Response to Selection for Drought Tolerance in Algerian Maize Populations for Spanish Conditions

Abstract

Drought is the main stress on maize, and, in order to improve drought tolerance, a breeding program for reduced anthesis-silking interval (ASI) was carried out in Algiers. The objective of this study was to investigate if the selection for reduced ASI made in Algiers had a positive effect on drought tolerance in northern Spain. Two populations selected for reduced ASI in Algiers were evaluated in Algiers and Pontevedra (northwestern Spain) under well-watered and drought conditions. The dry trial was not irrigated, while the well-watered trial was irrigated three times. Data were taken on agronomic and photosynthetic traits in the selection of reduced ASI and anthesis and increased yield for BTM and LOM. In the combined analyses of variance in locations, differences were significant among environments and among genotypes for most agronomic traits. Rank correlations between Algiers and Pontevedra were high and significant for flowering and correlations were higher when measured under the same water regime. In the Spanish environments, differences between the drought and well-watered selection and differences among genotypes within water regimens were significant for most agronomic traits. The agronomic performance of the selection cycles under drought and well-watered conditions indicated that selection for reducing ASI in Algiers was partially effective in Pontevedra. Photosynthetic traits did not respond to selection for ASI; nevertheless, stomatal conductance had positive effects and water use efficiency had a negative effect on plant height and yield. Therefore, base breeding populations after prebreeding in arid environments could be used for breeding programs in humid environments, and some physiological traits had limited effects on plant growth and yield.

1. Introduction

Maize (Zea mays L.) is one of the most important crops in the world because of its high productivity and adaptability [1] and is used for food, feed, or industrial products [2,3,4,5]. However, maize is susceptible to drought and heat [2,6,7,8]; actually, drought delays silking and increases the anthesis-silking interval (ASI) [9]. Maize grain yield in the temperate developed world is about 8.2 t/ha, compared to 3.5 t/ha in tropical developing countries. Drought and heat stress may cause yield losses of 15–20% per year in maize thorough the world [4,5,10], and the detrimental effects of drought are expected to worsen with climate change, particularly in developing countries [4,11,12,13]. Furthermore, the increasing demand for maize due to the growth of the world population requires selection of high yielding and drought-tolerant maize cultivars that can provide sustainable production of maize [3,14,15]. The main detrimental effect of drought is on yield, but drought damage affects all parts of the plant, since root development and stem elongation after flowering, causing shorter plants with reduced cumulative leaf area. The most important effect of drought occurs during flowering, when grain yield can be reduced two to three times more than at any other stage. Also, ear growth is reduced at this stage by decreasing grain number per ear, causing barren ears [2].

The selection of grain yield under stress is not efficient because of its low heritability and complex response to drought in the diverse phases of plant growth [4]. Conversely, using secondary traits in breeding programs is one of the best approaches for selecting stress-tolerant genotypes [16]. Bänziger et al. [9] proposed ASI, leaf senescence, and leaf rolling as secondary traits for selecting drought-tolerant genotypes, based on their high heritability and positive correlation with yield under stress conditions. Selection made under drought conditions have a favorable response under irrigated conditions, while selection under irrigated conditions may not show positive performance under drought stress [17]. Despite this, most breeding programs are made under non-stress conditions and are expected to increase performance under stress conditions [18].

The most efficient strategy for carrying out breeding programs is screening large collections of genetic resources to identify plant germplasms as potential sources of drought tolerance [19]. Current maize breeding focuses on stability across environments around the world but only use 5 to 10% of maize diversity because breeders focus on elite materials [20]. The limited use of genetic diversity is even more important in breeding for tolerance to biotic or abiotic stresses, as most of the collections of genetic resources have not been adequately evaluated.

