title: Heat-tolerant rice cultivars retain grain appearance quality under free-air CO2 enrichment.
abstract: BACKGROUND
  Heat-tolerant rice cultivars have been developed as a countermeasure to poor grain appearance quality under high temperatures. Recent studies showed that elevated CO2 concentrations (E-[CO2]) also reduce grain quality. To determine whether heat-tolerant cultivars also tolerate E-[CO2], we conducted a free-air CO2 enrichment (FACE) experiment with 12 rice cultivars differing in heat tolerance.
  
  
  RESULTS
  The percentage of undamaged grains of five standard cultivars (Akitakomachi, Kinuhikari, Koshihikari, Matsuribare, Nipponbare) averaged 61.7% in the ambient [CO2] (AMB) plot and 51.7% in the FACE plot, whereas that of heat-tolerant cultivars (Eminokizuna, Wa2398, Kanto 257, Toyama 80, Mineharuka, Kanto 259, Saikai 290) averaged 73.5% in AMB and 71.3% in FACE. This resulted in a significant [CO2] by cultivar interaction. The percentage of white-base or white-back grains increased from 8.4% in AMB to 17.1% in FACE in the sensitive cultivars, but from only 2.1% in AMB to only 4.4% in FACE in the heat-tolerant cultivars.
  
  
  CONCLUSIONS
  Heat-tolerant cultivars retained their grain appearance quality at E-[CO2] under present air temperatures. Further improvements in appearance quality under present conditions will be needed to achieve improvements under E-[CO2], because E-[CO2] will likely lower the threshold temperature for heat stress.
authors.affiliation: National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba 305-8604, Ibaraki, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Usui
authors.affiliation: National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba 305-8604, Ibaraki, Japan.
authors.forename: Hidemitsu
authors.initials: H
authors.lastname: Sakai
authors.affiliation: National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba 305-8604, Ibaraki, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tokida
authors.affiliation: Taiyo Keiki Co. Ltd, 1-12-3, Nakajujo, Kita-ku 114-0032, Tokyo, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Nakamura
authors.affiliation: NARO Agricultural Research Center, 3-1-1 Kannondai, Tsukuba 305-8666, Ibaraki, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakagawa
authors.affiliation: National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba 305-8604, Ibaraki, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Hasegawa
keywords: Chalky grains; Climate change; FACE (free-air CO2 enrichment); Heat-tolerant cultivars; Oryza sativa