Morphological and physiological changes among rice varieties used in the Philippines over the last seventy years

Field Crops Research, 8 (1984) 105--124 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

105

MORPHOLOGICAL AND PHYSIOLOGICAL CHANGES AMONG RICE VARIETIES USED IN THE PHILIPPINES OVER THE LAST SEVENTY YEARS

L.T. EVANS*, R.M. VISPERAS and B.S. VERGARA International Rice Research Institute, Los Ba~os (The Philippines) *Also CSIRO Division of Plant Industry, Canberra, A.C.T., Australia (Accepted 30 August 1983)

ABSTRACT Evans, L.T., Visperas, R.M. and Vergara, B.S., 1984. Morphological and physiological changes among rice varieties used in The Philippines over the last seventy years. Field Crops Res., 8: 105--124. Fifty varieties of rice grown in the Philippines this century were grouped chronologically for comparison in both glasshouse and field experiments at Los Bafios. The five groups of lowland, and two of upland, varieties each contained 5 to 11 entries. Plants were grown under three daylengths in the glasshouse experiment. In the field they had to be grown at a relatively low density and nitrogenous fertilizer level. Group comparisons revealed marked changes in growth habit, daylength response and inflorescence characteristics, not always consistently in one direction. Lowland varieties have become shorter, with smaller and more upright leaves and reduced daylength sensitivity. Panicle weight initially became heavier, and then lighter again with greatly increased panicle number. Despite these changes, there has been no change in photosynthetic rate, crop growth rate or kernel weight. However, there has been a marked increase in harvest index and in grain production per day, associated with reduced stature and earlier maturity. Although upland varieties have also become less sensitive to daylength, in other respects they have diverged from lowland varieties towards taller, more sparsely tillering, larger panicle types.

INTRODUCTION J u s t as the varietal resistance o f c r o p s to insect p e s t s and diseases m u s t be c h a n g e d as t h e s e o r g a n i s m s evolve, so also m u s t t h e i r m o r p h o l o g i c a l and p h y s i o l o g i c a l c h a r a c t e r i s t i c s be c h a n g e d in o r d e r t o a d a p t t o and t a k e adv a n t a g e o f d e v e l o p m e n t s in a g r o n o m y . I n t h e case o f rice g r o w i n g in t h e Philippines, p r o b a b l y the m o s t i m p o r t a n t a g r o n o m i c changes in this c e n t u r y h a v e b e e n t h e increasing e x t e n t o f irrigation, o f d r y season c r o p p i n g a n d o f fertilizer, p e s t i c i d e a n d h e r b i c i d e use (cf. H u k e et al., 1982). A t the beginning o f this c e n t u r y rice was g r o w n a l m o s t e n t i r e l y during the

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106

wet season, with little or no inputs of fertilizer and manure. Traditional varieties grew tall, overtopping weeds and being of comfortable height for harvesting, which was done panicle by panicle. Their flowering, controlled by daylength, often coincided with the end of the wet season. Under the low soil fertility conditions, and with no rice cultivation in the dry season, disease and pest organisms did not build up to high levels. All these features have now changed. Some irrigation had been practised for many years, as in the rice terraces at Banaue, but only about 4000 ha were irrigated in 1916 according to the Statistical Bulletin of the Philippine Islands. Ten years later this area had increased 15-fold, and the extent of irrigation continued to grow rapidly, to half a million ha by 1953 and to 1.3 million ha in 1981, equivalent to 40% of the area under rice. The area under dry season rice crops has increased correspondingly. Early flowering varieties suited to double cropping, like Binicol and Guinangang, were used initially, but as multiple cropping increased there was a growing need for earlier-maturing rice varieties less sensitive to daylength than most traditional varieties. This need was reinforced by the increasing use of fertilizers (Hayami and Kikuchi, 1975). Farmers had previously favoured the use of late-maturing varieties under low fertility conditions (Umali et al., 1956), but as the use of fertilizer increased along with irrigation and double cropping, earlier-maturing, daylength-insensitive varieties with shorter stature or stronger stems were needed. One objective of the present study, in which we examined changes in the characteristics of 50 rice varieties used in the Philippines over the last seventy years, was to see when these changes first became apparent. The other was to examine the physiological basis of any increase that may have occurred in the yield potential of Philippine rice varieties. Physiological changes during the domestication and improvement of rice have been examined by Cook and Evans (1983a,b). However, the experiments most comparable with those reported here were carried out by Tanaka et al. (1968) and Samoto (1971), who compared varieties of japonica rice prevalent in the Hokkaido area at various times since 1905. Tanaka et al. (1968) found no increase in rates of growth or photosynthesis among the more modern varieties, but a shift in growth habit towards shorter plants with more tillers and panicles and more erect leaves. Of importance in the Hokkaido environment was an increase in cold tolerance, as emphasized also in Samoto's (1971) comparative study, which indicated progressive changes in plant habit, particularly reductions in plant height, panicle length and leaf length, greater erectness of leaves, and increase in the number of tillers and panicles. Increased cold tolerance has not been required in the Philippines, but the other changes observed in Japan, which reflect adaptation to increasing levels of soil fertility, seem likely to have occurred also in the Philippines, al-

107 though possibly later and to a lesser extent. There may also have been additional changes not required in Japan, such as faster flowering and reduced sensitivity to daylength. MATERIALS AND METHODS

