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ThesisItem Restricted IDENTIFICATION OF MOLECULAR MARKER(S) ASSOCIATED WITH FIBRELESS TRAIT IN Gossypium arboreum L.(Punjab Agricultural University, Ludhiana, 2011) Baljinder KaurThe present investigation was carried out with the objectives (i) to study inheritance of fibreless trait in the cotton fibre mutant PAUFL1 and (ii) identification of molecular marker(s) linked to the fibreless trait. The experimental plant material consisted of parental lines viz. fuzzless, lintless and trichomeless mutant PAUFL1 and wild type parent LD902 with normal fuzz, lint and trichome development, F1, F2 population and respective backcross generations. F1 and BC1 (F1 x LD902) plants were observed to possess both fuzz and lint indicating that allele for fibre development was dominant over the allele governing fibreless condition. Of the 296 F2 plants, 230 plants were observed to be fuzzy and linted, whereas rest of the 66 plants was devoid of fibre (lint and fuzz). F2 population segregated into monogenic 3 fibred:1 fibreless ratio. The backcross population with mutant parent PAUFL1 did not deviate from ratio of 1:1 (fibred : fibreless) expected for a monogenic trait. Of the 124 plants, 66 plants were fibre bearing and rest 58 plants were observed to be fibreless. Monogenic recessive control of the fibreless trait in PAUFL1 is suggested. F1 hybrid and its wild type parent LD902 did not differ for span length, uniformity ratio, elongation, fibre stength and micronaire values. PAUFL1 did not bear any trichomes, whereas, in LD902, an average of 92.2 and 155.6 trichomes were counted on mature and young leaves respectively. In case of F1 plants, mean trichome number for young leaf was 118.4 and 53.5 for mature leaf. Mean trichome density for mature and young leaves was 47.7 and 104.2 respectively in F2 generation. A strong positive correlation between trichome density on young and mature leaf was observed. Deviation from normal distribution was recorded in distribution of leaf trichomes in young as well as mature leaf in F2 plants. The trichomeless condition co-segregated with the fuzzless and lintless condition. It is suggested that either the genes controlling fuzzless, lintless and leaf trichomless state are tightly linked or these three traits are under the control of a single gene which is involved in both fibre and leaf trichome development. 351 SSR primers were used for the molecular characterization of fibreless trait. Of the 40 primer pairs observed to be polymorphic between the parental lines, ten primers were found to be uncommon between the F2 bulks. Further, 190 individual F2 plants were genotyped using these primers. None of the primers showed association with the fibreless and trichomeless trait. Desi