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Significance of Leaf Orientation and Bract in Seed Yield in Sunflower

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Significance of Leaf Orientation and Bract in Seed Yield in Sunflower SIGNIFICANCE OF LEAF ORIENTATION AND BRACT IN SEED YIELD IN SUNFLOWER G. C. SRIVASTAVA, P. S. DESHMUKH AND D.P.S. TOMAR Division of Plant Physiology Indian Agricultural Research Institute New Delhi-110012. Received on September 13, 1976 SUMMARY Defoliation experiments in sunflower (Helianthus annus L. var. EC 68413) have been shown that seed yield and the size of head are built up mainly by the photo­ synthate from the upper leaves and the bracts proximate to head. The contribution from the leaves varied with their position on the stem. It was noticed to be the highest from the top 6 to 8 leaves followed by middle leaves and least from the leaves at the bottom. INTRODUCTION Investigations on the physiology of grain production in crop plants have highlighted the importance of different plant parts as the coutributors of organic assimilates. In this context, orientation of the leaves in plant canopy plays a signifi­ cant role. It is well documented that in many grain crop the upperleaves translocate their photosynthates (assimilates) mostly to the developing grain and stem, the lower leaves to the root and tillers and the leaves in an intermediate position, may send the assimilate in either or both directions. (Wardlaw 1965; Rowson and Hofstra, 1969). It has been recorded that in wheat and barley, the flag leaf and also second and third leaf to lesser extent (Lupton, 1961; Wardlaw, 1967; Rowson & Hofstra, 1969) and in corn, leaves above the ear (Allison and Watson, 1966; Hoyt and Bradfield, 1962) contribute its assimilate to the grain. Ample evidence indicate that not only the leaves but other plant parts such as fruit wall in peas (Bhardwaj and Raju, 1972), sepals in cotton (Patil and Mensink, 1972) and ear itself in barley (Thorne, 1965) also significantly contribute their assimi­ late to grain. Inspite oflarge leaf and bract area, the seed yield in sunflower is extremely poor and the reason being that most of the seeds remain partialy filled or unfilled due to lack of assimilate, translocated from the photosynthesizing organs. In this contest, it was considered necessary to determine the role of leaves and bracts and their extent of contribution to seed in sunflower. MATERIALS AND METHODS Healthy graded seeds of sunflower (Var. EC 68 413) were sown in field plots 1S2 G.C. SRIVSATAVA, P.S. DESHMUKH AND D.P.S. TOMAR (size 6 x 3 meters) in rabi season of 1973-74 in a randomized block design in four replicates at row to row distance of 60 ems and plant to plant 30 ems. Normal cultural practices were followed as and when required. Defoliation treatments of leaves and bracts were performed at the flower opening stage (SO% flower opening) and at 10 days after the flower opening. For defoliation of leaves, leaves were counted and devided into desired treatments. In all treatments comprised as follows : (A) Removal of leaves : T1 SO% lower removed T2 SO% upper removed T3 25% upper leaves from the top removed T4 2S% upper leaves from the middle removed TS 7S% from the top removed T6 7 S% from the base removed T7 Complete defoliation (100% leaves removed) T8 Control (No leaf removed) (B) Removal of bracts : T1 Ten bracts removed T2 Twenty bracts removed T3 Thirty bracts removed T4 All bracts removed TS Control (No bract removed) Head diameter, seed weight per plant and 100 seed weight were recorded for 20 plants from each replicate. RESULTS Defoliation of leaves.-From the results presented in table 1 it is seen that in general removal of leaves from the plant either at flower opening stage or 10 days later, reduced the size of head, seed weight per plant and 100 seed weight significantly. There was however, not much difference in the effect of two defoliation treatments. Removal of SO% upper leaves (Tl) at flower opening stage, decreased the seed yield to an extent of SS.4 per cent while the removal of SO% lower decreased it only by 23.7 per cent. When 25% leaves from top or middle (T3 or T4) were removed, the effect was the same and the reduction in seed yield per plant varied from 22.7 to 33.2%. In other treatments, severe reduction (64.S to 7S.6%) was observed when 75% leaves from the top (T5) or base (T6) were removed. Complete defoliation at any stage reduced the head size, seed yield and 100 seed weight severely. Defoliation of bracts.