Genetic evaluation of bread wheat spike length in diverse population derived from Roshan-D-01 line× Roshan cultivar

World food security depends on two major cereal crops, wheat and rice. Where wheat is more important for its market value and production amount. Grain yield is determined by the achievement and distribution of assimilates in sink organs. Sink size in wheat depends on the number of spikelets per spike, grains number per spikelet as well as the grain weight. Hence, increasing spikelet number and sink size is one of the most important breeding targets of wheat. The object of the present study was investigation the genetic of spikes and spikelets in a divers bread wheat population for number of spiklets per spike.

In a bread wheat breeding program for transferring the awn character from Mahdavi to Roshan cultivar, in the second generation of the third backcross (BC3F2), a single plant with large spikes was observed. The mentioned genotype was purified after several selfing. The pure line was named as Roshan-D-01. After the fourth backcross of Roshan-D-01 with the recurrent parent (Roshan) and a selfing generation, a near isogenic population (BC4F2) was developed to study spike length. Spike length along with its related traits was studied in the current population at the research field of Shahid-Bahonar University of Kerman, during growing seasons of 2020-2021.

The spike length with the heritability of 0.61 and the response to selection of 14.03% showed a negative significant correlation with days to heading (r=-0.44**) and a positive significant correlation with other traits. Days to heading had a negative significant correlation with all studied traits at this research. This result showed the positive effect of early heading on spike related traits. Among studied traits, flag leaf area with general heritability of 0.53, positive significant correlation with spike length (r=0.60**), the highest Phenotypic and genotypic diversity (PCV=28.5 and GCV=20.69), showed the most response to selection (%R=25.45). The positive correlation between flag leaf area and spike related traits indicate the importance of flag leaf area in improving wheat grain yield. Distribution frequency graph of progenies for spike length, spikelet number per spike and grains number per spike showed that these traits have quantitative inheritance and follow the normal distribution. Transgressive segregation observed for studied traits and the presence of elite lines, in comparison with parents, in the current population allows the introduction of large spikes genotypes with high grains number per spike to develop high-yielding cultivars.

Due to high diversity and transgressive segregation observed in the present study, the current population can represent a rich source of spike morphology for use in wheat breeding programs aimed for increasing grain yield potential via increasing grain number. Negative correlation of days to heading with spike related traits indicates the positive effect of early heading on grain yield of bread wheat, especially under end season drought and heat stress conditions. Due to the high, positive and significant correlation between the spike length and flag leaf area, selection for larger flag leaf area could improve grain yield.