irps 67 high-temperature stress in rice

8/3/2019 IRPS 67 High-Temperature Stress in Rice

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IRPS No. 67, October 1981 5

Table 2. Symptoms of heat stress and varietal differences in rice observed in the IRRI phytotron (IRRI 1975).

Growth stage Symptoms SusceptiblevarietiesVegetative White leaf tip I R2 6, C al ro se ,

Chlorotic bands and blotches BKN6624-46-2White bands and specksR ed uc ed t il le ri ngR ed uc ed h ei gh t

Reproductive White spikelets, white panicles I R2 4, C al ro se ,Reduced sp ikelet numbers

Anthesis Sterility C4-63G, H4, Calrose,P el it a 1 /1 , B as ma ti -3 70BKN6624-46-2

Ripening Reduced grain filling TN1, IR24, IR26, H4,Fujisaka 5, C4-63G,Pel ita 1/1

Table 3. Effect of high day temperature on the vegetative a/growth of IR747B2 -6. -

Plant D~night temj2erature (OC)characteristics 30/25 35/25 45/25 25/25

Plant height (cm) 60.6 34.2 22.9 b/x-Tiller number/plant 46.0 24.0 6.0 xShoot dry weight (g) 11.10 1. 65 0.26 xRoot dry weight (g ) 1. 78 0.41 0.05 xTotal dry weight (g)5::./ 12.88 2.06 0.31 xRoot weight/total w eight 0.14 0.20 0.16 xRGR (gg/wk) 1.5 1.0 0.5 x

~/Patel (1976): Plants were treated during 1 to 5 weeks after sowing. ~/Plants died 9 days after treatment.5 :: ./ In it ia ld ry w ei gh t: 0 .0 3 g /p la nt .

In 1977, white-tipped panicles were widely ob-served in Palawan, Philippines. Both spikelets andrachis were white. The symptom was conspicuous onimproved varieties such as C4-63G and IR26; nosuch symptom was found on traditional varieties.The symptom indicated cessation of panicle growthat early stages of panicle development. The white

spikelet was about 3-5 mm long, which correspondsto the most active elongation period of spikeletduring the reproductive growth stage.Wi th the above information, a detailed experimentwas conducted to examine the effect of high tem-perature on panicles CIRRI 1980). When the plants


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6 IRPS No. 67, October 1981

were subjected to 38/27C and 41/27C at 70 daysafter sowing (when panicle length was about 2 mm)about 20-25% white spikelets were observed (Fig.4). This symptom induced by the high temperatureswas identical to that observed in Palawan. At35/27C, however, only a few spikelets were white.In a separate experiment, the same variety had 38%spikelet sterility when the plants were subjectedto 35/27C at flowering. Thus, the critical tem-perature for white-tipped panicle is higher thanthat for sterility at flowering.

D a m ag e d f lo w e rs (%l25

F ir st d a y o f 5 -d a y h ig h -t e mp e ra tu re t re a tm e n t( d a ys a f te r s o w in g 1

Fig. 4. Effect of high temperature on occurrence ofdamaged spikelets (IRRI 1980).

Fertility (%)100

Control35Cor 4

..... 38Cor 4 h/day~ 41Cor 2 h/day

25 26 27 28 29 30 31 MarchFlowering date

Fig. 5. Fertility of the spikelets that floweredon the days before, during, and after high-tem-perature treatments. The variety IR747B-2-6 wassubjected to high temperature for 5 consecutivedays (211-30March). Source: Satake and Yoshida (1978).

In Palawan, the daily maximumair temperature isunlikely to exceed 38-41C. The temperature nearthe soil surface, however, can be 40C or higherunder strong sunshine, even when the air tem-perature is about 35C. Therefore, it is possiblethat the high soil temperature can inhibit spike-let growth if the growing panicle is near the soilsurface at the critical stage.

