Later, the discovery of the pi meson showed it to have the properties of Yukawa's particle.
From the en.wikipedia.org
He predicted the beta decay of a pi meson.
From the en.wikipedia.org
About one-thirtieth of the times that a pi meson hit a deuterium nucleus, out came the eta meson, which decays into three pions.
From the time.com
Also, when the muon was first detected it was originally thought to be the meson predicted by Yukawa a year earlier, which actually tiurned out to be the pi meson.