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Drought Tolerance Screening of Maize Inbred Lines at an Early Growth Stage
Plant Breed. Biotech. 2019;7:326-339
Published online December 1, 2019
© 2019 Korean Society of Breeding Science.

Bishnu Adhikari, Kyu Jin Sa, Ju Kyong Lee*

Department of Applied Plant Sciences, College of Agriculture and Life Sciences, Kangwon National University, Chuncheon 24341, Korea
Corresponding author: Ju Kyong Lee, jukyonglee@kangwon.ac.kr, Tel: +82-33-250-6415, Fax: +82-33-259-5558
These authors contributed equally.
Received August 19, 2019; Revised September 11, 2019; Accepted September 25, 2019.
This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Drought is one of the major abiotic factors that have a serious effect on the production of cereals crops including maize, which is grown widely in the world. Screening based on drought facilitates selection of inbred lines and an understanding of drought-tolerant traits. The effect of drought stress and rescue after stress on maize inbred lines was investigated in this study. Different plant growth attributes namely plant height, leaf area and weight, stem weight, root length, shoot and root fresh and dry weight, and total leaf chlorophyll content were measured. Six flint inbred lines (FLD 12, FLD 23, FLD 24, FLD 33, FLD 35, and FLD 37) were screened as drought-tolerant lines, whereas another six flint inbred lines (FLD 01, FLD 13, FLD 16, FLD 18, FLD 29, and FLD 31) were screened as drought susceptible lines. Growth attributes under different drought conditions were subjected to a correlation test and analysis of variance and showed highly significant relationships with each other. The drought effect differed with different inbred lines, indicating a wide variability of drought response at the early growth stage of maize plants. The results obtained from this study will be useful for selecting maize inbred lines in future breeding programs for enhancing drought tolerance.
Keywords : Drought, Screening, Tolerant, Plant growth attributes, Maize inbred lines
INTRODUCTION

Maize is grown throughout the world, with large differences in yield and productivity. Maize has the highest global production among grains, followed by wheat and rice, while maize ranks second after wheat in terms of growing area (FAO 2017). World production, area harvested, and the yield of maize is 1134.8 million tons, 197.2 million ha, and 5.2 t/ha, respectively (FAOSTAT, http://www.fao.org/faostat/en/#compare). With the expansion of worldwide maize growing areas, global maize production has been increasing. Under well-irrigated conditions, commercial maize yields 6-9 ton/ha with approximately 10-13% moisture content (Krishna 2012). The water utilization efficiency of maize ranges from 0.8-1.6 kg/m3 (Tsur 2010). Maize is an abundant source of protein, total lipid, carbohydrate, dietary fibers, sugar, and different minerals (USDA, https://ndb.nal.usda.gov/ndb/foods/show/305217). Furthermore, it is a high energy density food (365 kcal/100 g) with a rich starch (72%) and fat (4%) content (Nuss and Tanumihardjo 2010). It is consumed normally as food and drink products of its original or chemically extracted form. The United States, China, and Brazil are the top three maize producing countries in the world and contribute three fourths of world maize production (Ranum et al. 2014).

Water requirement for field crops starts from seed sowing to the final grain development stage. At any crop growth stage, water deficiency could reduce crop growth and production (Hammad et al. 2011). Drought stress is a serious threat to agricultural production and increases at an alarming rate with rises of global temperatures (Tůmová et al. 2018). In low-income countries especially, drought is the most acute abiotic factor that limits crop production. Drought drastically hampers plant growth and affects yield through different mechanisms across the whole plant life cycle. In 2017, drought caused agricultural production losses of approximately 19% around the world, which amounted to more than 17 billion USD (FAOSTAT 2017). Drought stress on plant growth and development is not reflected directly and is revealed through different physiological processes. Under drought stress, a plant seeks to reduce the impact of the lack of water by reducing the transpiration rate and increasing the efficiency of water acquisition from the soil (Zhang et al. 2018). With the rise of global temperatures, maize growing areas become drier and warmer along with the development of a new array of diseases and pests (Edmeades 2013). Drought remains a major constraint in maize growing areas (Fahad et al. 2017); however, the degree of sensitivity to drought stress varies depending on growth stages, inbred lines, growing conditions, and agro-ecological zones (Toscano et al. 2019).

For creating new varieties of crops, morphological traits are mostly used for understanding and accessing for better production (Martínez et al. 2007). Some drought screening programs include productivity parameters; however, measurement of yield and production parameters may be difficult and time consuming. Drought tolerance screening would be more reliable if plant growth attributes related to water stress conditions were well identified (Silva et al. 2007). Screening can be accomplished using different means such as drought avoidance, drought desiccation, or a combination of both well-watered and water-stressed conditions followed by the recovery method. In greenhouse experiments, a wide range of physiological and morphological measurements can be carried out including leaf area development and root growth distribution (Passioura 2012). Plant vegetative and reproductive stages have many critical water requirement stages, which ultimately need sufficient water for sustaining growth and development. As water stress is one of the major abiotic stresses with a high level of impact and occurrence (Vibhuti et al. 2015), the use of drought-tolerant species and cultivars is one of the most reliable strategies for reducing water stress on crop plants (Tani et al. 2019). Drought-tolerant varieties will provide a highly cost-effective way for stabilizing crop yield and farmers’ incomes (Shiferaw et al. 2014). There is a need for further improvement in the level of adaptability against drought stress to combat the global issue of food security. Because of global climate change and the extension of maize growing areas into drought-affected areas, the development of maize tolerant varieties is of particular importance to poor and developing countries, which prefer plant breeding as an improvement practice rather than the huge application of agronomic inputs (Boomsma and Vyn 2008).

