Abstract The present study in bread wheat was under- taken, firstly, to identify chromosomes carrying QTLs controlling 1000 grain weight (GW) and, secondly, to de- velop molecular marker(s) linked with this trait. Using the genotype Rye Selection111 (RS111), we carried out a monosomic analysis that suggested that 8 chromosomes (1A, 1D, 2B, 4B, 5B, 6B, 7A and 7D) carried QTLs con- trolling GW, with only 3 of these (1A, 2B, 7A) carrying alleles for high GW. To tag the QTLs present on these chromosomes, we crossed the genotype RS111 with high GW (56.83 g) with the genotype Chinese Spring (CS) with low GW (23.74 g) and obtained 100 RILs. These RILs showed normal distribution for GW. The parental genotypes were analysed with as many as 346 STMS primer pairs for detection of polymorphism. Of these, 267 primer pairs gave scorable amplification products, 63 of which detected polymorphism between the parents. Using each of these 63 primer pairs, we carried out bulked se- gregant analysis on RILs representing two extremes of the distribution. One primer pair (WMC333) showed an association of the marker locus Xwmc333 with grain weight. This was confirmed through selective genotyp- ing, and the co-segregation data on molecular marker lo- cus Xwmc333 and GW were analysed following a single marker linear regression approach. Significant regression suggested linkage between Xwmc333 and a QTL for GW. The results showed that the above QTL accounted for 15.09% of the variation for GW between the parents. The marker has been located on chromosome arm 1AS, and QTL was designated QGw1.ccsu-1A. Key words Bread wheat · Grain weight · Microsatellite · Monosomic analysis · QTL analysis · STMS Introduction Among the various grain related traits, grain weight (GW) is one of the more important ones, since it is phenotypically the most stable component of yield and is also positively correlated with flour yield. Grain weight has been shown to be controlled by a number of quanti- tative trait loci (QTLs) located on different chromo- somes (Halloran 1976; Bannier 1979; Khrabrova and Maistrenko 1980; Chojecki et al. 1983; Zheng et al. 1993; Giura and Saulescu 1996). Unfortunately, an im- provement in GW through plant breeding has generally been found to be of no consequence, since an increase in GW is known to be associated with a reduction in grain number per spike, thus neutralizing the benefit derived from the increased grain weight. Phenotypic selection for this trait is also laborious and time-consuming. Under these circumstances, the use of molecular markers for in- direct marker-assisted selection for improvement in GW should be a convenient alternative. With respect to wheat breeding molecular markers have already become available for a large number of economic traits (Gupta et al. 1999). In our own laborato- ry, a few sequence-tagged microsatelitte site (STMS) and sequence-tagged site (STS) markers for grain protein content and pre-harvest sprouting tolerance have been recently identified (Prasad et al. 1999; Roy et al. 1999). The study reported here was undertaken to identify chro- mosomes and to develop molecular markers associated with GW. For this purpose, two parents differing signifi- cantly in GW were selected, and a set of recombinant in- bred lines (RILs) were derived from a cross between these two parents. The parent with high GW was used for monosomic analysis, and the parents together with the RILs were used for identification of molecular mark- ers that are closely associated with QTLs for GW. A va- riety of available markers and techniques including ran- Communicated by P.M.A. Tigerstedt R.K. Varshney · M. Prasad · J.K. Roy · N. Kumar · H.S. Balyan P.K. Gupta ( ✉ ) Molecular Biology Laboratory, Department of Agricultural Botany, Ch. Charan Singh University, Meerut-250004, India Fax: +91-121-760577; 767018 e-mail: pkgupta@ndf.vsnl.net.in Harjit-Singh · H.S. Dhaliwal Biotechnology Centre, P.A.U., Ludhiana-141004, India Theor Appl Genet (2000) 100:1290–1294 © Springer-Verlag 2000 ORIGINAL PAPER R.K. Varshney · M. Prasad · J.K. Roy · N. Kumar Harjit-Singh · H.S. Dhaliwal · H.S. Balyan · P.K. Gupta Identification of eight chromosomes and a microsatellite marker on 1AS associated with QTL for grain weight in bread wheat Received: 15 September 1999 / Accepted: 9 November 1999