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Abstract Four Egyptian varieties of cowpea seeds, Vigna unguiculata (L.) namely: Cream 7, Kaha 1, Dokki 331 and Kafr El-Shekh 1 were used in the present investigation to test their relation (to cowpea weevil, Callosobruchus maculatus, a major pest of stored pulses. The whole seed from each variety was examined and several physical (phenotypic) characteristics were measured. Seeds from each variety were analyzed to characterize some of its nutritional and non-nutritional chemical contents and their correlation to the seed resistance. A bioassay using natural seeds was performed, and results have demonstrated that seeds expressed varied degrees of resistance, and the physicochemical properties of cowpea seeds did not seem to exert an overriding influence on pest susceptibility but may influence the oviposition behavior of C. maculatus females. When C. maculatus was provided with these cowpea varieties, the number of eggs per seed, the weight loss of seed, the developmental time and the percentage adults emerging were differed with seed variety. Clearly the differences between varieties were significant biologically as well as statistically and seeds of Cream 7 variety was found to be the highly susceptible (which referred to as susceptible variety) and Kafr El-Sheikh 1 the least susceptible (which referred to as resistant variety). Subsequently, these two varieties were selected for the purpose of studying the chemical bases of resistance. Larvae developing within the grain do the largest damage of stored seeds. By investigation of the feeding patterns of bruchid larvae living and growing within cowpea seeds, it was observed that larvae have feeding patterns in resistant seeds which are varied compared to susceptible ones. Larvae feeding in resistant seeds did not penetrate deeply into the seed cotyledons as those feeding on susceptible seeds. Results presented evidence that an interior zone in resistant seeds, in each cotyledon adjacent to the air space separating the two seed halves, is responsible for the high mortality and developmental delays experienced by bruchid larvae. It appears that the resistance factor is most concentrated in such zone. In order to study the biochemical basis of cowpea resistance to C. maculatus, Seed proteins were analyzed qualitatively and quantitatively to study the chemical basis of resistance to bruchid infestation. Higher amounts of proteins (albumins and globulins) were found in susceptible seeds. Seven protein bands found in resistant seeds and not visualized in the susceptible ones, which could be correlated with the resistance. Variant vicilins (storage globulins) were found in resistant seeds and were found to react with the polyclonal antibody used. These proteins were found in internal organs such as midgut, Malpighian tubules, fat body and haemolymph of larval C. maculatus and were considered as the main resistance factor. It has been suggested that the toxic properties of vicilins may be related to their recognition and interaction with glycoproteins and other membrane constituents along the digestive tract of the insect. Histological and histochemical characteristics of C. maculatus as affected by feeding upon the resistant seeds of V. unguiculata. The rearing of larvae on the resistant seeds resulted in several histopathological lesions in the larval tissue including all their internal organs and systems. The major histopathological lesions which could be recorded were: Cyplasmic vacuolation, nuclear pyknosis, apical degeneration of epithelia, disruption of junctional complexes, rupture and finally necrosis. The histochemical studies confirmed the recorded histopathological lesions at the sub-cellular level as follows: 1-The total carbohydrate content of larval tissue exhibited a marked decrease which recorded a statistically significant value. 2-The total protein content of the cells of the variant larvae exhibited also a marked decrease confirmed by the image analysis by a non- significant value. 3-The total DNA content of the cells of the variant larvae in its turn exhibited an obvious decrease. This decrease was statistically nonsignificant. |