Drought-tolerant germplasm from arid temperate areas has not been used in breeding programs. Maize accessions have been collected from the Algerian Saharan oases, where populations have been adapted to extreme conditions over several centuries [21]. A core collection of Saharan maize has been evaluated as potential source of drought tolerance because of its adaptation over several centuries to extreme conditions [22]. Algerian maize germplasm has a high phenotypic and genetic diversity [22] and are potential sources of favorable alleles for extreme conditions [23,24]. Algerian populations, such as BTM, TAO, and LOM were relatively stable under drought conditions, and IGS had short ASI [25]. However, Algerian maize populations have poor agronomic performance and need prebreeding to improve yield [21,25]. Four Algerian maize populations (BTM, TAO, LOM, and IGS) previously studied by Djemel et al. [25] were used to carry out three cycles of selection for ASI under both well-watered and drought conditions. Benchikh-Lehocine et al. [26] reported that selection for low ASI reduced ASI and days to flowering in BTM and IGS under drought conditions. Yield increased in BTM under well-watered conditions and in LOM under drought conditions. They proposed the use of those populations as sources of drought tolerance for temperate environments. Therefore, the objective of this study was to investigate if the selection for drought tolerance made in Algiers had a positive effect on drought tolerance in northern Spain.

2. Materials and Methods

2.1. Selection Program

Three cycles of selection for reduced ASI were carried out in four open-pollinated maize populations (BTM, TAO, IGS, and LOM) collected in Saharan oases, as previously described [25,26]. The Algerian populations were collected in four different provinces: BMT comes from Taghit (Bechar province, 30°55′00″ N 2°02′00″ W), TAO from Taourit (Bouïra, 36°23′00″ N 3°54′00″ E), IGS from Ain Salah (Tamanrasset, 27°11′42″ N 2°29′0″ E), and LOM from Ouled Mahmoude Lamtarfa (Adrar, 28°35′21″ N 0°8′59″ W). Selection was made under drought conditions by stopping irrigation two weeks before flowering. The selection criterion was reduced ASI with selection intensity of 20%. This program was made in Algiers (36°47′ N, 2°03′ E, altitude 32 m a.s.l.) with a silty-sandy soil type (36°47′ N, 2°03′ E, altitude 32 m a.s.l.). Algiers is a sub-humid region of the north of Algeria with 690 mm of annual rainfall. The driest months were April, May, June, and July, with an average of 35.06, 37.84, 2.54, and 0.78 mm of precipitation, respectively, in 2016, when this program was concluded.

2.2. Field Trials

The four Algerian populations and their cycles of selection were evaluated in Algiers along with the temperate check EPS5, which is a synthetic made with 16 American and European inbred lines, as described by Benchikh-Lehocine et al. [26]. The populations BTM and LOM had a significant increase in yield as an indirect response to selection for ASI [25,26]. Therefore, based on the results by Benchikh-Lehocine et al. [26], BTM and LOM were chosen for assessing the potential usefulness of the breeding program and the evaluation made in Algiers for northern Spain. The evaluation of the cycles of selection in Algiers was previously reported [26]. Subsequent evaluations were made in Pontevedra (northwestern Spain) by evaluating the populations BTM and LOM, along with their three cycles of selections and the Spanish check population EPS5 under well-watered conditions and under drought stress. Drought stress and well-watered experiments were sown in two adjacent blocks in the same field. The plots were laid out following a randomized complete block design with three replications. Each plot was an experimental unit consisting of one row with 25 hills separated 0.21 m apart with 0.80 m spacing between plots to give a final population density of approximately 60,000 plants ha⁻¹. Therefore, there were 18 plots or experimental units under well-irrigated conditions and 18 under drought conditions, and each plot consisted on 4.2 m², given a total of 75.6 m² + aisles per treatment. The field trials were sown on 27 May 2020 and harvested on 16 October. Maize trials were conducted at the experimental field of Misión Biológica de Galicia (CSIC) in Pontevedra, (northwest Spain) (42°24′, 8°38′ N, 20 m above sea level). The climate of Pontevedra is oceanic with a mean annual temperature of 15 °C (https://www.worldweatheronline.com/lang/es/pontevedra-weather-history/galicia/es.aspx, accessed 9 December 2024), and a mean annual precipitation above 1800 mm, July being the driest month and summer the driest season. Temperatures during summer are mild and episodes of severe drought were particularly intense in the summer of 2020. The recorded climatic values are within the range of typical values of this area, where unusual weather events are common during late spring (https://www.worldweatheronline.com/lang/es/pontevedra-weather-history/galicia/es.aspx). Previous crops were maize, and fertilization followed the recommendations of the respective agricultural services for each environment. The Spanish field was sandy loam with pH = 5.6, organic matter 5.6%, and P, K⁺, and Mg²⁺ 128, 220, and 60 mg kg^™1, respectively. The average soil at the experimental site before conducting the experiments was sandy loam, and its main physiochemical characteristics were pHH₂O = 5.5, 4.6% organic matter, 127 ppm available phosphorus and 202 ppm available potassium. The basal dressing was calculated according to optimum maize requirements and soil characteristics at a dose of 280 kg ha⁻¹ Fertitec (20% N, 10% P₂O₅, 5% K₂O), 49.6 kg ha⁻¹ Haifa MKP™ (52% P₂O₅, 34% K₂O) and 3055.4 kg ha−1 Lithothamne TimacAgro (36% CaO, 2.5% MgO). Top dressing fertilization with 409.76 kg ha⁻¹ of Nitramón (20.5% N) was applied when maize plants reached 80–100 cm, 63 days after sowing. The drought trial was not irrigated at all, while the well-watered trial was irrigated three times, after flowering, one month and two months later, with 60 L/m² each time.

