Disease and production Index (DPI) for selection of Cacao (Theobroma cacao) genotypes highly productive and tolerant to frosty pod rot (Moniliophthora roreri)

Authors: JAIMEZ, RAMON - Instituto Nacional De Investigação Agrária E Veterinária; VERA, DANILO - Instituto Nacional De Investigação Agrária E Veterinária; MORA, ARGENIUS - Universidad De Costa Rica; LOOR, REY - Instituto Nacional De Investigação Agrária E Veterinária; Bailey, Bryan

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2020
Publication Date: 5/1/2020
Citation: Jaimez, R.E., Vera, D.I., Mora, A., Loor, R.G., Bailey, B.A. 2020. Disease and production Index (DPI) for selection of Cacao (Theobroma cacao) genotypes highly productive and tolerant to frosty pod rot (Moniliophthora roreri). Plant Pathology. 69(4), p.698-712.

Interpretive Summary: Frosty pod rot, caused by the fungus Moniliophthora roreri, is a devastating disease on cacao severely reducing yields where it occurs throughout south and central America. Cacao breeders routinely screen cacao trees for resistance to frosty pod rot. Once identified, superior trees can be carried forward in their breeding programs or clonally propagated through grafts or rooted cutting for release to farmers. The most common process for estimating disease resistance is to calculate the percentage of cacao pods lost to the disease. Unfortunately, this does not necessarily identify cacao trees that produce high yields. A tree may be resistant to disease but have a low yield potential. A new measure, the disease and production index, was developed which combines the measure of a cacao trees disease resistance with its potential for producing high yields. This measure was used to identify cacao trees producing high yields despite the presence of disease. The disease and pod index will continue to be used by cacao breeders to select superior cacao trees for continued advancement in their breeding programs and ultimately to identify materials with high yield potential combined with resistance to frosty pod rot for distribution to cacao farmers.

Technical Abstract: Frosty pod rot (Moniliophthora roreri (Cif.) H.C. Evans et al.,1978) constitutes one of the main phytosanitary problems limiting cacao (Theobroma cacao L.) production in Ecuador and neighboring countries causing severe yield losses each year. One of the main sought after methods of frosty pod rot management is the selection of tolerant cacao genotypes. Typically, the selection of tolerant genotypes is carried out through the quantification of the percentage of diseased pods (PDP). However, PDP does not consider the relative productivity, or production potential, of the genotype. Production potential can vary greatly among cacao genotypes. Consequently, genotypes with similar production potential can have vastly different disease tolerance levels as measured by PDP. The disease and production index (DPI) was developed to integrate a genotype’s tolerance to M. roreri as measured by PDP, with its production potential. The variables evaluated were number of healthy pods, number of diseased pods, and weight of fresh pods for 29 genotypes grown in replicated five tree plots over 4 years. The data obtained was used to calculate the DPI for each genotype. Multivariate analysis verified that DPI discriminated between genotypes based on both productivity and disease tolerance. The DPI can be used in breeding programs focused on the selection of cacao genotypes with both characteristics, high production potential combined with greater tolerance to M. roreri.