Abstract:

Aims Understanding genetic differences in photosynthetic capacity of different wheat materials evolved from diploid to hexaploid and octoploid is important for breeding and cultivation management, but the physiological basis for late-growth photosynthetic characteristics and grain yield of different wheat evolutionary materials is unclear. This study investigates evolutionary patterns in photosynthetic and fluorescent parameters by examining grain yield during late growth period in different wheat evolutionary materials.
Methods Pot experiment used ten wheat materials: four diploid species (Triticale boeoticum, T. monococcum, Aegilops squarrosa and Secale cereale), three tetraploid species (T. dicoccoides, T. dicoccumand T. durum), two hexaploid cultivars (`Yangmai 158’ and `Yangmai 9’) and one octoploid species (Triticale). Each pot contained 7.5 kg of sieved soil containing 14.8 g[[rad]]kg ^-1 organic matter, 1.2 g [[rad]] kg ^-1 total N, 82.3 mg[[rad]]kg^-1 available N, 30.9 mg[[rad]]kg^-1 available P and 126.7 mg[[rad]]kg^-1 available K. Before sowing, 0.9 g N, 0.9 g K₂O and 0.36 g P₂O₅ were applied to each pot and topdressing of 0.3 g N was added at jointing stage. Fourteen seeds were sowed and thinned to seven plants in each pot at five-leaf- stage. The experiment was arranged in a completely randomized design with ten replications per treatment. 
Important findings The photosynthetic rates (P_n) of diploids and tetraploids were higher than that of hexaploids before anthesis, because diploids and tetraploids had higher stomatal conductance (G_s), maximum photochemical efficiency (F_v/F_m) and actual light transformation efficiency (ΦPSⅡ). However, the P_n of diploids and tetraploids declined faster and became lower than those of hexaploids beginning 5 days after anthesis, except in S. cereale. Moreover, F_v/F_m, ΦPSⅡand chlorophyll content (SPAD value) of diploids and tetraploids declined faster, while intercellular C O2 concentration (Ci) increased, which resulted in non-stomatal inhibition to Pn. Furthermore, the leaf area per plant of hexaploids and the octoploid declined slower after anthesis, as compared with diploids and tetraploids, although diploids and tetraploids had higher leaf area before anthesis. Mean number of spikes per plant of diploids and tetraploids was higher, but the kernels per spike, 1000 kernels weight and grain yield were lower than those of hexaploids and the octoploid, indicating grain yield was related to the increased kernels per spike an d 1000 kernels weight. This study indicate that improved photosynthetic capacity and duration after anthesis are important physiological bases for enhancing grain yield from increased grain weight during evolution from diploid to current normal wheat.