Map-based cloning of q LP_(A01.1),a favorable allele from the Gossypium tomentosum chromosome segment line

Cotton is an important natural fiber crop worldwide which plays a vital role in our daily life.High yield is a constant goal of cotton breeding,and lint percentage(LP)is one of the important components of cotton fiber yield.A stable QTL controlling LP,qLP_(A01.1),was identified on chromosome A01 from Gossypium hirsutum introgressed lines with G.tomentosum chromosome segments in a previous study.To fine-map qLP_(A01.1),an F2 population with 986individuals was established by crossing G.hirsutum cultivar CCRI35 with the chromosome segment substitution line HT_390.A high-resolution genetic map including 47 loci and spanning 56.98 cM was constructed in the QTL region,and qLP_(A01.1)was ultimately mapped into an interval corresponding to an~80 kb genome region of chromosome A01in the reference genome,which contained six annotated genes.Transcriptome data and sequence analysis revealed that S-acyltransferase protein 24(GoPAT24)might be the target gene of qLP_(A01.1).This result provides the basis for cotton fiber yield improvement via marker-assisted selection(MAS)and further studies on the mechanism of cotton fiber development.

Genetic mapping and identification of Lg^(f) loci controlling green fuzz in Upland cotton(Gossypium hirsutum L.)

Naturally colored cotton fiber is environment-friendly but has monotonous color and poor fiber quality.Identification of green fiber or fuzz genes would aid in investigating the biosynthesis of green pigments in cotton fibers. In this study, we established a mapping population and found that the Lg^(f) trait(white lint and green fuzz) from Gossypium hirsutum race latifolium is controlled by an incompletely dominant gene.The Lg^(f) locus was mapped to a 71-kb interval on chromosome 21 containing seven genes, including a transcription factor with similarity to Arabidopsis MYB9. Harboring 13 SNPs and a 4-bp insertion/deletion in its promoter, GhMYB9 was highly up-regulated in the critical period for green pigment development in fuzz. Virus-induced gene silencing of GhMYB9 in a green-fuzz accession of G. hirsutum race latifolium TX-41 conferred white or light green fuzz. These results suggest that GhMYB9 is an important contributor to green pigments in cotton fiber and shed light on the regulatory mechanism controlling green pigmentation.

Constructing a high-density linkage map for Gossypium hirsutum × Gossypium barbadense and identifying QTLs for lint percentage

To introgress the good fiber quality and yield from Gossypium barbadense into a commercial Upland cotton variety, a high‐density simple sequence repeat （SSR） genetic linkage map was developed from a BC1F1 population of Gossypium hirsutum × Gossypium barbadense. The map com-prised 2,292 loci and covered 5115.16 centiMorgan （cM） of the cotton AD genome, with an average marker interval of 2.23 cM. Of the marker order for 1,577 common loci on this new map, 90.36% agrees well with the marker order on the D genome sequence genetic map. Compared with five pub-lished high‐density SSR genetic maps, 53.14% of marker loci were newly discovered in this map. Twenty‐six quantitative trait loci （QTLs） for lint percentage （LP） were identified on nine chromosomes. Nine stable or common QTLs could be used for marker‐assisted selection. Fifty percent of the QTLs were from G. barbadense and increased LP by 1.07%–2.41%. These results indicated that the map could be used for screening chromosome substitution segments from G. barbadense in the Upland cotton background, identifying QTLs or genes from G. barbadense, and further developing the gene pyramiding effect for improving fiber yield and quality.