EFFECTOFHIGHTEMPERATURETM~THESISAs previously discussed, the rice plant is mostsensitive to high temperature at flowering. A fur-ther examination of the stage sensitive to hightemperature revealed that high temperature onflowering day causes sterility, and high tempera-ture, except 41C, for 5 consecutive days beforeor after flowering day does not disturb fertili-zation of spikelets provided the temperature onflowering day is below the critical high tem-perature (Fig. 5).Sato et al (1973) studied the response of NorinNo. 17, a japonica variety, to high temperature atflowering by subjecting the plants to 35/30C for3 consecutive days. They found that spikelets thatflowered on the third day of the high-temperaturetreatment had high percentages of sterility where-as those that f l.owe red on the first and second daywere hardly affected by high temperature. Theirfindings disagree with those of Satake and Yoshida(1978), who found that any spikelet that floweredduring high-temperature treatments had high per-centages of sterility. These findings were furtherconfirmed by studying the sensitive time of spike-lets to high temperature on flowering day. Hightemperature during.anthesis had a decisive effecton the incidence of sterility (Fig. 6) . High tem-perature after anthesis had less effect on steri-lity. High temperature before anthesis had consi-derably less effect on sterility than the above.At both 38 and 41C, the fertility percentage ofspikelets that flowered an hour before the high-temperature treatment or earlier was normal. Inrice, the pollen tube extends into the embryosac30 minutes after anthesis, and fertilization iscompleted within 1.5-4.0 hours after anthesis (Cho1956). Hence, spikelets that flowered at 29C anhour earlier were already near completion of fer-tilization. These considerations suggest thatspikelets at anthesis time are the most sensitiveto high temperature, and that reproductive pro-cesses occurring within an hour after anthesis,such as dehiscence of anther, pollen shedding,germination of pollen grains, and elongation ofpollen tubes, are disturbed by high temperature.

Causes of nonfertilizationSeveral lines of evidence show that sterilityunder high temperature is caused by disturbed pol-len shedding and impaired pollen germination butnot by inactivated pistil.First, artificial shedding of healthy pollens onthe stigmas of spikelets subjected to high tem-


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perature during anthesis time increases the spike-let fertility to a normal level or nearly so (Fig.7). The percentage of spikelet fertility ofBKN6624-46-2 was about 35% when subjected to 35Cfor 8 hours and increased to about 85% by artifi-cial pollen shedding. Similarly, the percentage ofspikelet fertility of IR747B-2-6 was about 3%whensubjected to 38C for 8 hours and increased toabout 65%. These results suggest that the majorcause of nonfertilization at 35C for BKN6624-46-2and at 38C for IR747-2-6 is disturbed pollenshedding or decreased viability of pollen grains,and the ability of the pistil to be fertilized isnormal. Failure of artificial pollen shedding toimprove the spikelet fertility of IR747B-2-6 at41C could be attributed to impaired germinationof pollen grains on the stigma. As will be shownlater, pollen grains of N22 can germinate at 41Cbut those of IR747B-2-6 cannot. Furthermore, thefact that the fertility of spikelets subjected to41C for 5 days before anthesis was increased byartificial pollen shedding (Fig. 7c) indicatesthat the ability of the pistil to be fertilizedremained unaffected by the high temperature.

Hours to flowering from the begining of the high-temperature treatmentFig. 6. Fertility of the spikelets of IR747B-2-6that flowered in the hours before, during, and afterhigh-temperature treatments. The treatments were38C for 4 h (A) and 41C for 2 h (B). High tempera-ture is indicated by the shaded area. Source:Satake and Yoshida (1978).

Second, the number of polIens on a stigma va riedamong the 3 varieties even at 29C; it was gen-erally more than 200 and was often too high tocount in N22 but was mostly about 50-200 inIR747B-2-6 and 3G-150 in BKN6624-46-2 (see Fig.8). For convenience, spikelets tha t floweredduring the high-temperature treatment were clas-sified into 3 groups according to the number ofpollen grains on a stigma -- spikelets with morethan 20 pollen grains, those with 1 to 19 pollengrains, and those with none. Varietal differencein the percentage of well-pollinated spikeletswith more than 20 pollen grains on a stigma wasclear even at 29C (Fig. 9). The percentage ofwell-pollinated spikelets decreased as temperatureincreased and the varietal difference in thatpercentage became more conspicuous.

IRPS No, 67 , October 1981 7

806040

A

80 B

c

o 2Doys to flowering from the beginning of the

high-temperature treatmentFig. 7. Effect of artificial pollen shedding on thefertility of spikelets subjected to hlgh temperatureduring anthesis. Treatments were: 35C for 8 h forBKN6624-46-2 (A), 38C for 8 h for IR747B-2-6 (B),and 41C for 4 h for IR747B-2-6 (C). Source: Satakeand Yoshida (1978).

Fig. 8. Varietal difference in the number of pollengrains on a stigma. Left: N22, Right: BKN6624-46-2.

