Browsing by Author "Minjas, Athanasio N"

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    Studies on the autecology of Commelina, Imberbishassk, a common weed
    (University of Dar es Salaam, 1976) Minjas, Athanasio N
    The main theme of the present work is to investigate seed germination and dormanay mechanisms, seedling establishment, early growth and competitive ability of C. imberis during the early growth phase with particular reference to soil nutrient levels and pH regime under controlled conditions. The seed structure and germination pattern in commelina imberbis was studied. The seeds were found to be somatically diamorphic and exhibit seed coat dormancy. The plug was found to be particular by responsible for dormancy. The two types of seeds, small and large, were shown to differ in the degree of dormancy and germination requirements. The seeds were found to germinate in a wide range of environmental factors once dormancy was broken. Mechanical scarification, plug removal and to a lesser extent concentrated sulphuric acid were found to be effective in breaking seed coat dormancy in C. imberbis. The growth of C. imberdis in relation to nutrients, pH and their interaction phosphorus, Potassium and their interaction, molybdenum, and salinity was studies. C. imberbis was shown to be very tolerant to a wide range of pH and nutrient regimes and highly plastic in its response. Potassium and to a lesser extent, Phosphorus were shown to affect the growth of C. imberbis independently. However, no phosphorus toxicity symptoms were observed. Varying molybdenum levels did not affect plant growth. C. imberbis was shown t be very sensitive to salinity levels. Competition between C. imberbis and maize was studied. When planted together, crop and weed did not affect each other's growth appreciably. Crop responded to its own density. However , when one of them was introduced into an established population of the other, the former's growth was reduced. The effects of delayed introduction was very pronounced on the growth of C. imberbis. The author draws the following conclusions: (a) Seed dimorphism and dormancy mechanisms, its capacity to flower within 3 to 4 weeks of germination, wide edaphic tolerance range and competitive power place C. imberbis among nozious weeds. It has been reported that weeding species of the genus commelina are rather resistant to growth regulator type of herbicides. Thus if hand-weeding is to practiced, it is imperative that weeding should be done as frequently as possible in order to achieve an effective control in the cultivated fields. (b) The above mentioned characteristics of C. imberbis, especially its capacity to produce a large volume of fine roots and roollets, make the plant a successful colonizer of cleared areas and crowded sites. Thus, this plant may in fact be gainfully used in such places to reduce erosion and leaching. (c) It has been shown that C, imberbis is very sensitive to varying salt concentrations. In the field, salinity seems to be one of the most important soil factors delimiting its distribution.