Varieties. Fifty varieties (all those listed in Table I, except IR 36) were grown in the glasshouse experiment, and the thirty lowland varieties marked with an asterisk in Table I were subsequently grown in the field experiment. The varieties were selected largely on the basis of the significance accorded to them over the years in The Philippine Agriculturist, The Philippine Agricultural Review, The Philippine Journal of Agriculture, Seed Board Varieties and Recommended Rice Varieties, subject to their availability from the I R R I germplasm collection. All our results are presented as means for the five groups of lowland varieties and t w o groups of upland varieties indicated in Table I. Some justification of these groupings is therefore required because the s~nificance of any trends discerned rests on their validity. The groupings were made on a chronological basis. No firm dates of introduction into use are available for most of the earlier varieties, so group allocations were made using references or comments on the varieties in early papers. Those referred to in Table I are not necessarily the earliest in the literature. Many different varieties of rice have been grown in the Philippines at any one time, over a wide range of environments, so we did n o t expect our groups to be homogeneous. The characteristics of many of the early varieties were u n k n o w n but it was h o p e d that those in each group would represent the varietal heterogeneity present at each stage. Group I consists of traditional local Philippine varieties. Mendiola { 1919) estimated that before the official introduction of foreign varieties began, there were more than one thousand traditional varieties of rice in the Philippines, of which 814 had been studied at Los Bafios at the College of Agriculture. These are represented in our experiments by eleven lowland and nine upland varieties, encompassing a considerable range in plant type, growth duration, yield components and grain characteristics. At least t w o of these accessions, Apostol and Guinangang, probably derived from early line selections, begun in 1909 (Serrano, 1953), while Elon-elon may have been selected from an early introduction (cf. Capinpin and Punyasingh, 1938). The official introduction of varieties from overseas began in 1902 (Borja et al., 1952), and at least 143 varieties had been introduced by 1936 (Umali and Bernardo, 1959). Group II includes six of these pre-World War II introductions. Two of the earliest varieties bred in the Philippines are also included in Group II, since they were derived from a crossing program begun in the 1920s (Serrano, 1953). One parent of both these varieties was Ramai, an early flowering, high tillering, upright-leaved, short-statured and high yielding variety introduced from Indo-China (Aragon, 1930), seed of which

108 TABLE I Philippine varieties of rice used in the glasshouse and field (*) experiments, with their I R R I Accession n u m b e r , origin and an early reference, arranged in the groups for which data m e a n s are presented in the following tables and figures Group

Cultivar

I. T r a d i t i o n a l local varieties (a) L o w l a n d Apostol* Binicol* Consejala* Elon-elon* Guinangang Kinalabao* Macan Pina Macan Pulot Magcumpol* Sinamp ablo* Sinariay a (b) U p l a n d Binocaue Carreon Guinata Kinanda K i n a n d a n g Pula K i n a n d a n g Puti PiniIing Daniel Pinulot Pinursigue

Accession

Origin

Reference

a n d early s e l e c t i o n s

5997 4021 817 5193 5994 19430 3786 5102 5215 3972 5782 3821 5993 4013 3933 733 4016 5160 4028 5425

Laguna Laguna --Laguna Nueva Ecija Tarlac Tarlac Batangas Pangasinan Los Banos

Camus (1921) C a m u s (1921) Calma and Paguio (1948) Aragon and Cada ( 1 9 3 9 ) Camus (1921) Camus (1921) Camus (1921) Capinpin and Punyasingh ( 1 9 3 8 ) Camus ( 1 9 2 1 ) Apostol ( 1 9 0 9 ) Calma and Palis ( 1 9 4 8 )

Batangas Batangas Iloilo Batangas Batangas Batangas Tarlac Bataan Pangasinan

Gonzaies (1934) Gonzales (1934) Camus (1921) G o n z a i e s (1934) Goco (1918) Camus (1921) Camus ( 1 9 2 1 ) Camus (1921) Apostol ( 1 9 0 9 )

IL P r e - w a r i n t r o d u c t i o n s a n d bred varieties Lowland K h a o Bai Sri* 6110 Thailand ( 1 9 1 9 ) Radin China 4 10 Malaya S e m u p Besar 15" 6109 Malaya ( 1 9 3 6 ) Seraup Kechil 36 Str. 482* 5282 Malaya (1936) Siam 29* 42 Malaya (1936) Thailand* 697 R a m i n a d Str. 3* 40 Locally bred Ramelon* 5240 Locally bred III. P o s t - w a r i n t r o d u c t i o n s a n d s e l e c t i o n s (a) L o w l a n d Fortuna* 4012 Taiwan/USA Rexoro* 6311 Philippines/USA B-E-3* 38 Burma (1951) Intan* 4230 Indonesia Tjere Mas* 34 Indonesia (1948) Peta* 35 Indonesia ( 1 9 4 8 ) Bengawan* 33 Indonesia ( 1 9 4 8 ) (b) U p l a n d s e l e c t i o n s Azucena 328 Bulacan Inintiw Str. I 0 7 4014 Maajaas Magsanaya 725 Mangarez 4025 Palawan 4020

Camus (1921) A r a g o n and Cada (1939) Aragon and Cada ( 1 9 3 9 ) Aragon and Cada ( 1 9 3 9 ) Aragon and Cada ( 1 9 3 9 ) Calma and Paguio (1948) Juliano ( 1 9 4 1 )

Capinpin and L o p e z (1948) Capinpin and Miguel (1949) Cada ( 1 9 5 8 ) Cada (1958) Cada ( 1 9 5 8 ) Cada (1958) Onate and De] Mundo (1963) Cada (1958) Umali and Bernardo (1959) Umali and Bernardo (1959) Umali and Bernardo (1959) Ramirez and Umaii (1956)

IV. L o c a l l y bred cultivars Milfor 6 (2) Mflpal 4 BPI-76* C-18" FB-121" FK-178-A* V . R e c e n t l y bred cultivars Lowland C4-63" IR-8* IR-5* IR-36" IR-42"

4032 3O6 39 295 36 298

16329 10320 10321

Ramirez and Umali (1956) Umali and Bernardo ( 1959) Onate and Del Mundo (1963) Onate and Del Mundo (1966) Onate and De] Mundo (1966) Onate and De] Mundo (1966)

Hargrove Hargrove Hargrove Hargrove Hargrove

et al. (1980) et al. (1980) et al. (1980) et aL (1980) et al. (1980)

109 was unfortunately no longer available. Raminad Str. 3 came from a cross with Inadhica, Ramelon from a cross with Elon-elon. After the war, a major cooperative program for selection, introduction and hybridization of rice was established (Umali and Bernardo, 1959). More than 2000 overseas varieties were assessed under Philippine conditions during the 1950's, and seven of these lowland varieties comprise Group III. One of these, Rexoro, had been selected from a traditional Philippine variety, Marong Paroc, many years before, and Fortuna had likewise been selected from a Taiwanese variety. The five accessions in Group III b are probably all derived from post-war selections of traditional Philippine upland varieties or, in the case of Azucena, from an old lowland variety (Cada, 1958). Inintiw, for example, had long been grown as an upland rice in the barrio of Maahas near Los Bafios, but strain 107 was selected from it during the rehabilitation period (Umali and Bernardo, 1959). Group IV consists of six locally bred varieties which were released during the 1950's and early 1960's, while the five varieties in Group V were chosen to represent the sequence of bred varieties released in recent years by IRRI and the University of the Philippines at Los Bafios.