Third, germination of shed pollen grains 'is im-paired by high temperature. Enomoto et al (1956)reported that the critical high temperature forpollen germination ranges from 41 to 45C. Satakeand Yoshida (1973) found large di fferences in thenumber of spikelets with more than 10 germinatedpollen grains among varieties and at differenttemperatures (Fig. 10). In rice, more than 10 ger-minated pollen grains on a stigma are needed for


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normal fertilization(Togari and Kashiwakura 1958).At 4,IC, N22_ had some germinated pollen grains butIR747B-2-6 had no germin.ated pollen grains. Ab-normal shape of clustered pollen grains thatfailed to germin.ate at 41C was clearly observedunder a microscope (Fig. 11). The percentage ofspikelets with more than 10 germinated pollengrain.s on a stigma was iden.tical wi th the per-cen.tage of spikelet fertility.Percentage of spikelets

D NograinsW 1 to 19 groins_ More than 20 grains

10080

604020

o 29 35 38 41(8) (8) (8) (4)

IR747B-2-6~"----.,z Q n n

m ~ I IIBKN6624 -46-2~~ n

~ l J29 35 38 41(8) (4) (4) (4)Treatment

Fig. 9. Proportion of the spikelets grouped by thenumber of shed pollen grain on a stigma of spikeletsthat flowered during high-temperature treatments.Source: Satake and Yoshida (1978).Percentage of spikelets

Dogroins~ I to 9 groins More thon 10 groins

29 35C(8) (8) (h)

N22~

40

29 35 38 41(8) (8) (8) (4)

29 35 38 41(8) (4) (4) (4)Treatment

BKN6624-46-2~

29 35C(8) (8) (h)

Fi8. 10. Proportion of the spikelets grouped by thenumber of germinated pollen grain on a stigma ofspikelets that flowered during high-temperature treat-ments. Source: Satake and Yoshida (1978).Thus, the major cause of n.onfertilized spikelet sin.duced by high temperature varies wi th variety --impaired germination. for N22, an.d insufficientpollen. sheddin.g for IR747B-2-6 and BKN6624-46-2.Between these two, pollen. shedding appears to bethe primary cause for varietal differences in heattoleran.ce. The reason for such varietal differen.ce

appears to relate to the dehiscence characteristicof the anther, which is illustrated in Figure 12.In N22, dehiscen.ce of an.thers starts right afterthe glume opens an.d is completed when. the an.thersstill remain in.side the glume on short filaments.Thus, pollen grains of N22 can easily be shed ontothe stigma. In IR7 4 7 B-2-6, dehiscence of anthersstarts when the anthers are about to emerge fromthe glume, and is completed when anthers stand onsomewhat longer filaments, just above the glume,or the anthers droop over the lip of the glume onlong, sagging filaments. BKN6624-46-2 has a de-hiscence characteristic of anther similar to thatof IR747B-2-6. Furthermore, many anthers remainclosed at high temperature, resulting in poorpollen shedding on the stigma.

Fig. 11. Pollen germination on a stigma at 35 and45C. Upper photo shows normal gerrrination at 35Cand lower photo shows failure of germination at 41C.It is clear that the position of the antherrelative to the glume at dehiscence time and thedegree of dehiscence are important characteristicsfor high temperature-tolerant varieties.

Relation between temperature at flowering andspikelet fertilityThe percentage of fertility of spikelets as af-fected by different temperatures is shown "inFigure 13.For convenience two critical temperatures (CT) canbe defined to characterize varietal response tohigh temperature -- the temperature when the per-centage of spikelet fertility begins to fall below


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80% (CT 80) and the temperature when the percent-age of spikelet fertility is decreased to 50% (CT50). From Figure 13, CT 80 was estimated at 36.5Cfor N22, 35C for IR74 7B-2-6, and 32C forBKN6624-46-2. Thus, the difference in CT 80 be-tween the heat-tolerant variety N22 and the heat-susceptible selection BKN6624-46-2 is more than4C. Likewise, CT 50 was estimated at 39c forN22, 36.5C for IR747B-2-i) and 33.5C forBKN6624-46-2. At 41C, the percentage of spikeletfertility of all 3 varieties was zero.

N22 BKN6624-46-2R747B-2-6

Fig. 12. Schematic diagram of varietal differencein anther dehiscence under high temperatures.Source: Satake and Yoshida (1978).

Fertility (%)100

_ N22'II-'Il IR747 B-2-60-0 BKN6624-46-2

26 29Day temperature (OC)

Fig. 13. Fertility of the spikelets that floweredat different day temperatures. Day temperature waskept for 8 h and night temperature was fixed at 21Cin each treatment. Source: Satake and Yoshida (1978).


