Assessing the Response of Local Cocoa Clones of South Sulawesi for Resistance to Dieback Disease Caused by Lasiodiplodia theobromae

Abstract

Lasiodiplodia theobromae causes several severe diseases in cocoa, including cocoa dieback disease. The dieback caused by L. theobromae on cocoa is considered an emerging disease in Sulawesi. The fungus colonises stem tissues, producing leaf chlorosis, wilting and sudden dieback. To cope with the dieback, selecting and planting existing clones with partial resistance to the pathogen would be a good strategy. The main objective of this study was to evaluate the resistance of locally selected cocoa clones in Sulawesi to L. theobromae infection. Ten cocoa clones were assessed in the laboratory and the greenhouse for disease severity caused by an isolate of L. theobromae. The responses of the clones visible in laboratory and greenhouse tests through stem-wounded inoculation ranged from susceptible to tolerant. The majority of the clones (nine clones) showed a significantly severe dieback and necrotic lesions. In contrast, another clone, designated MCC 02, performed consistently better in suppressing dieback and reducing necrotic lesions. Symptoms on the leaves varied, including chlorotic, yellowing on leaf veins and sudden browning, while in the stem, necrotic lesions and vascular streaking from dark brown to black were consistently visible. The clone MCC 02, with its superior resistance to L. theobromae, holds great potential for use in breeding programs to produce promising progeny clones with good resistance, yield and quality.