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Effect of temperature on the inverse of time to 50% germination of selected traditional South African leafy vegetables.
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Using laboratory incubation, the response of seed germination and emergence to variability in temperature and light was examined for spider flower (Cleome gynandra L.), amaranth (Amaranthus cruentus L.), non-heading Chinese cabbage (Brassica rapa L. subsp. chinensis), nightshade (Solanum retroflexum Dun.), pumpkin (Cucurbita maxima Duchesne), tsamm...
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... graded silica sand (SiO 2 , 98% Fe 2 O 3 0.18%)] moistened with distilled water for small seeds (0.0675 l kg − 1 sand) and large seeds (0.4675 l kg − 1 sand). Water was allowed to redistribute in the sand before incubation for 24 h at the designated treatment temperatures to allow the sand to attain the desired temperature. Small seeds were broadcasted evenly on top of moistened sand and fi rmly pressed into the substratum to allow contact with sand. Large seeds were sown at a depth of 1 cm. Spacer sticks were used to separate sample containers inside the incubators to allow suf fi cient circulation of air around the containers. Water was replenished as needed. Emergence was recorded every 24 h. Seeds were considered to have emerged once the cotyledons were visible above the surface of the sand (Koger et al., 2004; Maraghni et al., 2010). To investigate the effect of light on germination, seeds were incubated at a constant temperature of 25 °C, and exposed to alternating light (8 h dark and 16 h light) and continuous darkness in an environmental- ly controlled Labcon TM (220V, 50 Hz) low-temperature incubator and growth chamber. Light was provided by six OSRAM DULUXSTAR light bulbs (14 W/840, 220 – 240 V, 116 mA, 50/60 Hz). Seed germination was recorded every 24 h. In the light effect experiment, samples incubated under darkness received small quantities of light during daily evaluations, and this could have triggered germination and affected the fi nal germination percentage. For this reason, a second experiment was undertaken to determine the effect on light on fi nal germination percentage in which the short exposure to light of the continuous darkness treatment as part of daily germination counts was eliminated. Accordingly, seeds were kept in the respective incubators for 10 days (240 h) without daily evaluation and germination counts were done after 240 h. The reason for incubating the seeds for 240 h was that in the fi rst light-effect experiment fi nal germination had been reached in all treatments and for all species before 240 h had expired. Germination and emergence experiments were conducted in incubators set at constant temperatures which ranged from 4 °C to 44 °C with 4 °C increments, under continuous darkness. All experiments were incubated over a period of 14 days (336 h). In all experiments seeds were exposed to normal light during observations. All treatments were replicated four times with 50 seeds per treatment. Replicates were arranged in a completely randomized design in controlled incubators/ growth chambers. Seeds that showed signs of fungal growth were removed from the population. Germinated or emerged seeds were counted, removed and expressed as a percentage of the total number of tested seeds. The non-intercept sigmoid function as described in TableCurve® 2D (2002) was fi tted on the cumulative germination/emergence percentage to determine the time to 50% germination/emergence ( T 50 ) (Jami Al-Ahmadi and Ka fi , 2007): y 1⁄4 1 þ e ð a − x − c b Þ , where a is the maximum germination/emergence percentage, b is the turning point, c is slope of the line, x is the time (h) and y is the germination/emergence %. T 50 germination/emergence was calculated and subjected to an appropriate analysis of variance (ANOVA) using SAS® statistical software version 9.2 (SAS, 1999). The rate of germination/emergence was de fi ned as the reciprocal of the time taken for half the population to germinate/emerge (1/ T ). The optimum temperature ( T opt ) was determined by fi tting a simple piece- wise linear model (broken-stick regression) using a non-linear (NLIN) procedure with SAS between temperature and rate of germination/ emergence (1/ T 50 ) for each species separately. The rate of germination/ emergence increased linearly with temperature from a minimum ( T min ) to a sharply