Location: Crop Germplasm Research
Project Number: 3091-21000-046-013-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 15, 2025
End Date: Jun 30, 2026
Objective:
Botryosphaeria fungi are common pathogens of woody plants, including oak, peach, citrus, and walnut. Symptoms include cankers of the bark and phloem, which can result in dieback of branches or death of the tree. Neofusicoccum caryigenum is an emerging Botryosphaeria pathogen that causes Pecan Leaf Dieback disease, which is characterized by stem necroses of compound leaves, and was first reported in 2021. This year (2025), new symptoms caused by N. caryigenum were discovered on branches on USDA-ARS Pawnee in the USDA-ARS Pecan Breeding and Genetics Program and the Texas A&M Pecan Research orchards in College Station, TX, and previous season monitoring indicated infection of shucks, as well. Concurrently, trunk cankers on trees in the Species Block and a Mapping Population at the USDA-ARS Pecan Breeding and Genetics program caused by a Botryosphaeria fungus have also emerged. The objective of this work is to investigate these new stages of the disease cycle by N. caryigenum, and to identify the causal agent of other cankers in pecan. Sources of host resistance will be identified to further breeding program efforts for the release of improved pecan cultivars.
Approach:
Pecan trees located in the LxM mapping population and repository at the USDA-ARS Pecan Breeding and Genetics Program in College Station and Brownwood, TX, will be evaluated for the presence of disease symptoms. The ARS PI will develop a rating scale for continued monitoring of disease severity for determining sources of host resistance. Infected pecan plant samples will be harvested and provided to the cooperator for pathogen isolation. Additional diseased budwood samples will be used to graft healthy rootstocks to determine disease transmission from grafting and whether foliar symptoms emerge with new vegetative growth. Symptomatic tissue from the infected trees will be harvested for pathogen isolation to prove causal agent. The ARS PI will receive all fungal isolates from the cooperator, as well as in-house cultures, for PacBio sequencing. The ARS PI will perform the genome assemblies.