Being that drought is one of the major limiting factors in crop development, drought tolerance mechanisms need to be well understood (Farooq et al. 2009). Drought tolerance is complex and has quantitative traits that include different shoot and root morphological characters (Yadav and Sharma 2016). Under rain-fed conditions, drought tolerance screening is quite challenging because of environmental factors and the difficulty in determining the affected plant growth stages (Tuberosa 2012). There are no universal morphological traits that can be related to all the growth stages of the plant, and a better way would be to deal with specific traits (Passioura 2012). Drought screening on maize plants would provide insights for selecting inbred lines, which will eventually help in breeding programs for enhancing yield and productivity. Thus, the aim of the current study was to evaluate drought effects on maize inbred lines for identifying tolerant inbred lines by using morphological attributes.

MATERIALS AND METHODS

Plant materials

Thirty-eight maize inbred lines including two widely grown inbred lines of Korea were used for the study (Table 1). Seeds of the maize inbred lines were obtained from the Maize Research Institute, the Gangwondo Agricultural Research and Extension Services, Hongcheon, South Korea. Before sowing, seeds were soaked in water for 24 hours for uniform germination.

Experimental condition

Maize plants were sown in pots (9 cm × 9 cm) at normal greenhouse conditions of Kangwon National University in the beginning of August, 2018. Ten plants of each maize genotype were grown up to fourth leaf stages. Then the plants were grown in two different conditions as a control condition (well-watered condition) and drought-stressed condition following the procedure of Hao et al. (2009) with slight modifications. For the well-watered condition, plants were watered up to field capacity; whereas, in the drought-stressed condition, plants were subjected to restricted watering up to 15 days. After the completion of drought stress, the control and drought-stressed plants were harvested for the measurement of plant growth attributes. To obtain the nature of maize plants that was regained during the recovery stage, each inbred line was grown further for up to six days by watering to field capacity. We designed experiments with three conditions for each flint inbred lines: first is well-watered condition as a control, second and third are drought conditions. In the second condition, plants were treated with drought stress without re-watering to confirm their drought tolerance. Plants in the third condition were treated like those in the second condition, but were re-watered for 6 days after drought stress treatment to detect their recovery power against drought stress.

Measurement of plant growth attributes

Plant height (PH)

The height of maize inbred lines at drought and rescue conditions was measured using a measuring tape (KMT Korea Measuring tape, KMT Co., Seoul, Korea). Plant height was measured from the ground to the top axial part of the shoot.

Leaf and stem weight (LW and SW)

Leaf and stem fresh weight of both drought and rescue conditions were taken using a digital scale (Digital GSM scale, CAS Korea Co., Seoul, Korea).

Leaf area (LA)

Total leaf area of maize plants was measured using an area meter (LI-3100C area meter, LI-COR Inc., Nebraska, USA).

Shoot and root fresh weight (SFW and RFW)

Maize plants were gently uprooted from the pot and the soil particles adhering to the root were cleaned off with tap water. Shoot and root parts of the maize plants were separately weighed using a digital scale (Digital GSM scale, CAS Korea Co., Seoul, Korea).

Root length (RL)

Root length of both drought and rescue condition maize plants was measured carefully using an ordinary ruler.

Total chlorophyll content (TCC)

Chlorophyll content of maize plants of drought and rescue conditions was measured with an SPAD meter (SPAD 502, Minolta Co., Tokyo, Japan). The chlorophyll content was assessed from the top, middle, and bottom of a fully matured leaf.

Shoot and root dry weight (SDW and RDW)

The shoot and root parts of maize plant were oven-dried at 60℃ (VS-4150, Vision Scientific Co., Daejeon, Korea) for 48 hours following the procedure of Donnelly et al. (2018).

Statistical analysis

All data were subjected to analysis of variance (ANOVA) using SAS 9.4 (SAS Institute Inc. Cary, NC, USA). Results are expressed as mean ± SE (n = 5). Significant differences between the treatment means were determined by using Student’s t-test at 5% and 1% probability. Student’s t-test was used for estimation of the difference between the two water conditions for an identical genotype and between the inbred lines under an identical water condition. The correlation between the measured plant growth attributes was calculated using PROC CORR in SAS.

RESULTS

Plant height

Compared with the drought and rescue conditions, control plants had higher plant height than the treatment plants (Table 2, Supplementary Table S1). For the drought-stressed condition, maize inbred lines FLD33 (63.73 cm), FLD12 (57.98 cm), FLD24 (52.41 cm), FLD37 (49.68 cm), FLD35 (47.83 cm), and FLD23 (47.03 cm) showed no significant difference from their control lines. Also the rescue stage showed the same trend as the drought condition in which maize inbred lines that showed a significant difference under the drought conditions also showed a significant increase in plant height at the rescue stage. The maize inbred lines FLD01, FLD13, FLD16, FLD18, FLD29, and FLD31 had significantly lower plant height compared with the other inbred lines under drought condition. Some of these inbred lines could not regain well and showed significantly lower values even after rescuing (Table 2).