2.3. Data Recorded

The following traits were recorded in all evaluation trials: early vigor at five weeks after planting following a scale from 1 (weak plants) to 9 (vigorous plants), days to anthesis (from planting to 50% plants shedding pollen), days to silking (from planting to 50% plants showing silks), plant height (average length in cm from the soil to the top of the tassel of 10 plants per plot), ears per plant, and grain yield (weight of grains per hectare at 140 g kg⁻¹ of grain moisture, expressed in Mg per hectare). ASI was calculated as the difference between days to silking and days to anthesis. As the plants reached the grain filling stage, net CO₂ assimilation (A_N), stomatal conductance (g_s), substomatal CO₂ concentration (C_i), and transpiration rate (E) were measured in fully developed adult leaves of at least three plants per experimental unit. Measurements were performed between 11:00 and 14:00 using a LI-6400XT Portable Photosynthesis System (Li-Cor Inc., Lincoln, NE, USA). Intrinsic water use efficiency (WUE) was calculated as the ratio of CO₂ assimilation to transpiration (WUE = A_N/E), the reference being [CO₂] 600 µmol mol⁻¹ and the PAR 1000 µmol s⁻¹. Finally, when senescence began, maximum quantum efficiency of photosystem II calculated from minimum fluorescence (F_o) and maximum fluorescence (F_m) as F_v/F_m, where F_v = F_m – F_o, recorded in the second leaf by using a portable OS-30p Chlorophyll Fluorometer (Opti-Sciences, Hudson, NY, USA) after at least 20 min dark treatment by covering the leaf tissue with forceps for at least 20 min.

2.4. Statistical Analyses

Combined Algerian and Spanish environments analyses of variance were performed by using SAS 9.4 [27]. The sources of variation were environments, treatments, genotypes, repetitions, the appropriate interactions, and the error term. The genotypes and treatments were considered as fixed effects, and the genotype × treatment interaction was also fixed, whereas environment, repetitions, and their interactions were considered as random factors. Subsequent analyses of variance were made for the trials carried out in Pontevedra, with combined and individual analyses for each environment. Means were compared by using Fisher’s protected LSD (p = 0.05).