The results shown in Figure 13 were obtained from8 hours of high temperature per day. In a naturalenvironment, however, it is unlikely that the hightemperature lasts for 8 hours. In Figure 14, theduration of high temperature was varied from 2 to8 hours/day for 5 consecutive days. From thisfigure, the critical temperature duration to in-duce 20% sterility was estimat-ed at 38c for 4hours for N22, 38C for 2 hours, and 35C for 8hours for IR747B-2-6, and 38C for 2 hours and35C for 4 hours for BKN6624-46-2. At 41C eventhe 2-hour treatment induced high percentages ofsterility in the 3 varieties and hence the cri-tical temperature duration was difficult to esti-mate. From Figure 14 it appears that 35C can dis-criminate heat-susceptible BKN6624-46-2 from the 2other rices and 38C can discriminate heat-tolerant N22 from the others. The 41C temperatureis too high to detect any difference in heat tol-erance among the 3 varieties.

The effect of night temperature at flowering ons terili ty is shown in Figure 15. In this ex-:periment, night temperature was varied from 21.Cto 33c with a constant day temperature of 35Cfor 8 hours a day. Night temperatures from 21C to30C did not affect spikelet fertility but 33cclearly decreased the percentage of fertility whenit persisted for 16 hours. Such high night tem-pera ture for long duration may seldom occur, evenin the tropics, and hence it is unlikely that highnight temperature at flowering would induce a highpercentage of sterility.The temperature-rise pattern also affects spikeletfertility (Fig. 16). The percentage of spikeletfertility was only 11%when temperature was raisedby the one-step control and maintained at 41C be-tween 1000 and 1200 hours but was 50% when thehigh temperature hours were shifted to 1200-1400hours by the same procedure. In the multistep con-trol where the temperature was raised by 3C/hour,reached 41C at 1200 hour s, rnaintained at thattemperature until 1400 hours, and dropped by3C/hour to the base temperature (29c), thepercentage of spikelet fertility was 61%. In themultistep control, the plants were subjected totemperatures higher than the base temperature forlonger duration than the one-step control, yet thepercentage of spikelet fertility of those plantswas higher than that of the others.These results appear to indicate that the occur-rence of sterility relates to the time of anthesisrelative to the onset of the critical high tem-perature. In those treatments where lower percent-ages of sterility were observed, more spikeletsmust have completed anthesis before the onset ofcritical high temperature. This is because spike-let sterility is induced by high temperature atanthesis and because high temperature does not- af-fect fertility if it comes 1 hour after anthesis.

AVOIDANCEOF HIGHTEMPERATURE-INDUCEDTERILITY BYEARLYMORNINGANTHESISAmong the 3 varieties, IR747B-2-6 flowered morethan 30 min earlier than BKN6624-46-2 and N22 in


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Fertility (%)100

o 2 4 8Duration of high- temperature treatment (h)

..... N22'I}--JV IR747B-2-60-0BKN6624-46-2III,II

"II,I~\\.\" .",8

Fig. 14. Fertility of the spikelets subjected to different durationsof different day temperatures. After the rice plants were subjectedto high temperatures for specified number of hours, they were movedback to 29/21C regime every day. Source: Satake and Yoshida (1978).

Fertility (%)10080 6040

200

Night temperature ( O e )Fig. 15. Fertility of the spikelets of IR747B-2-6subjected to different night temperatures for 5flowering days. Day temperature was kept at 35Cfor 8 hlday in each treatment. Source: Satakeand Yoshida (1978).

the morning. Early morning a nthe sis is highly de-sirable because high temperature is avoided andhence high temperature-induced sterility isreduced.Rice varieties usually open flowers about 1000-1200hours (this depends on varieties, and climatic, eda-phic, and cultural conditions; local time must alsobe taken into consideration). Air temperature goesup rapidly in the mornirig and exceeds the criticaltemperature (35C) about 1000 hours in many high-temperature areas. Thus, the advancement of floweropening to early morning is one way to avoid hightemperature-induced sterility.

Fertility (%)60

4029 20

29

35

29

oTime

Fig. 16. Three different temperature-rise patternsand the fertility of spikelets of IR747B-2-6 thatflowered in these regimes. Fertility is indicatedby the shaded area. Source: Satake and Yoshida(1978) .The flowers of Oryza glaberrima, an African-cultivated rice species, open in the early morningCIRRI 1978). This characteristic of O. glaberrimacan be incorporated into O. sativa (Fig. 17). The


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earliest flower opening line in the O. sativa andO. glaberrima crosses had a peak of 0900-1000hours, about 1 hour earlier than that of IR36. Theflowering peak of O. glaberrima occurred at 0700-0800 hours, 3 hours earlier than that of IR36.Even an hour advancement in the flower openingtime may have a signiEicant effect on sterility,because air temperature rises at a rate of3C/hour or more around 1000 hours.

