Abstract
A field experiment was conducted during 2012-2013 and 2013-2014 agricultural seasons at the Field Crops Research Unit, Research Station of the College of Agriculture, University of Tripoli, with the aim of studying the effect of modifying the source-sink relationship on grain weight, furthermore, studying the efficiency of the dry matter partitioning and the possibility of suggesting important selection criteria to enhance yield potential. Two varieties of six-row barley (Hordeum vulgare L.) were used. The experiment was carried out under full irrigation under a completely randomized block design with three replications. At flowering, the flag leaf removal treatment was carried out for ten culms, as well as removing half of the spikelets lengthwise from the spikes of other ten culms to adjust the ratio between the source and the sink. Other culms were also selected to be used as a control, and this factor was considered as a secondary factor within the main plots, which represent the varieties, then another sub-secondary factor was adopted, which is the position of the grain on the spike, so that the spike was divided into three parts (upper, middle, and lower), and the split-split plot design was adopted. Results showed that the two varieties did not differ in general in grain weight, as it was 40.88 mg for ACSAD-176 variety and 40.14 mg for Raihan variety (P = 0.780). The effect of the different treatments on grain weight was highly significant compared to the control treatment (P = 0.010). This effect was more pronounced when treated with half of the spikelets removed (44.41 mg) compared to the control treatment (39.57 mg), whereas, the grain weight after removing the flag leaf (37.55 mg) did not differ significantly from the control treatment, which confirms that these two varieties are source limited. The factor most influencing grain weight was the position of the grain on the spike (P < 0.001). Average grain weight in the middle part of the spike (43.32 mg) was the highest, which differed significantly from the grain weight in the upper and lower parts (39.46 and 38.75 mg) respectively. One of the most important morphological traits that enhances the negative relationship between stems and spikes is the plant height, and this is also observed from the negative relationship between this trait and the percentage of dry matter partitioned to the grains. This competitive relationship for dry matter also appears at the spike level between the chaff (glumes, awns and rachis) and the produced grains. It appears that spike length is one of the most important traits that supports enhancing the proportion of dry matter directed to the grains, which can be one of the selection criteria to increase yield potential.