de fi ned optimum ( T opt ) beyond which the rate decreased linearly with temperature. The maximum temperature ( T max ) was taken as the highest temperature where 50% germination/emergence was reached. Analysis of variance (ANOVA) was used to test for temperature and light treatment effects. Treatment means were separated using Fisher's protected least signi fi cant difference test at the 1% instead of the 5% level of signi fi cance (Snedecor and Cochran, 1980), because of hetero- geneity of variances. For light experiment 2, treatment means were separated at the 5% level of signi fi cance. The data were analysed using the statistical program GenStat® (Payne et al., 2007). Rate of germination/emergence (1/ T 50 ) of the different ALVs increased linearly as temperature was raised up to the optimum at which maximum germination/emergence percentage was recorded and then decreased linearly as temperature was elevated further. The ALVs for which the 1/ T 50 for the two processes were calculated and their estimated cardinal temperatures are shown in Table 1. Optimum germination temperatures ( T opt ) ranged from 29 to 36 °C (Fig. 1), with C. olitorius (35 °C) and V. unguiculata (36 °C) recording higher optima than B. rapa subsp. chinensis (29 °C), A. cruentus (31 °C), C. lanatus (30 °C), C. gynandra (31 °C), and C. maxima (32 °C). Estimated T min values ranged from 8 °C for B. rapa subsp. chinensis and C. lanatus to 15 °C for C . gynandra . The 1/ T 50 values for emergence indicated optima ranging from 25 to 31 °C (Fig 2). B. rapa subsp. chinensis and V. unguiculata (25 °C) had the lowest optimum temperatures and C. olitorius and C. maxima (31 °C) the highest. Noteworthy was that B. rapa subsp. chinensis , V. unguiculata and C. olitorius demonstrated a relatively wide optimum temperature range, whilst for the other three species in Fig 2 the optimum temperature range was narrow. Estimated T opt for emergence compared well T opt for germination for most species except with B. rapa subsp. chinensis and V. unguiculata , for which the optimum temperature for seedling emergence was lower than that for seed germination as the two exceptions. Estimated 1/ T 50 T min values for seedling emergence were higher than those for germination for C. lanatus , C. olitorius and V. unguiculata , lower for A. cruentus and B. rapa subsp. chinensis , and the same for C. maxima . Important was that most species germinated and emerged well at high temperatures. Using 1/ T 50 germination (Fig. 1) and 1/ T 50 emergence (Fig. 2) as a theoretical model to predict cardinal temperatures, the T min , T opt and T max germination of the ALVs ranged between 8 – 15 °C, 29 – 36 °C and 36 – 44 °C, respectively. The T min, T opt and T max for ALVs seedling emergence was 2 – 13 °C, 25 – 31 °C and 32 – 40 °C, respectively (Table 1). Sensitivity to light in relation to onset of germination and fi nal germination percentage of the eight vegetable species is presented in Table 2, which also lists their 100 seed weight. Positive effects of light on the onset of germination were recorded for B. rapa subsp. chinensis , A. cruentus and C. olitorius , and negative effects for C. lanatus and V. unguiculata . For B. rapa subsp. chinensis the positive effect of light was signi fi cant ( p 0.01) throughout the incubation period, and in C. lanatus and S. retro fl exum exposure of the seed to light increased fi nal percentage germination signi fi cantly ( p 0.01). Light did not have a signi fi cant effect on the fi nal germination percentage of A. cruentus , C. gynandra , C. olitorius , C. maxima and V. unguiculata , but this effect tended to be positive for all of these species except V. unguiculata. Whilst the cardinal temperatures ( T min and T opt ) for germination of the ALVs tended to be higher than those for seedling emergence this did not apply to all the ALV species. For example, in C. lanatus and C. maxima no material differences between the cardinal temperatures of these two processes were observed. Differences in cardinal temperatures for seed germination and seedling growth are not anomalous and were also reported by Cochrane et al. (2011). Saeidnejad et al. (2012) indicated that such differences could be due to genetic variability among the seeds used or to differences in latitude at which accessions of seeds were collected. The fairly high optimal temperature ( T opt ) for both germination and seedling growth indicated that most ALV species, with the