Cytological and genetic analysis of a virescent mutant in upland cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.)

It is well known that genetic mutation could be generated by physical treatment (for example, γ-irradiation) and chemical treatment (for example methylnitrosourea and ethyl methanesulfonate). Here we reported identification of a virescent mutation (vsp) after exposing the upland cotton (Gossypium hirsutum L.) CCRI58 seeds in space environments. vsp mutant was characterized at the morphological, agronomic, cellular and genetic levels. vsp mutant showed an earlier virescence and specific only to true leaves. Agronomic traits of vsp mutant, such as plant height, number of bolls, boll weight, yield and fiber quality were significantly lower than those of CCRI 58. Chlorophyll level, carotenoid level and photochemical efficiency of vsp mutant true leaves were significantly lower compared to CCRI 58 at young leave stage. Anatomical studies of chloroplasts showed that vsp mutant lacked grana in the thylakoids of the mesophyll cells at young leave stage, while CCRI 58 showed normal grana in the thylakoids of the mesophyll cells at young leave stage. This indicated that chlorophyll and carotenoid levels were related with chloroplast structure. Genetic analysis indicated that vsp was controlled by one recessive gene in nucleus. Allelic tests showed that vsp was nonallelic to 12 virescent genes currently available at Anyang, China. In summary, we identified a vsp mutant after exposing the upland cotton (Gossypium hirsutum L.) seeds in space environments. vsp could be a newly identified virescent gene. vsp may also be used as a marker in cotton breeding programs. Exposing seeds in space environments could cause new spectrum of genetic mutations and could be used for breeding programs.