Glasshouse experiment Seeds were germinated in trays of soil and the seedlings were transplanted 10 days after sowing into 8-1itre pots of soil. Each replicate consisted of two pots each containing four plants. Each cultivar was grown from transplanting under three daylengths (10, 12 or 16 h) to allow assessment of their response to photoperiod and of the length of their basic vegetative phase (BVP), defined by Vergara and Chang (1976) as the juvenile growth stage not affected by photoperiod, and estimated from time from sowing to flowering in 10 h days minus 35 days for inflorescence development. All plants were grown on trolleys which were moved daily into an open-sided glasshouse between 07.00 and 17.00 h, after which they were distributed among air conditioned darkrooms at 21°C in which supplementary light of 450 lux intensity from incandescent and fluorescent lamps extended the photoperiod by the requisite amount. Day temperatures in the glasshouse were generally in the range 27--36°C. Fertilizer was applied to plants at the rate of 20 g ammonium sulphate, 4 g superphosphate and 4 g muriate of potash per pot. All. plants were grown under continuously flooded conditions. The experiment was sown on 4 February 1978, flowering began in midMarch and it continued through the remainder of the dry season. Thus the plants grew under relatively high and increasing natural irradiance. They remained in their allotted daylength until 10 days after flowering on the main stem, after which they stood in the glass house until harvested 30 days after flowering.

110 Main stem leaves were marked, and the number of leaves and tillers as well as plant height were measured periodically. The rate of photosynthesis by leaf blades was measured on plants in the 16 h daylength treatment at two stages, when leaf 5 on the main stem was fully expanded and on the uppermost fully-expanded leaf blade two weeks later. The leaves were held vertically in an air-sealed assimilation chamber {Wolf et al., 1969) of 0.3 cm × 2 cm cross section, the air flow rate being varied between 1 and 4 1 min :1 to keep the fall in CO2 concentration comparable between varieties. The airstream, almost saturated with water vapour and at a temperature of about 23°C when passed over the leaf, was drawn from the atmosphere, and its COs content was monitored so that all photosynthetic rates could be corrected to 300 ppm CO2 mean leaf concentration. Illuminance at the leaf surface was 66 klux (1100 g E m -2 s - j ) from a bank of incandescent lamps with an 18 cm wide water bath interposed between the lamps and the assimilation chamber. A Beckman Plantass D4A infrared gas analyser was used to measure the photosynthetic rates. Leaf areas were measured with a Hayashi Denko area meter. The date of panicle emergence on the main stem of each plant was recorded daily, and at final harvest measurements were made of plant height, flag leaf inclination (measured from base to tip, as degrees from vertical), panicle exsertion, leaf number, internode lengths, tiller and panicle number, grain yield components of the main stem panicle, and grain and straw weight for both the main stem and the whole plant.

Field experiment The thirty lowland varieties used in the field experiment (those marked with an asterisk in Table I) were sown on 20 May 1979 and transplanted on 8 June into randomized field plots, each 8 m × 2.5 m, with t w o replications. The spacing between individual plants was 25 cm each way, giving a density of 160 000 plants ha -1. The field was kept flooded throughout the experiment. Nitrogenous fertilizer at a rate of 40 kg N ha- 1, was incorporated into the soil before final harrowing. Plant height, tiller number, leaf area index (LAI) and light transmission through the canopy (at the midpoint between four plants at two places in each of the two replicate plots) were measured 49, 56 and 64 days after sowing, and five plants from each replicate plot were harvested to allow crop growth rates and nitrogen contents to be estimated. These measurements were repeated at flowering, and the lengths of main stem internodes and the length and inclination of the uppermost leaves, were also measured. At maturity, shoot weight and yield components were measured on five plants, and grain yield on an area of 2 m 2, in each replicate. The time of first flowering ranged from 8 August to 20 November, and of harvest from 10 September to 14 December, so that comparisons of final grain yield are confounded by greater than two fold differences in time to

111 flowering and maturity. Moreover, the rather low density of planting and low level of nitrogen fertilizer application, which was necessary in order to restrict lodging and disease among the older varieties, meant that the higher yield potential of the newer varieties could n o t be realized. These factors, together with the high level of boron subsequently found in these plots, were probably responsible for the relatively low LAI values and grain yields obtained in the field experiment. At Los Bafios (14.2°N) the daylength, including civil twilight, ranges from a minimum of 12 h 04 min in December to a maximum of 13 h 45 min in June. The dry season usually extends from December to May, b u t broke in April in 1979. Monthly irradiance usually rises from a minimum in December to a maximum -- almost twice as great -- in April. Temperature follows a similar course, b u t ranges only from 27.8°/22.3°C (maximum/minimum) in January to 32.8°/25.1°C in May. During the 1979 growing season minim u m temperatures were slightly below these average values. RESULTS Data for the 50 varieties are n o t presented individually, but rather for the groupings indicated in Table I in order to expose trends in their characteristics more clearly. There was considerable variation within many of these groups, some of which will be mentioned.

Glasshouse experiment Leaf appearance. The results in Table II suggest that there has been little change in the rate of leaf appearance on the main stem. The rate was highest for the modern lowland varieties as a group (V), b u t several older varieties had the highest individual scores, the highest being B-E-3. Across all 50 varieties there was a highly significant negative correlation between leaf number after 37 days and the area of the fifth leaf (r -- -0.90).