Flowers thot opened (%)

77I8

III

138I9

9I1 0

10III

T im e (h)'f J Q q /a be n if T lJ ( o v e ra g e cI 2 lin es )'f H yb rid ( the e a rl ie s t l in e i n f l ow e r o p e ni ng ) H yb rid (o ve ra g e o f 25 lin e s ) H yb rid (th e late st lin e in flo we r o pe nin g )o IR36

Fig. 17. Flower opening time of Oryza glaberrima xQ. sativa hybrids, Q. glaberrima, and IR36. Source:Nishiyama and Blanco (1980).

GENETICS OF HIGH TEMPERATURE-INDUCED STERILITYTOLERANCE

A diallel-cross experiment of six rice lines hasshown that general and specific combining abi-lities for heat tolerance are highly significant.The general combining ability and specific combin-ing ability variance for the six parents are shownin Table 4. Although IR2006-PI2-12-2-2 has a goodgeneral combining ability, it has a high specificcombining ability variance, indicating thepresence of nonadditive genetic variance. N22 hasa good general combining ability for heat tol-erance but it would probably not be an ideal donorfor this trait because of its poor plant type andthe high amount of genetic sterility in its hybridprogeny. IET4658 and IR2006-PI2-12-2-2 shouldprove good donors for heat tolerance in a breedingprogram.

The heritabilities for heat tolerance in thediallel cross were 76% for the broad-sense heri-tability and 71% for the narrow-sense. This indi-


cates that heat to l.era nc e has a fairly high heri-tability and that raost genetic variation is addi-tive. The cross IRS2/IR2006-PI2-12-2-2 was studiedfurther by growing the parents, Fl, F2, bothbackcrosses, and the F3 generation in the phyto-tron and subjecting them to 3S/27"C duringflowering. Nonallelic genetic interaction for per-centage of filled grains was low. The narrow-senseheritability vias calculated as 81.91%. This againindicates that It should not be difficult toselect for heat tolerance provided that the envi-roume n taL variation is low.In the above six diallel parents and two Fl hy-brids, heat tolerance was found highly associatedwith the number of pollen grains on the stigma(Fig. 18). Tolerant genotypes shed more pollengrains on the stigma at both norma l. and high tem-pera t ur es than susceptible genotypes. In the sus-ceptible genotypes the amount of pollen shed onthe stigma vias markedly reduced at high tem-perature. The correlation coefficients of the num-ber of pollen grains per stigma at 29/21C and38/27C with percent fertility (transfonmed) at38/27C were 0.94, and 0.98, respectively. It thusappears that differences in the pollination abil-ity of the genotypes could be distinguished evenat the control temperature (29/21C). These geno-typic differences can be attributed to two im-portant characteristics -- the po sItLon of theanther relative to the glume at dehiscence timeand the degree of dehiscence.

Table 4. General combining ability effects andspecific combining ability variance for heattolerance of the six diallel parents.~/

Parents Generalcombiningability

TolerantN22 6.80 15.16IR2006-P12-12-2-2 4.08 18.07IET4658 (UPR96-1-1-1) 3.02 3.33

SusceptibleIR28 -3.40 7.09IR1561-228-3-3 -4.92 9.49IR52 -5.58 14.76

Heritability: narrow sense, h~2 6 a/ '11 (1981)B = 0.7 . - MacKl .

0.71, broad sense,


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P o ll e n g ra i ns p e r s ti qr m Fertility (%1

100 Pollen groins per stigma at 29/21 C30Pol len qro ins per stigma at 38I2JDC---.- . .\

'\\"-, - , - , ........ "

. . . . . . .

" " ....................

. - % ferti li ty at 38/27C8020

60 l-:10

40o

20f-

IR2006 N22 IET4658 lET4658 IR28X XIR 1 561 I R 1561

F,

Fig. 18. Mean number of pollen grains per stigma at29/21C and 38/27C and percentage of fertility at38/27C for the 6 diallel parents and 2 Fl hybrids(D. J. MacKill, 1981).

Plants (no)

IR2006f------O------

Pollen groins/stigno

Fig. 19. Distribution of pollen grains per stigmafor F2 plants from the cross IR52/IR2006-P12-2-2.Plants were treated at 35/27C for 10 days duringflowering. The mean and range of the parents and Flare shown (D. J. MacKill, 1981).Genetic differences in the number of pollen grainsper stigma were further confirmed by examining in-dividual F2 plants and their parents (Fig. 19).This trait is apparently controlled by more thanone ge ne, because few of the F2 plants we re ashigh as the parent IR2006-P12-12-2-2. The skewnessof the distribution suggests that some nonallelicgene interaction is present. The phenotypic andgenetic correlation coefficients for the number ofpollen grains per stigrul and percentage of filled

grains were 0.62 and 0.68, respectively. Thisagain indicates the importance of pollen sheddingfor heat tolerance.Table 5. Examples of heat-tolerant and heat-susceptible varieties.