exception of B. rapa subsp. chinensis and V. unguiculata , were adapted to high day-time temperatures, which are characteristic of tropical and subtropical regions. This trait is considered to be an important pre-adaptation for the weedy or wild habit of species (Cristaudo et al., 2007) and helps to prevent the seeds of these plants from germinating too early or too late. For most species the T max could not be estimated because they still germinated and emerged well at the highest temperature of 40 °C. This supports the notion that most of these plant species have a high tolerance to high temperatures during germination, when high rates of respiration and failure of metabolic activity in the seed could cause reduced emergence by inhibiting hypocotyl elongation (Ndunguru and Summer fi eld, 1975). The T min estimated indicates tolerance of ALV to low temperatures during germination. Conversely, longer exposure at such temperature range may cause sub- stantial reduction in the rate of germination and subsequent growth of the crop (improper development of seedlings). This could evidently cause increased seedling exposure to pathogens in the soil, leading to decreased emergence due to seed and seedling diseases (which cause rotting of the cotyledons) (Soltani et al., 2006; Souza and Fagundes, 2014). Poor germination at very low and high temperatures reported in legume species, such as V. unguiculata (Balkaya, 2004), and in Brassica species (Tokumasu et al., 1985) may indicate that little or no germination will take place during winter or mid-summer and could be seen as a protection mechanism against excessive seedling ...
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... quantities of light during daily evaluations, and this could have triggered germination and affected the fi nal germination percentage. For this reason, a second experiment was undertaken to determine the effect on light on fi nal germination percentage in which the short exposure to light of the continuous darkness treatment as part of daily germination counts was eliminated. Accordingly, seeds were kept in the respective incubators for 10 days (240 h) without daily evaluation and germination counts were done after 240 h. The reason for incubating the seeds for 240 h was that in the fi rst light-effect experiment fi nal germination had been reached in all treatments and for all species before 240 h had expired. Germination and emergence experiments were conducted in incubators set at constant temperatures which ranged from 4 °C to 44 °C with 4 °C increments, under continuous darkness. All experiments were incubated over a period of 14 days (336 h). In all experiments seeds were exposed to normal light during observations. All treatments were replicated four times with 50 seeds per treatment. Replicates were arranged in a completely randomized design in controlled incubators/ growth chambers. Seeds that showed signs of fungal growth were removed from the population. Germinated or emerged seeds were counted, removed and expressed as a percentage of the total number of tested seeds. The non-intercept sigmoid function as described in TableCurve® 2D (2002) was fi tted on the cumulative germination/emergence percentage to determine the time to 50% germination/emergence ( T 50 ) (Jami Al-Ahmadi and Ka fi , 2007): y 1⁄4 1 þ e ð a − x − c b Þ , where a is the maximum germination/emergence percentage, b is the turning point, c is slope of the line, x is the time (h) and y is the germination/emergence %. T 50 germination/emergence was calculated and subjected to an appropriate analysis of variance (ANOVA) using SAS® statistical software version 9.2 (SAS, 1999). The rate of germination/emergence was de fi ned as the reciprocal of the time taken for half the population to germinate/emerge (1/ T ). The optimum temperature ( T opt ) was determined by fi tting a simple piece- wise linear model (broken-stick regression) using a non-linear (NLIN) procedure with SAS between temperature and rate of germination/ emergence (1/ T 50 ) for each species separately. The rate of germination/ emergence increased linearly with temperature from a minimum ( T min ) to a sharply de fi ned optimum ( T opt ) beyond which the rate decreased linearly with temperature. The maximum temperature ( T max ) was taken as the highest temperature where 50% germination/emergence was reached. Analysis of variance (ANOVA) was used to test for temperature and light treatment effects. Treatment