Leaf s/ze. Comparisons of the fifth leaf on plants grown in 16 h days (Table II) indicate that leaf length was greatest in the upland and old lowland varieties, and was much shorter in the modern lowland varieties. Some shortening of leaf length was apparent in three of the Group IV varieties, b u t all those in Group V had even shorter leaves. Several o f the older varieties had narrow leaves of small area despite their considerable length. Many of the older varieties did not flower in 16 h photoperiods, so the data in Table II for flag leaves are for plants from 12 h photoperiods. With these also the leaves were largest in the traditional lowland (Ia) varieties, and shortest and smallest in the modern lowland varieties (V). However, several of the older lowland varieties, such as Binicol (I) and Siam 29 (II) had flag leaves as small as those of Group V varieties and considerable variation in flag leaf size in

112 TABLE II Some characteristics of Philippine rice varieties, grouped as in Table I, when grown in the glasshouse under 12 or 16 h days Variety type

Lowland

Variety group

Ia

A. Plants in 16 h days No. o f main stem leaves a Length of leaf 5 (crn) b Area of leaf 5 (cm2) b No. o f tillersa Photosynthetic rate (rag CO2 dm -~ h - ' ) -- Leaf 5 b -- Leaf 8/9 c B. Plants in 12 days d Flag leaf length (cm) Flag leaf area (cm 2) Stem h e i g h t ( c m )

Upland

II

IIIa

IV

V

Ib

IIIb

7.9 -+0.2 36.2 -+1.4 24.9 -+2.5 3.6 -+0.2

8.7 -+0.1 31.9 -+0.8 16.4 -+1.0 3.8 -+0.2

8.3 +0.3 32.4 -+1.2 21.3 -+2.7 3.8 -+0.2

8.1 -+0.2 33.2 -+2.3 19.2 ±1.7 3.2 -+0.1

8.8 +0.1 23.8 -+0.6 14.6 -+1.1 4.5 -+0.1

7.7 -+0.3 34.0 +1.2 25.1 ±3.1 3.1 -+0°1

7.4 50.2 36.8 51.2 29.5 ±2.9 3.0 ±0.1

33.5 +1.2 33.7 -+1.6

28.2 -+1.6 35.8 -+1.4

31.9 52.2 32.5 -+1.3

30.3 -+1.0 31.8 51.8

32.5 +2.2 35.0 -+1.9

34.2 -+1.9 37.5 -+2.5

36.5 -+3.2 37.6 -+1.0

24.5 +2.7 35.2 -+5.7 73.2 -+10.6

40.1 ±2.5 64.6 -+3.1 142.3 -+5.0

46.4 -+4.1 69.8 -+9.9 165.4 +3.1

50.8 50.4 36.6 41.8 •+3.9 54.9 52.3 -+3.1 80.4 54.2 52.3 62.7 -+9.0 -+11.8 -+3.0 -+3.0 149.9 151.5 145.0 141.7 -+7.4 - + 3 . 3 -+8.4 510.3

a 37 days after sowing. b when leaf 5 had fully expanded. c measured 2 weeks after b. d at maturity.

l o w l a n d v a r i e t i e s h a s b e e n p r e s e n t a t all s t a g e s , w h e r e a s n e a r l y all u p l a n d varieties have large leaves.

Leaf inclination. A l t h o u g h s o m e r e d u c t i o n in flag l e a f l e n g t h w a s a p p a r e n t in G r o u p I I I v a r i e t i e s , a m a r k e d c h a n g e t o w a r d s m o r e u p r i g h t f l a g l e a v e s w a s e v i d e n t o n l y in t h e G r o u p V v a r i e t i e s e x c e p t C 4 - 6 3 , a n d in o c c a s i o n a l e a r l i e r v a r i e t i e s s u c h as S e r a u p K e c h i l ( I I ) , S i a m 2 9 ( I I ) , a n d s o m e e a r l y u p l a n d v a r i e t i e s s u c h as G u i n a t a a n d K i n a n d a ( I b ) . I R 8 ( V ) h a d t h e m o s t u p r i g h t f l a g l e a v e s , 17 ° t o t h e v e r t i c a l { d a t a n o t p r e s e n t e d b u t cf. F i g . 2).

Stem height. T h e a v e r a g e h e i g h t o f t h e s t e m o f p l a n t s g r o w n in 12 h o u r d a y s showed no significant reduction uatil the Group V cultivars were reached. T h e a v e r a g e h e i g h t o f t h e s e w a s h a l v e d , d u e t o r e d u c t i o n s in t h e l e n g t h o f all

113

the upper internodes whereas stem height increased among the selected upland varieties. The tallest variety was Macan Pifia (stems 182 cm), and tile shortest was IR 8 (53 cm). A somewhat different result was obtained with plants grown in a daylength of 10 h, in which all stem heights were less than in 12 hour days. Under these conditions, the Group IV varieties had shorter stems than those in Groups Ia and II (100 cf. 128 and 125 cm), although still substantially longer than those of Group V varieties (57 cm). The relatively shorter stems of the Group IV varieties uncler 10 h days was associated with their much earlier flowering.

Tillering. Tiller number was measured at various stages of growth, b u t the results given in Table II, for plants under 16 h photoperiods 37 days after sowing, are representative. These indicate that tillering was more sparse in upland varieties, and that there was little change among lowland varieties until Group V, in which tillering was faster. Binocaue (Ib) and Rexoro (IIIa) had the fewest tillers, IR 42 (V) the most. Photosynthesis. Photosynthetic rates were all measured under non-limiting irradiance on plants grown in 16 h days with a high level of nitrogenous fertilizer. The results of two series of measurements, each requiring 4 days and made during active growth of well established plants under high natural irradiance, are given in Table II. The rates for leaf 8/9 were somewhat higher than those for leaf 5, b u t the results indicate that there has been no significant trend towards increase in photosynthetic rate even among recent varieties. In fact, the highest rate recorded (49.2 mg CO2 dm -2 h -1) was for leaf 8 of Kinandang Pula (Ib), one of the oldest varieties, while the highest rate for leaf 5 {42.6 mgCO2 um -2 h -1) was for Inintiw Str 107 (IIIb) selectecl from a traditional variety. The lowest rate recorded (21.1 mg CO2 dm -~ h -1 ) was for leaf 5 of Thailand (II) and B-E-3 (IIIa). As may be judged from the standard errors of the group means a comparable range of values was found in each group.