-The removal of bracts from the head in any amount reduced had size, seed weight per plant and 100 seed weight significantly (Table II). A progressive decline in the yield was recorded when the number of bracts removed increased. It was further recorded that when 30 developed bracts were removed from the outer surface of the head, the decrease in seed yield was the same as noted for complete removal of bracts. SIGNIFICANCE OF LEAF ORIENTATION 153 Table I. Effect of removal of leaf on head size, seed weight and 100 seed weight in sunflower (var. EC 68413). No. Treatment (leaves Time of Head Seed wt/pl. 100 seed wt. removed) treatment ----- ----- diameter % (em) % reduction reduction T! 50% from the base at flower 11.47 25.74 23.70 6.303 opening 5.95 10 days 10.96 25.32 24.90 later 6.397 4.55 T2 50% from the top at flower 8.73 15.05 55.40 opening 4.628 30.94 10 days later 9.70 20.18 40.15 6.069 T3 9.44 25% from the top at flower 10.67 26.05 22.74 opening 6.346 5.31 10 days 10.99 3122 7.41 later 6.310 5.84 T4 25% upper from at flower 10.25 22.52 33.21 middle oppening 6.001 10.45 10 days 9.97 24.63 26.95 later 6.402 4.47 T5 75% from the top at flower 7.16 8.20 75.68 opening 3.850 42.55 10 days 9.81 16.80 50.17 later 4.057 39.46 T6 75% from the base at flower 8.31 11.85 64.56 opening 3.850 42.55 10 days 9.97 17.74 47.39 later 4.116 38.58 T7 Complete defoliation at flower 5.64 1.95 94.2 opening 2.829 57.78 10 days 9.31 12.47 63.01 later 4.363 34.90 T8 Control 11.12 33.72 (No defoliation) 6.702 C. D for treatments at 5% 4.39 3.34 at 1% 0.164 5.91 4.51 Stage 0.221 N.S. N.S. N.S. 154 G.C. SRIVASTAVA, P.S. DESHMUKH AND D.P.S. TOMAR Table II: Effect of removal of bracts on head size, seed weight and 100 seed weight in sunflower (var. EC 68413) Treatments Time of Head Seed weight 100 seed wt. No. (Bracts removed) treatment diameter ------ ------ (em) % % reduction reduction T1 10 bracts at flower 10.8 3!.8 8.0 6.634 2.3 opening 10 days 10.7 34.0 1.9 6.598 2.8 later T2 20 bracts at flower 10.9 28.6 17.3 6.057 10.8 opening 10 days 10.8 30.9 10.7 6.388 5.9 later T3 30 bracts at flower 9.4 21.2 39.0 5.240 22.9 opening 10 days 10.5 23.8 31.2 6.251 8.0 later T4 All bracts at flower 9.3 20.6 40.4 5.292 22.1 opening 10 days 9.6 22.2 32.4 6.191 18.8 later T5 Control 12.6 34.6 6.788 No bract (removed) C. D for treatments at 5% 1.23 1.37 0.456 at 1% 1.67 1.84 N. S Stage N. S N.S N. S DISCUSSION The present study suggests that leaves are contributing differentially towards the seed development in sunflower. The extent of contribution of assimilates by the leaves appeared to depend on their orientation. The upper most leaves contribute the maximum, followed by the middle and lower ones. These findings find their confirma­ tion in results obtained in other crops (Rawson and Hofstra, 1969, Wittwer and Robb, 1964). It has generally been suggested that the possible contribution of assimilates of different plant parts to the grain yield are based on (a) potential photosynthetic activity (b) longevity of the tissues during the repening period and (c) light environ­ ment in a crop canopy (Yoshida, 1972). In sunflower, the leaves of the lower half, starts senescing much earlier, even at the flower opening stage and, therefore, the seed SIGNIFICANCE OF LEAF ORIENTATION 155 filling primarily depends upon the assimilates contributed by leaves at the top or upper half, since they remain green for a longer period and are active in photosynthesis. The number of leaves on a sunflower plant varies from 20 to 35 depending on the variety and season. The leaf during the rabi season varies from 25 to 36 and 25 per cent from the top constitutes usually 6 to 8 developed leaves. It is evident that these leaves contribute the highest assimilates to developing seeds. It is difficult to point out the particular leaf contributing highest assimilate, since the removal or even shadding of green parts, causes the enhancement in photosynthetic activity in other tissues and the deficit caused thereby is compensated by the other (Kesselbach, 1948) King and Wardlaw, 1967). Sunflower has large number of bracts comprising large total area and attached with proximate to head, its contribution of assimilates to seed bears much significance.
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