means were separated using Fisher's protected least signi fi cant difference test at the 1% instead of the 5% level of signi fi cance (Snedecor and Cochran, 1980), because of hetero- geneity of variances. For light experiment 2, treatment means were separated at the 5% level of signi fi cance. The data were analysed using the statistical program GenStat® (Payne et al., 2007). Rate of germination/emergence (1/ T 50 ) of the different ALVs increased linearly as temperature was raised up to the optimum at which maximum germination/emergence percentage was recorded and then decreased linearly as temperature was elevated further. The ALVs for which the 1/ T 50 for the two processes were calculated and their estimated cardinal temperatures are shown in Table 1. Optimum germination temperatures ( T opt ) ranged from 29 to 36 °C (Fig. 1), with C. olitorius (35 °C) and V. unguiculata (36 °C) recording higher optima than B. rapa subsp. chinensis (29 °C), A. cruentus (31 °C), C. lanatus (30 °C), C. gynandra (31 °C), and C. maxima (32 °C). Estimated T min values ranged from 8 °C for B. rapa subsp. chinensis and C. lanatus to 15 °C for C . gynandra . The 1/ T 50 values for emergence indicated optima ranging from 25 to 31 °C (Fig 2). B. rapa subsp. chinensis and V. unguiculata (25 °C) had the lowest optimum temperatures and C. olitorius and C. maxima (31 °C) the highest. Noteworthy was that B. rapa subsp. chinensis , V. unguiculata and C. olitorius demonstrated a relatively wide optimum temperature range, whilst for the other three species in Fig 2 the optimum temperature range was narrow. Estimated T opt for emergence compared well T opt for germination for most species except with B. rapa subsp. chinensis and V. unguiculata , for which the optimum temperature for seedling emergence was lower than that for seed germination as the two exceptions. Estimated 1/ T 50 T min values for seedling emergence were higher than those for germination for C. lanatus , C. olitorius and V. unguiculata , lower for A. cruentus and B. rapa subsp. chinensis , and the same for C. maxima . Important was that most species germinated and emerged well at high temperatures. Using 1/ T 50 germination (Fig. 1) and 1/ T 50 emergence (Fig. 2) as a theoretical model to predict cardinal temperatures, the T min , T opt and T max germination of the ALVs ranged between 8 – 15 °C, 29 – 36 °C and 36 – 44 °C, respectively. The T min, T opt and T max for ALVs seedling emergence was 2 – 13 °C, 25 – 31 °C and 32 – 40 °C, respectively (Table 1). Sensitivity to light in relation to onset of germination and fi nal germination percentage of the eight vegetable species is presented in Table 2, which also lists their 100 seed weight. Positive effects of light on the onset of germination were recorded for B. rapa subsp. chinensis , A. cruentus and C. olitorius , and negative effects for C. lanatus and V. unguiculata . For B. rapa subsp. chinensis the positive effect of light was signi fi cant ( p 0.01) throughout the incubation period, and in C. lanatus and S. retro fl exum exposure of the seed to light increased fi nal percentage germination signi fi cantly ( p 0.01). Light did not have a signi fi cant effect on the fi nal germination percentage of A. cruentus , C. gynandra , C. olitorius , C. maxima and V. unguiculata , but this effect tended to be positive for all of these species except V. unguiculata. Whilst the cardinal temperatures ( T min and T opt ) for germination of the ALVs tended to be higher than those for seedling emergence this did not apply to all the ALV species. For example, in C. lanatus and C. maxima no material differences between the cardinal temperatures of these two processes were observed. Differences in cardinal temperatures for seed germination and seedling growth are not anomalous and were also reported by Cochrane et al. (2011). Saeidnejad et al. (2012) indicated that such differences could be due to genetic variability among the seeds used or to differences in latitude at which accessions of seeds were collected. The fairly high optimal temperature ( T opt ) for both germination and seedling growth indicated that most ALV species, with the exception of B. rapa subsp. chinensis and V. unguiculata , were adapted to high day-time temperatures, which are characteristic of tropical and subtropical regions. This trait is considered to be an important pre-adaptation for the weedy or wild habit of species (Cristaudo et al., 2007) and helps to prevent