Experimentation Site

Experiments were carried out during three consecutive cropping seasons (2012/2013 to 2014/2015) on the experimental site at the Cropping Research Station of the Technical Institute of Field Crops (TIFC) located 4 km to the South-West of Sétif (1081 m a.s.l., 05°21′N, 36°05′E), in the highlands of northeastern Algeria.

Plant Material

The Durum wheat plant material comprised three crosses (Ofanto/MBB, Ofanto/Mrb5, Ofanto/Waha) representing all the late generations (F5, F6, F7). These crosses were cultivated at the Cropping Research Station mentioned above. Durum wheat varieties Ofanto, MBB, Mrb5, and Waha, representing the crossed parents were taken as plant material and the Bousselam variety as a control. Among these varieties were landraces, including those introduced by the International Center for Agricultural Research for Dry Areas (ICARDA) in Syria as part of the cooperation with the TIFC in Algeria.

Measurements

Measurements were made on all lines (parents and individuals of generations) during the heading stage, as follows:

(1)

(2)

(3)

(4)

Statistical Data Analysis

The gain was calculated relative to the mean of the parents (Gain/XPar), which is the difference between the mean of the selected part (µ’) and the mean of the parents (µPar), as shown by ^{Mather and Jinks’s (1982)} Equation (5):

(5)

The response to selection (Rs) representing the difference between the mean of selected lines (µ’) and the mean of the population (µ_population) was calculated using ^{Al-Aswd et al.’s (2014)} Equation (6):

(6)

Statistical analyses were performed by ^{CropStat.7.2.3. (2009)} software and the mean of variables were compared relative to the least significant difference (LSD) at the 1% level.

The late selection was applied to the F5 generation. The direct and linked response and relationships were investigated on subsequent F6 and F7 generations using the previously presented graphical and descriptive statistical estimates to isolate resistant lines adapted to drought conditions, according to the study on late generations of barley reported by ^{Benmahammed (2005)} and ^{Benmahammed et al. (2010)}. They found that late generations are more stable for phenomorpho-physiological traits, which allowed the breeder to isolate performing lines derived from cross parents.

Sixth-generation (F₆) and Seventh-generation (F₇) Response to late Selection of the Fifth-generation (F₅)

Analysis of variance in cultured parents between the F₆ and F₇ generations shows significant differences between parents for all traits studied; these results perfectly agree with the studies conducted by ^{Fellahi et al. (2020)} and ^{Zeeshan et al. (2014)}. It suggests the efficiency of late selection due to the diversity of the genetic base among individuals of the cultivated generations (table 1).

F₆ Generation Individuals’ Response to Direct and Indirect Late Selection

It is crucial to monitor and understand the behavior of late generations in plant breeding programs to isolate desirable traits, especially in semi-arid regions with strong climatic fluctuations from one cropping season to another (^{Adjabi et al., 2014}; ^{Benmahammed, 2005}). The response of Durum wheat genotypes of the F₆ generation selected by direct late selection in F₅ for grain yield was above the population average, where a significantly significant increase in grain and economic yield was observed at 49.4 and 58.9 g/linear m, respectively, and compared to the parent average. The response was also positive, with an increase of 44.0 and 66.4 g/m linear (table 2). Direct selection based on grain yield resulted in a significant increase in NS (10 spikes/linear m).

Table 1. The mean squares of ANOVA on the traits measured in the parents cultivated in the F₆ and F₇ generations 

^**Significant effect at the 1% level

CT: Canopy temperature (°C), Gr.YLD: Grain yield (g/linear m), Ec.YLD: Economic yield (straw) (g/linear m), RWC: Relative water content (%), LA: Leaf area (cm²), PREC: Precocity in calendar days, DSI: Drought susceptibility index (%), PH: Plant height (cm), NS: Number of spikes per linear meter.

Source: Elaborated by the authors

These results indicate a positive correlation between these three traits and that it is possible to select one of them. This conclusion confirms the results in the previously recorded response and the selection based on economic yield and NS, both of which affected a significant increase in grain and economic yield of the lines selected in F₅ (table 2, figure 1). Among these three traits, we find that NS/linear m was the most influential in the increase in grain yield, with a difference of +16.9 g/ linear m compared to grain yield itself. When combining them with other traits, we find that they are non-correlated with any trait, especially resistance traits, except for the 11.4 cm PH increase for the selection based on economical yield (table 2).

These results corroborate those of ^{Laala et al. (2009)}. They found that grain yield, biomass, and NS applied in the breeding process to improve the grain yield of Durum wheat give better results than others, such as Ph and the earliness of spikes.

The response of the selected lines did not achieve the desired increase in grain and economic yield compared to resistance-related traits (CT, RWC, PREC, LA) (figure 1), but rather a regression, particularly in the lines selected for the LA where the decrease was significant (-33.6 g/linear m) (Table 2) due to the lack of correlations with the generations of these traits for grain and economic yield. The correlation coefficient between the two generations F6/F5 was estimated for grain yield with CT (r = -0.036), RWC (r = -0.095), PREC at the heading stage (r = -0.006), and LA (r = -0.222) (Table 3). This is consistent with ^{Adjabi et al. (2014)}, who indicated no inter-population correlation in Durum wheat cultivars due to the influence of environmental factors in semi-arid regions.

