Characterization of monogenic lines for blast resistance

A set of near-isogenic lines (NILs) with single gene for blast resistance is useful as differentials and gene source in rice (Oryza sativa L.). However, the development of NILs for blast resistance has been limited to a small number of genes (Mackill et.al., 1992). The authors have been trying to develop and characterize monogenic lines with single blast resistance genes to be used as differentials in the absence of NILs. A total of 31 monogenic lines with 24 kinds of resistance genes - Pia, Pib, Pill (t), Pil 2 (t), Pii, Pi3, Pik-s, Pik, Pik-p, Pik-h, Pik-m, Pil, Pi7 (t), Pish, Pit, Pita, Pita-2, Piz, Piz-5, Piz-t, Pi5 (t), Pi 9 (t), Pil 9 (t), and Pi20 - were developed. These genes originated from 25 resistant donors. These lines were bred by backcross method to transfer the single gene into the recurrent parent, a Chinese japonica variety Lijiang xintuanheigu (LTH), without any known resistance genes in the genetic background. Backcross generations were inoculated with isolates avirulent to the target gene and homozygous resistant lines were selected. Twenty representative isolates from the Philippines were used to confirm the reaction pattern of each monogenic line. Monogenic lines showed distinct reaction patterns. However, Pik alleles could not be differentiated and there was no incompatible isolates for Pit and Pil 9 (t). The plants were cultivated under screenhouse and field conditions. Morphological traits such as culm length, panicle length, leaf width, leaf length, days to heading, spikelet fertility and 100-seed weight were also investigated. Each monogenic line was fixed in these traits, but there were wide variations in all the traits among the monogenic lines. Culm, panicle and leaf lengths, leaf width and days to heading were higher under the screenhouse than under field conditions. Spikelet fertility and panicle number were higher under field condition. Under both conditions, all traits were significantly different at the 5% level of significance