Leaf area

There was a significant difference in leaf area between control treatment and drought treatment for both drought and rescue conditions (Table 2, Supplementary Table S2). In drought conditions, FLD12 had the largest leaf area (59.15 cm2) followed by FLD33 (53.90 cm2), FLD24 (47.98 cm2), FLD37 (41.90 cm2), FLD35 (39.18 cm2), and FLD23 (37.25 cm2). Meanwhile, FLD33 showed a significant difference from the control. The inbred lines FLD01, FLD13, FLD16, FLD18, FLD29, and FLD31 showed significant differences from their controls. After rescue, these inbred lines showed significant differences except for FLD31 from the control (Table 2).

Leaf and stem weight

Inbred lines that showed no significant differences in leaf and stem weight under drought-stressed condition were FLD12 (1.89 g, 2.26 g respectively), FLD23 (1.30 g, 1.64 g), FLD24 (1.30 g, 1.66 g), FLD33 (1.95 g, 2.05 g), FLD35 (1.35 g, 1.84 g), and FLD37 (1.15 g, 1.12 g) (Table 3). Although the control plants had higher leaf and stem weight than that of the treatment plants, the inbred lines showing a high value for drought stress showed no significant differences from their controls (Supplementary Table S3, S4). The maize inbred lines FLD01, FLD13, FLD16, FLD18, FLD29, and FLD31 showed significant differences in leaf and stem weight in drought conditions compared with their respective controls (except FLD13 in leaf weight). Although drought stressed plants were re-watered after drought treatment, these susceptible inbred lines still showed significant difference in leaf and stem weight (except FLD13 in leaf weight).

Shoot and root fresh weight

Shoot and root fresh weight of maize inbred lines showed a significant decrease under the drought-stressed condition in comparison with the control treatment (Supplementary Table S5, S6). With drought stress imposed on the plants, maize inbred lines FLD12, FLD23, FLD24, FLD33, FLD35, and FLD 37 had better performances for shoot and root fresh weight compared with the other inbred lines (Table 4). Under the drought condition, the largest shoot and root fresh weights were found with FLD12 (4.15 g, 2.14 g, respectively), followed by FLD33 (4.00 g, 1.71 g) and FLD24 (2.96 g, 1.04 g). Meanwhile, FLD01 (2.05 g, 0.77 g), FLD13 (3.38 g, 1.18 g), FLD16 (3.62 g, 0.99 g), FLD18 (2.84 g, 0.35 g), FLD29 (1.33 g, 0.17 g), and FLD31 (2.04 g, 0 .47 g) showed no significant difference with their controls under the drought condition. The inbred lines that showed statistically significant differences in shoot and root fresh weight compared with their respective controls maintained significant differences even after the rescue effect.

Root length and total chlorophyll content

An extensive and deep root is one of the key morphological traits for plant growth and development. The root length of drought-stressed plants was notably decreased compared with control plants (Supplementary Table S7). Among the inbred lines under the drought condition, the longest root length was recorded on FLD33 (25.63 cm) followed by FLD12 (21.50 cm), FLD24 (18.38 cm), FLD37 (18.25 cm), and FLD35 (17.28 cm) (Table 5). The root length of maize genotype FLD29 (11.13 cm) was the shortest under the drought condition followed by FLD31 (14.38 cm), FLD18 (14.83 cm), FLD13 (17.75 cm), FLD16 (18.63 cm) and FLD01 (19.25 cm). Inbred lines showing poor development of root under the drought condition did not perform well in the rescue condition and showed the least growth and development (Table 5). The growing maize plants recorded different concentrations of chlorophyll in both drought and rescue stages (Supplementary Table S8). Under the drought condition, inbred lines FLD12, FLD23, and FLD24 showed significant difference in total chlorophyll content compared with their respective control lines (Table 5). Under the drought condition in susceptible lines, the four maize inbred lines FLD13, FLD16, FLD29, and FLD31 had significant differences in total chlorophyll content compared with their controls. Rescuing did not enhance the chlorophyll content of these inbred lines, and they contained significantly lower total chlorophyll content even after rescue. However, FLD16 showed no significant difference with the control.

Shoot and root dry weight

The shoot and root dry weight results showed differences between the control and drought-stressed plants under both the drought and rescue conditions (Supplementary Table S9, S10) with the control plants having higher shoot and root dry weight than the treatment plants. Under the drought condition, both shoot and root dry weight of the inbred lines FLD12 (0.60 g, 0.31 g respectively), FLD23 (0.43 g, 0.13 g), FLD24 (0.54 g, 0.14 g), FLD33 (0.59 g, 0.35 g), FLD35 (0.49 g, 0.14 g), and FLD37 (0.47 g, 0.19 g) showed no significant differences compared with their control lines (Table 6). The perfor mance of these inbred lines was the same after rescuing, and they had significantly higher shoot and root dry weight values. The inbred lines that showed significant differences in shoot and root dry weight were FLD01 (0.52 g, 0.27 g respectively), FLD13 (0.56 g, 0.23 g), FLD16 (0.53 g, 0.28 g), FLD18 (0.55 g, 0.14 g), FLD29 (0.26 g, 0.08 g), and FLD31 (0.50 g, 0.11 g) between control and drought-stressed plants. These inbred lines did not perform well even after the rescue condition and are listed as the worst performing inbred lines (Table 6).

Correlation and ANOVA study of plant growth attributes

Under four different drought conditions, plant height, leaf area, leaf and stem weight, shoot and root fresh weight, root length, and shoot and root dry weight were statistically significantly correlated at P < 0.05 and P < 0.01 with other plant growth attributes except for with total chlorophyll content under drought-stressed control conditions (Table 7). An ANOVA study showed that the effects of interaction of inbred lines and drought treatments on plant growth attributes were highly statistically significant (P < 0.01) for all plant growth attributes except plant height, which showed no statistically significant effect (Table 8).