In order to estimate genetic gain over selection cycles, data from each population and their respective cycles under both water treatments were subjected to regression analyses using the PROC REG procedure of SAS 9.4 [27]. Coefficients of regression of traits were obtained for each treatment selection condition combination. Spearman rank correlations were calculated between traits measured in Algiers and Pontevedra and under drought and well-watered conditions in order to figure out if agronomic performance in Algiers under each treatment was related to the same trait measured in another environment and location. Finally, multiple regression analyses were made in order to investigate if photosynthetic traits were involved in agronomic performance of these maize germplasms. Multiple regression analyses with the stepwise method were made for plant height and yield as dependent variables, and photosynthetic traits were recorded in Pontevedra as independent variables by using the PROC REG of SAS [27].

3. Results

In the combined analysis of variance across the three Algerian and Spanish environments, most sources of variation, including environments, treatments (well-watered and drought) and the genotype × environment interactions, were significant (p = 0.05) for all traits, namely early vigor, flowering time, plant height, ears per plant, and yield; though treatments were not significantly different for pollen shedding. The drought and well-watered conditions treatments were analyzed separately. Drought reduced early vigor, plant height, ears per plant and yield, and delayed silking date. The analyses combined over environments under drought conditions showed that all effects were significant for pollen shedding, silking, and plant height. Differences were significant among genotypes for ears per plant, and among environments and genotypes for yield. Under well-watered conditions, differences were significant among environments for early vigor; all effects were significant for pollen shedding, silking, plant height, and ears per plant; and environments and genotypes were significantly different for yield.

The relationships between traits measured in Algiers and in Pontevedra were assessed by using rank correlation analyses (

Table 1. Spearman (rank) correlations between agronomic traits from three mass selection cycles derived from two Algerian maize populations (BTM and LOM) under drought conditions evaluated under well-watered (W) and drought (D) at Algiers (A) and Pontevedra (P).

	MAW	MAD	MPW	MPD	FAW	FAD	FPW	FPD	AAW	AAD	APW	APD	PAW	PAD	PPW	PPD	YAW	YAD	YPW
MAD	0.85 **
MPW	0.86 **	0.90 **
MPD	0.73 *	0.98 **	0.83 *
FAW	0.99 **	0.83 *	0.83 *	0.71 *
FAD	0.92 **	0.97 **	0.95 **	0.91 **	0.90 **
FPW	0.86 **	0.90 **	1.00 **	0.83 *	0.83 *	0.95 **
FPD	0.85 **	1.00 **	0.90 **	0.98 **	0.83 *	0.97 **	0.90 **
AAW	−0.87 **	−0.78 *	−0.78 *	−0.66	−0.85 **	−0.79 *	−0.78 *	−0.78 *
AAD	0.86 **	0.60	0.67	0.48	0.83 *	0.74 *	0.67	0.60	−0.68
APW	−0.97 **	−0.77 *	−0.81 *	−0.63	−0.96 **	−0.84 **	−0.81 *	−0.77 *	0.94 **	−0.83 *
APD	0.89 **	0.69	0.76 *	0.57	0.86 **	0.81	0.76 *	0.69	−0.79 *	0.98 **	−0.87 **
PAW	−0.65	−0.31	−0.55	−0.14	−0.62	−0.51	−0.55	−0.31	0.56	−0.83 *	0.70	−0.81 *
PAD	−0.29	0.14	−.14	0.26	−0.31	−0.01	−0.14	0.14	0.18	−0.48	0.35	−0.38	0.60
PPW	−0.73 *	−0.55	−0.76 *	−0.40	−0.67	−0.67	−0.76 *	−0.54	0.79 *	−0.76 *	0.77 *	−0.85 **	0.81 *	0.38
PPD	−0.28	0.07	−0.21	0.17	−0.28	−0.08	−0.21	0.07	0.18	−0.48	0.34	−0.38	0.67	0.93 **	0.38
YAW	0.00	0.10	−0.24	0.19	0.05	−0.05	−0.23	0.10	−0.05	−0.07	0.02	−010	0.52	0.14	0.40	0.26
YAD	−0.52	−0.72 *	−0.65	−0.75 *	−0.54	−0.70	−0.65	−0.72 *	0.21	−0.25	0.35	−0.25	0.04	−0.17	0.04	−0.06	0.02
YPW	0.07	0.14	−0.17	0.24	0.12	0.01	−0.17	0.14	−0.07	0.05	−0.4	0.00	0.40	0.02	0.36	0.10	0.98 **	−0.04
YPD	0.46	−0.71 *	−0.64	−0.76 *	−0.48	−0.67	−0.64	−0.71 *	0.18	−0.17	0.29	−0.19	−0.05	−0.26	0.02	−0.17	0.05	0.99 **	0.00

