B. VENKATESWARLU and T.E. SRINIVASAN. All-India Coordinated Rice Improvement Project, Rajendrdnagar, Hyderabc:d Received on May 12, 1977

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1 INFLUENCE OF LOW LIGHT INTENSITY ON GROWTH AND PRODUCTI VITY IN RELATION TO POPULATION PRESSURE AND VARIETAL REACTION IN IRRIGATED RICE (ORYZA SATIVA L.) B. VENKATESWARLU and T.E. SRINIVASAN All-India Coordinated Rice Improvement Project, Rajendrdnagar, Hyderabc:d Received on May 12, 1977 SUMMARY Studies on shading effect (40-50i' of natural light) were conducted with Sona and RP 4-14 under field conditions at different growth phases with two densities of population (50 and 100 hills/m2) and assessment of varieties (6 of early duration and 9 of medium duration group) was done. Although yield losses were maximum at reproductive and ripening phases, higher population density compensated the loss in some measure. Varietal responses differed for total dry matter, panicle number and grain yield under shade suggesting the need for further screening of varieties to identify plants with relative tolerance to reduced light conditions. Slow complex heritable approach was considered desirable in breeding programmes to synthesise plants to suit to low light intensity stress situations. INTRODUCTION The actual yields of the short statured varieties during monsoon season are relatively lower despite their reported high yield potential. That the low light intensity is one of the important constraints for lower yields in monsoon season has been reported by several workers in rice. Tanaka et al., (1964) reported lower dry matter accumulation and decreased photosynthesis under shaded conditions. Stansel et al., (1965), stated that sterility increased, taller plants were produced and yields reduced under low light intensity conitions..venkateswarlu et a/., (1971) observed that yields were progressively reduced with, low light intensity appearing in succession at different growth phases. The effect was more critical during ripening phase. That the yields were reduced from primordial initiation onwards under shade was also reported by Stansel et a/., (1965), CRRI (1972) and Yoshida (1975). The present study is aimed at the elucidation of information whether increased density of population would compensate the losses due to shade. Earlier studies at the AICRIP Centre with three varieties (Venkateswarlu et a/., 1917) indicated variations for different growth parameters even at different growth phases. Efforts were, therefore, made in the present study to assess certain promising pre-release cultures belonging 6 to early duration and 9 to medium duration under shade for identifying possible varietal variation for different growth parameters.

2 EFFEcT OF LOW LIGHT INTENSITY ON RICE 163 MATERIAL AND METHODS.. Thirty day seedlings of Sona and RP 4-14 were transplanted with the present recommended spacing of 20x 10 cm (50 hills/m 2 ) and a close spacing of lox 10 cm (IOO hills/cm 2 ) in 4 X 3 m plots during rabi The plot'> were shaded by thick Kora (marking) cloth such that 40-50% of natural light was only received on the crop canopy_ The shades were erected in the field in the form of small tents. The cloth was fastened tight to the wire which served as a lining connecting the wooden supports all round both at the bottom and top of the supports (Fig. 1). The natural incident light intensity received was Klux (Dry season) measured with Toshiba Lux meter. The treatments were (1) Control (Continuous natural light So), (2) shading during vegetative phase (SI), (3) shading during reproductive phase (Sa). (4) shading during ripening phase (Sa) and (5) continuous shading throughout the crop period (S4)' The fertilizer schedule adopted was 60 kg N+ 15 kg P+25 kg K per hectare. Half the dose. ofn was applied 15 days after planting and the rest split into two doses one at mid tillering and the other around panicle initiation while P and K were applied as basal. The mean maximum temperatures during the crop period ranged from 28 C to 39 C and the mean minimum from 12 to 24 C. The temperature under shade was I-2 C less in comparison to atmospheric temperature. There was free wind flow but shade induced slight changes in relative humidity and CO 2 levels around the plant canopy. Observations were recorded on leaf area index, dry matter content. panicles. spikelet and grain numbers, partiauy filled grains, besides grain yield.