Designation Fertility (%)at 35C

88908684'!_/868886

4~//27

196667396258504227483974374862463647174767

0000018271

Tolerant varietiesAgbedeCarreonDularN22OS4PI 215936Sintiane Diofor

Susceptible varietiesBasmati-370BKN 6624-46-2C4-63GH4Pelita 1/1

IRRI varietiesIR5IR8IR20IR22IR24IR26IR28IR29IR30IR32IR34IR36IR38IR40IR42IR43IR44IR45IR46IR48IR50

Cold-tolerant varietiesC-21Dourado AgulliaLengkwangPrataoSilewahSomewakeSorachiThangonea/- Mean value of several measurements.VARIETAL DIFFERENCES IN HIGH TEHPERATURE-INDUCEDSTERILIlYThere are clear varietal differences in high tem-perature-induced spikelet sterility (Table 5).Tolerant varieties have fertility percentages


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higher than 84% while susceptible ones have lessthan 10%. In our work on high-temperature tol-erance both in the phytotron and the heat-proneareas, we use C4-63G and BKN6624-46-2 as suscep-tible checks and N22 as a tolerant check. AmongIRRI varieties, IR36, IR8, IR20, and IR50 appearto be tolerant of high temperature. These resultsare in good agreement with those reported by Osadaet 'I.] (1973) that. BKN662 4-46-2 and C4-63G sufferedhigh percentages of empty grains when grown in thehot part of the dry season in Thailand whereas IR8maintained a normal fertility percentage. In manyheat-prone areas, low temperature is a problem atearly stages of rice growth. There is also areport that cold-tolerant varieties might be tol-erant of high temperature (National HokkaidoAgricultural Experiment Station, unpubl.). Forthese reasons, we have tested the heat toleranceof 8 cold - tolerant varieties. All the cold-tolerant varieties tested are highly susceptibleto high temperature at anthesis time (Table 5).Early maturity is one of the requirements for ricevarieties to be grown in the heat-prone areas.Early maturity fits into the rice cultivationsystem in the heat-prone areas and also economizeswater use. It is not difficult to find varietiesthat are heat tolerant and early maturing (Table6). In fact, in a field trial at AI-Hassa, SaudiArabia, all the entries selected in the IRRIphytotron were heat tolerant and early maturing(see Table 6,7).

IRPS No. 67,October 1981 I3

Table 6. H ea t- to le ra nt , e ar ly -m at ur in g l ine s.

Lines Fertility Days to flower(%) at Los Banos

IR9129-136-2 86 66IR9209-26-2 85 67IR9209-263-3 81 70IR9224-117-2 83 72lE T 4094!!_/ 62 72lE T 4658 71 72lET 4700 85 71lE T 4701 72 71lE T 5688 74 60lET 5714 88 70lE T 5734 75 70lET 6187 75 57lET 6238 75 60

!!_/IETis an abbreviation of Initial EvaluationTrial, All-India Coordinated Rice Project, India.

Table 7. Grain yield and percentage of fertility of some selected varieties/lines in AI-Hassa, Saudi Arabia,Saudi Arabia, 1980. ~/

Fertility GrainVariety/line yield(% ) (t;/ha)

lET 4094 73 3.5

lE T 4658 80 4. 3lE T 4700 61 3. 6lET 5688 74 2.8lET 5734 50 2.2lE T 6238 70 4.3N.T.U. No. 30 6 35 2.3Hovayzeh 33 0.7C4-63 G 17 0. 8Hassa No. 50 2.6

Remarks

From India; selectedin the Phytotron

From TaiwanFrom Southern IranSu sc ep ti bl e ch ec kLocal check

a/- Data were obtained by C. I. Lin (pers. comm.) in collaboration with IRRI.