*, ** Significant at p = 0.05 and 0.01, respectively; MAW: male flower Algiers water; MAD: male flower Algiers drought; MPW: male flower Pontevedra water; MPD: male flower Pontevedra drought; FAW: female flower Algiers water; FAD: female flower Algiers drought; FPW: female flower Pontevedra water; FPD: female flower Pontevedra drought; AAW: ASI Algiers water; AAD: ASI Algiers drought; APW: ASI Pontevedra water; APD: ASI Pontevedra drought; PAW: plant height Algiers water; PAD: plant height Algiers drought; PPW: plant height Pontevedra water; PPD: plant height Pontevedra drought; YAW: yield Algiers water; YAD: yield Algiers drought; YPW: yield Pontevedra water; YPD: yield Pontevedra drought.

). Rank correlations between male and female flowering recorded in Algiers and Pontevedra, under drought and well-watered conditions were always very high and significant (p = 0.05). Correlations were slightly higher when the traits were measured under the same treatment (drought or well-watered); therefore, days to male or female flowering were consistent in Algiers and Pontevedra. That consistency was higher when they were recorded under the same water regime. For ASI measured under drought or well-watered conditions in Algiers and Pontevedra, rank correlations were moderate to high and almost all of them were significant, except ASI measured in Algiers under drought and well-watered conditions. Furthermore, correlations were negative except for ASI measured under well-watered conditions in Algiers and Pontevedra, and for ASI measured under drought conditions in Algiers and Pontevedra. Correlations between ASI and male and female flowering were negative and significant when ASI was recorded under well-watered conditions, while they were negative and rarely significant when recorded under drought conditions. For plant height, correlations were high, positive and significant only when recorded under the same treatment in Pontevedra and Algiers; furthermore, flowering dates had significant negative correlations with plant height when recorded in Pontevedra under well-watered conditions. Correlation between yield recorded in Algiers and Pontevedra was highly positive and significant when recorded under well-watered or under drought conditions. Furthermore, the yield recorded under drought conditions in Algiers or Pontevedra showed moderate, negative, and significant correlations with male flowering under drought conditions in Algiers or Pontevedra, as well as with female flowering in Pontevedra; in the rest of the cases, the correlation was not significant.

In the analyses of variance for the Spanish environments, differences between drought and well-watered conditions were significant for female flowering, plant height, ears per plant, yield, quantum efficiency of photosystem II, stomatal conductance, substomatal CO₂ concentration, transpiration, and WUE, and the genotype × treatment interaction was significant for plant height and yield. Female flowering, quantum efficiency of photosystem II, and WUE were higher under drought than under well-watered conditions, while plant height, ears per plant, yield, stomatal conductance, substomatal CO₂ concentration, and transpiration were higher under well-watered conditions (

Table 2. Means ^a of agronomic traits from three mass selection cycles derived from two Algerian maize populations (BTM and LOM) under drought conditions evaluated under well-watered and drought conditions at Pontevedra.

