Blast is one of the worst rice diseases. I believe that, thanks to the breeders, most modern varieties have decent levels of resistance. After all, they can be used in varietal mixtures to protect traditional glutinous rice varieties from blast. ((Zhu, Y., Chen, H., Fan, J., Wang, Y., Li, Y., Chen, J., Fan, J., Yang, S., Hu, L., Leung, H., Mew, T., Teng, P., Wang, Z., & Mundt, C. (2000). Genetic diversity and disease control in rice. Nature, 406 (6797), 718-722 DOI: 10.1038/35021046 Also see this post.)) Unfortunately, much of this resistance is not durable, because the pathogen overcomes it with time.
For a long time, durable resistance has been known to exist in some Japanese varieties. But these varieties have not been useful for resistance breeding, as the resistant parent also brought along undesired characteristics: the offspring always had poor eating quality.
Shuichi Fukuoka and colleagues have found out why. They report in Science ((Fukuoka, S., Saka, N., Koga, H., Ono, K., Shimizu, T., Ebana, K., Hayashi, N., Takahashi, A., Hirochika, H., Okuno, K., & Yano, M. (2009). Loss of Function of a Proline-Containing Protein Confers Durable Disease Resistance in Rice Science, 325 (5943), 998-1001 DOI: 10.1126/science.1175550
see also Normile, D. (2009). New Strategy Promises Lasting Resistance to a Rice Plague Science, 325 (5943), 925-925 DOI: 10.1126/science.325_925)) that it is because of a tight genetic linkage. Resistance is conferred by the Pi21 locus, and:
The eating quality of plants carrying the elite cultivar’s chromosomal sequence from a point less than 2.4 kb downstream of the Pi21 locus was equivalent to that of the elite cultivar, and the plants showed a high level of blast resistance. In contrast, plants carrying the donor chromosomal sequence up to 37 kb downstream of the Pi21 locus showed inferior eating quality.
By crossing in just the right bit of the chromosome, and making sure that the neighboring areas do not tag along, resistance can now be transferred, without spoiling the taste.
