J. Agronomy & Crop Science 180, 129^-136 (1998) Tj 1998 Blackwell Wissenschafts-Verlag, Berlin ISSN 0931-2250 Institute of Postgraduate Studies in Agriculture. Gazipur, Bangladesh Drought Stress Effects on Seed Yield, Yield Attributes, Growth, Cell Membrane Stability and Gas Exchange of Synthesized Brassica napus L. Abul Hashem, M. N, Amin Majumdar. Abdul Hamid and M. M. Hossain Authors' addresses: Abul Hashem (corresponding author), Dryland Research institute. Agriculture Western Australia. P.O. Box 432, Merredin, Australia 61415, M N. Amin Majumdar. Abdul Hamid, Department of Agronomy, and M. M, Hossain, Department of Horticulture, institute of Postgraduate Studies in Agriculture. Gazipur 1703. Bangladesh fVith 5 figures and 6 tables Received Jum- 12. 1995: accepted February 5, 1997 Abstract Drought stress effects on leaf gas exchange, cell mem- brane stability, seed yield and yield attributes of syn- thesized Brassica napus L. cv, Bangla kale and Bangla cabbage were compared. Drought stress treatments were imposed at early vegetative, late vegetative and flowering stages by withholding watering. Bangla cabbage pro- duced greater pods/plant, larger seed size, greater total dry matter/plant, seeds/pot, and ] 7 % greater yield than Bangla kale. The seed yield in plants stressed at early vegetative, late vegetative and flowering stages were 59. 74, 88 % lower respectively, than watered plants. Drought stress reduced leaf photosynthesis by 67 to 97 %. Bangla cabbage had 68 % greater photosynthesis and 56% greater stomatal conductance than Bangla kale under stress at tlowering stage. Leaf temperature was 1 to 2 C higher in stressed plants than watered plants. The cell membrane stability (CMS) increased up to 83 % at flowering stage under stress compared to 21 % under watered conditions. Although Bangla cabbage had high seed yield, yield attributes and photosynthesis under stressed conditions at flowering stage, its CMS values were lower than those of Bangla kale. Key words: Brassica napus — drought stress — cell membrane stability — growth — seed yield — gas exchange Introduction Synthesized Brassica napus L. is a newly developed crop species that produces seed during winter and grows well in early summer in Bangladesh (Hossain et al. 1990). However, its growth, development and productivity are affected by drought. Effect of drought was reported on cowpea (Turk et al. 1980, Turk and Hall 1980), black alder {Seiler 1985), leg- umes (Machow 1985), mungbean {Sadasivam et al. 1988, Uprety and Bbatia 1989), sunflower (Human et al. 1990), barley (Hussain and Aspinall 1970), Capsicum annum (Rao et al. 1988), alfalfa (Halim et al. 1989), wheat and triticale (Uprety and Sirohi 1987), Viciafaha L. (Koscielniak ct al. 1989). Bras- sica sps (Dabas and Sheoran 1984), and maize (Pre- machandra et al. 1991b), The effects of drought stress on crop plants vary with the crop species, the stage of crop plant at which the drought occurs, and the duration of drought stress. Pandey et al. (1984a) observed that the number of pods in extremely drought-stressed plants of mungbean. cowpea, soybean and peanut were, respectively, 63, 46, 52 and 53 % lower than those in unstressed plants. Rao et al. (1988) observed significant reduction in leaf area of Capsicum annua L. due to drought stress. Drought stress affects the gas exchange charac- teristics in plants (Nicolodi et al. 1988; Hamid et al. 1990a). One way to understand the tolerance of plants to drought stress is to determine the cell mem- brane stability (CMS) (Sullivan and Ro.ss 1979, Pre- machandra et\l. 1989). Synthesized Brassica napm L. cv. Bangla kale and Bangla cabbage is being tried for its adaptability and potentiality to produce seed during winter and grow it as vegetable during summer. Agronomic studies showed that these varieties of Brassica napus L. grow well in Bangladesh under irrigated con- ditions. However, very little information is avail- able on the growth and development of this crop under moisture-stressed conditions. This study was conducted to; (i) assess the tolerance of synthesized Brassica napus L. to drought stress at various growth stages; (ii) investigate the effect of drought stress on leaf gas exchange; and (iii) determine the seed yield performance under drought stress. Materials and Methods An experiment was conducted to evaluate the effect of drought stress on the gas exchange characteristics, cell U.S. Copyright Clearance Cent.r Cod. Su,.menl: 0 9 3 1 -2250/98/8003-01 29 $ 14.00/0