the seeds of these plants from germinating too early or too late. For most species the T max could not be estimated because they still germinated and emerged well at the highest temperature of 40 °C. This supports the notion that most of these plant species have a high tolerance to high temperatures during germination, when high rates of respiration and failure of metabolic activity in the seed could cause reduced emergence by inhibiting hypocotyl elongation (Ndunguru and Summer fi eld, 1975). The T min estimated indicates tolerance of ALV to low temperatures during germination. Conversely, longer exposure at such temperature range may cause sub- stantial reduction in the rate of germination and subsequent growth of the crop (improper development of seedlings). This could evidently cause increased seedling exposure to pathogens in the soil, leading to decreased emergence due to seed and seedling diseases (which cause rotting of the cotyledons) (Soltani et al., 2006; Souza and Fagundes, 2014). Poor germination at very low and high temperatures reported in legume species, such as V. unguiculata (Balkaya, 2004), and in Brassica species (Tokumasu et al., 1985) may indicate that little or no germination will take place during winter or mid-summer and could be seen as a protection mechanism against excessive seedling mortality (Chanyenga et al., 2012). Although the cardinal temperatures of some of the ALV species were fairly speci fi c and constant, indicating potential for modelling of emergence, it has been pointed out that most cardinal temperatures for non-crop species are unstable due to genetic variability, positional effects, environmental factors and seed size (Wang, 2005; Souza and Fagundes, 2014). Germination of smaller seeded species may be expected to be faster providing a greater competitive advantage in early successional stages compared to that of larger seeds since larger seeds have higher amounts of reserves in their cotyledons and require extended periods to incorporate these nutrients in seedling tissues (Souza and Fagundes, 2014). In our study, only three ALVs would be classi fi ed as having larger seeds based on their average seed weights; these being C. lanatus , C. maxima and V. unguiculata (Table 2). However, rate of germination/emergence was not found to be that much different to that of smaller seeds. Although our study did not investigate effects of seed size on seed germination and seedling emergence, this seed trait is expected to vary among species in relation to their ecological strate- gies for seed dispersal and seedling establishment (Soriano et al., 2011). Cardinal temperatures for seed of C. gynandra and S. retro fl exum ...
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... up to the optimum at which maximum germination/emergence percentage was recorded and then decreased linearly as temperature was elevated further. The ALVs for which the 1/T 50 for the two processes were calculated and their estimated cardinal temperatures are shown in Table 1. Optimum germination temperatures (T opt ) ranged from 29 to 36 °C ( Fig. 1), with C. olitorius (35 °C) and V. unguiculata (36 °C) recording higher optima than B. rapa subsp. chinensis (29 °C), A. cruentus (31 °C), C. lanatus (30 °C), C. gynandra (31 °C), and C. maxima (32 °C). Estimated T min values ranged from 8 °C for B. rapa subsp. chinensis and C. lanatus to 15 °C for C. ...
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... was that most species germinated and emerged well at high temperatures. Using 1/T 50 germination (Fig. 1) and 1/T 50 emergence (Fig. 2) as a theoretical model to predict cardinal temperatures, the T min , T opt and T max germination of the ALVs ranged between 8-15 °C, 29-36 °C and 36-44 °C, respectively. The T min, T opt and T max for ALVs seedling emergence was 2-13 °C, 25-31 °C and 32-40 °C, respectively (Table ...
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... Brassica napus required only three days to reach 50 % germination when kept at 8 • C, compared to approximately 13 days at 2 • C. It has been demonstrated that low temperatures have an adverse effect on seed germination rates or that low temperatures have a more substantial effect on seed germination days than ordinary temperatures. The low-temperature effect was more pronounced in B. rapa because even after 20 days of sowing, emergence was less than 50 % at 2 • C (Angadi et al., 2000a;Haj Sghaier et al., 2022;Motsa et al., 2015). ...
