrids caused by 4 day-long exposures to chill. This observation is evidence that the chill injuries were predetermined through increased cell permeability to the mentioned ions at room temperature.
Changes in the electric potential of leaves in conditions of lowered temperature preceded the injuries of leaves, which became apparent after a longer period of exposure to chill. Thus, as the leakage of Mg²⁺ and Ca²⁺ ions occurs, changes in the electric potential may supply early information about the predisposition of the particular maize hybrids to chilling injuries. Leakage measurements of Mg²⁺ and Ca²⁺ ions from the leaves at room temperature may find application in the selection of chill-tolerant maize genotypes.