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Weed seeds of sweet clover were collected from matured weed plant growing in wheat field. The seeds were cleaned and then sun dried. The experiment was carried out in glass bowls of 250 ml capacity. A 0.8 percent agar-jel was prepared and the agar-media was incorporated with sodium chloride solution to get 0.0, 0.2 and 0.4 percent salinity levels. Fifty ml of each salinized agar-media was poured into sterilized glass bowls of 250 ml capacity for seed planting. Seeds of wheat (cv. Pavon) and weed seed of sweet clover were surface sterilized by 1% sodium hypochlorite solution for three minutes and then rinsed with distilled water. Ten healthy wheat seeds were placed in a circle on the surface of each bowl containing weed seed and agar-media salinized solution. A set containing no weed, seed and no NaCl was also kept and treated as control. All. the bowls were then covered with sterilized petri dishes and incubated at 28°C The treatments were kept in a randomized design with four replication. The experiment was terminated after 5 days. The germinated seeds were noted and their shoot and root lengths were measured. The data has been analyzed and presented in Table1.

The weed seed of sweet clover and NaCl levels had no effect on seed germination (Table 1). Weed seed alone, and in combination with 0.2 % NaCl and 0.4 % NaCl alone had similar decreasing effects on shoot length, and reduced the shoot lengths by 57.5, 56.3 and 61.0 %, respectively compared to control. The NaCl level of 0.4 % in combination with weed seed had significantly reduced the shoot length by 74.4 % compared to control. The weed seed alone and in combination with 0.2 % and 0.4 % NaCl significantly reduced the root lengths by 85.8, 86.0 and 87.8 %, respectively over to control and the salinity levels alone (0.2 and 0.4 % NaCl) reduced the root length by 31.4 and 60.4 %, respectively when compared to control (Table 1).

Sweet clover seed in the present study, did not show any effect on seed germination, but it has significant decreasing effect on both shoot and root lengths of wheat. This shows that for germination phenomenon, there was a tolerance behavior in wheat seed to bear the effects negative of two stresses, and thus there was no harmful effect of the treatments on seed germination. Seed germination is considered to be the most critical stage, especially under stress conditions. The first requirement of seed germination of any crop is water for hydrolysis of reserves, as a medium of translocation, hydration of enzymes, for operational conformation of cell membranes and organelles and finally to provide the driving force for cell expansion induced by germination. The findings of Hadas (1977) suggest that the germination rate and the final seed germination decrease with the decrease of the water movement into the seeds during imbibition. It is also known that during germination, rapid biochemical changes take place which provides the basic frame work for subsequent growth and development. The initial metabolic changes that occur immediately after the imbibition of water are the increase in the hydrolytic enzymes such as alpha amylase and protease.

In the present experiment, the root length was affected more than the shoot. Although, we did not determine the biochemical parameters, but it is obvious that the seed of sweet clover contains leachable allelochemicals, which have more profound effect on roots than shoot. Unfortunately, there is no report on the effect of seed extracts of sweet clover. Literature suggests that different parts of sweet clover contain large amount of coumarin, o-coumarin, melilotic acid as the major active compounds (Langer and Hill 1982, Nicollier et al. 1985) and is considered to be highly effective in reducing plant growth. Sweet clover extract has been shown to reduce germination, shoot and root length of corn (McCalla and Duley 1948). It exhibited high inhibition of radicle growth in corn, bean and squash (Anaya et al. 1987). Saraswat (1987) found adverse allelopathic effect on rice growth. It was concluded from this study, that seeds of sweet clover had no inhibitory effect on seed germination, but it had depressive effects on shoot and root lengths of wheat crop.
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