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This study was carried out with the aim of utilizing the Arduino UNO R3 in seed germination. Seed germination is the process by which seeds emerge from their dormant state. Germination is the first stage of a plant's life cycle, and it is also the most difficult to maintain and care for. The researchers aimed to develop an automated okra seed germinator that could reduce the following factors: soil moisture, temperature, humidity, and light, all of which affect seed germination, concentrating on soil moisture, which has a significant impact on seed performance. The main materials required for this study are an Arduino UNO R3, a soil moisture sensor, a servo motor, an LCD, and okra seeds. For the other components to function properly, code was uploaded to the Arduino UNO R3. Two setups were observed: setup A received treatment, while Setup B did not receive any treatment. Within 15 days, the experiment was conducted entirely through observation. Based on the findings, using an Arduino UNO R3 to germinate okra seeds yielded no significant difference between the germination duration of the seeds germinated by the prototype and the manual method. However, the experiment showed 55% and 35% germination percentages respectively. Further, the germination percentage of the okra seeds grown by the prototype is higher than the germination percentage of the okra seeds grown manually Thus, the researchers recommend experimenting with different vegetable seeds if varying environmental needs. to widen the use of the automated okra seed germinator thereby upgrading it into an automated vegetable seed germinator.
... According to Milbau et al. (2009), the most significant factor influencing germination has been demonstrated to be temperature. It is the most prominent environmental factor regulating the growth and development of plants (Koger et al., 2004;Motsa et al., 2015). The frequency of seeds germination and the distribution of species are both strongly influenced by temperature (Guan et al., 2009). ...
... However, any temperature beyond the optimum germination temperature will negatively affect seed germination and species survival. Motsa et al. (2015) reported that the temperature (optimum) at which the maximum germination and emergence percentage are recorded tends to differ among crops. Increased temperatures have made some stages of the life cycles of the majority of the world's crops susceptible to heat stress (Grass and Burris, 1995). ...
This study was carried out in the Forest Nursery of the Department of Forestry and Wildlife Management, University of Port Harcourt, to determine the effect of temperature on germination and early growth of Chrysophyllum albidum. The experiment was laid out in a completely randomised design with five treatments (temperature regimes simulating night/day temperature fluctuations): 20/32 o C±3°C (T1), 22/33°C±3°C (T2), 23/34°C±3°C (T3), 25/35°C±3°C (T4), and 27/36°C±3°C (T5). A total of 500 seeds of C. albidum were used for the germination experiment, while 125 seedlings, equally divided among the five treatments, were used for the evaluation of the effect of temperature on early growth. Observations on germination were made and recorded daily; this was terminated after sixty days. Initial shoot parameter measurements were done on all seedlings immediately after transplanting and monthly thereafter for four months. An analysis of variance and a Duncan multiple range test at P ≤ 0.05 were used for mean separation. There were no significant differences (p > 0.05) in germination emergence and duration among temperature regimes, while germination percentage varied significantly (p ≤ 0.05). The earliest emergence and shortest duration (8 and 28.25 days, respectively) were observed in T5, while the highest percentage of germination (65%) was found in T4. Seedlings of C. albidum grown at different temperatures displayed significant differences (p ≤ 0.05) in height and collar diameter and non-significant differences (p > 0.05) in leaf number and biomass. The highest height at months 2 to 5 (14.96, 15.54, 15.98, and 16.88 cm, respectively) and collar diameter (0.99, 1.29, 1.43, and 1.63 mm, respectively) were found in T5. Plant biomass (fresh weight, dry weight, and moisture) were highest in T5, followed by T4, and lowest in T1. The study showed that the temperature for better growth of C. albidum is between T4 and T5.
... However, it has been widely reported that temperatures below the optimum result in a delay of seed germination due to reduced respiration-related enzyme activity and cellular metabolism (Taiz et al., 2017). Each variety has a minimum temperature and a limit temperature below and above which germination does not occur (Motsa et al., 2015) as is the case in this study for 10 and 40°C. The decrease in the percentage of germinated seeds from 30 to 35°C for the cowpea varieties Agboloto, Akounado, FUAMPEA1, IT97K-499-35, IT97K-556-6 and Sanzi could be explained by the fact that increasing temperature (5°C) reduced the percentage of seed germination by causing thermal stress, leading to inhibition of germination, and may cause thermal dormancy, affecting seed viability as reported by Bewley et al. (2013); Barrios et al. (2020). ...
