The Effect of Spike Row Type on the Grain Yield and Grain Filling Parameters in Barley (Hordeum vulgare L.) Genotypes under Semi-arid Conditions

Barley (Hordeum vulgare L.), is an annual monocotyledonous plant. Barley genotypes are classified according to ear structure as either 2-row or 6-row. Barley has been used as animal fodder, as a source of fermentable material for beer and certain distilled beverages and as a compound of various health foods. The growing demand for barley by the food industry is mainly because of its health-promoting beta-glucan, acetylcholine, lysine, thiamine and riboflavin contents and the easy digestibility (Marwat et al., 2012). The understanding of the potential grain yields of 2 and 6 row and of the ways in which their yield is obtained may help the plant breeder. Grain filling, the final process associated with yield performance, is a crucial determinant of grain yield in cereal crops. Moreover, abiotic stress (drought and heat) during grain filling stage of the barley growth cycle limit its productivity. Many studies reported a significant effect of terminal drought conditions on barley yield ranging from 27 to 41% (Przulj and Momcilovic, 2012). Several authors reported a significant effect of grain filling rate and grain filling duration on final individual grain weight in barley genotypes. Grain yield and its components are the major selection criteria for evaluating drought tolerance under field conditions. Samarah et al., (2009), suggested that under water and heat stress conditions the six-rowed genotypes achieved better yield than two-rowed genotypes. The six-rowed barley proved to be more stable behavior to environmental variations, but the yield of two-rowed barley proved to be more responsive inter-annual variation. The aim of this study is to compare the comportment of two and six rowed barley genotypes based on the grain filling parameters in relationship with grain yield and thousand kernel weight.

Plant material and experiment designs
 
Eight Barley genotypes (Hordeum vulgare L.) were planted during two cropping seasons (2017-2019), in randomized block design with three replicates at the experimental fields of ITGC, Setif, Algeria (5°20'E, 36°8'N, 958 m above sea level). Plots were 5 m × 6 rows with 0.20 m row spacing and sowing density was adjusted to 250 g m^-2.
 
Agronomical and grain filling parameters
 
The grain yield and thousand kernel weight were estimated at harvest. The grain filling parameters are presented in Table 1.
 
 
 
Statistical analysis
 
To evaluate significant differences between genotypes, the one-way analysis of variance (ANOVA) was performed. Fisher’s LSD multiple range test was employed for the mean comparisons.

Grain yield and TKW
 
The genotypes effect was significant for the grain yield and thousand-kernel weight during the both cropping seasons (Table 2). For the first cropping season, the values of grain yield are varied between 43.99 Q/ha for the local genotype Rihane 03 to 74.4 Q/ha for the local genotype Fouarra and during the second cropping season, the values of grain yield are varied between 48.02 Q/ha for the introduce genotype G4 to 97.79 Q/ha for the local genotype Fouarra. Based on the results of the two cropping seasons, the test of means comparison showed that the genotype with highest grain yield is the local genotype Fouarra. Among all introduce genotypes the genotype G1 have the good grain yield during the first and second cropping season (68.39 and 65.69 Q/ha, respectively). As shown in Table 2, the highest TKW during the first and second cropping season is registered by the local genotype Saida 183 (55.91 and 44.88 g, respectively). Over all, the introduce genotype (2 rows) G1 has the highest TKW during the two-cropping season among all introduce genotypes tested. The ANOVA results of the spike type effects showed a significant effect on the grain yield just during the second cropping season, the mean grain yield in the 6 row (71.08 Q/ha) better than the 2 row (55.03 Q/ha). Among the genotypes with 6 rows spike type the local genotype Fouarra have high grain yield (97.79 Q/ha) with a deviation of 37.57% from the total mean of the genotypes with 6 row spike type. Many studies proved that in 6-row barleys, the magnitude of contribution of grain number in grain yield was higher than contribution of grain weight (Vaezi et al., 2010; Bavi et al., 2011; Mirosavljević et al., 2018).
  

