Climate change and rapid population growth have become key challenges to global food security. One promising solution is the use of plant growth regulators (PGRs) to increase crop yields and overcome unfavorable growing conditions such as desert climates. Recently, the carotenoid zaxinone and two of its analogues (MiZax3 and MiZax5) have demonstrated promising growth-promoting activity in cereal and vegetable crops under greenhouse and field conditions. Here, we further investigated the effects of different concentrations of MiZax3 and MiZax5 (5 μM and 10 μM in 2021; 2.5 μM and 5 μM in 2022) on the growth and yield of two high-value vegetable crops in Cambodia: potatoes and strawberries. Arabia. In five independent field trials from 2021 to 2022, application of both MiZax significantly improved plant agronomic characteristics, yield components and overall yield. It is worth noting that MiZax is used in much lower doses than humic acid (a widely used commercial compound used here for comparison). Thus, our results show that MiZax is a very promising plant growth regulator that can be used to stimulate the growth and yield of vegetable crops even in desert conditions and at relatively low concentrations.
According to the Food and Agriculture Organization of the United Nations (FAO), our food production systems must nearly triple by 2050 to feed a growing global population (FAO: The world will need 70% more food by 20501). In fact, rapid population growth, pollution, pest movements and especially high temperatures and droughts caused by climate change are all challenges facing global food security2. In this regard, increasing the gross yield of agricultural crops in suboptimal conditions is one of the indisputable solutions to this pressing problem. However, plant growth and development are mainly dependent on the availability of nutrients in the soil and are severely constrained by adverse environmental factors, including drought, salinity or biotic stress3,4,5. These stresses can negatively impact the health and development of crops and ultimately lead to reduced crop yields6. In addition, limited freshwater resources severely impact crop irrigation, while global climate change inevitably reduces arable land area and events such as heat waves reduce crop productivity7,8. High temperatures are common in many parts of the world, including Saudi Arabia. The use of biostimulants or plant growth regulators (PGRs) is useful in shortening the growth cycle and increasing the yield of crops. It can improve crop tolerance and enable plants to cope with unfavorable growing conditions9. In this regard, biostimulants and plant growth regulators can be used in optimal concentrations to improve plant growth and productivity10,11.
Carotenoids are tetraterpenoids that also serve as precursors for the phytohormones abscisic acid (ABA) and strigolactone (SL)12,13,14, as well as the recently discovered growth regulators zaxinone, anorene and cyclocitral15,16,17,18,19. However, most actual metabolites, including carotenoid derivatives, have limited natural sources and/or are unstable, making their direct application in this field difficult. Thus, over the past few years, several ABA and SL analogues/mimetics have been developed and tested for agricultural applications20,21,22,23,24,25. Similarly, we have recently developed mimetics of zaxinone (MiZax), a growth-promoting metabolite that may exert its effects by enhancing sugar metabolism and regulating SL homeostasis in rice roots19,26. The mimetics of zaxinone 3 (MiZax3) and MiZax5 (chemical structures shown in Figure 1A) showed biological activity comparable to zaxinone in wild-type rice plants grown hydroponically and in soil26. Moreover, treatment of tomato, date palm, green pepper and pumpkin with zaxinone, MiZax3 and MiZx5 improved plant growth and productivity, i.e., pepper yield and quality, under greenhouse and open field conditions, indicating their role as biostimulants and use of PGR27. . Interestingly, MiZax3 and MiZax5 also improved the salt tolerance of green pepper grown under high salinity conditions, and MiZax3 increased the zinc content of the fruit when encapsulated with zinc-containing metal-organic frameworks7,28.
(A) Chemical structure of MiZax3 and MiZax5. (B) Effect of foliar spraying of MZ3 and MZ5 at concentrations of 5 µM and 10 µM on potato plants under open field conditions. The experiment will take place in 2021. Data are presented as mean ± SD. n≥15. Statistical analysis was performed using one-way analysis of variance (ANOVA) and Tukey’s post hoc test. Asterisks indicate statistically significant differences compared to simulation (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; ns, not significant). HA – humic acid; MZ3, MiZax3; MZ5, MiZax5. HA – humic acid; MZ3, MiZax3; MZ5, MiZax5.
