Abstract

The rice blast (Magnaporthe grisea) is a serious constraint to rice production in many rice producing countries including Uganda. Yield losses of up to 100% are attributed to the blast disease in different rice growing regions. In addition to these, the inheritance of resistance to the disease has not yet been studied under Ugandan condition.

Experiment was conducted under controlled conditions by using three resistant and four susceptible elite genotypes as parental lines for population development in half dialled mating design with the aim of providing relevant genetic information as a contribution towards the development of rice varieties with resistance to blast disease. A total of 18 crosses were advanced to F2 level. The F2 segregates and their corresponding parents were evaluated in the screen house against single virulent isolate of rice blast pathogen in 4 by 7 alpha lattice design in three replications.

These results showed that there was significant variation for rice blast resistance among genotypes. Significant general and specific combining abilities were observed, indicating that both additive and non-additive gene effects were important for rice blast resistance, although the additive effect was predominant. A High coefficient of genetic determination in the broad sense (0.99) and narrow sense (0.85), were obtained on a genotype mean basis with a high Baker’s ratio of 0.86, indicating primarily additive inheritance among crosses.

The segregation pattern for resistance to rice blast showed single dominant gene in some elite susceptible × resistant crosses, duplicate recessive epistasis in other elite susceptible × resistant crosses and two genes with duplicate dominant epistasis in resistant × resistant crosses. The crosses between susceptible by susceptible genotypes did not show segregation. Overall, resistance was highly heritable, with mainly additive gene action between crosses. Results suggest that simple breeding strategies with selection in early generations would be effective for rice blast resistance.

Keywords: Genetics, Segregation, Rice, Blast, Resistance