It is important to note that any resistance based on a single
R gene can be easily broken by the pathogen. The Pi-ta gene
has been effectively used for blast control in the southern USA
since 1990 (Moldenhauer et al. 1990). Despite spontaneous
occurrences of virulent blast races in rice fields, occasionally
resulting in significant yield loss (Lee et al. 2005), the Pi-ta
gene is still effective in preventing blast races containing AVRPita.
Highly homologous AVR-Pita alleles were identified
from M. grisea races collected over 30 years in the southern
USA and worldwide (Jia et al. 2005). These findings not only
reflect the fact that the Pi-ta gene has been durable in tropical
japonica rice production areas in the USA, but also suggest
that the Pi-ta gene has potential for broader application
worldwide.