In this work, we evaluated MiZax (MiZax3 and MiZax5) at three foliar concentrations (5 µM and 10 µM in 2021 and 2.5 µM and 5 µM in 2022) and compared them with potato (Solanum tuberosum L). The commercial growth regulator humic acid (HA) was compared to strawberries (Fragaria ananassa) in strawberry greenhouse trials in 2021 and 2022 and in four field trials in the Kingdom of Saudi Arabia, a typical desert climate region. Although HA is a widely used biostimulant with many beneficial effects, including increasing soil nutrient utilization and promoting crop growth by regulating hormonal homeostasis, our results indicate that MiZax is superior to HA.
Potato tubers of the Diamond variety were purchased from Jabbar Nasser Al Bishi Trading Company, Jeddah, Saudi Arabia. Seedlings of two strawberry varieties “Sweet Charlie” and “Festival” and humic acid were purchased from Modern Agritech Company, Riyadh, Saudi Arabia. All plant material used in this work complies with the IUCN Policy Statement on Research Involving Endangered Species and the Convention on Trade in Endangered Species of Wild Fauna and Flora.
The experimental site is located in Hada Al-Sham, Saudi Arabia (21°48′3″N, 39°43′25″E). The soil is sandy loam, pH 7.8, EC 1.79 dcm-130. Soil properties are shown in Supplementary Table S1.
Strawberry (Fragaria x ananassa D. var. Festival) seedlings at 3 true leaf stages were divided into three groups to evaluate the effect of foliar spraying with 10 μM MiZax3 and MiZax5 on growth characteristics and flowering time under greenhouse conditions. Spraying leaves with water (containing 0.1% acetone) was used as a modeling treatment. MiZax foliar sprays were applied 7 times at one week intervals. Two independent experiments were conducted on September 15 and 28, 2021, respectively. The initial dose of each compound is 50 ml, then gradually increased to a final dose of 250 ml. For two consecutive weeks, the number of flowering plants was recorded every day and the flowering rate was calculated at the beginning of the fourth week. To determine growth traits, leaf number, plant fresh and dry weight, total leaf area, and number of stolons per plant were measured at the end of the growth phase and at the beginning of the reproductive phase. Leaf area was measured using a leaf area meter and fresh samples were dried in an oven at 100°C for 48 hours.
Two field trials were carried out: early and late plowing. Potato tubers of the “Diamant” variety are planted in November and February, with early and late ripening periods, respectively. Biostimulants (MiZax-3 and -5) are administered in concentrations of 5.0 and 10.0 µM (2021) and 2.5 and 5.0 µM (2022). Spray humic acid (HA) 1 g/l 8 times a week. Water or acetone was used as a negative control. The field test design is shown in (Supplementary Figure S1). A randomized complete block design (RCBD) with a plot area of 2.5 m × 3.0 m was used to conduct the field experiments. Each treatment was repeated three times as independent replicates. The distance between each plot is 1.0 m, and the distance between each block is 2.0 m. The distance between plants is 0.6 m, the distance between rows is 1 m. Potato plants were irrigated daily by drip at the rate of 3.4 l per every dropper. The system runs twice a day for 10 minutes each time to provide water to the plants. All recommended agrotechnical methods for growing potatoes under drought conditions were applied31. Four months after planting, plant height (cm), number of branches per plant, potato composition and yield, and tuber quality were measured using standard techniques.
Seedlings of two strawberry varieties (Sweet Charlie and Festival) were tested under field conditions. Biostimulants (MiZax-3 and -5) were used as leaf sprays at concentrations of 5.0 and 10.0 µM (2021) and 2.5 and 5.0 µM (2022) eight times a week. Use 1 g of HA per liter as a foliar spray in parallel with MiZax-3 and -5, with an H2O control mixture or acetone as a negative control. Strawberry seedlings were planted in a 2.5 x 3 m plot in early November with a plant spacing of 0.6 m and row spacing of 1 m. The experiment was carried out at RCBD and was repeated three times. Plants were watered for 10 minutes each day at 7:00 and 17:00 using a drip irrigation system containing drippers spaced 0.6 m apart and with a capacity of 3.4 L. Agrotechnical components and yield parameters were measured during the growing season. Fruit quality including TSS (%), vitamin C32, acidity and total phenolic content33 was assessed at the Laboratory of Postharvest Physiology and Technology of King Abdulaziz University.
