Key findings:

Two wheat genotypes were studied over two seasons in Sudan. Positive correlations were found between grain yield and traits such as number of grains per plant, spikelet number, and spike length. Plant height, tillers per plant, and 1000-grain weight also correlated positively with yield, suggesting they could be targeted for improved crop yield.

What is known and what is new?

Existing knowledge suggests that wheat yield is influenced by various agronomic traits, including spikelet number, spike length, and plant height. This study adds to this by specifically evaluating wheat genotypes in Sudan's Newhalfa region, identifying correlations between these traits and grain yield. The finding that certain traits like plant height and spikelet number correlate positively with yield provides new insights for targeted breeding and management practices in the region.

What is the implication, and what should change now?

The implication of this study is that breeding programs and agronomic practices in the Newhalfa region should focus on traits such as plant height, spikelet number, and spike length to improve wheat yield. Farmers and researchers should prioritize these traits in their selection and management strategies to enhance wheat productivity in Sudan. Additionally, further research could investigate the specific genetic factors underlying these traits to facilitate targeted breeding efforts.

Worldwide, wheat (Triticum aestivum L.) importance as a food crop is well known. To meet the requirements of the consistently increasing world population (around 7 billion). Rosegrant and Agcaoili (2010) [1] observed that the increasing demand on the wheat consumption by increasing world population must be met by an annual increase in wheat production of 2% till 2050. In Sudan wheat, is important stable food for a large number of citizens, especially in urban areas, Being a temperate cool crop, it is not indigenous to Sudan; yet it was traditionally grown since early times in the Northern states (Latitude. 18º -22´ N) that are characterized by a relatively cooler and longer winter season than the center [2]. As yield is a complex and polygenic, and highly affected by other genetic factors and environmental variations. Moreover, plant breeder added that, direct selection for yield as such is unpredictable, thus successful selection needs an information on the genetic variability and association of agronomic characters with grain yield.

Associations among the characters provide a better understanding of the inter- relation of different traits with grain yield [3]. Understanding of the inter-relation between yield, yield components and other growth attributes in wheat is very important, because selection in one character may improve or deteriorate associated characters, depending on the nature and magnitude of the association among them. Genetic correlations are the most important, and are caused by linkage or pleiotropy or both [4,5]. Adam 1967 [6], however, believed that correlations may be developmental rather than genetic per se and are postulated to be due to genetically independent components, developing in sequential patterns. Grain yield and its quality are the principal characters of a cereal crop [7]. They are complex quantitative characters, which are affected by numerous yield related traits. Therefore, the selection for desirable genotypes should not only be based on yield per se, and the other yield components should also be undertaken. Direct selection for yield is often unpredictable in wheat because the crop yield is a complex trait. 

For effective using of the genetic pool in crop improvement, information of mutual inter-relationship between yield and yield components is quite important. It is therefore, necessary to know the association of different component traits with yield and among each other’s. The correlation coefficients among yield and yield related traits usually show a complex chain of interacting relationship. The objective of this study was to find out simple correlations between yield, yield components including Spike length cm (SL), Number of Spikelet/Plant, Number of Grains/Plant, Grain yield/Plant g, 1000 Grain weight g, and other growth attributes and to determine the most important characters can be used as selection criteria for improving grain yield in wheat.

The experiment was carried out for two consecutive seasons(2017/2018 and 2018/2019), at three sites of New Halfa irrigated scheme, eastern Sudan, namely, Hajer (HA) represents South of the scheme, Faculty of Agriculture and Natural Resources (FA) of the University of Kassala, represents central area of the scheme and Shebiake (SH) which represent North part of the scheme. (Latitude 15º 19´ N, Longitude 35 º 36´ E. and Altitude 450m asl.), (see Fig. 1). The soil is calcareous, alkaline (PH= 8.3), nonsaline, nonsodic and moderately fertile. It is classified as Typic Haplusterts, very fne, semectic, isohyperthermic [8]. Two wheat cultivars seeds (Bohain and Debiara) were offered from the Agricultural Research Corporation (ARC) of New Halfa. At each location, a randomized complete block design with three replicates was used. The plot size was 4.5 x 6 m, sowing date was on 12^th and 14^th November, for the first and the second seasons, respectively. All cultural practices were followed as recommended from ARC. Data were collected on the following parameters: plant height(cm), (PH), Number of tillers/plant (NTPP), Number of leaves/plant (NLPP), Leaf Area cm² (LA), Spike length cm (SL), Number of Spikelet/Plant (NSPP), Number of Grains/Plant(NGPP), Grain yield/Plant g (GYPP), 1000 grain weight g (1000 GW), All the data were analyzed according to the procedure described by Gomez and Gomez (1984) [9] using statistix computer software package (version 9-1) to calculate simple Spearman correlation coefficients among the different pairs of the nine characters for each genotype.