Evaluated Under Well-Watered Conditions
Genotype b	Vigor (1–9)	Female Flower (Days)	Male Flower (Days)	Plant Height (cm)	Ears per Plant	Yield (Mg ha−1)
BTMC0	4.5	76.5	77.5	194.7	1.70	2.6
BTMC1	4.0	78.5	79.5	176.9	1.58	2.3
BTMC2	1.0	88.5	90.0	145.0	1.00	0.2
BTMC3	3.5	79.5	80.5	175.3	1.61	1.4
LOMC0	5.5	71.0	72.5	190.2	2.44	2.7
LOMC1	6.0	70.0	71.0	174.2	1.43	2.9
LOMC2	7.0	67.0	69.0	178.7	2.44	2.3
LOMC3	4.0	75.0	76.0	167.4	3.44	1.8
EPS5	6.5	65.0	67.0	198.7	1.09	4.4
LSD (0.05)	2.7	11.0	10.3	16.1	2.2	1.8
CV	23.6	5.4	5.9	3.6	49.1	32.2
Evaluated under drought conditions
BTMC0	3.5	82.5	88.5	112.8	1.05	1.1
BTMC1	3.5	88	93	88.3	0.85	0.6
BTMC2	3.5	78.5	84	109.3	0.90	1.0
BTMC3	2.5	84.5	88	93.7	1.34	0.6
LOMC0	5.0	72.5	77	124.7	1.00	1.6
LOMC1	4.0	73.5	80.5	93.6	0.87	0.7
LOMC2	4.5	71	74	112.9	1.19	1.4
LOMC3	4.0	68.5	71.5	103.7	0.87	1.1
EPS5	6.0	64.5	70.5	145.2	0.84	2.2
LSD (0.05)	1.6	10.8	10.6	28.2	0.80	0.8
CV	16.9	5.7	6.1	11.2	35.1	32.6

^a Means are significantly different (p = 0.05) if they differ according to Fisher’s protected least significant difference (LSD), that is, provided when differences among genotypes in the analysis of variance; ^b C0 is the original population (BTM or LOM), C1, C2, and C3 are the first, second, and third cycles of selection for reduced ASI, respectively.

and

Table 3. Means ^a of photosynthetic traits from three mass selection cycles derived from two Algerian maize populations (BTM and LOM) under drought conditions evaluated under well-watered and drought conditions at Pontevedra.

Evaluated Under Well-Watered Conditions
Genotype	Fo	Quantum Efficiency of Photosystem Fv/Fm	Net CO2 Assimilation (AN) (µmol CO2 m−2 s−1)	Stomatal Conductance (gS) (mol H2O m−2 s−1)	Substomatal [CO2] (Ci) (µmol mol−1)	Transpiration (E) (mmol H2O m−2 s−1)	WUE (mmol CO2/ mol H2O)
BTMC0	53.8	707	28.24	0.17	47.48	5.09	5.70
BTMC1	52.5	698	26.55	0.18	74.91	4.83	5.61
BTMC2	55.5	681	35.93	0.27	101.09	7.12	5.04
BTMC3	56.1	702	29.81	0.19	48.36	5.53	5.58
LOMC0	53.8	737	31.97	0.23	78.94	5.96	5.99
LOMC1	52.7	702	31.27	0.24	94.27	5.45	6.19
LOMC2	53.2	743	28.13	0.24	127.03	5.85	4.96
LOMC3	53.0	759	33.42	0.24	76.45	6.28	6.69
EPS5	53.3	687	35.44	0.23	60.01	5.68	6.61
CV	5.5	4.9	11.6	23.0	42.5	29.8	25.1
Evaluated under drought conditions
BTMC0	58.1	731	28.02	0.16	43.52	4.23	6.88
BTMC1	56.1	740	31.32	0.155		5.33	5.92
BTMC2	54.3	725	29.04	0.16	26.03	4.73	6.29
BTMC3	54.2	740	25.97	0.15	37.52	3.49	7.45
LOMC0	53.2	716	32.76	0.21	62.66	4.17	8.00
LOMC1	51.7	761	26.65	0.15	36.54	4.01	6.81
LOMC2	51.5	733	28.80	0.185	68.46	4.24	6.97
LOMC3	50.9	749	28.29	0.145	7.52	3.96	7.27
EPS5	53.7	761	28.51	0.18	71.59	3.67	7.90
CV	3.4	6.7	7.3	23.4	111.4	17.4	13.6

^a LSD values are not provided because genotypes were not significantly different at p = 0.05.