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14 IRPS No. 67, October1981

FIELD EXPERH1ENTSAs part of the International Rice Testing Program(IRTP), heat tolerance has been field tested atseveral sites -- AI-Hassa, Saudi Arabia; Mishkab,Iraq; Dokri, Pakistan; and Imperial Valley, USA.In general, there is a good agreement between phy-totron and field tests (Table 8). In the fieldtrial, we normally include two check varieties --N22 as the tolerant check and C4-63G as the sus-ceptible check. At AI-Hassa, N22 and Hovayzeh,supposedly heat tolerant, had low percentages offertility. The same varieties, however, had highpercentages of fertility at Imperial Valley. Ap-parently, some factors other than heat toleranceaffected the performance of the two varieties atAI-Hassa. On the other hand, C4-63G, a susceptiblevariety, did not have high sterility at Mishkab.This may suggest that high temperature was not theproblem at Mishkab in that particular crop period.Many lET lines from India, which were selected forheat tolerance in the IRRI phytotron, performedwell in AI-Hassa (Table 7) . Grain yields of lET4658 and lET 6238 was 65% higher than that ofHassa No.1, a local check. The higher yields ofthe lET lines are attributed to higher degrees ofheat tolerance as indicated by higher percentageof fertility.Table 8. Agreement between phytotron and field tests(1979-80) . ! ! _ _ /

Variety/lineImperialValley,USA

AI-Hassa,Saudi Arabia Mishkab,Iraq

lET 4094 o olET 4658 ooHovayzeh oN22 x o oC4-63G x oa/- Agreement with phytotron evaluation:X = No, - = not determined. o Yes,

ACKI-lOI.JLEDGHETWe thank the following scientists for theirparticipation in the heat tolerance collaborativeproject, International Rice Testing Program.

Dr. I. M. Bhatti, director, Rice ResearchInstitute, Dokri, District Larkana, Pakistan.Prof C. I. Lin, leader, Chinese AgriculturalTechnical Mission to the Kingdom of SaudiArabia, P. O. Box 143, Hofuf, AI-Hassa, SaudiArabia.

Dr. W. F. Lehman, agronomist, Imperial ValleyField Station, 1004 East Holton Road,Elcentro, California 92243, USA.Dr. Lssam AI-Najjar, Mishkab Rice ResearchStation, Naijaf, Iraq.

REFERENCES CITED

AI-Najar, I. 1968. Introduction and breding of newvarieties with high yield potential improve-ment of rice production in Iraq. Inter-national Rice Commission Working Party onRice Production and Protection, 12th session.Peradeniya, Ceylon.Chang, W. L., H. P. Su, and F.H. Lin. 1978. Theresponse of rice varieties to extreme tem-peratures in Saudi Arabia. SABRAO J. 10:10-23.Chao, L. F. 1959. Report to the government of Iraqon rice production. FAO Rep. 1081. 25 p ,Cho, J. 1956. Double fertilization in Oryza sativaL. and development of the endosperm withspecial references to the aleurone layer.Bull. Natl. Inst. Agric. Sci., Ser. D., 6:61-101.Dingle, W. R., and T. T. Trinh. 1976. Problems ofrice selection under Sahelian conditions.Paper presented at the WARDA Varietal Im-provement Seminar, 2D, Bonake.EI-Shamma, W. S. 1967. Research on rice

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Enomoto, N., 1. Yamada, and K. Hozumi. 1956. Onthe artificial germination of pollen in riceplants. IV. Temperature limits of pollengermination in rice varieties. Proc. CropSci. Soc. .Jpn , 25:69.IRRI (International Rice Research Institute). L 1 9 6 i /Annual report 1963. Los Banos, Philippines.199 p.IRRI (International Rice1975. Annual reportPhilippines. 384 p.

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Ito, H. 1963. The necessity, the possibility andthe means of rapidly increasing rice pro-.duc tLon in Iraq. Ministry of Agriculture,Iraq. 68 p , (unpub L, ) ,

Kusanagi, T., and O. Washio. 1974. The phytotronat Chugoku National Agricultural ExperimentStation. Bull. NatL, Agric. Exp , Stn., SereA, 23:53-89.

Mackill, D. J. 1981. Studies on the mechanism andgenetics of high temperature tolerance inrice. Ph D Thesis, University of California,Davis. 182 p ,

Mann, H. S., and J. S. Kanwar. 1972. Cropping pat-terns in di f ferent s ta tus. Pages 110-122 inK. B. Nair, ed. Proceedings of the symposiumon cropping patterns in India. Indian Councilof Agricultural Reseqrch, New Delhi.

Moafizad, M., and M. S. Chaudry. 1977. Ricegrowing and research in Iran Rice ResearchStation, Rasht. (unpubl.).

Moriya, M., and M. Nara , 1971. Influence of airtemperature on ripening of lowland rice.Pages 110-115 in Ministry of Agriculture andForestry, Research Council of Agriculture,Forestry, and Fisheries, Japan. Studies onmaximizing rice yield. Res. Rep. 49.

Nishiyama, I., and L. Blanco. 1980. Avoidance ofhigh temperature sterility by flower openingin the early morning. JARQ 14:116-117.

