Leaf Photosynthetic Characteristics In Cotton Lines With Different Tolerance To High Temperature

With radical global warming, high temperature stress has become one of major factors exerting a major influence on crop production. In cotton(Gossypium hirsutum L.)-growing areas of China, unexpected periodic episodes of extreme heat stress usually occur in July and August, the peak time of cotton flowering and boll loading, resulting in lower boll set and lint yield. Understanding the mechanism of high temperature tolerance in cotton and breeding programs for screening high temperature-tolerant cotton germplasm and cultivars are urgent at present in order to stabilize and increase yield in the current and future warmer weather conditions. The leaf photosynthetic characteristics and their response to high temperature stress at peak flowering stage were analyzed comparatively among three cotton lines with different high-temperature tolerance in the paper to provide value reference for disclosing high temperature tolerant mechanism in cotton and screening and identifying germplasm and developing cultivars tolerant to high temperature stress. The main results were as follows:1. The tolerant line HLY11 had the greatest maximum pollen germination and tube length among the three cotton lines during cultural temperatures from 10 to 45℃, and also had larger pollen germination and tube growth at medium temperature above 35℃than moderate susceptible line xinyoumian 68 and susceptible line TS18. The boll retention and boll numbers per plant in the late August were significant among the three lines under natural planting fields, and the tolerant line HLY11 had the highest boll retention and boll numbers.2. The three cotton lines nearly had the same chlorophyll a and b content at peak squaring stage, and the tolerant line had more chlorophyll a and b in developed leaves on main stem than the sensitive lines, xinyoumian 68 and TS18, at peak flowering stage and boll-setting stage. No difference in total chlorophyll content (Ca+b), but significant difference in chlorophyll a/b value was detected among the three lines at peak squaring, flowering and boll-setting stages.3. The tolerant line HLY11 had significant higher net photosynthetic rate (Pn) and water use efficiency (WUE) as compared to the sensitive lines xinyoumian68 and TS18 at peak squaring stage and boll-setting stage, while the stomatal conductance (Gs), intercellular CO2 concentration (Cj), transpiration rate (Tr), and stomatal limitation (Ls) did not differ significantly among the three cotton lines. 4. Pn and Gs in leaf of main stem at the same nodes were higher in HLY11, followed by xinyoumian 68 and TS18, while Tr and leaf temperature (T1) were higher in TS18, followed by xinyoumian 68 and HLY11 at peak flowering stage. At peak boll-setting stage, Pn, Gs and Tr at the same nodes were still higher in HLY11, followed by xinyoumian 68 and TS18 and HLY11 had lower T1 than xinyoumian 68 and TS18.5. At peak squaring stage, the effective quantum yield (EQY) and the photochemical quenching co-efficient (qP) reduced with the increase of photosynthetic active radiation (PAR), and the decrease was lower in HLY11 than xinyoumian 68 and TS18. The electron transport rate (ETR) and the non-photochemical quenching co-efficient (NPQ) increased with the enhancement of PAR, and the increase was higher in HLY11 than xinyoumian 68 and TS18. The changing trends of EQY, qP, ETR and NPQ in the three cotton lines at peak flowering and boll-setting stages were the same as the ones at peak squaring stage.6. High temperature stress at peak flowering stage caused a decline in Pn, Gs and WUE, and an increase in Tr and Ls, but did not affect Gj. The Pn in xinyoumian 68 and TS18, but not in HLY11, was reduced significantly after stressed. The decrease of Gs was higher, whereas the increase of Tr was lower in xinyoumian 68 and TS18 than in HLY11.7. The maximum photochemical efficiency of photosystem II (Fv/Fm), the quantum yield of electron transport (Opsu), and the qP were reduced, and accompanied by an increase in the NPQ under high temperature stress at peak flowering stage. Among the three cotton lines, the Fv/Fm in TS18 was declined dramatically, the reduction of Opsn and qP was higher, and the increase of NPQ was lower significantly in xinyoumian 68 and TS18 than in HLY11.