Fig. 1: New Halfa Irrigated Scheme Map

Tables 1, 2 and 3 show simple correlation coefficients between yield, yield components and the growth attributes for the two genotypes of wheat grown at the three sites of New halfa irrigated scheme, Hajer, Faculty of Agriculture and Natural resources and Shebaik for the two consecutive seasons 2017/2018 and 2018/2019. Plant height, showed positive and significant correlation at the three sites of the study and in both seasons with leaf area and spike length and it showed positive significant correlation with number of leaves per plant at the three sites and in both seasons, except the Faculty site in the first season, Shebaik in the first and second seasons. However, plant height was significantly negatively correlated with 1000 Grain weight at the three sites and over the two seasons, and significantly negatively correlated with grain yield per plant at the three sites and for the two seasons except, at the faculty site in both seasons and Shebaik site in the second season. At the three sites and over the two seasons, number of tillers per plant was highly significantly positively correlated with the number of leaves per plant and with leaf areas except at Hajer in the first season and Shebaik site in the second season. Number of leaves per plant was highly significantly and positively correlated with the leaf areas at the three sites and over the two seasons. The spike length showed positive significant correlation with number of grains per plant at all sites, except at the Faculty and Shebaik in the first season and Hajer in the second season. The number of spike lets per plant and number of grains per plant were highly and significantly positively correlated with grain yield per plant and with each others. 1000-grain weight and grain yield per plant were significantly positively correlated almost at the three sites of the study. These results were in accordance with that reported by Kumar et al., (1998); Narwal et al., (1999); Ashok Kumar et al., (2000); Subhani (2000); Esmail (2003); Singh et al., (2006), Saktipada et al., (2008) and Bilgi (2006) [10-18]. In this study, most of the yield components and some other essential growth attributes were highly positively associated with yield of wheat almost at the three sites of the study and over the two seasons and hence direct selection for these traits could improve the yield of the crop. [16] attributed the genetic correlation to peilotropy or linkage or both. In peilotropy, the same gene, the same gene determines the expression of two or more characters, and the correlation here is unbreakable. However the correlation arising from linkage is transient and can be manipulated. Knowledge of associations is important in assessment of changes brought about by selection that simultaneously that influence other correlated traits. In general, plant height, number of tillers per plant, number of spikelets per spike, number of grain per plant, spike length and 1000-grain weight are the most important for grain yield since these traits had high correlation, Therefore, direct selection for these characters should be of concern to the breeders, for improving the yield of the crop.

Table 1: Simple Correlation Coefficients between Growth Attributes, Yield and Yield Components in Two Wheat Genotypes at Hajer Site in Season 2017/2018(Upper Diagonal) and 2018/2019 (Lower Diagonal).

*, **, *** Significant at 0.05, 0.01 and 0.001 Probability, Respectively

ns; not Significant

Table 2: Simple Correlation Coefficients between Growth Attributes, Yield and Yield Components in Two Wheat Genotypes at Faculty of Agriculture Site in Season 2017/2018(Upper Diagonal) and 2018/2019 (Lower Diagonal).

*, **, *** Significant at 0.05, 0.01 and 0.001 Probability, Respectively

ns; not Significant

Table 3: Simple Correlation Coefficients between Growth Attributes, Yield and Yield Components in Two Wheat Genotypes at Elshebaik Site in Season 2017/2018(Upper Diagonal) and 2018/2019 (Lower Diagonal).

*, **, *** Significant at 0.05, 0.01 and 0.001 Probability, Respectively

ns; not Significant

Funding: No funding sources 

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee of University of Kassala

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