Table 2. The performance response of F₆ lines selected from F₅ directly and indirectly for the traits measured 

RS: Response to the selection, µPar: Mean of parents, µ’: Mean of the lines selected, Gain/XPar: Gain compared to average parents, CT: Canopy temperature (°C), Gr.YLD: Grain yield (g/ linear m, Ec.YLD: Economic yield (straw) (g/ linear m), RWC: Relative water content (%), LA: Leaf area (cm²), PREC: Earliness (precocity) at the heading stage in calendar days, DSI: Drought susceptibility index to stress (%), PH: Plant height (cm), NS: Number of spikes per linear meter.

Source: Elaborated by the authors

Source: Elaborated by the authors.

Figure 1. The response of F6 generations to Gr.YLD and Ec.YLD under direct and indirect selection of the selected part (i) of the F5 generation (i = 30% = five lines per group). 

The effect of grain and economic yields on DSI was positive, with a respective increase of 21.7 and 32.7 g/linear m (table 2). This increase is accompanied by an increase in PH of 11.3 cm and NS of 16.8. The response of the selected lines to DSI at the F₅ generation was positive only at the F6 generation. The significant contradiction of DSI by -10.9% confirms the negative correlation for these two traits (PH, NS) between F6 and F5 (r = -0.242) (table 3). Figure 2 shows that the response of the traced lines of the F6 generation selected from the F₅ generation could not maintain their superiority of CT, as shown by the correlation coefficient between F6/F5, which appears very low (r = -0.037) (table 4). This result may be due to the effect of the semi- arid environment, corroborating ^{Bouzerzour and Benmahammed’s (2009)} findings. They discovered that the environment of semi-arid regions affects the adaptation and production of cultivars, mainly physiological functions such as CT control.

Source: Elaborated by the authors.

Figure 2. Response of the F6 generation to canopy temperature (CT), under direct and indirect selection (i) of the F5 generation (I = 30% = five lines per group). 

Table 3. The phenotypic correlations between measured traits and grain yield in generations F₅, F₆, and F₇ 

n-2 = 43, r5% = 0.2942

Source: Elaborated by the authors.

Table 4. The phenotypic correlations for each measured trait in generations F₅ F₆ and F₇ 

Source: Elaborated by the authors.

F₇ generation individuals’ response to direct late selection

In the selection and improvement of cereals, ^{Benmahammed et al. (2010)} and ^{Benmahammed (2005)} suggested that, follow up the late selection method, whether direct or indirect because early selection seems inefficient due to the effects of the G * E interaction, which nullifies any genetic progress. In this study, late direct selection based on grain yield showed that a response from the selected lines increased grain and economic yield over the mean of the F₇ generation, 35.1 and 33.3 g/linear m, respectively (table 5). Direct late selection improved water stress resistance by decreasing the DSI significantly by -13.2%, but also a non-significant decrease of -1.4 °C in CT. Among the variable traits linked to yield, an increase in the NS was recorded by 15.8 spikes and PH by 10.1 cm. Regarding LA, RWC and PREC were not affected by late selection based on grain yield (table 5).

Table 5. Performance of the F₅ selected lines to F₇ by direct and indirect selection of the traits measured 

RS: Response to the selection, µPar: Mean of parents, µ’: Mean of the selected lines, Gain/XPar: Gain compared to parents, CT: Canopy temperature (°C), Gr.YLD: Grain yield (g/linear m), Ec.YLD: Economic yield (straw) (g/linear m), RWC: Relative water content (%), LA: Leaf area (cm²), PREC: Earliness at the heading stage in calendar days, DSI: Drought susceptibility index (%), PH: Plant height (cm), NS: Number of spikes per linear meter.

Source: Elaborated by the authors

F₇ generation individuals’ response to indirect late selection

By the indirect late selection applied to the fifth generation (F₅), the selected lines were improved compared to some of the measured genotypes, such as a grain and economic yield chosen based on economic yield by 23.7 and 30. 5 g/ linear m and NS of 49.9 and 57.0 (Table 5). These results consolidate those of ^{Laala (2018)}, who found in a study on three Durum wheat populations that the response to selection was better in economic yield and NS, in addition to grain yield itself even. Besides the gain in grain yield when selecting based on economic yield and NS, the selected lines respond by increasing the NS in both traits of 10.2 and 15.0 spikes/linear m and the RWC over the mean parent gain (gain/XPar) by 6, 8, and 7.7%, respectively (table 5).

The responses of the selected lines based on the CT were the same as the previous generations (figure 4). It did not decrease compared to the population’s and the parents’ average (table 5), which demonstrates as a non-significant correlation for this trait across generations (r (F₅/F₇) =0.032) due to the G * E interaction effect (table 4). Also, the lines could not respond by increasing the yield in the seventh generation, although it was significantly higher in the fifth generation for the same lines (table 5, figure 3).