Data are expressed as means and variations are expressed as standard deviations. Statistical significance was determined using one-way ANOVA (one-way ANOVA) or two-way ANOVA using Tukey’s multiple comparison test using a probability level of p < 0.05 or a two-tailed Student’s t test to detect significant differences (*p < 0.05, * *p < 0.01, ***p < 0.001, ****p < 0.0001). All statistical interpretations were performed using GraphPad Prism version 8.3.0. Associations were tested using principal component analysis (PCA), a multivariate statistical method, using the R package 34 .
In a previous report, we demonstrated the growth-promoting activity of MiZax at concentrations of 5 and 10 μM in horticultural plants and improved the chlorophyll indicator in the Soil Plant Assay (SPAD)27. Based on these results, we used the same concentrations to evaluate the effects of MiZax on potato, an important global food crop, in field trials in desert climates in 2021. In particular, we were interested in testing whether MiZax could increase the accumulation of starch, the end product of photosynthesis. Overall, the application of MiZax improved the growth of potato plants compared to humic acid (HA), resulting in an increase in plant height, biomass and number of branches (Fig. 1B). In addition, we observed that 5 μM MiZax3 and MiZax5 had a stronger effect on increasing plant height, number of branches, and plant biomass compared to 10 μM (Figure 1B). Along with improved growth, MiZax also increased yield, measured by the number and weight of tubers harvested. The overall beneficial effect was less pronounced when MiZax was administered at a concentration of 10 μM, suggesting that these compounds should be administered at concentrations below this (Figure 1B). In addition, we observed no differences in all recorded parameters between acetone (mock) and water (control) treatments, suggesting that the observed growth modulation effects were not caused by the solvent, which is consistent with our previous report27.
Since the potato growing season in Saudi Arabia consists of early and late maturation, we conducted a second field study in 2022 using low concentrations (2.5 and 5 µM) over two seasons to evaluate the seasonal impact of open fields (Supplementary Figure S2A) . As expected, both applications of 5 μM MiZax produced growth-promoting effects similar to those in the first trial: increased plant height, increased branching, higher biomass, and increased tuber number (Fig. 2; Supplementary Fig. S3). Importantly, we observed significant effects of these PGRs at a concentration of 2.5 μM, whereas GA treatment did not show the predicted effects. This result suggests that MiZax can be used even at lower concentrations than expected. In addition, MiZax application also increased the length and width of tubers (Supplementary Figure S2B). We also found a significant increase in tuber weight, but the 2.5 µM concentration was only applied in both planting seasons.
Plant phenotypic assessment of the impact of MiZax on early maturing potato plants in the KAU field, carried out in 2022. Data represent mean ± standard deviation. n≥15. Statistical analysis was performed using one-way analysis of variance (ANOVA) and Tukey’s post hoc test. Asterisks indicate statistically significant differences compared to simulation (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; ns, not significant). HA – humic acid; MZ3, MiZax3; MZ5, MiZax5. HA – humic acid; MZ3, MiZax3; MZ5, MiZax5.
To better understand the effects of treatment (T) and year (Y), two-way ANOVA was used to examine their interaction (T x Y). Although all biostimulants (T) significantly increased potato plant height and biomass, only MiZax3 and MiZax5 significantly increased tuber number and weight, indicating that the bidirectional responses of potato tubers to the two MiZax were essentially similar (Fig. 3)). In addition, at the beginning of the season the weather (https://www.timeanddate.com/weather/saudi-arabia/jeddah/climate) becomes hotter (average 28 °C and 52% humidity (2022), which significantly reduces the overall tuber biomass (Fig. 2; Supplementary Fig. S3).