DISCUSSION

Drought has a major effect on maize plant growth, development, and quality. For the past few decades drought tolerance phenotyping has been attracting much research (Passioura 2012). Under water-limited conditions, such unique phenotyping could enable the development of inbred lines for expressing valuable traits that are heritable and easily selectable (Rebetzke et al. 2013). In our study, the drought tolerance indices used were plant height, leaf area, stem and leaf weight, fresh shoot and root weight, total chlorophyll content, and shoot and root dry weight. Maize inbred lines with high values of drought-tolerant indices can be recognized as drought-tolerant inbred lines (Naghavi et al. 2013). Inbred lines FLD12, FLD23, FLD24, FLD33, FLD35, and FLD 37 did not show any significant differences from the control lines and were identified as drought-tolerant inbred lines because they had high drought tolerant indices. Meanwhile, FLD01, FLD13, FLD16, FLD18, FLD29, and FLD31 with low drought tolerant indices generally exhibited significant differences from their control lines and are considered as drought susceptible lines.

As a result of drought stress in the growing stages of the maize plant, the plant height of the control plants was significantly greater than that of the drought-stressed plants, although some drought-stressed plants were less affected and their plant height was similar to that of the control inbred lines. In this study, the best response in terms of plant height under the drought condition was achieved by FLD33, FLD12, and FLD 24, which exhibited relatively smaller declines in plant height (Table 2) compared with the control condition. With the imposition of drought stress, FLD29, FLD01, and FLD13 showed the greatest failure to achieve a decent plant height. Growth of all maize inbred lines decreased under drought stress conditions compared with the control values. However, the drought lines that were screened as tolerant did not have any significant differences compared with their controls. Maize inbred lines under the control and drought-stressed conditions continued to grow in the recovery stage, although growth of drought-stressed plants was significantly less than that of the control plants during the recovery stage. Only a few of the inbred lines were able to regain plant growth and development to a level near to that of the control value. Tolerant inbred lines showed a quick recovery following re-watering, which suggests that the plant reaction center of tolerant inbred lines could play an important regulatory role in preventing the plant from suffering damage (Efeoğlu et al. 2009).

Under different drought conditions, a definite relationship was found between the plant growth attributes because the correlation between the attributes was positive and highly significant (Table 7). Correlation analysis helps to reveal the interrelationship between plant growth attributes and enable recognition of attributes that could be used for selecting maize drought tolerant inbred lines at an early stage (Akinwale et al. 2018). In particular, taller varieties with higher shoot fresh weight was more produce green biomass than shorter varieties. Maize inbred lines showed large variations in shoot and root fresh and dry weight, and high shoot and root dry mass indicate an adaptation mechanism for enhancing shoot and root growth as well as maintaining osmotic pressure (Maiti et al. 1996).

In this study, fresh shoot and root weight in the well-watered condition were greatly higher than shoot and root dry weight in the well-watered condition. A higher weight of fresh shoot and root parts indicates a higher uptake of water during well-watered conditions, which finally evaporates after drying (Yaqoob et al. 2012). A deep and thick root is one of the most important traits for improving crop production under a drought regime because the root has extensive branching abilities for extracting water from deep soil (Kashiwagi et al. 2005; Yadav et al. 2010). Usually, longer roots are considered as the primary basis of tolerance in maize plant as a longer root helps in the uptake of available resources from the soil (Zhu et al. 2010). Reduction in the growth of the roots because of low water supply includes reduction in root characteristics, especially root length, root density, and root thickness. The overall trend of root length for all 38 inbred lines showed increases under the control condition, but there were decreases under the drought condition (Table 5, Supplementary Table S7). Similar results were obtained by Riaz et al. (2013a) in marigold where increasing drought stress decreased the root length. Water deficit for the maize plant reduces leaf area because the plants counter the drought stress by controlling foliage development and reducing the size of young leaves (Ghanbari et al. 2013). Leaves of drought-stressed plant become spindly and stunted to mitigate extreme transpiration. In maize early growth stages, water stress strongly limits the shape and size of the leaves (Cakir 2004).

Chlorophyll plays a key role in plant photosynthesis for energy absorption from light, and the entire leaf has different concentrations of chloroplast (Li et al. 2018). In the present study, total chlorophyll content of maize inbred lines decreased when they were faced with drought stress. Plant photosynthesis efficiency generally depends upon the chlorophyll content as chlorophyll pigments have a crucial role in the photochemical reaction (Sayyad-Amin et al. 2016). By damaging the photosynthetic organelles and chlorophyll components, drought stress severely obstructs the photosynthesis process in plants (Wang et al. 2018). Different studies suggest that the chlorophyll content of maize plants is markedly reduced under drought conditions (Efeoğlu et al. 2009; Homayoun et al. 2011; Khayatnezhad and Gholamin 2012).

The analysis of variance revealed that inbred lines and treatments were highly correlated with plant growth attributes. The interactions between inbred lines and treatments were also strongly correlated with each other (Table 8). The finding of notable variations among inbred lines with regard to growth attributes under the drought and rescue conditions provides good prospects for the selection of drought resistance inbred lines. Maiti et al. (1996) mentioned that assessing genotypic variability is one of the important factors for screening drought resistance maize cultivars.