For the selection based on the CT and at generation F₅, a significant and negative correlation is observed between grain yield and CT; this is not valid for generation F₇ (r = -0.120) (table 3). This result is consistent with ^{Adjabi et al. (2014)}, where the effect of environment and climate on the production of Durum wheat varieties was proven because their output was different and variable from one cropping season to another. What is remarkable when selecting by CT is that the DSI decreased significantly by -11.3% (table 5). This opens the way to designing lines resistant to abiotic stress, which could be hybridized in the future with lines with high grain yield that combine resistance and productivity traits, as suggested by ^{Bouzerzour and Benmahammed (2009)} due to the specificity of the semi-arid climate. Among the traits (RWC, PREC, DSI, and LA), only DSI affected the grain and economic yield in the seventh generation, recording 19.1 and 33.7 g/ linear m, respectively (table 5).

By selecting based on LA, the answer was to decrease the grain yield (-36.9 g), the economic yield (-22.4 g), RWC (-2.2%), PH (-7.7 cm), and NS (-18.2 spikes). It shows the pointlessness of selection vy large LA in semi-arid regions since if it coincides with drought, it leads to deep imbalances in plant morphology and physiology and a decrease in grain yield (^{Sadeghzadeh & Alizadeh, 2005}). In this study, the LA, PREC, and RWC were most affected by the G * E interaction, so selection did not improve most of the characters studied. This is shown by the correlations of these two characters for grain yield between generations F₅ and F₇, as shown in Table 3, where the correlation coefficient was insignificant for Gr.YLD/PREC (r = -0.026) and Gr.YLD/RWC (r = -0.136).

Source: Elaborated by the authors.

Figure 3. The response of the F₇ populations to Gr.YLD and Ec.YLD. under direct and indirect selection of the selected part (i) of the F₅ generation (i = 30% = five lines per group). 

Source: Elaborated by the authors.

Figure 4. The response of the F₇ generations to canopy temperature (CT) under direct and indirect selection (i) of the F₅ generation (i = 30% = five lines per group). 

Monitoring the response to direct selection for each trait studied showed that the grain yield at the F₅ generation is positively correlated with that of the F₆ generation (r (F₅/F₆) = 0.368) and the F₇ generation (r (F₅/F₇) = 0.440). The grain yield of the F6 generation is positively correlated with that of the F₇ generation (r (F₆/F₇) = 0.659) (table 4). The same observations were recorded for both economic yield and PH. This shows that these traits are not affected by G * E interaction and that the strong correlation between them does not change from one cropping season to another. These results agree with ^{Benmahammed et al.’ (2004)} work, who found that grain yield is correlated to itself from one generation to another in a study on three barley populations. Furthermore, NS had a significant and positive correlation between the F5 and F7 generations (r (F₅/F₇) = 0.430). An absence of correlation was observed between the F5 and F6 generations (r (F₅/F₆) = 0.239) and the F₇/F₆ generations (r (F₆/F₇) = 0.191). The same observations concerned the PREC of the heading stage and the DSI (table 4). On the other hand, some traits are not correlated between themselves and between generations, such as RWC, LA, and CT (table 4).

Late selection, whether direct or indirect, showed that the lines L₁, L₈, L₁₄, L₂₈, L₃₂, L₃₅, L₃₆, and L₄₀ in the F₅ generation had a higher cereal yield than the average these lines have kept their production in the future generations. A tremendous increase in yield was observed in the L₃₆ line at the F₆ generation (122.9 g) (figure 5). Table 6 shows that all these superior lines were selected based on characters linked to productivity (grain yield, economic yield, and NS). These traits correlate with grain productivity and provide the same information as breeding programs. These results agree with ^{Benmahammed’s (2005)} findings in a study of three barley populations that were selected under semi-arid conditions and with ^{Belkharchouche et al.’s (2009)}, who also advise selection for these traits, as they contribute to increasing the grain yield of Durum wheat in these semi-arid regions of the high plains of eastern Algeria.

Lines selected based on resistance did not increase grain yield from one generation to another, except for line L8, selected based on CT and DSI (table 6, figure 5). This line showed an exceptional response to grain yield, which did not drop below the average population over all generations. The emergence of a single line among many lines selected based on different resistance traits proves how difficult it is to improve resistance and productivity in semi-arid areas. ^{Benmahammed (2005)} and ^{Sallam et al. (2019)} found that selection for resistance leads to lower yields under challenging circumstances. However, some lines, like the L1, brought together many selection traits (table 6).

These results demonstrate how important it is to apply late selection in plant breeding programs since G * E interaction is reduced, paving the way for genetic progress (^{Ahmed et al., 2014}; ^{Benmahammed, 2005}). In the future, these lines can be isolated and monitored to study further their behavior in semi-arid climatic conditions that characterize our regions to extrapolate genotypes that are both highly productive and resistant to abiotic stresses.

Table 6. High-performing lines at late selection for various traits studied in F₅ populations 

Source: Elaborated by the authors.

Source: Elaborated by the authors.

Figure 5. The gains in grain yield (Gr.YLD) by direct selection of the high grain yield of lines through generations F₅, F₆, and F₇ (n = 24 lines (L) per group).