Osada, A., V. Sasiprada, M. Rahong, S. Dhammanu-vong, and M. Chakrabandhu. 1973. Abnormal oc-currence of empty grains of indica riceplants in the dry, hot season in Thailand.Proc. Crop Sci. Soc. Jpn. 42(1):103-109.


Patel, A. L. 1976. Effect of light and temperatureon growth of the rice plant. Ph D thesis,Indian Agricultural Research Institute, NewDelhi, India. 90 p.

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Trinh, T. T. 1976. Highlights of rice improvementin Mauritania. Paper presented at the WARDAVarietal Improvement Seminar, 2D, Bonake.

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The International Rice Research InstituteP O . B ox 93 3 , M anila, P hilipp ine s

O th er p ap ers i n this se riesFOR NUMBERS 1-20, TITLES ARE LISTED ON THE LAST PAGE OF NO. 46 AND PREVIOUS ISSUES

No. 21 Sulfur nutrition of wetland riceNo, 22 Land preparation and crop establishment for rainfed lowland riceNo. 23 Genetic interrelat ionships of improved rice variet ies in AsiaNo. 24 Barrier s to efficient capital inves tment in Asian agricul tureNo. 25 Barriers to increased rice production in eastern IndiaNo. 26 Rainfed lowland rice as a research priority - an economist's viewNo. 27 Rice leaf folder: mass rearing and a proposal for screening for varietal

resistance in the greenhouseNo. 28 Measuring the economic benefits of new technologies to small rice

farmersNo. 29 An analysis of the labor -intensive continuous r ice product ion system at

IRRINo. 30 Biological constraints to farmers ' r ice yields in three Philippine provincesNo. 31 Changes in rice harvesting systems in Central Luzon and LagunaNo. 32 Variat ion in varietal react ion to rice tungro disease: possible causesNo. 33 Determining superior cropping patterns for small farms in a dryland rice

environment: test of a methodologyNo. 34 Evapotranspirat ion from rice fieldsNo. 35 Genetic analysis of traits related to grain characteristics and quality in

two crosses of riceNo.36 Aliwalas to r ice garden: a case study of the intensi fication of r ice farming

in Camarines Sur, PhilippinesNo.37 Deni trif ication loss of fert ilizer ni trogen in paddy soi ls - it s recogni tion

and impactNO.38 Farm mechanizat ion, employment , and income in Nepal : t raditional and

mechanized farming in Bara DistrictNo. 39 Study on kresek (wilt) of the rice bacterial blight syndromeNo. 40 Implication of the international rice blast nursery data to the genetics of

resistanceNo. 41 Weather and climate data for Philippine rice researchNo.42 The effect of the new rice technology in family labor util ization in LagunaNo. 43 The contribut ion of varietal tolerance for problem soi ls to yield stabili ty

Innee

ISSN 0115-3862

No. 44 IR42: a rice type for small farmers of South and Southeast AsiaNo. 45 Germplasm bank informat ion retr ieval systemNo. 46 A methodology for determining insect control recommendationsNo. 47 Biological ni trogen fixation by epiphytic microorganisms in rice fieldNo. 48 Quality characterist ics of milled r ice grown in different count riesNo. 49 Recent developments in research on nitrogen fertil izers for riceNo. 50 Changes in community institutions and income distribution in a We

Java villageNo. 51 The IRRI computerized mailing list systemNo. 52 Differential response of rice varieties to the brown planthopper

international screening testsNO.53 Resistance of Japanese and IRRI differential r ice varieties to pathotype

of Xanthomonas oryzae in the Philippines and in JapanNo. 54 Rice production in the Tarai of Kosi zone, NepalNo. 55 Technological progress and income distr ibution in a rice vi llage in We

JavaNo. 56 Rice grain properties and resistance to storage insects: a reviewNo. 57 Improvement of native rices through induced mutat ionNo. 58 Impact of a special high-yielding-rice program in BurmaNo. 59 Energy requirements for alternative rice production systems in t

tropicsNo. 60 An illustrated description of a traditional deepwater rice variety

BangladeshNo.61 React ions of di fferential varieties to the rice gall midge, Orseo/ia oryza

in Asia. Report of an international col laborative research projectNo. 62 A soil moisture-based yield model of wetland rainfed riceNo. 63 Evaluat ion of double-cropped rainfed wetland riceNo. 64 Trends and strategies for rice insect problems in tropical AsiaNo. 65 Landforms in the rice-growing areas of the Cagayan River BasinNo. 66 Soil fertility, fertilizer management, tillage, and mulching effects o

rainfed maize grown after rice

irps 67 high-temperature stress in rice

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