Flowering response to daylength. The strong control by daylength of flowering in the older lowland rice varieties can be seen from the data in Table III. All the older lowland variety groups contained a substantial proportion of varieties which did not flower at all in 16 h days. Group II was the most sensitive to daylength, with only one o u t of eight varieties flowering in long days, whereas 36, 57 and 60% of the varieties flowered in each of Groups Ia, IIIa and IV, respectively, and all of those in Group V. Thus, there has been a pronounced reduction in the sensitivity of lowland rice varieties to daylength, b u t some of the older varieties such as Kinalabao, Macan Pifia and Sinampablo in Ia flowered in long days. Upland varieties, with one exception, were relatively insensitive to daylength. They were slowest to flower in

12 12 12

No. of spikelets

Kernel weight (rag)

16

12

10

Basic vegetative phase (days) No. of panicle branches

Days to flowering

(h) 67.7 -+4.7 86.4 •+4.4 (110.0) -+5.9 33 12.7 -+0.5 176 •+12 20.8 -+1.7

Ia

Variety group Daylength

Lowland

Variety type

32 12.9 -+0.7 167 -+16 19.9 -+1.3

66.7 -+3.7 116.2 -+6.8 (101)

II

67.9 -+6.9 95.4 -+8.6 (137.2) -+3.3 33 13.0 -+1.3 190 -+17 20.4 -+0.9

IHa

58.2 -+8.5 95.3 -+4.5 (117.0) t6.0 23 11.9 -+0.6 169 -+21 21.4 -+1.1

IV

Ib

77.0 77.6 -+3.8 -+6.6 93.7 87.1 -+2.8 -+5.5 124.7 (117.4) -+7.3 -+3.7 42 43 9.3 12.3 -+0.4 -+0.8 80 174 -+10 -+19 18.9 20.5 -+1.3 -+1.0

V

Upland

87.0 -+6.4 89.8 -+4.0 111.4 -+3.7 53 15.9 -+0.4 224 -+25 22.3 -+1.9

IIIb

Effect of daylength o n days to flowering of Philippine rice varieties (grouped as in Table I), together with some inflorescence characteristics for plants in 12 h days. (brackets indicate that only some varieties flowered in 16 h days)

TABLE III

b.A

115

10 h days and the fastest in 16 h days, in which all upland varieties except Carreon (Ib) flowered. In most cases, the ability to flower in 16 h days was associated with reduced responsiveness to daylength in the range from 10 to 12 h. For example, upland varieties took only slightly longer to flower in 12 h days than in 10 h days (12% longer for Group Ib, 3% for IIIb), and the modern lowland varieties (V) required only 21% more time. By contrast, lowland varieties in Groups II, III and IV required 41--74% more time to flower in 12 h days, indicating their greater sensitivity to daylength. The most sensitive varieties over the 10--12 h range were Seraup Besar (II), Siam 29 (II), B-E-3 (IIIa), FB-121 and BPI-76 (IV), in which the time to flowering in 12 h was more than twice as long as in 10 h days. Thus, sensitivity to daylength appears first to have increased from that found in the old local varieties of Group I to a peak in Group II, in which only Thailand flowered in long days. Groups III and IV also contained some highly sensitive varieties, but along with these were the Indonesian varieties (Intan, Peta, Tjere Mas and Bengawan) and others such as Milfor 6 (2), BPI-76 and C-18 which flowered in 16 days like the modern Group V varieties. However, whereas the daylength-insensitivity of the Group V lowland varieties was associated with a longer basic vegetative phase (Table III), as also in the upland varieties, the Group IV varieties had a distinctly shorter BVP. Its relation to the number of leaves to flowering is shown in Fig. 1. This indicates the wide range of varietal behaviour within each group, while the curvilinear relation suggests that leaf production may have been slower in varieties with a longer basic vegetative phase. A significant negative correlation (r = -0.52} was found between the length of the BVP and the number of leaves in plants 37 days old.

Inflorescence characteristics. As would be expected from the results in the preceding section, daylength had little effect on the characteristics of the inflorescences of upland varieties and of Group V lowland varieties. With the older lowland varieties, however, the numbers of panicle branches, of spikelets and of grains per panicle increased to a small extent with increase in daylength from 10 to 12 h (results not presented). Comparing across varietal groups, there was no difference in the number of branches per panicle among the early lowland and upland groups (12.3-13.0 branches), but branching was reduced in the modern lowland group (V) to only 9.3 and increased in the selected upland varieties (IIIb) to 15.9, for plants grown in 12 h days (Table III). The total number of spikelets per inflorescence followed a similar trend, from 167 to 190 in the Groups I--IV lowland and older upland varieties, down to only 80 in the Group V lowland, and up to 223 in the selected upland varieties, for plants in 12 h days. The number of filled spikelets, and grain weight per panicle followed similar

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trends. Kernel weight showed no clear trend (Table III), being largest by far in the old lowland variety Kinalabao {35.3 mg in 12 h days) and smallest in Pinulot (14.8 mg). The shorter modern varieties suffered some shading by the taller older varieties during the later stages of their growth in the glasshouse experiment, reinforcing the varietal differences associated with height, but the trend towards smaller panicles in the modern lowland varieties, and to heavier panicles in the tall selected upland varieties was clear. Grain weight per panicle was greatest in the variety Palawan (5.86 g in 10 h days). The heavier panicles of the upland and older lowland varieties were not associated with greater harvest index. Plants grown in 10 h days tended to have a higher harvest index than those grown in 12 h days, but no clear trend was apparent across the groups of varieties in the glasshouse experiment, probably because the modern varieties were shaded by the taller, older varieties, a problem which could be avoided in the field experiment (cf. Table IV). Field experiment Growth habit. Changes in stem height and leaf length and inclination have already been discussed for plants grown in the glasshouse. The results for the 30 varieties grown in the field are summarized in Fig. 2. Here again, stem height was greatest in the Group II lowland varieties, and was progressively less in the later groups due to the shortening of all inter-

117

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Fig. 2. Diagrammatic illustration of changes among lowland rice varieties in the length of stems, internodes, leaf blades and panicles, and in the inclination (from base to tip) of the four uppermost leaves, based on the mean values at anthesis for each group of varieties grown in the field.