The present study indicates a range of diversity among inbred lines of maize plants that could have practical use in breeding programs for improving maize cultivation. Characterization and screening of maize inbred lines with better tolerance traits is essential for the success of such a breeding program. Shoot and root dry weights are some of the primary selection criteria for screening drought-tolerant inbred lines to help in genetic improvement (Riaz et al. 2013b). For breeding programs for drought resistance, shoot and root mass under drought are important (Polania et al. 2017). Different drought studies have mentioned that shoot and root growth are repressed by drought, and the ratio of the shoot to the root is greatly reduced because shoot growth is more sensitive than root growth (Pace et al. 1999; Avramova et al. 2016; Widuri et al. 2018), and this study also confirmed similar results for relationship between shoot and root growth. Under drought stress, plants allocate fewer resources to shoot growth because resources are mostly used for water uptake and reducing the evaporation rate (Chimungu et al. 2014). In terms of root dry weight, the better-performing maize inbred lines FLD12, FLD23, FLD24, FLD33, FLD35, and FLD37 showed an effectiveness for water resource acquisition (Table 6). Although drought-stressed plants all produced considerably lower performances than the control plants, the better performing inbred lines may have developed some plant mechanisms to counter drought stress, which enabled them to recover well after the rescue treatment.

Supplementary Information

PBB-7-326_Supple.pdf

ACKNOWLEDGEMENTS

This study was supported by the Cooperative Research Program for Agriculture Science & Technology Develop ment (project no. PJ01315701 and PJ013157), Rural Development Administration, Republic of Korea.

Tables

List of maize inbred lines used for the study.

Entry No. Accession name Source
FLD01 00hf1 Eongdan14
FLD02 00hf11 P3525
FLD03 00hf17 N2BE/B73
FLD05 00hf25 Hwaseong 1
FLD06 00hf28 Pioneer synthetic
FLD07 00hf29 P3352
FLD08 00hf33 P3790
FLD09 00hf36 Eongdan14
FLD10 00hf41 P3352
FLD12 hc5 Ho-5
FLD13 hc2 NK487
FLD14 hc3 NK692
FLD15 hc4 8112
FLD16 hc6 Unknown
FLD17 NC300 Unknown
FLD18 HF1 Unknown
FLD19 HF2 Unknown
FLD20 CML177 Unknown
FLD21 B84 Unknown
FLD22 KS85 Unknown
FLD23 KS118 Unknown
FLD24 SIM6 Maysin collection
FLD25 EPM6 Unknown
FLD26 Oh43 Unknown
FLD27 Wf9 Unknown
FLD29 07S8004 IP144
FLD30 07S8009 IP152
FLD31 07S8011 1P161
FLD32 07S8016 00Pop A (Early)
FLD33 06S8001 ISU pop T-C 8644-27/ISU POP 5
FLD34 06S8008 9071/6B-6
FLD35 06S8013 ISU INB. 1368/(B87/B73-12)B#
FLD36 06S8019 8321-18/12B-2
FLD37 06S8030 EV43-SR/9B-5
FLD38 06S8042 IB89A-D14 1368/ISUINB 7B-1
FLD39 05S8011 96KPC midearly/early2
WAXY KW7 Korean waxy maize inbred line
DENT Mo17 U.S. Corn Belt inbred line

Plant height (cm) and leaf area (cm2) of maize inbred lines at drought and rescue conditions.

Trait Maize inbred lines Drought condition Rescue condition


Control treatment Drought treatment Control treatment Drought treatment
Plant height Tolerant
FLD12 64.33 ± 1.083 57.98 ± 1.025
FLD23 50.83 ± 0.598 47.03 ± 3.071
FLD24 56.00 ± 1.837 52.41 ± 0.675
FLD33 70.90 ± 1.522 63.73 ± 1.974
FLD35 56.75 ± 0.747 47.83 ± 2.347
FLD37 51.13 ± 1.179 49.68 ± 1.267
Susceptible
FLD01 53.25 ± 0.712 45.25 ± 0.753** 59.58 ± 1.080 50.13 ± 0.607**
FLD13 54.10 ± 0.919 48.30 ± 2.251 65.13 ± 0.726 59.33 ± 1.074
FLD16 58.50 ± 0.421 49.05 ± 0.499** 59.98 ± 0.809 56.13 ± 1.007
FLD18 62.10 ± 0.864 50.75 ± 1.043** 70.50 ± 2.339 54.40 ± 0.469*
FLD29 56.18 ± 0.708 40.48 ± 1.818** 58.80 ± 0.425 45.25 ± 0.781**
FLD31 66.33 ± 1.633 50.50 ± 2.464* 72.43 ± 2.561 64.60 ± 1.107

Trait Maize inbred lines Drought condition Rescue condition


Control treatment Drought treatment Control treatment Drought treatment

Leaf area Tolerant
FLD12 60.95 ± 3.064 59.15 ± 2.674
FLD23 37.53 ± 1.232 37.25 ± 1.878
FLD24 64.70 ± 2.479 47.98 ± 2.364
FLD33 70.90 ± 1.043 53.90 ± 2.230*
FLD35 42.69 ± 1.923 39.18 ± 0.870
FLD37 48.48 ± 0.795 41.90 ± 2.022
Susceptible
FLD01 68.05 ± 2.430 34.05 ± 0.602** 269.98 ± 14.448 93.08 ± 9.366**
FLD13 68.63 ± 4.705 41.83 ± 2.557* 247.73 ± 8.365 169.85 ± 6.661*
FLD16 57.00 ± 1.515 43.26 ± 1.315* 270.10 ± 14.944 193.15 ± 2.850*
FLD18 76.15 ± 3.936 43.80 ± 2.035* 279.68 ± 15.552 176.04 ± 4.534*
FLD29 49.46 ± 1.682 18.52 ± 1.020** 128.64 ± 10.698 56.01 ± 2.965*
FLD31 48.13 ± 1.086 38.00 ± 1.610* 172.60 ± 2.765 151.10 ± 8.357

Results are expressed as mean ± SE (n = 5).