3 '1... > Z Table l. Effect ofshading at different growth phases on certain growth parameters. <: Shading during vegetative phase Shading during reproductive phase Shading during ripening phase t"ll _._ _._ z T.D.W fm (g) L.A.I. Tillersfm2 T.D.W./m (g) L.A.I. Tiliers/mo T.D.W./ml(g) Panicles/m" Yield(tfha) > ;\ Cont Shade Cont- Shade Cont- Shade Cont- Shade Cont- Shade Cant- Shade Cont- Shade Cont- Shade Cont- Shade rol rol rol rol rol rol rol rol rol > c:: lsfml) s/m') 590 > Z S I !: \ :;:a Z <I>

4 EFFECT OF LOW LIGHT INTENSITY ON RICE 165 Varietal assessment.-six varieties belonging to early duration and 9 to medium duration group were assessed under shade at different growth phases. The shading treatments for medium duration group were similar as earlier described but for the absence of continuous shading (S4) treatment, while for the early duration cultures only two shades were created i.e., (1) From planting to flowering (SI) and (2) from flowering to maturity (S2)' The same 'fertilizer schedule was adopted as already described. Observations were recorded on total dry matter content, panicle number and grain yield. RESULTS AND DISCUSSION Growth parameters under shading.-there was a decrease in the total dry matter content and reduction in tihering (Table I) under shading irrespective of growth phase. The leaf area index was not altered significantly. These findings in general were in conformity with the earlier findings of Stansel et al., (1965), Venkateswarlu et 01., (1977) and Sridharan (1975). Variety Sona RP 4-14 Table II. lox 10 em (100 hills/m O ) 20x20 em (50 hills/mo) IOxl0 em Influence oj shading on growth and yield at different densities oj population (Rabi. 1975) So S, So S, So S1 20x20 em S, S, Panicles! m S So=Contro1 (normal light intensity) S,=Shading during vegetative phase =Shading during reproductive phase =Shading during ripening phase S,=Shading throughout crop period T.D.W. g/m' Yield t/ha Harvest index

5 166 D. VENKA'rESWAkLU AND T.E. SlUNIVASAN The flowering was advanced by 6-8 days in Sona and 5-6 days in RP 4-14 due to shading at 8 1 stage only. The decreases in growth parameters and yield reduction in the present study are greater at the lower population density (50 mills/m ll ) than at higher density (Table II). The influence of higher population density compounded over shades and varieties clearly led to higher dry matter content, greater panicle number and increased grain yield. These results suggest that during monsoon season when low light intensity is a general problem, resorting to increased density of population over the normal density recommended for this group of varieties would compensate the losses in yield in some reasonable measure. However, the new situation could create necessary micro-climatic conditions favourable for the development of pests and. diseases. The influence of shade was critical during reproductive and ripening phases (Table III), in respect of spike lets and grain production and consequently the grain yield. Although, the results in general agree with Table III. Influence ofshading on spikelets, grains, partially filled grains and chaff percentages at two different densities ofpopulation Spikelets Grains Filled Partially Variety No. (lo')/m* (WS)!m" grains filled Chaff' % grains % % Sona loxloem So S S, xl0 cm S S, S, RP xl0 em S, S l.2 s S, xlOcm S S, So Control (normal light intensity) S1 = Shading during vegetative phase Shading during reproductive phase = Shading during ripening phase = Shading throughout crop period.

6 EFFECT OF LOW LIGHT INTENSITY ON RICB 167 the earlier findings (Stansel et al., 1965; Yoshida, 1975; and Venkateswarlu et 01., 1977), the advantage of higher density of population in realising higher yields is illustrated through this study only. Spikelets and grains.-the spikelet and grain production per m 2 was greater at higher plant density in both the varieties. Continuous shading (SJ led to low spikelet and grain production. Shading during vegetative and reproductive stages also caused lower production of spikelets irrespective of variety and spacing (Table III), thereby indi cating that these two phases require more light intensity for greater production of spik lets. Cock and Yoshida (1973) and Yoshida (1975) also reported that increasing photosynthetic rate during reproductive phase when spikelet number or the potential sink size of the rice crop is determined may lead to increased grain number or sink size. Though the spikelet production at S3 stage (ripening phase) was similar to control (Table III), realisation of grains was far lower and almost equal to the grains produced at Sa stage (shading during reproductive phase). But at Sa, the spikelet production was less in comparison to control and S3 stage, whije realisation of grains is equal to Sa. These differeitces in spikelet production and grain formation indicate the importance of current photosynthesis during the ripening stage. Table IV. Influence oflow light intensity (50% of normal light) at different growth phases on total dry weight, panicles and grain yield in early duration varieties (Rabi, 1975) TOW/ Panicles/ Yield Variety m a (g) ml t/ha Cauvery 8 0 S1 Pusa 2 21 SI let let 1444 let So S (3) (4) (6) (I) o (2) (3) (6) (2) (4) (5) (4) (6) (3) (2) (1) CR So S1 660(5) 623 (1) (5) (Figures in parenthesis indicate rank positions) So = Control (nonnallight intensity) S1 Shading from planting to flowering S2 = Shading during ripening