nodes. Leaf length has also been reduced, and the upper leaves have become progressively more erect. Exsertion of the panicle has been reduced to the point where the lower part remains within the sheath of t h e flag leaf in Group V varieties. Leaf area index, light transmissmn and crop growth rate. Because of the relatively low planting density and nitrogen fertilizer application, really dense crop canopies did not develop even with Group V varieties. The leaf area index (LAI) increased progressively up to flowering, when group means averaged only 2.3--3.1, with the variety Tjere Mas (III) reaching the highest value (4.1). Light transmission through the canopy at flowering was greatest (12.4%) for the Group V varieties, as would be expected because of their more upright leaves. The relation between LAI and light transmission through the canopy is shown in Fig. 3. With most older varieties the fall in light transmission with increase in LAI corresponds to extinction coefficients (Monsi and Saeki, 1953) of 0.5--0.6 whereas Group V varieties had extinction coefficients of less than 0.4, presumably associated with the more vertical orientation of their leaves. Canopies of the older varieties with more upright leaves (Magcumpol (I), Seraup Kechil (II), Rexoro, Peta (IIIa) and C-18 (IV)) had intermediate extinction coefficients of 0.4--0.5. This range of values is comparable to that found by Hayashi and Ito (1962) with Japanese varieties. Crop growth rates were estimated for three intervals, those given in Table IV being from 56 to 64 days after sowing. No significant change has oc-

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curred during rice improvement. The relation between LAI 56 days after sowing and crop growth rate during the succeeding 8 days is shown in Fig. 4. Tjere Mas (III), with the highest LAI, had the highest crop growth rate {27.4 g m -2 d-'), but the relation between these two parameters was not close. However, it is clear from Fig. 4 that the modem lowland varieties did not have higher crop growth rates than older varieties with comparable LAI values. Thus, no advantage was gained from their more upright leaves at these relatively low LAI values. Varieties with crop growth rates on the high side of the regression were not characterized by higher photosynthetic rates nor by higher nitrogen contents per unit leaf area. Nitrogen content was highest in the Group V varieties (3.15 + 0.07% average cf. 2.75 + 0.07% for Group I).

Flowering. As was to be expected from the wide range in the length of the basic vegetative phase and in sensitivity to daylength (Table III), flowering of the varieties in the field occurred over a very long period. The first varieties to flower, after 80 days, were Binicol (I) and IR 36 (V), while the last, 184 days after sowing, were Seraup Kechil and Ramelon, both in Group II. In fact. flowering was slowest by far in Group II and fastest in Group V varieties (Table IV). The varieties which flowered in less than 4 months in the field were those able to flower in long days in the glasshouse experi-

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ment, and their time to flowering in the field correlated closely (r = 0.89, Fig. 5a) with their time to flowering in 16 h days but not with the length of their basic vegetative phase. Among the 13 late flowering varieties in the field, none of which flowered in 16 h days, time to flowering in 12 h days in the glasshouse correlated closely (r = 0.92, Fig 5b) with time to flowering in the field where daylength had, by then, declined to about 12 h. Thus, time to flowering in the field could be largely explained in terms of the daylength responses found in the glasshouse experiment, with some variation associated with differences in the basic vegetative phase.

Grain yield. The great differences between varieties in time to flowering, paralleled by those in time to maturity, make it difficult to draw meaningful comparisons of yield. As may be seen from Table IV, the increase in grain yield (as g m -2) from Group I to Group V varieties was modest {11%) and not significant. The two highest yielding varieties were Magcumpol of Group I and IR 42 of Group V. To some extent the absence of any increase in yield may have been due to the relatively low level of nitrogen fertilizer which could be applied in order to avoid lodging of the older, taller varieties. In consequence, the capacity of the modern varieties to produce more panicles could not be fully expressed (c.f. Tanaka et al. 1968), although their superiority in this respect is evident in Table IV. IR 42, IR 36 (V) and Thailand (II) produced the most panicles (218--222 m-2), while Group I varieties Sinampablo and Kinalabao produced the fewest (91--99 m-2). However, Thailand, IR 36 and IR 8 had the fewest grains per panicle (77-80}, compared with 185 in FK-178 A (IV) and 170 in Elon-elon (I). On average,

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Fig. 5. Relation between days to flowering in the field and in the glasshouse experiment under: (a) 16 h photoperiods for the varieties which flowered at that daylength; or (b) 12 h photoperiods for varieties which remained vegetative in 16 h days. Fig. 6. Relation between days to maturity and grain production per day from sowing to maturity for varieties in the field experiment. The sloping line represents the relation for yields of 380 g m -2.

Group V varieties had the smallest panicles, Group IV the largest. Kernel weight again showed no consistent trend, being greatest in Kinalabao (34.6 mg) and smallest in Siam 29 (19.7 mg). In view of the great differences in time to maturity, varieties were compared in terms of grain production per day for each crop. By this criterion the group means given in Table IV indicate a significant improvement from Group II to Group V, with IR 42 reaching the highest value, 3.91 g m-2 d-'. Fig. 6 indicates the relation between time to maturity and grain production per day for all varieties, the sloping line representing the relation for grain yields of 380 g m -2. It is evident that the major trend revealed in our field experiment is the capacity of newer varieties to produce a similar yield in a progressively shorter time. Associated with that trend there has been a steady rise from Group II to Group V in the harvest index (Table IV), which was highest (0.53} in IR-36.

121 TABLE IV Characteristics of 30 Philippine lowland rice varieties grown in the field (grouped as in Table I) Group I Crop growth rate (g m -2 d -1 )a 17.2 Days to flowering Grain yield (g m -2) No. of panicles per rn 2 No. of grains per panicle Kernel weight (mg)

II 16.8

III 17.0

IV 16.4

V 15.0

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123.1

165.7

120.1

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101.2

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-+13.2

+-9.1

+-18.4

394.0 +-32.1 138.9 +-14.1 122.3

375.0 +16.2 170.7 +-10.3 97.9

411.7 +-16.0 156.6 +-10.4 102.4

+-11.0

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+-15.7

+-4.7

24.9

24.4

26.1

24.2

25.1

+-1.9

+1.3

+-1.2

+-1.3

+-1.6

2.8 +-0.1 0.37 +-0.02

2.1 2.9 3.3 3.6 +-0.2 -+0.2 -+0.2 -+0.1 0.28 0.38 0.41 0.47 -+0.03 -+0.02 -+0.04 -+0.02

463.6 +-34.6 136.0 +-8.9 146.2

+-6.0

437.9 +-30.8 192.8 +-11.2 91.2

Grain production per day (g m -2 d - 1 )

Harvest index a 56--64 days after sowing.

