Cherif, M., Rezgui, S., Devaux, P. and Harrabi, M. 2008. Genetic analysis of net blotch resistance in a two-row six-row cross of barley, using doubled-haploid lines. Can. J. Plant Sci. 88: 257Á266. The effect of spike type on net blotch resistance is not fully understood in barley (Hordeum vulgare L.). A doubled-haploid barley population derived from a cross between a susceptible two-row (Roho) and a resistant six-row (line 90) genotypes was used to study the genetics of net blotch resistance and to determine the effect of spike type on net blotch resistance at the adult plant growth stage across three environments. Net blotch rating was evaluated using a mass disease index, area under the disease progress curve and the apparent infection rate. Partial resistance to Pyrenophora teres was observed in many DH lines and in the parental line 90 in the three environments. This result indicated that selecting for partial resistance is feasible under severe net blotch conditions where differential responses among DH lines were noted as in Mograne in 2003Á2004. The normality test and/ or the means comparison method suggested that additive)additive epistasis effects influenced the expression of all disease parameters in the three environments. Both the coefficient of skewness and the number of transgressive lines indicate the presence of a complementary gene interaction for most disease parameters. Results showed that two-row lines were particularly associated with net blotch resistance in Mograne 2002Á2003 and in Tunis greenhouse 2004. A strategy for improving the level of quantitative resistance to P. teres in later generations is recommended. Cherif, M., Rezgui, S., Devaux, P. et Harrabi, M. 2008. Genetic analysis of net blotch resistance in a two-row six-row cross of barley, using doubled-haploid lines. Can. J. Plant Sci. 88: 257Á266. L'effet du nombre de rangs de l'e´pie´pi sur la re´sistancere´sistance de l'orge (Hordeum vulgare L.) a` la rayure re´ticuleére´ticuleé est mal compris. Une population haploı¨dehaploı¨de doubleé issue d'un croisement entre un cultivar a` deux rangs sensible (Roho) et une ligneé locale a` six rangs re´sistantere´sistante (ligneé 90) a e´teútiliseée´teútiliseé pour e´tudiere´tudier la ge´ne´tiquege´ne´ge´ne´tique de la re´sistancere´sistance et pour de´terminerde´terminer l'effet du nombre de rangs de l'e´pie´pi sur la re´sistancere´sistance a` la rayure re´ticuleére´ticuleé au stade adulte dans trois environnements. La reáction a` la rayure re´ticuleére´ticuleé a e´teé´valueée´teé´e´teé´valueé moyennant l'indice d'attaque, la surface au-dessous de la courbe d'e´volutione´volution de la maladie et le taux d'infection apparent. De nombreuses ligneés haploı¨dehaploı¨de-doubleés ainsi que la ligneé 90 ont manifesteúne re´sistancere´sistance quantitative a` Pyrenophora teres dans les trois environnements. Cette e´tudee´tude indique que la seíection pour la re´sistancere´sistance partielle a` la rayure re´ticuleére´ticuleé serait plus facile en conditions de forte e´pide´miee´pide´e´pide´mie,o...