 
Grain filling parameters
 
The grain growth of genotypes studied follows a sigmoid curve similar to that described by Triboi (1990) and Guendouz and Maamori (2012) (Fig 1). As described by Yoshida (1981) the grain filling, is the final process associated with yield performance, is a crucial determinant of grain yield in cereal crops; grain growth of field crops is initially slow, enters a linear phase where the growth rate is fast and then slows down toward maturity. During the first season (2017-2018) the duration of grain filling ranged between 24 days for Saida 183 and 28 days for Rihane 03, for the group of genotypes with 6 rows. In addition, the duration of grain filling for the 2 row genotypes varied from 24 days for G4 to 28 days for genotype G2. During the second season (2018-2019) and for the genotypes with 6 rows, the duration of the grain filling varied from 21 days for the Saida 183 and 26 days for the genotype Fouarra, for the genotypes with 2 rows the duration of grain filling ranged from 21 days for the genotype G2 to 26 days for the genotype G3. Under environmental stress, e.g. high temperatures after anthesis, grain yield will be reduced due to a decline of single grain weight (Porter and Gawith, 1999), over the range of 12 to 26°C increase in mean temperature during grain filling, grain weight is reduced at a rate of 4 to 8% / °C (Wardlaw et al., 1980). In addition, water stress during grain filling affect directly the grain weight is, however, reduced (Hochman, 1982) due to a shortening of the grain filling period resulting from accelerated senescence of flag leaf. As shown in Table 2, all grain filling parameters are affected by the genotypes and spike type during the two cropping seasons. Based on the ANOVA analysis of the genotypes effects, the introduce genotype G2 with 2 row spike type has the highest MGW and GFR among all genotypes tested. In addition, the ANOVA analysis based on the spike type showed a significant difference between the 2 and 6 row and the highest values of MGW, GFR and MFR is registered by the genotypes with 2 row (the introduce genotypes G1 and G2). The results demonstrate that the group of the genotypes with 2 rows has mean velocity of grain filling more than the group of genotypes with 6 rows, these results proved that the genotypes with 2 rows more sensitive to water stress in comparison with the genotypes with 6 rows. A long duration of grain filling is often indicator of photosynthetic activity optimum, but a high velocity of filling is indicative effects of water stress (Sofield et al., 1977). The correlation analysis between the grain filling parameters, GY and TKW demonstrate a significant and positive correlation between TKW and MGW and GFR (r=0.82* and r=0.84*, respectively) just during the first cropping season; this results in agreement with the results of the study of Samarah et al., (2009) and González et al., (2007), which registered a significant correlation of GY with MGW, TKW, MFR and GFR was also positive but lower. These results suggest that the genotypes with high values in MGW and GFR had highest TKW. The GFD and GFR are related negatively but weakly (r = -0.40), i.e. a lower speed of grain filling is not necessarily offset by an increase in duration of filling. While, (Wang et al., 2009; Jocković et al., 2014) found a strong negative correlation between these two components. This a strong correlation indicate compensation between these two variables, but Triboi (1990) found that this compensation phenomenon no effect on the final dry weight of grain.
 

The genotypes effect was significant for the grain yield and thousand-kernel weight during the both cropping seasons. Based on the rustles of the two cropping seasons, the test of means comparison showed that the genotype with highest grain yield is the local genotype Fouarra with 6 rows. Among all introduce genotypes (2 rows group) the genotype G1 has the good grain yield during the first and second cropping season. In addition, the highest TKW during the first and second cropping season is registered by the local genotype Saida 183 (6 rows). Over all, the introduce genotype (2 rows) G1 has the highest TKW during the two cropping season among all introduce genotypes tested. The grain growth of genotypes studied follows a sigmoid curve. The ANOVA analysis of the genotypes effects, proved that the introduce genotype G2 with 2 row spike type has the highest MGW and GFR among all genotypes tested. In addition, the ANOVA analysis based on the spike type showed a significant difference between the 2 and 6 row and the highest values of MGW, GFR and MFR is registered by the genotypes with 2 row (the introduce genotypes G1 and G2). The genotype variation in grain filling velocity and duration was responsible for the difference in grain yield and the improvement in grain yield was achieved by the increasing in velocity or duration of grain filling.