).

Differences among genotype were significant for early vigor, male and female flowering, plant height and yield, both under well-watered and drought conditions. The check EPS5 had the highest early vigor, along with the cycles 0, 1, and 2 of LOM and the cycle 0 of BTM (Table 2). The earliest flowering genotypes were the four cycles of LOM and EPS5, under well-watered and drought conditions. The genotypes with the tallest plants were EPS5, the cycle 0 of BTM and the cycles 0 and 2 of LOM under well-watered conditions, and EPS5, and the cycle 0 of LOM. Yield was highest for EPS5, the cycle 0 of BTM and the cycles 0 and 1 of LOM under well-watered conditions, while under drought conditions it was for EPS5 and cycles 0 and 2 of LOM. Therefore, the original populations (BTMC0 and LOMC0) had better agronomic performance than the cycles of selection for ASI under well-watered and drought conditions. The selection for reducing ASI in Algiers had significant effects on flowering time, particularly, days to silking was reduced under well-watered and drought conditions.

Regressions of ASI on the three cycles of selection from Algerian maize populations selected for reduced ASI under drought conditions in Algiers evaluated in Pontevedra were significant and negative for LOM under drought conditions with a high regression coefficient (R² = 0.9757, p = 0.012), while it was not significant for BTM (R² = 0.7978, p = 0.1068) (Figure 1). Therefore, the reduction in ASI made in Algiers was relatively consistent in Pontevedra. Conversely, the selection for reduced ASI under drought conditions in Algiers had no significant effect in Pontevedra under well-watered conditions. On the other hand, considering the other agronomic traits, selection for reduced ASI under drought conditions in Algiers caused a significant reduction only in male and female flowering in Pontevedra.

The genotypes were not significantly different for photosynthetic traits under well-watered or drought conditions (Table 3). Therefore, these results indicate that selection for reduced ASI under drought conditions in Algiers had no significant effects on photosynthetic traits in Pontevedra, under well-watered or drought conditions.

In order to investigate if photosynthetic traits were involved in agronomic performance of this maize germplasm, multiple regression analyses (following the stepwise method) were made for plant height and yield on the photosynthetic traits recorded in Pontevedra1. These were the resulting equations:

Plant height = 232.5 + 193.5 × Conductance − 18.4 WUE
(R² = 0.09 *, and 0.69 ** for Conductance and WUE, respectively, being *, ** significant at p = 0.05 and 0.01, respectively)
Yield = 20.59 − 0.196 × Fo + 0.017 × Conductance − 1.010 WUE
(R² = 0.06, 0.21 **, and 0.56 ** for Fo, Conductance and WUE, respectively)

Under drought conditions in Pontevedra, the significant effects followed these equations:

Plant height = 210.1 − 11.3 WUE (R² = 0.64 *)
Yield = 13.4 − 0.18 Fo (R² = 0.65 *)

Therefore, increase conductance had a positive effect on plant growth and yield, while higher WUE resulted in lower plant growth and yield. Furthermore, under drought conditions in Pontevedra, WUE and minimal fluorescence (Fo) had significant negative effects in yield and plant height and Fo in yield.

