NAFRI 15th Anniversary conference, Vientiane, Laos, 9th April, 2014 Spikelet sterility observed in popular rice variety, Thadokkham1 (TDK1), during the hot, dry season in Southern Laos Tsutomu Ishimaru,1,2* Xaiyalath Seefong,3 Mayumi Yoshimoto,4 Lathvilayvong　Phoudalay,3 Samson　Benjamin,1 Toshihiro Hasegawa,4 and Kei-ichi Hayashi1,2 (1．IRRI，2．JIRCAS，3．PAFO, 4. NIAES) Keywords; heat stress, panicle temperature, spikelet sterility, TDK1, time of day of flowering (TDF)

Vegetative stage: White leaf tip, reduced tillering and plant height Heat stress affects plant growth differently depending on the growth stage Vegetative stage: White leaf tip, reduced tillering and plant height Booting stage: reduced spikelet, low fertile pollen and spikelet Flowering stage: low fertile spikelet Grain filling stage: low grain weight, high chalkiness. Yoshida, 1981

Effect of heat stress at anthesis Chamber experiments revealed that high temperature over 35 oC induced spikelet sterility at anthesis Induced over 35 oC Most sensitive at flowering stage Variety: Akihikari (Japonica) (Kim et al. 1996) How spikelet sterility at flowering stage is induced by heat stress? (Satake and Yoshida 1978)

Less pollens released to stigma Anther dehiscence is important factor for fertilization under heat stress Yellow anther: Less pollen release Anther High temperatures (35oC<) Stigma Aberrant dehiscence Less pollens released to stigma Lesser chances in fertilization Sterility Pollens drop from dehisced anther to stigma

Record-setting high temperature in the summer of 2007 in Japan Daily maximum temperatures Maximum temperature is normally around 34 oC, but it went up to 38.5 oC in 2007 Spikelet sterility (%) by date of full heading Heat-induced spikelet sterility was occasionally observed in the temperate Japan

Heat vulnerable regions in the world Southern Lao is one of the most heat-vulnerable regions Maximum temperature > 35oC for 10 days during rice flowering stage Laborte et al. 2012 Reports on actual damage by heat stress at anthesis are limited. HISS is occuring in popular variety in Southern Laos?

Maximum and minimum temperature in the dry season of 2013, Savannakhet Experimental site:Thasano Rice Research and Seed Multiplication Center Heading period of 1st batch Heading period of 2nd batch Daily air temperature (oC) Date Temperatures in 2nd batch was much hotter than those in 1st batch

Shading net experiment Variety: Thadokkham1 (TDK1) Hypothesis Key method: Shading treatment at flowering stage (Only for 5-7 days by 60% shading net) Decrease in panicle temperature Decrease in spikelet sterility Idea from Wakamatsu et al. (2009) “White-back type of chalkiness increases by the combination stress of heat and solar radiation”. ‘Hot spot’ for heat-induced sterility

Shading treatment reduced sterility by 13 % Spikelet sterility under shaded and unshaded condition **Significant at 1% level by Tuckey’s test Shading treatment reduced sterility by 13 %

TDK1 flowered around noon Anther color is white around 11:00. *Panicles at border were used 35.5oC Percentage of opened spikelet in a day (%) 36.5oC Anther color was yellow around 13:00. 37.3oC Time of day (h) Spikelets that flowered at the later hour would be at the higher risk to be sterile.

Estimated panicle temperatures at late time of day of flowering at 1230h Panicle temperatures calculated by Integrated Micrometeorology Model for Panicle And Canopy Temperature (IM2PACT) Date Time of day (h) Treatment Air temperature (oC) Relative humidity (%) Wind speed (m/s) Solar radiation (W/m2) Panicle temperature (oC) 6th March 1230 Unshaded 30.2 49 1.8 913 30.4 4th April 37.6 47 2.2 799 34.6 Shaded 320 32.6 5th April 36.5 796 33.9 318 31.7 IM2PACT; Yoshimoto et al. 2012 Panicle temperatures could reduce by 2 oC in shaded condition

Summary and future prospects Heat-induced spikelet sterility at anthesis occurred in TDK1 in Southern Lao during the hot period of the dry season in 2013. Solar radiation is considered to be related to the induction of spikelet sterility. More detailed analyses will be required with local popular varieties (i.e. TDK8, TDK11, Thasano varieties). Upgrading heat tolerance or heat escape is required to cope with expected future vulnerable climates in the dry season.

International Rice Congress, Bangkok Thank you for your attention! IRRI-Japan project funded by MAFF Development of technologies for mitigation and adaptation to climate change in agriculture, forestry and fisheries by MAFF. Abstract submission, 26th April ! International Rice Congress, Bangkok October 27- November 1, 2014 t.ishimaru@irri.org

Tolerance and escape strategy Points of heat-induced sterility at anthesis (Satake and Yoshida 1978) Spikelets flower during 9-12AM in the cultivated rice. →Higher risk to be exposed to high temperature during daytime 2) One-hour exposure to high temperature can cause sterility. →Higher risk under the era of global warming 3) Flowering stage is the most sensitive for heat. →Varietal differences. 35oC is a threshold →N22 is known as most heat-tolerant variety 4) High temperatures one hour after flowering doesn’t cause sterility →Heat escape with early-morning flowering (EMF) trait is effective approach Tolerance and escape strategy

Development of IR64-EMF IR64 EMF IR64 Nanjing-EMF x F1 IR64 x BC1F1 1 2 3 4 5 6 7 8 9 10 11 12 F1 IR64 x qEMF3 MAS BC1F1 IR64 x MAS BC2F1 IR64 x MAS 82 SSR markers BC3F1 MAS 2014DS, IRRI BC3F2 BC3F3 (IR64-EMF) Opened spikelets (%) Nanjing-EMF temperate IR64-EMF tropics

Detection of QTL and development of NIL for EMF 33 oC 37 oC 40 oC Percentage of flowered spikelets (%) Flowering pattern NIL for EMF （平林ら 2010） EMF-NIL Nanjing 11 Higher fertility in EMF QTL also works at IRRI (tropics) EMF-NIL Nanjing11

Global Research Network Thasano station TNAU Partner Local varieties Shading net experiment Meteorological data IRRI Phytotron test MAS, genetics Protocol Global-scale collaboration toward the mitigation of heat-induced spikelet sterility