Euphytica 112: 125–135, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 125 QTL analysis and mapping of pre-harvest sprouting resistance in Sorghum Diego Lijavetzky 1 , M. Carolina Mart´ ınez 1 , Fernando Carrari 1 & H. Esteban Hopp 1,2 1 Instituto de Biotecnolog´ ıa, CICV INTA Castelar, CC 77, (1708) Mor´ on, Buenos Aires, Argentina; 2 Departamento de Biolog´ ıa, Facultad de Ciencias Exactas Naturales, Universidad de Buenos Aires, Argentina Received 18 May 1998; accepted 30 August 1999 Key words: dormancy, molecular markers, pre-harvest sprouting, QTL mapping, Sorghum bicolor, Vp1 Summary One of the most important agronomic problems in the production of sorghum [Sorghum bicolor (L.) Moench] in humid climates is pre-harvest sprouting (PHS). A molecular linkage map was developed using 112 molecular markers in an F 2 mapping population derived from a cross between IS 9530 (high resistance to PHS) and Redland B2 (susceptible to PHS). Two year phenotypic data was obtained. By means of interval mapping analysis, two significant QTL were detected in two different linkage groups with LOD scores of 8.77 and 4.39. Each of these two QTL individually explained approximately 53% of the phenotypic variance, but together, in a two-QTL model, they explained 83% of the phenotypic variance with a LOD score of 12.37. These results were corroborated by a one-way ANOVA in which the four flanking markers of the most likely QTL positions displayed highly significant values in the F-test, and significant variation in trait expression was associated with marker genotypic classes. The four markers with highest effect in the one-way ANOVA were also detected in the second year replication of the F 2 population, and significant genotype × environment interactions was observed. The putative relationship between PHS resistance in sorghum and the maize Vp1 gene is also discussed. Abbreviations: GI – germination index; PHS – pre-harvest sprouting Introduction Pre-harvest sprouting (PHS) is one of the most import- ant problems in grain sorghum [(Sorghum bicolor (L.) Moench] production in Argentina and other parts of the world, particularly when grain maturation takes place under high humidity and rainfall conditions (Maiti et al., 1985). This situation leads to reduced seed viability and promotes hydrolysis of starch in the endosperm. Starch hydrolysis results in both a decreasing in grain weight and establishment of a favorable environment for saprophyte fungi (Castor & Frederiken, 1977). Traditionally, this problem has been partiality solved by growing genotypes with high tannin content. While tannins inhibit PHS (Chavan & Jadhav, 1984), they result in unacceptable reductions in feed value (Chavan & Jadhav, 1984; Elkin et al., 1991; Agrawal & Chitnis, 1995). Thus, this kind of sprouting resistance may not be the best for use in elite grain sorghums. The physiological basis of PHS in sorghum has been widely studied using resistant and susceptible genotypes containing low levels of tannin (Benech Arnold et al., 1991; Benech Arnold et al., 1995a; Benech Arnold et al., 1995b; Steinbach et al., 1995; Steinbach et al., 1997). One of the most dramatic effects is reported in Steinbach et al. (1995) where embryos from susceptible genotypes were found to be 10-fold less sensitive to inhibitory effects of abscisic acid compared with embryos from resistant genotypes. Although these genotypes have been known for a long time, the genetic basis of resistance to sprouting has not received due attention. The difficulty in elucidating the genetic basis of traits with quantitative behavior like PHS may be due to the lack of knowledge about the location, num-