DISCUS SION T h e c h r o n o l o g i c a l grouping o f the 50 Philippine varieties o f rice used in the e x p e r i m e n t s r e p o r t e d h e r e reveals clear t r e n d s in some characteristics and n o a p p a r e n t change in others. T h e trends have m u c h in c o m m o n with t h o s e f o u n d b y T a n a k a et al. ( 1 9 6 8 ) and S a m o t o ( 1 9 7 1 ) a m o n g rice varieties used in J a p a n over a c o m p a r a b l e p e r i o d o f time. T h e i r studies were based on the c o m p a r i s o n o f one or t w o varieties f r o m each decade. B y c o n t r a s t , o u r comparisons are b e t w e e n groups, each c o n t a i n i n g 5 t o 11 varieties o f similar b u t less c e r t a i n vintage, and each e n c o m p a s s i n g a considerable range o f behaviour. Nevertheless, several t r e n d s e m e r g e quite clearly, w i t h o u t obscuring the varietal variety at each stage. T h e o t h e r striking aspect o f the results is t h a t some o f the changes have n o t been c o n s i s t e n t l y in one d i r e c t i o n . B e f o r e considering the sequence o f changes t h a t have o c c u r r e d , we should n o t e some o f the characteristics which have n o t changed significantly across the g r o u p s o f varieties listed in Table I. As also f o u n d b y T a n a k a e t al. ( 1 9 6 8 ) and C o o k and Evans ( 1 9 8 3 a , b), t h e p h o t o s y n t h e t i c rate does n o t app e a r t o have changed, n o r has the crop g r o w t h rate, in any c o n s i s t e n t way a l t h o u g h t h e r e was a considerable range in b o t h these p a r a m e t e r s a m o n g t h e varieties (Tables II and IV). Likewise, kernel weights revealed no c o n s i s t e n t t r e n d , as C o o k and Evans ( 1 9 8 3 a ) also f o u n d .

122

Lowland varieties. The group of pre-war introductions and bred varieties (II) differed in many respects from the traditional Philippine lowland rices of Group I. On average, their leaves were shorter and much smaller in area, and they tillered more heavily. As a group they were the most sensitive to daylength, only one of the eight varieties flowering in 16 h days. Their time to flowering was m u c h greater in 12 h than in 10 h days, and (with the exception of Thailand) they were the last to flower in the field experiment. They had many more panicles than the traditional varieties, but these were smaller, with fewer spikelets and grains. Late flowering, tallness and small panicles combined to give this group the lowest harvest index in the field experiment. Several of these changes were reversed in the post-war introductions and selections of Group III. Stems started to become shorter and leaves more upright (Fig. 2). There were fewer tillers and panicles, but they were rather larger. Flowering was less sensitive to daylength, and faster both in 12 h photoperiods and in the field, the four Indonesian varieties being remarkably uniform in this respect. The locally bred cultivars of Group IV, released in the 1950's and early 1960's, continued several of these trends. Stems became shorter, leaves smaller and more upright, $illers and panicles still fewer. In fact, Group IV varieties had the fewest panicles of all, but the largest, with the most grains. This group was the first to flower in 10 h days, though not in 12 h days or in the field, and had a higher harvest index and grain production per day than Groups II and III. However, the recently bred cultivars of Group V showed the greatest differences from their predecessors. Figure 2 indicates that their stems were much shorter, as also their leaves, which were oriented much more vertically. This resulted in greater light penetration within the crop canopy and a lower extinction coefficient (Fig. 3), but did not result in faster crop growth rates at the relatively low LAI values in the field experiment (Table IV). The shorter stems were associated with faster leaf and tiller production, and with failure of the panicle to be fully exserted at anthesis. Panicle number rose from being least in Group IV to greatest in Group V, but panicle size fell from being largest in Group IV to smallest in Group V (Table IV). This parallels the shift in Japanese varieties found by Tanaka et al. (1968) and Samoto (1971) from the "ear weight t y p e " to the "ear n u m b e r type". This shift might have been expected to result in a fall in harvest index but in fact this rose to its highest level of all, probably because of the earlier flowering and shorter stature of Group V varieties. Earlier flowering, in turn, was associated with a reduced sensitivity to daylength (Table III), and occurred in spite of a marked increase in the length of the basic vegetative phase. As a result, grain production per day, like harvest index, reached its highest levels among the modern varieties. Indeed, these attributes were closely correlated (r = 0.93) among the 30 varieties. Upland varieties. The traditional upland varieties of Group I were not markedly different from traditional lowland varieties, as was to be expected

123 since some traditional varieties, such as Apostol, Azucena, Binicol, Piniling Daniel and Pinursigue, used to be grown under both lowland and upland conditions in the early years of this century. Upland varieties tillered rather less, but the main difference appeared to be that they were less sensitive to daylength, all except Carreon flowering relatively quickly in 16 h days, whereas over half of the traditional lowland varieties remained vegetative. The group of upland varieties subjected to selection (IIIb) differed quite strongly from the traditional upland rices. They were notably taller, in fact the tallest group of all, with the slowest rates of leaf and tiller formation. They were the group least sensitive to daylength, substantially less so than the m o d e r n lowland varieties of Group V, and t h e y had the longest basic vegetative phase (Table III). They also had the heaviest panicles (3.91 g) with the most branches (15.9), most spikelets (224) and most grains {154). However, their stems were even heavier, relative to other groups, with the result that their harvest index was low (0.25 in 12 h days). Thus, while their daylength response has shifted in the same direction as the m o d e r n lowland varieties, their growth habit, height and panicle characteristics have diverged in the opposite direction. Thus, these rice varieties of the Philippines reveal the pronounced changes that have occurred over the years in growth habit, sensitivity to daylength and panicle characteristics of both lowland and upland varieties. Several of the characteristics of the m o d e r n lowland varieties such as shorter stature, more upright leaves and reduced sensitivity to daylength, had apparently begun to be selected for in the earlier groups, but the changes in others -such as tillering and panicle characteristics -- have followed a more varied course. It is notable that, in spite of these pronounced changes, photosynthetic rate, crop growth rate and kernel weight have not changed. ACKNOWLEDGEMENTS We are grateful to Dr T.T. Chang for help with the selection of varieties to be used in this work, and for the provision of seeds; to Dr Esteban Cada and Dr. P. Escuro for advice on the grouping of varieties, to E. Vidal and Cheryl Blundell for technical assistance; and to Mary Cook, Rod King and Ian Wardlaw for their helpful comments on the manuscript.

