Detection of a major QTL conditioning trichome length and density on chromosome arm 4BL and development of near isogenic lines targeting this locus in bread wheat

Trichomes are differentiated epidermal cells and can be found on above ground organs of nearly all land plants. Results from previous studies show that trichomes play important roles against a wide range of both biotic and abiotic stresses. By examining differences between parental genotypes of available populations, we identified a population of recombinant inbred lines showing clear segregation for trichome density and length. Assessing the F8 lines of the population growing in the field detected a major locus on chromosome arm 4BL. This locus was detected based the assessments of either fully expanded third leaves or flag leaves after anthesis. Based on the position of the QTL, an SSR marker was used to identify heterozygous plants at this locus from F5 lines derived from the same cross for the F8 population. Three pairs of near isogenic lines targeting this locus were obtained from these heterozygous plants. Difference in trichome length between the two lines with opposite alleles for each of these NIL pairs were similar to that between the two parental genotypes for the mapping populations, confirming that this single locus is mainly responsible for the trichome characteristics measured in this study. The allele with long and dense trichome is dominant as this characteristic was shown by the heterozygous individuals at this marker locus. Apart from the targeted locus, NIL pairs have highly homogeneous genetic backgrounds. Thus, the NILs could be invaluable in understanding the relationship between trichome density and resistance or tolerance to various biotic and abiotic stresses.