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Genotype and plant type affect photosynthetic production by changing the canopy structure in crops. To analyze the mechanism of action of heterosis and plant type on canopy structure in cotton ( Gossypium hirsutum L.), we had selected two cotton hybrids (Shiza 2, Xinluzao 43) and two conventional varieties (Xinluzao 13, Xinluzao 33) with different plant types in this experiment. We studied canopy characteristics and their correlation with photosynthesis in populations of different genotypes and plant types during yield formation in Xinjiang, China. Canopy characteristics including leaf area index (LAI), mean foliage tilt angle (MTA), canopy openness (DIFN), and chlorophyll relative content (SPAD). The results showed that LAI and SPAD peak values were higher and their peak values arrived later, and the adjustment capacity of MTA during the flowering and boll-forming stages was stronger in Xinluzao 43, with the normal-leaf, pagoda plant type, than these values in other varieties. DIFN of Xinluzao 43 remained between 0.09 and 0.12 during the flowering and boll-forming stages, but was lower than that in the other varieties during the boll-opening stage. Thus, these characteristics of Xinluzao 43 were helpful for optimizing the light environment and maximizing light interception, thereby increasing photosynthetic capability. The photosynthetic rate and photosynthetic area were thus affected by cotton genotype as changes in the adjustment range of MTA, increases in peak values of LAI and SPAD, and extension of the functional stage of leaves. Available photosynthetic area and canopy light environment were affected by cotton plant type as changes in MTA and DIFN. Heterosis expression and plant type development were coordinated during different growth stages, the key to optimizing the canopy structure and further increasing yield.

We compared the photosynthetic characteristics in relation to yield of two F1 cotton hybrids (Shiza 2-F1 and Xinluzao 43-F1), their parental lines (NT2, H2 and 4-14) and their F2 descendants at different growth and development stages. The two F1 exhibited heterobeltiosis in net photosynthetic rate (Pn) by 8.1-52.1%, canopy apparent photosynthetic rate (CAP) by 8.2-57.6% and canopy respiration rate (CR) by 3.0-78.7% during the growing season. They also exhibited mid-parent heterosis by 2.0-5.2% in leaf chlorophyll content (SPAD) during the late growth and development stages. Regression analysis showed that both parents contributed to increase in Pn, SPAD and CAP in the F1. A low CR in the F1 matched a low CR of the parental line. Photosynthetic characteristics in the F2 were mainly dependent upon the magnitude and degeneration rate of the F1. Mid-parent heterosis in CAP and in CR during the late growth and development stage reduced the degeneration of the F2. Average dry matter accumulation was 10.7-34.7% higher in the parental lines of Xinluzao 43-F1 than in the parental lines of Shiza 2-F1. Heterobeltiosis in dry matter accumulation was 7.0-23.1% greater for Xinluzao 43-F1 than for Shiza 2-F1. Dry matter accumulation in the F1 was affected by either the dry matter accumulation of parents or heterobeltiosis. Dry matter accumulation in the F2 was mainly influenced by dry matter accumulation in the F1. The yields of the two F1 were 39.1-46.3% higher than their respective parents and 26.4-45.9% higher than that of the conventional cultivar Xinluzao 33. The yields of the two F2 were 9.2-12.8% higher than the parents and 14.9-27.4% higher than that of Xinluzao 33. The photosynthetic production and yield of the F1 and F2 were higher than that of their parents. The increases in Pn and CAP of the F1 and F2 were dependent on the photosynthetic characteristics of their parents. It is thus concluded that the photosynthetic performance, light use efficiency and yield of the F1 can be improved by using at least one parent with low CR, but high CAP, Pn and SPAD. This strategy might also improve the value of the F2.