REFERENCES

Apostol, S., 1909. Report on rice cultivation in Zambales and Pangasinan. Philipp. Agric. Rev., 2: 269--275. Aragon, V.B., 1930. Ramai rice and its introduction and culture in the Central Luzon Agricultural School. Philipp. Agric., 18 : 535--542. Aragon, V.B. and Cada, E., 1939. A preliminary report on the performance of ten rice varieties from the Federated Malay States. Philipp. Agric., 27 : 635--646. Borja, V. Torres, J.P. and Octubre, F.P., 1952. Fifty years of rice research. In: A Half Century of Philippine Agriculture. Graphic House, Manila, pp. 179--189.

124 Cada, E., 1958. S o m e oustanding results of rice breeding at the Maligaya rice experiment station. Philipp. J. Agric., 23: 125--137. Calma, V.C. and Paguio, M.D., 1948. The performance of five varieties of lowland rice. Philipp. Agric., 31: 298--304. Calma, V.C. and Palis,N.C., 1948. Inintiw and Sinariaya as secondary crops on succession to a primary rice crop. Philipp. Agric., 32: 50--54. Camus, J.S., 1921. Rice in the Philippines.Philipp. Bur. Agric. Bull. 37. Capinpin, J_M. and Lopez, R.R., 1948. Variability in plant and grain characters of Fortuna rice as influenced by methods of culture. Philipp. Agric., 32 : 150--164. Capinpin, J.M. and Miguel, G.B., 1949. Analytical studies of Rexoro, Nira, and Iola rice varietiesgrown in the College of Agriculture. Philipp. Agric., 32 : 223--230. Capinpin, J.M. and Punyasingh, K., 1938. A study of varietalcrosses and hybrid vigor in rice. Philipp. Agric., 27 : 255--277. Cook, M.G. and Evans, L.T., 1983a. Some physiological aspects of the domestication and improvement of rice (Oryza spp.). Field Crops Res., 6 : 219--238. Cook, M.G. and Evans, L.T., 1983b. Nutrient responses of seedlings of wild and cultivated Oryza species.Field Crops Res., 6: 205--218. Goco, A.A., 1918. Performance of selectionsof best local upland ricesunder fertilization. Philipp. Agric. For., 6: 155--167. .~ Gonzales, L.G., 1934. Outstanding results of agronomic and horticultural research. Philipp. Agric., 23: 3 8 0 - 3 9 9 . Hargrove, T.R., Coffman, W.R. and CabaniUa, V.L., 1980. Ancestry of improved cultivars of Asian rice. Crop Sci., 20 : 721--722. Hayami, Y. and Kikuchi, M., 1975. Investment inducements to public infrastructure: irrigation in the Philippines. I R R I Dep. Agric. Econ. Pap. 75-15, 26 pp. Hayashi, K. and Ito, H., 1962. Studies on the form of plant in rice varieties with particular reference to the efficiency in utilizing sunlight. I. The significance of extinction coefficient in rice plant communities. Proc. Crop Sci. Soc. Jpn., 30: 329--333. Huke, R.E., Cordova, V. and Sardido, S., 1982. San Bartolome: beyond the Green Revolution. I R R I Res. Pap. 74, 13 pp. Juliano, J.B., 1941. Progress in rice research in the Philippines. Philipp. J. Agric., 12: 125--196. Mendiola, N.B., 1919. A review of rice investigations at the College of Agriculture. Philipp. Agric., 8: 145--160. Monsi, M. and Saeki, T., 1953. Uber den Lichtfaktor in den Pflanzengesellschaften und seine Bedeutung f'tir die Stoffproduktion. Jpn. J. Bot., 14: 22--52. Ofiate, L.U. and Del Mundo, A.M., 1963. Eating quality of seven varieties of lowland rice. Philipp. Agric., 47 : 208--214. Ofiate, L.U. and Del Mundo, A.M., 1966. Consumer and Laboratory panel evaluation of Seed Board rice varieties. Philipp. Agric., 50: 301--309. Ramirez, D.A. and Umali, D.L., 1956. The nature of lodging in rice. Philipp. Agric., 40: 335--351. Samoto, S., 1971. (Alteration of the important characteristics in the breeding programs of high yield rice varieties). Hokkaido Nat. Agric. Exp. Stn. Rep., 7 8 : 2 3 - - 7 3 . Serrano, F.B., 1956. New Philippine rice hybrids and their commercial possibilities. In: Proc. Eighth Pacific Science Congress, 16--28 November 1953, University of the Philippines. National Research Council of the Philippines, Quezon City, pp. 1 7 9 - 1 8 2 . Tanaka, A., Yamaguchi, J., Shimazaki, Y. and Shibata, K., 1968. Historical changes in plant type of rice varieties in Hokkaido. J. Sci, Soil Manure Jpn., 39: 526--534. Umali, D.L. and Bernardo, F.A., 1959. Fifty years o f rice improvement in the U.P. College o f Agriculture. Philipp. Agric., 43 : 76--97. Umali, D.L., Torres, J.P., Honrado, P.A., Manio, R.V. and Rigor, E., 1956. Cooperative rice improvement program in the Philippines. IRC Newsl., 18: 1--7. Vergara, B.S. and Chang, T.T. 1976. The flowering response of the rice plant to photoperiod. International Rice Research Institute, Los Bafios, Philippines, 75 pp. Wolf, D.D., Pearce, R.B., Carlson, G.E. and Lee, D.R., 1969. Measuring photosynthesis of attached leaves with air sealed chambers. Crop Sci., 9: 24--27.