7 168 B. VENKATESWARLU AND T.E.SRINIVASAN The data on percentage of filled grains (Table III) varied differently and in some cases showed almost same figures under different treatments. In Sona, the percentage of filled grains was 64 at both &! and S2. but the number of grains realised was 35.0 and 26.5 thousand/mil respectively. Further, in certain shades although the percentage of filled grains was higher than in control plots, the actual number of grains obtained were either lower or similar to control. This clearly suggests that indicating filled grain per cent alone would cover only a part of the story, but when given in association with the spikelet number clearly conveys the gap and infers about the built in constraints in a given situation. Varietal screening.-shades for early duration cultures were provided only at two phases i.e., from planting to flowering (SI) and during ripening phase (Sa). Dry matter accumulation and panicle number were important during SI phase and hence the ranking of the varieties was done at this stage only. Yield was considered at SII for comparisons. Among early cultures included in the study (Table IV) let 1444 produced more total dry matter content (898 g/m2) under shade and occupied first position while let 2508 (638 g/m2) occupied 6th rank. CR was rated as number one with 6:23 panicles/m 2 while Pusa 2-21 occupied 6th position with 408 panicles per sq.m. As regards yield, let 849 ranked first (4.52 t/ha) while Pusa 2-21 occupied sixth rank (3.50 t/ha). Thus, there was varietal variation for different growth parameters under shade. For medium duration varieties shading was provided at all the three growth phases. Comparison for total dry matter was done at Sa as dul ing this phase panicles (potential sink size) and leaves synchronously develop and hence critical for dry matter accumulation. Panicle number by and large is determined through tillering during vegetative phase (SI) and, therefore, this phase was considered important for comparisons. For grain yield, Sa phase (ripening) was important as it involves grain filling. RP is rated first (953 g/m2) for dry matter while RP occupied eighth position (765 g/m2) (Table V). let 2812 occupied first position for panicles (47S/m2) at SI while RP was rated ninth (310 panicles/m2). For grain yield, RP 4-14 occupied first position (4.40 t/ha) while let 3093 is rated ninth (3.20 t/ha). This information is new. The data clearly suggest the need for the screening of germplasm for the different characteristics such that improvement could be effected by combining the required traits in the desired direction. This naturajly takes us to a purposeful crossing programme to evolve better plants suited to such situations. The present work is of preliminary nature and the data suggest the need for more extensive screening of the material for indentifying genotypes possessing the desired traits. During monsoon season as light is one of the major constraints in eastern and south peninsular region of the country, aiming for combination of such traits would make rice improvement programme more purposive. Thus, slow complex heritable approach appears to be more appropriate not only to raise the yield potential but stabilise production in the vast monsoonic areas of the country. ACI<NOWLEDGEMENTS The authors are grateful to Dr. R. Seetharaman, Project DireCtor, All-India Coordinated Rice Improvement Project, Hyderabad for his encouraging suggestions and comments on the manuscript.

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9 170 B. VENKATESWARLU AND T.E. SRINIVASAN REFERENCES Cock, H. James and Yoshida, (1973). Changing sink and source relations in rice (Oryza sativa L.) using carbon dioxide enrichment in the field. Soil Sci. Plant Nlltr., 19 (3): CRRI, (1972). Annual Technical Report of Central Rice Research Institute, Cuttack. India. SHU. Murty, K., Na)'ak K. and Sahu, G. (1975). Effect of low light stress on rice crop. Proceedings of the symposium on "Crop plant response of environmental stresses", held at Vivekananda Parvatia KriShi Anusandhan Shala, Almora, U.P., India. Sridharan, C. (\975). Studies on the influence of climatological factors on rice under different water management practices. Ph. D. thesis submitted to the Orissa University of Agriculture and Technology, Bhubaneswar, India. Stansel, I.W., Bollich, C.N. and Thysell, J.R. (1%5). The influence of light intensity and N fertility on rice yield and components of yield. Rice J., 68: , Tanaka, A., Navasero, A. Garcia, C.V., Parao. F.T., and Ramirez, E. (1964). Growth batit of the rice plant in the tropics and its effect on nitrogen response. Technical Bulletin 3. The International Rice Research Institute, Philippines, p Venkateswarlu, B., Prasad, V. V. and Rao, A. V. (1977). Effects of low light intensity on different growth phases in rice (Oryza sativa L.). Plant and Soil, 47 No. 1: Yoshida, (1975). Eco-physiology of rice. Paper Presented at the symposium on tropical and sub-tropical crops held at the Centro de Pesquisas do Cacan, Brazil, from May 26 to 30, 1975.