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Kernel Base Phloem Area (mmA/10° )

Figure 6. The area of the vascular tissue of the kernel base phloem compared to the area of the kernel base vascular tissue and to the rate of kernel weight gain of six wheat cultivars differing in final seed weight measured in two separate years. The regression line through the data points of each comparison is presented

There does appear to be a relationship between the amount of phloem area in the culm and the rate of import into the head (53). Examining the relationship of the rate of dry matter accumulation and vasculature of the head in six cultivars of wheat over two years a significant phenotypic correlation (0.8296 significant at the 5% level) in one year between the rate and the area of the kernel base xylem was found. Significant phenotypic correlation over two years was found between the total vascular area of the spike and that of the spike phloem (0.9448 1% level, Fig. 5) and between the total area of the vasculature of the base of the kernel and that of the kernel base phloem area (0.9326 at the 1% level, Fig 6). The phloem area of the crease region was not significantly correlated with the total vascular area of the crease region (Fig 7). The xylem area of the kernel base was significantly correlated both with the total (0.9465 at the 1% level) and phloem (0.8526 at the 5% level) areas of the kernel base across years. The relationship between the area of the phloem in all three of these regions was not related to the rate of dry matter deposition in the kernel (Fig 5-7). It is interesting that unloading of the crease sieve element and or companion cells is believed to be the important region for control of sugar import into the kernel (63).

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