Location: Tropical Crops and Germplasm Research
Project Number: 6090-21000-061-018-T
Project Type: Trust Fund Cooperative Agreement
Start Date: Jun 1, 2025
End Date: Mar 31, 2030
Objective:
Theobroma cacao, the key ingredient in chocolate, is in high demand worldwide. Cacao production by rural farmers in Puerto Rico and worldwide is affected by prolonged water stress and several diseases while the recent expansion of cacao cultivation has encountered new critical pathogens. Given these key constraints, the objectives of this proposal are: 1) germplasm screening and population development for drought tolerance; 2) germplasm screening to identify resistance to the cacao pod rot and dieback pathogens; and 3) Screening, vector characterization, and host-range testing of CaMMV in cacao.
Approach:
1) Germplasm screening to drought tolerance and population development: A portion of the USDA-TARS cacao germplasm collection will be genotyped using a cooperator SNP marker platform associated with abiotic, rootstock, and compatibility traits, and validated phenotypically. Developed a multi-parent segregating population by crossing selected germplasm with EET400 to stack favorable alleles into elite rootstock material. Validated allele stacking effects through field experiments to evaluate rootstock field performance.
2) Germplasm Screening to cacao pot rot and dieback pathogens: Detached cacao pods in the USDA-TARS cacao germplasm collection will be inoculated with the local fungus Lasiodiplodia, Diaporthe spp. and Colletotrichum spp. Resistance response will be determined based on area infected using ImageJ program. Since every pathogen cannot be assayed at the same time due to pods number limitations, the inoculation will be prioritized for the pathogen isolates that shows the strongest pathogenicity phenotypes across cacao clones.
3) Screening, vector characterization, and host-range testing of CaMMV in cacao: The USDA-TARS cacao collection will be screened for signs and symptoms of cacao mild mosaic virus (CaMMV) to determine the susceptibility of outperforming cacao genotypes. Koch’s postulates will be used to evaluate symptom expression and confirm transmission of the virus by suspected insect vectors (Pseudococcidae). The spatial distribution of CaMMV host-range will be assessed using geospatial analysis (ArcGIS) across various farms in Puerto Rico.