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118 History of the International Rice Research InstituteThe maximum tillering stage of both varieties was reached at about thesame time (during the first week of July), when Peta had 35 tillers/plant andTainan 3 had only 20 (the spacing at transplanting time was 30 x 30 cm with 1plant/hill). The important finding was that although Peta had many moretillers than Tainan3 at the maximum tillering stage, after that the tillers on Petastarted dying at a fast rate because of lack of light penetration and only 14 Petatillers were alive on each plant at maturity. On Tainan 3, however, all 20 tillerswere still alive and 83% of them bore panicles.Panicle initiation took place at the maximum tillering stage in Tainan 3 butwas 30 days later for Peta. This meant, of course, that flowering and maturingwere much delayed in Peta. Peta took 151 days to reach maturity, whereasTainan 3 matured 123 days after sowing (102 days after transplanting).The panicle-straw ratio for Tainan 3 was 0.81; Peta’s was 0.57.An important observation was that although the average stem of Petaproduced 21 leaves, by the time it reached the flowering stage only the twouppermost leaves were entirely active, the next two were half dead, and therest were entirely dead. Each culm of Tainan 3 produced only 15 leaves, but allexcept the 2 lowest ones were still functioning at flowering time. From theseobservations, Tanaka correctly concluded that Tainan 3 depended mostly onproducts assimilated during the ripening stage, whereas spikelet filling in Petawas the result of carbohydrates stored in the straw before flowering.Tanaka did another series of experiments in 1962, growing Peta, Tainan 3,and BPI-76 at different spacings and nitrogen levels. Peta gave its highestyields at wide spacings and medium nitrogen levels; Tainan 3 and BPI-76produced maximum yields at maximum (30 x 30) spacing and at higher levelsof nitrogen.In 1963, Tanaka continued his studies of plant type in relation to yield, withvariations in spacing, nitrogen levels, and date of planting. It was then that hediscovered the great advantage of the Taichung Native 1 plant type and highyields were possible with tropical varieties when grown during the dry seasonunder abundant sunshine instead of during the cloudy rainy season. PlantingTaichung Native 1 on 20 December 1962 and harvesting it about 4 months later,Tanaka obtained the unprecedented yield (for the tropics) of 8.23 t/ha.In that same experiment, he planted a U.S. short variety, Century Patna 231,which Beachell had developed in Texas for direct seeding. It was inherently alow-tillering variety and yielded respectably only when it was closely spacedand heavily fertilized with nitrogen. Its shortness and its stiff stems kept it fromlodging but that was not enough. The experiment demonstrated clearly thatfor transplanted rice, heavy tillering capacity was an important characteristic.That same year, Tanaka conducted intensive greenhouse studies of mutualshading (the shading of the lower leaves of a plant by its upper leaves and theshading among competitive plants in a rice stand). He demonstrated thatmutual shading was a significant cause of a lack of nitrogen response in the tall,leafy, tropical varieties.Taichung Native 1 is a half-sister of IR8 and has a similar plant type withshort stature, upright leaves, and numerous tillers. Peta, although also heavy
Early research and training results 119tillering, is much taller, has long drooping leaves, and matures later. Tanakameasured the leaf area of the two varieties in the field and found that at themaximum tillering stage, Peta had the highest leaf area index (LAI). 2 But by thetime the plants reached the flowering stage, so many of the leaves of Peta haddied that its LAI was much lower than that of Taichung Native 1.The findings just cited seem commonplace information today, but at thetime, they represented pioneering work. Tanaka’s data gave IRRI scientists anunderstanding of why the traditional tropical rice varieties were incapable ofyielding heavily.While Tanaka was studying plant morphology and growth responses inrelation to yield, Vergara made extensive studies of the response to photoperiodof a collection of rice varieties, including many that were being used asparents in IRRI’s breeding program. Rice is a short-day plant, meaning thatshort day lengths decrease the growth period. Vergara showed that there weregreat differences in the extension of the growth period when day length wasincreased artificially. He grew his plants in pots on carts that could be movedabout by hand. All varieties were exposed to an 8-hour day in the greenhouseand then wheeled into chambers where artificial light was controlled by a timeclock. Varying the total exposure to light from 8 to 24 hours, he recordedflowering delays. Some varieties were so insensitive to day length that thedifference in time from sowing to flowering was less than 10 days over theentire range, whereas some of the sensitive varieties exposed to artificial daylengths of 16 hours or more did not flower at all even after 200 and more daysof exposure. At that time, IRRI plant breeders were trying to create varietiesthat were relatively insensitive to day length and Vergara’s studies clearlyidentified the insensitive varieties that could be used as parents.Vergara later made more basic studies on the photoperiod response, determiningthe growth period when photoperiod induction took place and theimpact of the number of photoperiod-inductive cycles on plant characteristicssuch as panicle emergence and size. Furthermore, he and Chang conductedcooperative research on the mode of inheritance of photoperiod sensitivity.From 1964 through 1967, the Plant Physiology Department conductedinnumerable studies, some of them basic. Space does not permit either adetailed description or even a complete listing of that research. However,because much of it was being done for the first time in the tropics, some of thebasic principles established during that period are listed here:• Culm length and thickness are the most important factors affectinglodging resistance and nitrogen responsiveness. The ideal culm lengthfor wetland rice production under controlled water supply is about100 cm.• Culm length, although affected by environment, is largely a geneticfactor. Short and tall varieties have similar numbers of nodes, but in the2LAI is the area of leaves above a unit area of ground. For example, it a rice stand had 6 m 2 of leafarea above 1 m2 of ground, its LAI would be 6.
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An Adventurein Applied Science:A HI
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ContentsDedication viiAbout this pu
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About this publication . . .In 20 y
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xiname, and release varieties. Thus
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PrefaceThe International Rice Resea
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CHAPTER 1An international institute
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An international institute for rice
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CHAPTER 2Developing and staffingthe
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Developing and staffing the program
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Page 100 and 101: 86 History of the International Ric
Page 107 and 108: Princess (now Queen)Beatrix of theN
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Page 111 and 112: In the early years, IRRIused its ow
Page 117 and 118: Chapter 4Early Researchand training
Page 119 and 120: Early research and training results
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Page 161 and 162: CHAPTER 5Financing of IRRIThe purpo
Page 163 and 164: Financing of IRRI 149foreign assist
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Page 175 and 176: Creation of other international cen
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Page 181 and 182: Aerial view of IRRI in1981.However,
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172 History of the International Ri
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IRRI today 181neering Department: K
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IRRI today 183In spite of this high
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IRRI today 185turn, received geneti
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IRRI today 1871. Research to assist
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Appendices 189materials could readi
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Appendix 2OVERSEAS DEVELOPMENTINTER
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Appendices 193ate to concentrate on
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Appendices 195estimates for buildin
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Appendices 197(4) Development of pr
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Appendices 199was approved for the
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Appendices 201association, or perso
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Appendices 203b. To pass upon the b
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Appendices 205Article VIIMISCELLANE
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