USE OF GAMMA-RAYS TO INDUCE MUTANTS RESISTANT TO COCOA SWOLLEN SHOOT DISEASE IN THEOBROMA-CACAO L

Vegetative buds of three cocoa varieties, 'Amelonado' (P30), 'Trinitar io' (K5) and 'Upper Amazon' (T85/799) were irradiated with 15, 20 and 25 Gy of gamma-rays, respectively, and budded on to rootstocks to gene rate MV1 shoots. The terminal buds of the shoots were removed to induc e the formation of MV2 shoots, from which MV3 shoots were similarly de rived. The MV3 plants were screened for resistance to the Cocoa Swolle n Shoot Virus (CSSV) by patch-graft inoculation of the rootstocks. Onl y a few plants from each of the three cocoa varieties were found to be symptomless after indexing. These plants were multiplied by budding t o the MV4 and MV5 stages and screened at each stage for CSSV resistanc e by inoculation using virus-carrying mealybugs. At the MV5 stage, som e plants still remained symptomless and this was confirmed with enzyme -linked immunosorbent assay (ELISA). The study reveals that gamma-rays can be used to induce genetic variability for resistance to CSSV in c ocoa, as well as for other traits such as chlorophyll deficiency.