*and**show the significant differences with the control treatments using Student’s t-test at the 0.05 and 0.01 probability levels, respectively.


Leaf and stem weight (g) of maize inbred lines at drought and rescue condition.

Trait Maize inbred lines Drought condition Rescue condition


Control treatment Drought treatment Control treatment Drought rescue treatment
Leaf weight Tolerant
FLD12 2.08 ± 0.152 1.89 ± 0.103
FLD23 1.73 ± 0.063 1.30 ± 0.123
FLD24 1.81 ± 0.121 1.30 ± 0.119
FLD33 2.19 ± 0.211 1.95 ± 0.115
FLD35 1.82 ± 0.147 1.35 ± 0.063
FLD37 1.22 ± 0.010 1.15 ± 0.017
Susceptible
FLD01 2.10 ± 0.069 0.86 ± 0.048** 6.51 ± 0.345 2.73 ± 0.259**
FLD13 2.28 ± 0.113 1.88 ± 0.177 6.03 ± 0.385 4.89 ± 0.287
FLD16 2.60 ± 0.058 1.68 ± 0.105** 7.01 ± 0.391 3.99 ± 0.269*
FLD18 3.24 ± 0.125 1.72 ± 0.096** 10.23 ± 0.498 2.13 ± 0.104**
FLD29 1.31 ± 0.044 0.54 ± 0.054** 2.76 ± 0.149 1.09 ± 0.119**
FLD31 2.02 ± 0.098 1.05 ± 0.067** 5.14 ± 0.191 3.53 ± 0.221*

Trait Maize inbred lines Drought condition Rescue condition


Control treatment Drought treatment Control treatment Drought rescue treatment

Stem weight Tolerant
FLD12 2.97 ± 0.153 2.26 ± 0.208
FLD23 1.79 ± 0.151 1.64 ± 0.060
FLD24 2.26 ± 0.160 1.66 ± 0.113
FLD33 2.14 ± 0.145 2.05 ± 0.096
FLD35 2.74 ± 0.120 1.84 ± 0.076*
FLD37 1.23 ± 0.106 1.12 ± 0.070
Susceptible
FLD01 3.78 ± 0.194 1.19 ± 0.088** 13.75 ± 0.231 3.49 ± 0.238**
FLD13 3.08 ± 0.238 1.49 ± 0.114* 9.21 ± 0.374 6.46 ± 0.203*
FLD16 3.19 ± 0.161 1.94 ± 0.165* 7.77 ± 0.352 4.98 ± 0.340*
FLD18 4.66 ± 0.255 1.12 ± 0.053** 15.13 ± 0.557 2.36 ± 0.255**
FLD29 1.28 ± 0.048 0.80 ± 0.040** 3.32 ± 0.201 1.60 ± 0.123**
FLD31 1.48 ± 0.041 0.99 ± 0.075* 8.60 ± 0.266 6.62 ± 0.156*

Results are expressed as mean ± SE (n = 5).

* and ** show the significant differences with the control treatments using Student’s t-test at the 0.05 and 0.01 probability levels, respectively.


Shoot and root fresh weight (g) of maize inbred lines at drought and rescue conditions.

Trait Maize inbred lines Drought condition Rescue condition
Control treatment Drought treatment Control treatment Drought rescue treatment
Shoot fresh weight Tolerant
FLD12 5.05 ± 0.208 4.15 ± 0.266
FLD23 3.51 ± 0.176 2.94 ± 0.080
FLD24 4.07 ± 0.264 2.96 ± 0.092
FLD33 4.34 ± 0.104 4.00 ± 0.167
FLD35 4.57 ± 0.265 3.19 ± 0.137
FLD37 2.45 ± 0.190 2.27 ± 0.061
Susceptible
FLD01 5.88 ± 1.052 2.05 ± 0.121** 20.27 ± 0.280 6.22 ± 0.381**
FLD13 5.35 ± 0.271 3.38 ± 0.155* 15.24 ± 0.757 11.35 ± 0.489*
FLD16 5.78 ± 0.211 3.62 ± 0.256* 14.78 ± 0.663 8.97 ± 0.608*
FLD18 7.90 ± 0.378 2.84 ± 0.052** 25.36 ± 1.042 4.49 ± 0.359**
FLD29 2.59 ± 0.080 1.33 ± 0.096** 6.08 ± 0.343 2.60 ± 0.240**
FLD31 3.50 ± 0.139 2.04 ± 0.139* 13.74 ± 0.452 10.15 ± 0.252*