Climate change presents scenarios of extreme temperature variations that will limit agricultural productivity further when the need for efficient production systems cannot be over emphasized. Aside breeding for tolerance, the development of new varieties of crops such as Cowpea, it is important to evaluate the temperature tolerance of new varieties prior to their release and commercialization. Therefore, in this study we evaluated the effect of the high temperatures on germination of 13 newly developed cowpea varieties resistant to major insect's pest and drought under laboratory conditions. The 13 cowpea varieties were evaluated for germination at 10°C, 20°C, 30°C, 35°C and 40°C. There was no germination for all the varieties at the extremes of 10°C and 40°C. However, at 20°C high germination percentage was recorded on the varieties IT93K-452-1 (100%), IT97K-499-35 (100%), Komcalle (100%), Kumassi (93.33%), Tvu-1509 (100%) while at 30°C the high germination percentage was recorded on Agbloto (100°C),, Komcalle (100%), Sanzi (90%). The temperature 35°C only provided high (100%) germination percentage for Komcalle. The variety TVU-1509 had the highest speed of germination. The variety IT 98K-205-8, and TVU-1509 had the highest homogeneity at the different temperatures. The results provide useful information for breeders on which varieties to release in a target environment and in formulating efficient selection and breeding programs.
... However, AsA concentrations differed between trials. Salinity induced eustress affected internal AsA concentrations along with other factors, such as environmental stressors [32] . Some factors such as room Table 3. Results for vitamin C and proline concentration in broccoli and purslane microgreens for trials 1 and 2. ...
Most controlled environments utilize municipal water for crop irrigation. Many of these sources exceed the EPA guidelines of < 500 mg·L⁻¹ total dissolved salts. Issues can arise when tap water with the above limit salt concentrations is used for irrigation. Eustress is defined as the use of slight stress (from stressors such as salinity, temperature, or light) to induce positive effects without distress. While eustress is commonly used on mature plants, the effects on early growth stages of plants, such as microgreens, are not well documented. As microgreens are typically more stress sensitive, the concentrations of salinity to induce eustress may be lower than for mature plants. To identify how eustress affects microgreens, salinity concentrations commonly found in tap water were used in these experiments. Brassica oleracae (moderately salt tolerant) and Portulaca oleracea (highly salt tolerant) microgreens were evaluated. Both species of microgreens were cultivated using salinity irrigation treatments ranging from 0 dS·m⁻¹ to 1.5 dS·m⁻¹. Plants were analyzed for microgreen yield (fresh weight and dry weight), percent moisture content (% MC), percent dry matter (% DM), vitamin C (T-AsA, AsA) and proline concentrations. The results indicate that yields of both variety remained unaffected by the salinity treatments. However, %MC and proline significantly increased under 1 and 1.5 dS·m⁻¹ NaCl in broccoli. Vitamin C also decreased as salinity increased in broccoli microgreens. Purslane microgreen vitamin C and proline remained unaffected by salinity. In conclusion, while low salinity levels had no negative impacts on microgreen yields, there were varied impacts on the phytochemistry between each variety.
... In plants, high temperature at the sowing time lowers seed germination, potentially triggering seedling mortality, leading to poor crop stand and low seed yield [37]. Prior studies have demonstrated that transient daily heat stress during flowering in canola (Brassica napus L.) poses an increasing threat to grain production in this oilseed crop [38]. In leafy vegetables, exposure to a temperature of 40 • C decreased seed germination [39]. This decrease in seed germination is due to cell death, which negatively impacts the Life 2023, 13, 738 13 of 17 seedling establishment rate in wheat [40]. ...
Wild species are weedy relatives and ancestors of domesticated crops that store economically important traits. Due to their natural tolerance to many biotic and abiotic stresses, they are widely used in plant breeding and crop improvement programs. Using a source of tolerance from crop wild relatives (CWRs), and introgressing the genetic factors into elite cultivars may improve resilience in modern crop cultivars. However, the lack of best practices and opportunities to systematically assess CWRs limits their use in crop improvement programs. The current study was conducted with Brassica’s wild and U-triangle species, which varied in their potential to withstand heat and drought stress, in an attempt to identify genotypes with a high degree of tolerance to abiotic stresses. Screening was performed at the germination and early seedling stages, for which morphological data and biochemical analyses were conducted.
