ASSESSING THE COCOA GENOTYPES FOR RESISTANCE TO BLACK POD USING THE AREA UNDER THE DISEASE-PROGRESS CURVE (AUDPC)

Khim Ph. Chong, Albert Sh. Ch. Ling, Chong M. Ho, Mohd J. Ahmad Kamil

Abstract: In breeding for resistance to black pod, it is important to use an effective and economical method to screen the cocoa genotypes. The detached pod test has been regarded as the most economical and effective screening method as compared to selection of resistant genotypes in the field. This study evaluated the accuracy of the assessment technique used in the detached pod test between the estimation of the area under the disease-progress curve (AUDPC) and the standard assessment of diameter lesion recorded in the sixth day after inoculation of four genotypes at different resistant categories to black pod (KKM4 – susceptible, KKM5 – moderate suscetipble, BR25 – moderate resistant and QH1003 – resistant) at two development pod stages(young and mature pods. The steps involved in the assessment using AUDPC are measured the diameter of the established lesions for six days after inoculation with Phytophthora palmivora and calculated the disease severity, fitting the disease progress curve with the nonlinear model, calculated the AUDPC and ranked the cocoa genotypes’ resistant based on the AUDPC value. The results indicated that the assessment of the mature cocoa genotypes for resistance to black pod using AUDPC gave better accuracy (100%) of resistant level compared to standard assessment (50%) meanwhile both assessment technique on young pods gave similar percentage (50%) of accuracy. The obtained information will be used as the guide for screening the cocoa genotypes for resistance to black pod.

Keywords: area; black pod; cocoa; curve; detached pod test; disease progress; nonlinear model

Date published: 2018-01-15