Trait Maize inbred lines Drought condition Rescue condition


Control treatment Drought treatment Control treatment Drought rescue treatment

Root fresh weight Tolerant
FLD12 2.83 ± 0.070 2.14 ± 0.134
FLD23 0.60 ± 0.023 0.35 ± 0.035
FLD24 1.54 ± 0.133 1.04 ± 0.060
FLD33 2.10 ± 0.104 1.71 ± 0.042
FLD35 0.68 ± 0.084 0.40 ± 0.027
FLD37 0.83 ± 0.160 0.42 ± 0.018
Susceptible
FLD01 2.88 ± 0.118 0.77 ± 0.091** 4.77 ± 0.226 1.11 ± 0.117**
FLD13 1.81 ± 0.103 1.18 ± 0.016* 4.35 ± 0.255 2.66 ± 0.185*
FLD16 2.09 ± 0.145 0.99 ± 0.033* 4.18 ± 0.192 2.28 ± 0.223*
FLD18 1.99 ± 0.049 0.35 ± 0.038** 3.46 ± 0.239 1.06 ± 0.068**
FLD29 0.32 ± 0.020 0.17 ± 0.016* 1.31 ± 0.089 0.68 ± 0.033*
FLD31 0.95 ± 0.042 0.47 ± 0.034** 2.47 ± 0.149 0.94 ± 0.118**

Results are expressed as mean ± SE (n = 5).

* and ** show the significant differences with the control treatments using Student’s t-test at the 0.05 and 0.01 probability levels, respectively.


Root length (cm) and total chlorophyll content of maize inbred lines at drought and rescue conditions.

Trait Maize inbred lines Drought condition Rescue condition


Control treatment Drought treatment Control treatment Drought rescue treatment
Root length Tolerant
FLD12 27.13 ± 1.888 21.50 ± 1.510
FLD23 18.00 ± 0.669 16.40 ± 3.238
FLD24 19.75 ± 1.120 18.38 ± 0.640
FLD33 31.38 ± 1.505 25.63 ± 1.320
FLD35 17.93 ± 0.487 17.28 ± 0.674
FLD37 19.13 ± 1.038 18.25 ± 1.033
Susceptible
FLD01 21.88 ± 1.218 19.25 ± 0.554 35.30 ± 1.454 29.25 ± 1.675
FLD13 34.67 ± 1.663 17.75 ± 1.068** 43.26 ± 2.236 28.75 ± 1.625*
FLD16 20.00 ± 0.479 18.63 ± 1.239 33.18 ± 1.697 27.25 ± 0.747
FLD18 18.65 ± 1.586 14.83 ± 0.624 24.37 ± 1.161 18.95 ± 0.427
FLD29 18.50 ± 0.323 11.13 ± 0.461** 29.86 ± 1.285 16.85 ± 0.495**
FLD31 22.50 ± 1.051 14.38 ± 0.425* 30.20 ± 0.508 22.10 ± 1.073*

Trait Maize inbred lines Drought condition Rescue condition


Control treatment Drought treatment Control treatment Drought rescue treatment

Total chlorophyll content Tolerant
FLD12 33.35 ± 0.462 26.39 ± 0.230*
FLD23 26.58 ± 0.525 18.33 ± 0.607*
FLD24 26.68 ± 0.628 18.08 ± 1.449*
FLD33 31.50 ± 1.283 27.80 ± 1.389
FLD35 22.84 ± 0.831 17.78 ± 1.242
FLD37 25.75 ± 1.070 22.23 ± 1.054
Susceptible
FLD01 24.88 ± 0.793 22.31 ± 0.781 29.93 ± 0.595 25.06 ± 0.798
FLD13 23.02 ± 0.934 16.56 ± 0.449* 25.26 ± 0.336 20.18 ± 0.596*
FLD16 25.43 ± 0.162 19.36 ± 0.500* 29.43 ± 1.028 23.86 ± 0.941
FLD18 27.62 ± 0.808 23.62 ± 1.071 31.82 ± 1.236 27.16 ± 1.196
FLD29 22.95 ± 0.757 15.28 ± 0.604** 27.08 ± 0.612 19.13 ± 0.523**
FLD31 26.40 ± 0.599 21.99 ± 0.303* 28.27 ± 0.530 23.52 ± 0.668*

Results are expressed as mean ± SE (n = 5).

* and ** show the significant differences with the control treatments using Student’s t-test at the 0.05 and 0.01 probability levels, respectively.


Shoot and root dry weight (g) of maize inbred lines at drought and rescue conditions.

Trait Maize inbred lines Drought condition Rescue condition


Control treatment Drought treatment Control treatment Drought rescue treatment
Shoot dry weight Tolerant
FLD12 0.76 ± 0.031 0.60 ± 0.041
FLD23 0.59 ± 0.036 0.43 ± 0.050
FLD24 0.75 ± 0.089 0.54 ± 0.031
FLD33 0.61 ± 0.049 0.59 ± 0.025
FLD35 0.62 ± 0.020 0.49 ± 0.028
FLD37 0.54 ± 0.040 0.47 ± 0.046
Susceptible
FLD01 1.22 ± 0.144 0.52 ± 0.027** 2.46 ± 0.045 0.84 ± 0.039**
FLD13 1.09 ± 0.077 0.56 ± 0.060* 1.76 ± 0.124 0.89 ± 0.065*
FLD16 1.10 ± 0.066 0.53 ± 0.039* 1.48 ± 0.050 1.02 ± 0.041*
FLD18 1.38 ± 0.041 0.55 ± 0.054** 2.10 ± 0.138 0.74 ± 0.011**
FLD29 0.47 ± 0.014 0.26 ± 0.010** 0.57 ± 0.012 0.30 ± 0.031**
FLD31 0.91 ± 0.013 0.50 ± 0.052** 1.04 ± 0.042 0.65 ± 0.066*