Study the effects of 5 µm treatment (T), year (Y) and their interaction (T x Y) on potatoes. Data represent mean ± standard deviation. n ≥ 30. Statistical analysis was performed using two-way analysis of variance (ANOVA). Asterisks indicate statistically significant differences compared to simulation (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; ns, not significant). HA – humic acid; MZ3, MiZax3; MZ5, MiZax5.
However, Myzax treatment still tended to stimulate the growth of late maturing plants. Overall, our three independent experiments showed beyond doubt that the application of MiZax has a significant effect on plant structure by increasing the number of branches. In fact, there was a significant two-way interaction effect between (T) and (Y) on the number of branches after MiZax treatment (Fig. 3). This result is consistent with their activity as negative regulators of strigolactone (SL) biosynthesis26. In addition, we have previously shown that Zaxinone treatment causes starch accumulation in rice roots35, which may explain the increase in size and weight of potato tubers after MiZax treatment, since the tubers are mainly composed of starch.
Fruit crops are important economic plants. Strawberries are sensitive to abiotic stress conditions such as drought and high temperature. Therefore, we investigated the effect of MiZax on strawberries by spraying the leaves. We first provided MiZax at a concentration of 10 µM to evaluate its effect on strawberry growth (cultivar Festival). Interestingly, we observed that MiZax3 significantly increased the number of stolons, which corresponded to increased branching, while MiZax5 improved flowering rate, plant biomass, and leaf area under greenhouse conditions (Supplementary Figure S4), suggesting that these two compounds may vary biologically. Events 26,27. To further understand their effects on strawberries under real-life agricultural conditions, we conducted field trials applying 5 and 10 μM MiZax to strawberry plants (cv. Sweet Charlie) grown in semi-sandy soil in 2021 (fig. S5A). Compared to GC, we did not observe an increase in plant biomass, but found a trend towards an increase in the number of fruits (Fig. C6A-B). However, MiZax application resulted in a significant increase in single fruit weight and hinted at a concentration dependence (Supplementary Figure S5B; Supplementary Figure S6B), indicating the influence of these plant growth regulators on strawberry fruit quality when applied under desert conditions. influence.
To understand whether the growth promotion effect varies by cultivar type, we selected two commercial strawberry cultivars in Saudi Arabia (Sweet Charlie and Festival) and conducted two field studies in 2022 using low concentrations of MiZax (2.5 and 5 µM). For Sweet Charlie, although the total number of fruits did not increase significantly, the fruit biomass of plants treated with MiZax was generally higher, and the number of fruits per plot increased after the MiZax3 treatment (Fig. 4). These data further suggest that the biological activities of MiZax3 and MiZax5 may differ. In addition, after treatment with Myzax, we observed an increase in the fresh and dry weight of plants, as well as the length of plant shoots. Regarding the number of stolons and new plants, we found an increase only at 5 μM MiZax (Fig. 4), indicating that optimal MiZax coordination depends on the plant species.
The effect of MiZax on plant structure and strawberry yield (Sweet Charlie variety) from KAU fields, conducted in 2022. Data represent mean ± standard deviation. n ≥ 15, but the number of fruits per plot was calculated on average from 15 plants from three plots (n = 3). Statistical analysis was performed using one-way analysis of variance (ANOVA) and Tukey’s post hoc test or two-tailed Student’s t test. Asterisks indicate statistically significant differences compared to simulation (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; ns, not significant). HA – humic acid; MZ3, MiZax3; MZ5, MiZax5.
We also observed similar growth-stimulating activity in terms of fruit weight and plant biomass in strawberries of the Festival variety (Fig. 5), but did not find significant differences in the total number of fruits per plant or per plot (Fig. 5). . Interestingly, application of MiZax increased plant length and number of stolons, indicating that these plant growth regulators can be used to improve the growth of fruit crops (Fig. 5). Additionally, we measured several biochemical parameters to understand the fruit quality of the two cultivars collected from the field, but we did not obtain any differences between all treatments (Supplementary Figure S7; Supplementary Figure S8).
