BIOCHEMICAL MARKERS FOR BRUCHID RESISTANCE IN COWPEA SEEDS

As known, legume seed resistance to storage pest attack can be related to antinutritional and toxic compounds present in seeds. Data previously collected have shown that the cowpea resistance to Callosobruchus maculatus cannot be related to the content of only one inhibitor class. Consequently, it was supposed that several antinutritionals present in the seeds may have an active role in the resistance mechanism. If this were true, resistant lines should have the highest contents of total antimetabolites. In order to verify this hypothesis, the attention has been focused on the following lines : TVu 2027, IT84D-453, IT84D-434, IT81D-985, IT81D-1007, TVu 36, TVu 801 and IFE BROWN, characterized by different resistance degrees. For the aforementioned lines, the content of inhibitors of the principal digestive enzymes has been measured. Amylase from two different sources (Bacillus species and porcine pancreas), trypsin and chymotrypsin are the enzymes used in this study. Submitting the contents of the tested inhibitors and the bruchid attack extent to the correlation analysis it has been observed that no one of the inhibitors, when considered separately, can provide a good screening procedure for checking storage pest resistance. The data collected in this study have been also submitted to the principal component analysis (SAS system package). The results of this analysis have shown that two components provide a good summary of data since they account for 87% of the standardized variance. The first component is mainly a measure of the proteolytic activity inhibition, the second evaluates principally the inhibition of starch hydrolysis. Using these components to describe the inhibitor activity in the tested samples, it has been observed that susceptible lines are characterized by high inhibition either of proteolytic activity or of starch hydrolysis. Conversely, resistant lines have high inhibition of both. Of course the effectiveness of selecting lines with high amylase and trypsin inhibitor contents, in order to prevent bruchid attack, is related to the possibility of preserving the inhibitor activity unchanged during storage. Preliminar investigations on this topic have shown that trypsin inhibitors are strongly affected by the storage conditions. A loss of TI activity has been observed for all the storage conditions tested. At present it may be concluded that cowpea resistance to storage pests is related to several antinutritionals. Among the ones evaluated, trypsin and amylase inhibitors seem to be more effective. This suggests a better characterization of these two inhibitors to ascertain the possible existance of different isoinhibitor patterns for the resistant and susceptible cowpea lines. Further investigations will be carried out also on the effects of storage conditions on the activity of other antinutritional factors.