Rice blast [Pyricularia grisea (Cooke) Sacc.] is an internationally devastating rice (Oryza sativa L.) disease. This study was conducted to determine the inheritance of rice blast resistance to the blast fungus races IB‐49 and IC‐17. Nine parents were crossed in all possible combinations. Parents, F1, F2, and selected F2‐derived lines in the F3 were tested for their reactions to blast fungus races IB‐49 and IC‐17 separately in the greenhouse during 1986 and 1987. The parents ‘Starbonnet’, ‘Newbonnet’, and ‘M‐201’ were susceptible to both races; ‘Raminad Strain 3’, ‘Pi No. 4’, and ‘Katy’ were resistant to both races; ‘Mars’ and ‘Zenith’ were susceptible to race IB‐49 and resistant to race IC‐17; and ‘NP 125’ was susceptible to race IC‐17 and resistant to race IB‐49. Inheritance of resistance to race IC‐17 was dominant and monogenic in crosses involving resistant parents. Inheritance to race IB‐49 was dominant and monogenic in crosses with the parents Raminad Strain 3, Pi No. 4, and Katy, but was controlled by two dominant complementary genes in crosses involving NP 125. Allelic relationships among the resistant parents indicate that one locus controlled the resistance to race IB‐49 and three loci controlled the resistance to race IC‐17. Resistance to both races was conferred by one gene or group of tightly linked genes in Katy. Diverse sources of resistance are necessary to avoid genetic vulnerability. Resistance to race IC‐17 and IB‐49 is simply inherited and should be relatively easy to incorporate into rice cultivars.

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Five indica photo-thermo sensitive genic male sterile (PTGMS) lines as female parents and 5 restorers lines as male parents were used to make 25 F 1 hybrids by diallel cross to study the combining ability and standard heterosis of 10 agronomic traits. The results showed that the characters of PTGMS lines are determined by the effects of general combining ability (GCA) and specific combining ability (SCA) of both the sterile and restorer lines and the GCA was found to be more effective. Pei'ai64S was the best general combiner among sterile lines followed by NS30g, while the Minghui63 was the best general combiner among the restorer lines followed by Sh623. Significant differences in combining ability among the sterile lines and positive correlation between the values of GCA and standard heterosis of hybrids were observed. The higher GCA of parents exhibited stronger standard heterosis in hybrids.

Expression of variable degree of spikelet sterility in Indica / Japonica inter-subspecific crosses is one of the barriers in the exploitation of higher degree of heterosis manifested in such crosses. Two cytoplasmic male sterile (CMS) and their maintainer lines (B) one of them was Japonica (Giza177 A and Giza177 B) and the other was Indica (IR 69625 A and IR 69625 B) were crossed as female parents in lines x tester mating design with twenty seven diverse tester lines to study their behavior and combining ability for wide compatibility traits pollen fertility, spikelet fertility and filled grains panicle). The results indicated that the mean squares of genotypes and including parental lines were highly significant for all studied WC traits at the two years and their combined data, indicating the presence of large variations among them. The interactions of genotypes, parents, crosses and parents VS crosses with years were highly significant for all studied traits. Combining ability analysis revealed that both additive and non-additive gene action contributed in the genetic expression of the studied traits. The results also indicated that the tester lines, Giza175, Giza178, Giza181, Giza182, IR25571-31, GZ5121, GZ1368, GZ6296-12-1-4, GZ6296-12-1-2, IR56381-139 and BR1141-28-37 showed high fertilities with Indica CMS line (IR69625 A) and their maintainer line IR69625 B in the two years and their combined data and were identified as restorer lines. On the other hand, the tester lines IR65598-112, Palawan, 02428-p7-1, Pecos and Dular showed high fertility with both Indica and Japonica maintainer lines and confirmed as wide compatibility (WC) rice varieties. In addition, the tester lines Mars, 02428-p7-1, Pecos, Dular and Lambyque showed complete sterile with both of the Indica and Japonica CMS lines and defined as a maintainer lines to increas the probability of getting new CMS and maintainers lines with the WC gene. This investigation was carried out at the Experimental Farm of Rice Research and Training Center (RRTC), Sakha, Kafr El-Sheikh, Egypt, during the three successivel growing seasons from 2003 to 2005. The genetic materials used in this investigation included two cytoplasmic male sterile (CMS) lines and their maintainers (B) lines. The CMS line Giza177A their maintainer and Giza177B were used as Japonica lines while, IR69625A and IR69625B, used as Indica lines. The aforementioned four female lines were crossed as parents with twenty seven male lines selected as testers to produce 108 F1 hybrids seeds according to 4 x27 Line x Tester mating design during 2003 growing season. All the genotypes were evaluated in a randomized complete blocks design (RCBD) experiment with three replications during the second week of May of 2004 and 2005 seasons. The observations were recorded on ten plants which were taken at random from each test entry in each replication for three WC and restoring ability traits i.e. Pollen fertility (%), spikelet fertility (%) and filled grains panicle -1 . The analysis of variance were made fo...