Enhanced photosynthetic nitrogen use efficiency and increased nitrogen allocation to photosynthetic machinery under cotton domestication.

Domestication involves dramatic phenotypic and physiological diversifications due to successive selection by breeders toward high yield and quality. Although photosynthetic nitrogen use efficiency (PNUE) is a major trait for understanding leaf nitrogen economy, it is unclear whether PNUE of cotton has been improved under domestication. Here, we investigated the effect of domestication on nitrogen allocation to photosynthetic machinery and PNUE in 25 wild and 37 domesticated cotton genotypes. The results showed that domesticated genotypes had higher nitrogen content per mass (Nm), net photosynthesis under saturated light (Asat), and PNUE but similar nitrogen content per area (Na) compared with wild genotypes. As expected, in both genotypes, PNUE was positively related to Asat but negatively correlated with Na. However, the relative contribution of Asat to PNUE was greater than the contribution from Na. Domesticated genotypes had higher nitrogen allocation to light-harvesting (NL, nitrogen in light-harvesting chlorophyll-protein complex), to bioenergetics (Nb, total nitrogen of cytochrome f, ferredoxin NADP reductase, and the coupling factor), and to Rubisco (Nr) than wild genotypes; however, the two genotype groups did not differ in PNUEp, the ratio of Asat to Np (itself the sum of NL, Nb, and Nr). Our results suggest that more nitrogen allocation to photosynthetic machinery has boosted Asat under cotton domestication. Improving the efficiency of nitrogen use in photosynthetic machinery might be future aim to enhance Asat of cotton.

[Genetic analysis of fuzzless in cotton germplasm].

The present study was conducted to evaluate genetic analysis of fuzzless seed trait in cotton. One hundred and two upland cotton (G. hirsutum) and eighty-five island cotton (G. barbadense) were used to cross with the same lines, TM-1 (G. hirsutum) and Xinhai 13 (G. barbadense), respectively. Two different F1 populations obtained were assessed to specify the dominant and recessive inheritance of fiber fuzziness in these lines. Three F1 populations (Kuguangzi × TM-1, Luwuxu × TM-1, and SA65 × TM-1) displaying recessive fiber fuzziness inheritance were selected to construct the F2 population for a further genetic study of fuzzless seed trait. The results of this study indicated that (1) the same materials showed different quantities of fuzzy fiber in different environments. Less fuzzy fiber was found in Xinjian and Hainan compared to Anyang. Thus, the quantity of fuzzy cotton seed depends on ecological environment. (2) In upland cotton, the inheritance of fiber fuzziness was dominant for 26 accessions (25.49%), incompletely dominant for 8 accessions (7.84%), and recessive for 22 accessions (21.57%). The inheritance of fiber fuzziness in island cotton was dominant for 5 accessions (5.88%), incompletely dominant for 16 accessions (18.82%), and recessive for 9 accessions (10.59%). Analysis of F2 population indicated that the fiber fuzziness of Kuguangzi was controlled by two recessive complementary effect alleles. The fiber fuzziness of Luwuxu was controlled by two recessive additive effect alleles, and a single recessive gene controlled the same trait for SA65. Fiber fuzziness evaluation in cotton germplasm provides the genetic and basic information for cotton fiber development study and breeding.