Physiological basis for the differences of productive capacity among tillers in winter wheat

The quality or structure of a wheat population is significantly affected by the compositions of tillers. Little has been known about the physiological basis for the differences of productive capacity among tillers. Two winter wheat cultivars, Shannong 15 (SN15) and Shannong 8355 (SN8355), were used to investigate the differences of productive capacity among tillers and analyze the physiological mechanisms that determine the superior tiller group. Low-position tillers (early initiated tillers) had a higher yield per spike than high-position tillers (late initiated tillers) in both cultivars, which was due to their more grain number per spike, more fertile spikelet per spike, less sterile spikelet per spike and higher grain weight. According to cluster analysis, tillers of SN15 were classified into 2 groups: superior tiller group including main stem (0), the first primary tiller (I) and the second primary tiller (II); and inferior tiller group including the third primary tiller (III) and the first secondary tiller (I-p). Tillers of SN8355 were classified into 3 groups: superior tiller group (0 and I), intermediate tiller group (II and III) and inferior tiller group (I-p). In comparison with other tiller groups, the superior tiller group had higher photosynthetic rate of flag leaves, higher antioxidant enzyme (SOD, POD and CAT) activities and lower levels of lipid peroxidation in leaves, higher grain filling rate in both superior and inferior grains during grain filling, higher single-stem biological yield and larger single-stem economic coefficient. Correlation analysis showed that yield per spike was positively and significantly correlated with the flag leaf photosynthetic rate, grain filling rate, the antioxidant enzyme activities and soluble protein content (except for SN15 at 5 days post-anthesis (DPA)) of flag leaf, the single-stem biological yield, and the single-stem economic coefficient. Remarkable negative correlation was also found between yield per spike and MDA content of flag leaf. These results suggested that superior tiller group had stronger leaf photosynthetic capacity, more predominance in terms of grain filling, slower senescence rate, higher biological yield and larger economic coefficient, and therefore, showed greater productive capacity than other tiller groups.