Page:Report of the Puerto Rico Experiment Station (IA CAT31294391015).pdf/8



R. H. Hageman and C. Pagán

The MG clones of Derris elliptica var. Changi No. 3 grown at this station have long, bare, twining stems and generally lack foliage. These stems are at first erect, but as they grow longer they bend down ward forming an arc with the tip reaching the ground. Shortly thereafter the apical section usually dies back to the top of the arc, and one or more of the axillary buds becomes dominant and the process is repeated. Usually the only leaves that are retained are on the erect portion of the main or branch stems. This type of growth should result in reduced yields of roots and rotenone. Preliminary experiments precluded nutrition and shade as contributing factors, and indicated that a more normal growth and leaf retention was obtained by trellising the shoots vertically. Another more comprehensive trellising experiment showed that trellising the young shoots vertically increased stem growth significantly and promoted leaf set and retention. On the other hand trellising the stems downward produced stunting, dieback, and loss of leaves. This latter type of trellising stimulated the natural growth habits and resulted in a similar type of injury. A cooperative experiment with a commercial grower is now under way to determine if vertical trellising is of agronomic importance. Applications of indolebutyric acid in concentrations ranging from 0.2 to 0.001 percent in a 50-percent alcohol solution produced injury and reduced stem growth.

C. Pagán and R. H. Hageman

Derris roots are sold on the basis of rotenone content, though this is not the best criterion of their insecticidal value. Other chemical values such as total chloroform extractives, red-color value, and transmission are obtained by simpler and faster procedures and are better indications of toxicity. Of these three methods, that of total chloroform extractives is the best in both rapidity and accuracy.

Statistical studies of Derris grown in Puerto Rico showed that there is a constant relationship between rotenone and total chloroform extractives for any given variety. A similar relationship between total chloroform extractives and toxicity (rotenone equivalent) determined by the guppy method has also been established. Regression equations were found to be the best means of showing these relationships because they do not give the exaggerated errors at the maximum and minimum values as is true with ratios. The regression equations for two commercial varieties, Changi No. 3 MG and Sarawak Creeping of Derris elliptica, obtained by analysis of the data of eight separate agronomic experiments covering a 5-year period were as follows Changi No. 3 MG, B,=0.4lE-0.20; Sarawak Creeping, R=0.3lE-0.39. The regression equations for toxicity to total chloroform extractives for these two varieties were established from data obtained over a 2-year period. These were as follows: Changi No. 3 MG, T=0.76E-0.27 Sarawak Creeping, T=0.48E + 2.80.

Five samples each of five varieties of Derris were analyzed for the Complementary Crops Division of the Office of Foreign Agri-