Trait Maize inbred lines Drought condition Rescue condition


Control treatment Drought treatment Control treatment Drought rescue treatment

Root dry weight Tolerant
FLD12 0.32 ± 0.013 0.31 ± 0.030
FLD23 0.14 ± 0.004 0.13 ± 0.006
FLD24 0.18 ± 0.024 0.14 ± 0.003
FLD33 0.43 ± 0.047 0.35 ± 0.011
FLD35 0.20 ± 0.020 0.14 ± 0.006
FLD37 0.22 ± 0.007 0.19 ± 0.004
Susceptible
FLD01 0.54 ± 0.074 0.27 ± 0.014** 0.99 ± 0.039 0.39 ± 0.014**
FLD13 0.45 ± 0.028 0.23 ± 0.011** 0.71 ± 0.041 0.35 ± 0.028*
FLD16 0.43 ± 0.047 0.28 ± 0.009 0.46 ± 0.011 0.35 ± 0.020
FLD18 0.26 ± 0.020 0.14 ± 0.004* 0.71 ± 0.054 0.28 ± 0.023*
FLD29 0.14 ± 0.004 0.08 ± 0.006** 0.33 ± 0.013 0.13 ± 0.008**
FLD31 0.21 ± 0.006 0.11 ± 0.014* 0.36 ± 0.019 0.20 ± 0.010*

Results are expressed as mean ± SE (n = 5).

* and ** show the significant differences with the control treatments using Student’s t-test at the 0.05 and 0.01 probability levels, respectively.


Correlation among plant growth attributes of 38 maize inbred lines on different growing conditions.

a) Drought condition control plants (above diagonal) and drought condition stressed plant (below diagonal).
PH LA LW SW SFW RFW RL TCC SDW RDW
PH 1 0.372** 0.422** 0.347** 0.408** 0.420** 0.350** 0.289** 0.363** 0.289**
LA 0.540** 1 0.545** 0.556** 0.601** 0.509** 0.327** 0.05 0.469** 0.346**
LW 0.481** 0.587** 1 0.673** 0.866** 0.493** 0.281** 0.158 0.510** 0.247**
SW 0.489** 0.601** 0.500** 1 0.953** 0.530** 0.252** 0.169* 0.531** 0.357**
SFW 0.560** 0.686** 0.863** 0.869** 1 0.561** 0.286** 0.179* 0.568** 0.343**
RFW 0.521** 0.626** 0.617** 0.588** 0.695** 1 0.501 0.278** 0.499** 0.617**
RL 0.427** 0.462** 0.556** 0.413** 0.559** 0.545** 1 0.271** 0.362** 0.420**
TCC 0.467* 0.446** 0.432** 0.394** 0.477** 0.491** 0.429** 1 0.126 0.243**
SDW 0.420** 0.516** 0.385** 0.370** 0.436** 0.433** 0.326** 0.374** 1 0.379**
RDW 0.422** 0.464** 0.551** 0.458** 0.581** 0.607** 0.472** 0.452** 0.398** 1

* and ** show the significant differences at the 0.05 and 0.01 probability levels, respectively.

b) Rescue condition control plants (above diagonal) and rescue condition stressed plant (below diagonal).
PH LA LW SW SFW RFW RL TCC SDW RDW

PH 1 0.435** 0.437** 0.391** 0.423** 0.445** 0.245** 0.305** 0.372** 0.270**
LA 0.486** 1 0.839** 0.798** 0.844** 0.739** 0.352** 0.163* 0.641** 0.461**
LW 0.563** 0.664** 1 0.857** 0.946** 0.649** 0.308** 0.250** 0.643** 0.419**
SW 0.543** 0.646** 0.830** 1 0.978** 0.584** 0.268** 0.182* 0.756** 0.474**
SFW 0.580** 0.679** 0.924** 0.959** 1 0.632** 0.294** 0.217** 0.739** 0.468**
RFW 0.469** 0.488** 0.653** 0.680** 0.677** 1 0.421** 0.370** 0.523** 0.549**
RL 0.384** 0.421** 0.447** 0.528** 0.497** 0.530** 1 0.176* 0.343** 0.430**
TCC 0.344** 0.398** 0.367** 0.405** 0.412** 0.329** 0.442** 1 0.207* 0.241**
SDW 0.502** 0.554** 0.592** 0.674** 0.661** 0.494** 0.382** 0.329** 1 0.545**
RDW 0.418** 0.384** 0.475** 0.539** 0.529** 0.571** 0.458** 0.474** 0.479** 1

* and ** show the significant differences at the 0.05 and 0.01 probability levels, respectively.

Analysis of variance (ANOVA) of plant growth attributes in 38 maize inbred lines.

Source of
variability
DF F-value

PH LA LW SW SFW RFW RL TCC SDW RDW
Inbred lines 37 21.55** 20.32** 24.35** 36.75** 37.93** 54.36** 16.60** 12.73** 17.45** 29.11**
Treatment 3 147.42** 988.80** 707.47** 1162.94** 1201.34** 434.03** 267.94** 271.97** 229.36** 236.25**
Inbred lines × Treatment 111 1.210 6.78** 6.33** 12.75** 11.29** 4.96** 1.74** 1.03 3.69** 3.92**
Error 456 MS: 313.82 MS: 20760.43 MS: 14.00 MS: 31.61 MS: 85.42 MS: 7.33 MS: 220.32 MS: 94.91 MS: 0.63 MS: 0.14
Corrected total 607

**shows the significant differences at the 0.01 probability level.

DF: degree of freedom, MS: mean square.


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