Effect of MiZax on plant structure and strawberry yield in the KAU field (Festival variety), 2022. Data are mean ± standard deviation. n ≥ 15, but the number of fruits per plot was calculated on average from 15 plants from three plots (n = 3). Statistical analysis was performed using one-way analysis of variance (ANOVA) and Tukey’s post hoc test or two-tailed Student’s t test. Asterisks indicate statistically significant differences compared to simulation (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; ns, not significant). HA – humic acid; MZ3, MiZax3; MZ5, MiZax5.
In our studies on strawberries, the biological activities of MiZax3 and MiZax5 turned out to be different. We first examined the effects of treatment (T) and year (Y) on the same cultivar (Sweet Charlie) using two-way ANOVA to determine their interaction (T x Y). Accordingly, HA had no effect on the strawberry cultivar (Sweet Charlie), whereas 5 μM MiZax3 and MiZax5 significantly increased plant and fruit biomass (Fig. 6), indicating that the two-way interactions of the two MiZax are very similar in promoting strawberry production.
Assess the effects of 5 µM treatment (T), year (Y) and their interaction (T x Y) on strawberries (cv. Sweet Charlie). Data represent mean ± standard deviation. n ≥ 30. Statistical analysis was performed using two-way analysis of variance (ANOVA). Asterisks indicate statistically significant differences compared to simulation (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; ns, not significant). HA – humic acid; MZ3, MiZax3; MZ5, MiZax5.
Additionally, given that MiZax activity on the two cultivars was slightly different (Fig. 4; Fig. 5), we performed a two-way ANOVA comparing treatment (T) and the two cultivars (C). First, no treatment affected fruit number per plot (Fig. 7), indicating no significant interaction between (T x C) and suggesting that neither MiZax nor HA contribute to total fruit number. In contrast, MiZax (but not HA) significantly increased plant weight, fruit weight, stolons and new plants (Fig. 7), indicating that MiZax3 and MiZax5 significantly promote the growth of different strawberry plant cultivars. Based on two-way ANOVA (T x Y) and (T x C), we can conclude that the growth-promoting activities of MiZax3 and MiZax5 under field conditions are very similar and consistent.
Evaluation of strawberry treatment with 5 µM (T), two varieties (C) and their interaction (T x C). Data represent mean ± standard deviation. n ≥ 30, but the number of fruits per plot was calculated on average from 15 plants from three plots (n = 6). Statistical analysis was performed using two-way analysis of variance (ANOVA). Asterisks indicate statistically significant differences compared to simulation (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; ns, not significant). HA – humic acid; MZ3, MiZax3; MZ5, MiZax5.
Finally, we used principal component analysis (PCA) to evaluate the effects of the applied compounds on potatoes (T x Y) and strawberries (T x C). These figures show that HA treatment is similar to acetone in potatoes or water in strawberries (Figure 8), indicating a relatively small positive effect on plant growth. Interestingly, the overall effects of MiZax3 and MiZax5 showed the same distribution in potato (Figure 8A), whereas the distribution of these two compounds in strawberry was different (Figure 8B). Although MiZax3 and MiZax5 showed a predominantly positive distribution in plant growth and yield, PCA analysis indicated that growth regulation activity may also depend on plant species.
Principal component analysis (PCA) of (A) potatoes (T x Y) and (B) strawberries (T x C). Score plots for both groups. A line connecting each component leads to the center of the cluster.
In summary, based on our five independent field studies on two valuable crops and consistent with our previous reports from 2020 to 202226, MiZax3 and MiZax5 are promising plant growth regulators that can improve plant growth of various crops. , including cereals, woody plants (date palms) and horticultural fruit crops26,27. Although the molecular mechanisms beyond their biological activities remain elusive, they have great potential for field applications. Best of all, compared to humic acid, MiZax is applied in much smaller quantities (micromolar or milligram level) and the positive effects are more pronounced. Therefore, we estimate the MiZax3 dosage per application (from low to high concentration): 3, 6 or 12 g/ha and the MiZx5 dosage: 4, 7 or 13 g/ha, making these PGRs useful for improving crop yields . Quite doable.
Post time: Mar-15-2024