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30 Rice Today July-September 2012

Maps

Rice thrives in hot and dry tohumid climates. However,extreme heat episodes canirreversibly damage rice

yield, grain quality, and plantprocesses such as germination andfertilization.

Rice is highly susceptible toheat stress, particularly during thereproductive and ripening stages.Extremely high temperatures, evenfor a few hours, during oweringcan cause complete sterility, whilehigh temperatures during ripeningcan lead to reduced grain llingand poor milling quality (i.e., more

broken grains). And, in combinationwith other constraints such as lackof water, canopy temperatures canincrease even further.

Unfortunately, hot days andwarmer nights have increasedrecently. Higher nigh imetemperatures, in particular, havereduced rice yields—by as muchas 10% for every 1 oC increase inminimum temperature.

1

In 2003,heat stress a ected about 3 millionhectares of rice, resulting in losses of

5.18 million tons in the Yang e RiverValley in China.2

In 2010, extremenigh ime air temperatures adversely

by Alice Laborte, Andrew Nelson, Krishna Jagadish, Jorrel Aunario,Adam Sparks, Changrong Ye, and Ed Redoña

Heat waves are expected to be more intense and frequent in the future,which could jeopardize more rice areas.

a ected the milling quality of ricegrown in Arkansas in the U.S.

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Changing cropping systems

and management are strategies tomeet the increasing demand for ricein areas prone to heat stress. Thismeans that farmers may need toadjust planting dates, change croprotations, and use varieties withshorter maturity to avoid high-temperature periods. Researchers

1 Peng S, Huang J, Sheehy JE, Laza RC, Visperas R M, Zhong X, Centeno GS, Khush GS, Ca ssman KG. 2004. Rice yields decline with higher night temperatu re from global warming.Proc. Natl. Acad. Sci. USA 101:9971-9975.

2 Tian X, Luo H, Zhou H, Wu C. 2009. Research on heat stress of rice in China: progress and prospect. C hin. Agric. Sci. Bul l. 25:166-168.3 Lanning SB, Siebenmorgen TJ, Counce PA, Ambardekar AA, Mauromoustakos A. 2011. Extreme nighttime air te mperatures in 2010 impact rice chal kiness and milling quality. Field

Crops Res. 124:132–136.4 Daily temperature f rom NASA Prediction of Worldwide Energy Resource (POWER, http://power.larc.nasa.gov/ ) corrected using station data (Sparks A, u npublished data).

therefore seek to introduce newrice varieties with improved heattolerance.

To identify hotspots for daytimeand nigh ime heat stress, wecompared daily maximum andminimum temperatures duringcritical rice growth stages from1983 to 20114 against temperaturethresholds obtained from publishedliterature (Fig. 1).

F g. . em era ure res lds a r al gr s ages r e.

Daytime heat stress

Nighttime heat stress

Maximum temperature > 35 °Cfor 10 days during the period

Minimum temperature > 25 °Cfor 15 days during the period

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31Rice Today July-September 2012

Fig. 2. Hotspots of heat stress on rice and frequency of occurrence: daytime (top) and nighttime (bottom).

Our preliminary analysis showsthat many rice areas in mainlandAsia and parts of western Africahave been experiencing frequentheat stress events over the past threedecades (Fig. 2).

Spatial assessments of rice areasthat are vulnerable to heat stressare important for planning andtargeting appropriate adaptation andmitigation strategies to ensure foodsecurity.

Dr. Laborte, Dr. Sparks, and Dr. Ye are postdoctoral fellows; Dr. Jagadish is a pla pathologist; Mr. Aunario is a specialist on geospatial programming; and Dr. Redoñais a plant breeder, all working at IRRI.

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