Evaluation of relationship between growth indices and yield in bread wheat promising lines under Irrigation and Rainfed Conditions

Title:
Evaluation of relationship between growth indices and yield in bread wheat promising lines under Irrigation and Rainfed Conditions
Introduction:
Wheat, as one of the main constituents in ensuring food security, provides 20% of the total calories and protein of the world's population. In this regard, recognizing and studying physiological growth indices is very important in analyzing the factors that affect yield and its components. This can aid in determining plant growth stages and evaluating and crop production (Soleymani Fard et al., 2011). Although RGR is the main indicator of growth and determines dry matter accumulation and ultimate yield, its components including NAR, LAR, LWR and SLA appear to be better choice under extreme stress than RGR.

Material and Methods:
This experiment was counducted to study the growth indices and their relationships with the yield of promising bread wheat lines during the 2018-19 cropping year at the Agricultural Research Station of West islamabad, under two separate irrigation and rainfed conditions. The studied genotypes included 9 advanced bread wheat lines along with the two top cultivars, namely, Pishgam and Baharan as a control, which were selected and assessed in a completely randomized block design. Leaf surface was measured using a scanner and ImageJ and Photoshop software packages. The samples were separated into leaves, stems and spikes and their dry weight was calculated after being placed in an oven at 72 °C for 48 hours. Thousand kernel weight was measured by an electronic scale with an accuracy of one thousandth of a gram. Data analysis of variance was performed using SAS software and graphs were also drawn using excel software.

Results and Discussion:
Based on the test results, the rainfed condition decreased grain yield, biological yield, straw yield, thousand kernel weight and harvest index in all lines by 25%, 21%, 19%, 13% and 4% compared to the irrigation condition, respectively. Based on the positive and significant correlation of grain yield performance under the irrigation conditions against the rainfed conditions (r= +0.782**), high yield potential can be an important factor in selecting drought tolerant cultivars, but this factor alone is not enough and due to its correlation with the growth indices, the latter can be used in this regard. LAR and SLA indices showed a positive and significant correlation with grain yield under the irrigation condition and at the sensitive developmental stages including heading (r=+0.663* and r=+0.608*) and 10 days after anthesis (r=+0.704* and r=+0.673*). Under the rainfed condition, a positive and significant relationship (r=+0.647*) was observed between LAR and grain yield in the last stage of sampling. There was a positive and significant relationship between RGR and NAR, biological yield and straw yield. RGR also showed a positive and significant relation with LWR (r=+0.640*) in the second stage of sampling. Among the components of RGR, NAR was the main and effective factor, which had a negative and non-significant correlation with LAR, so that the lines with higher LAR had lower NAR and therefore lower RGR. There was a positive and significant relationship between LAR components such as LWR and SLA with LAR. In general, among the RGR components (LAR and NAR), it can be said that the LAR index and among the LAR components (LWR and SLA), the SLA index, while having a positive and significant relationship with grain yield at the sensitive developmental stages, are considered as effective factors in grain yield. Consequently, it seems that these two parameters can be identified as important growth indicators related to grain yield.

Keywords: Drought stress, Growth indices, Growth stage, Wheat

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