Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/1/1996
Publication Date: N/A
Technical Abstract: Panicle blight (PB) symptoms which result in unfilled or partially filled seed heads have been observed frequently at the Beaumont rice station. It has been considered a physiological malady as attempts to isolate a casual organism or demonstrate a response to foliar fungicides have been unproductive. 1995 was unique in that very severe PB was observed throughout the Beaumont breeding nursery plots and in commercial fields in Texas. Symptoms were associated with late planted rice and caused speculation that a weather phenomenon may be related. We evaluated 4 years of available weather data that provided hourly summaries during the cropping season to determine if 1995 was unique in terms of weather patterns. 1995 did not appear unusual for daytime temperatures, accumulation of light, or heat index. However, it had 95 hours where the nighttime temperatures exceeded 26 C as compared with the other years (ca 46 h) and this occurred near flowering for many of the plots. We also found that July had about twice as many hours with low daytime relative humidity suggesting that the plants may have also been stressed during the day. We evaluated 443 progeny from 52 crosses which were grown under conditions having severe PB symptoms to determine if there was an association of parentage with susceptibility. The parents Toro 2, Guichow, Rosemont, and Katy were rated highly susceptible while Newbonnet, Rexmont, Jodon, Cypress, RU8703196, Lemont, Gulfmont, Maybelle and Teqing were less so. Highly susceptible progeny yielded nil and the seed quality of what grain was harvested was very poor. This suggest that extreme nighttime temperatures may predispose rice to PB but that genotype and environment play important roles in determining the level of susceptibility.