4. Discussion

Variability among genotypes was significant for most traits; therefore, there was important diversity for agronomic performance in these Algerian maize populations, as previously reported in precedent reports with this Algerian germplasm [21,25]. Genotype × treatment interactions were significant, and relative performance was not consistent among well-watered and drought environments, indicating that breeding Algerian maize populations for improved performance has to be carried out under the specific target environment, rather than carrying out a breeding program in one place for diverse environments. Similar results have also been reported by Bolaños and Edmeades [14]. These Algerian populations are potential sources of drought tolerance, confirming Algerian maize as a potential source of drought tolerance for maize breeding; however, these populations need to be selected to maximize their agronomic performance; similar conclusions have been previously published [21,25]. Selection for ASI reduced agronomic performance under drought conditions compared to well-watered conditions in Algerian maize, are in agreement with the results previously reported by Bolaños and Edmeades with tropical maize [28]. The timing of anthesis was less affected by drought than ASI because female flowering was delayed. The explanation is that the plants invest resources in pollen production rather than in grain development when water availability is limited for guaranteeing seed production, as previously reported by Edmeades et al. in tropical maize [29]. Silk elongation is strongly inhibited by plant water deficits, and this inhibition can lead to severe losses in grain yield [30].

The reduction in ASI in the breeding program made in Algiers showed consistent results in Pontevedra; in fact, selection for reduced ASI under drought conditions in Algiers evaluated in Pontevedra was significant and negative for LOM under drought conditions with a high regression coefficient, while it was not significant for BTM. Conversely, under well-watered conditions, selection for reduced ASI under drought conditions in Algiers had no significant effects in Pontevedra, as expected. Similarly, Benchikh-Lehocine et al. [26] reported that selection under drought conditions was more efficient than under well-watered conditions, which is consistent with previous publications, as Arboleda-Rivera and Compton [17] postulated that selection is more successful when performed under drought stress. Monneveux et al. [15] confirmed the effectiveness of recurrent selection under drought conditions as a means of improving tropical maize source populations for performance under drought stress. Selection reduced ASI under drought conditions but ASI increased under well-watered conditions in some cases. Indirect increase in yield was also found in some populations. Consequently, it was checked if selection for reducing ASI in arid environments of Algeria was efficient also in a humid environment in Pontevedra. Based on the current results, these improved Algerian populations can be considered as promising base populations for breeding programs focusing on improving drought tolerance in Spain; accordingly, Benchikh-Lehocine et al. [26] proposed these populations as base populations for breeding in other environments. The results in Algiers and Pontevedra were reasonably consistent, based on rank Spearman correlation, which were higher when measured under the same water regime. Generally, selection for reducing ASI in Algiers was moderately effective in Pontevedra, though there were no significant indirect effects in agronomic traits. The disagreement between the response in the original and the final environment could be explained because the selection environment should mirror the target environment, as stated by Ribaut et al. [31]. There was neither response to selection on photosynthetic traits; However, multiple regression showed that stomatal conductance had positive effects and water use efficiency had a negative effect on plant height and yield. The relationship between photosynthetic traits and drought are a matter of research nowadays because drought causes severe damage to photosystems and blocks the electron transport chain [32]. It also causes stomatal closure, which reduces the efficiency of the photosystem and, consequently, the photosynthetic rate. The complex interactions of diverse photosynthetic mechanisms under drought require additional research, which is essential for developing drought-resistant varieties and ensuring agricultural sustainability.

ASI was associated with silking date, which was affected by stress, in agreement with previous results showing that source and sink strengths are genetically linked in maize plants subjected to water deficit [7]. The response to selection for flowering date was usually effective in the current experiment, as previously shown in the literature [20]. The observed reduction in female flowering could be explained because early flowering is a mechanism to escape drought [25]. The effects of selection for reducing ASI in Algiers under arid conditions were relatively consistent in northwestern Spain. There were no effects on photosynthetic parameters, but conductance had positive effects and WUE negative effects on plant growth and yield. Therefore, Algerian maize from the Saharan Desert is a promising source of improved varieties with drought tolerance and a convenient material for searching genes for drought avoidance, as this material comes from extreme environments.

5. Conclusions

Selection for reducing ASI made in Algiers had a positive effect on drought tolerance in northern Spain. Therefore, base breeding populations after prebreeding in arid environments could be used for breeding programs in humid environments and stomatal conductance. WUE had limited effects on plant development and yield and water use efficiency and minimal fluorescence negatively affected plant height and yield, respectively.