Combining Infection Sources, Periods, and Persistence into the Integrated Management of Bitter Rot on Apples

View the project final report

Commodities

• Fruits: apples

Practices

• Education and Training: extension
• Pest Management: cultural control, integrated pest management, sanitation
• Production Systems: holistic management

Growing apples in the humid northeastern US is challenging due to fungal diseases like bitter rot, caused by fungi in the genus Colletotrichum. Historically a southern disease, northeastern apple growers are reporting increased problems with bitter rot. While the basic bitter rot disease cycle was discovered over 100 years ago, much remains unknown about inoculum sources and spore dispersal periods. We therefore propose to use the highly sensitive quantitative (q) PCR pathogen detection technique to identify and quantify infection sources and timing of dispersal in and around orchards, focusing on apple buds, the tree canopy, the orchard floor, and nearby wooded areas. It is well known that infected apples from one year can be a source of spores the next year unless the infected apple is degraded by other microbes. The degradation of infected apples on the orchard floor and reduction of Colletotrichum will be measured with q-PCR. The successional microbes (bacteria and fungi) that presumably drive that degradation will be identified with metagenomic amplicon sequencing and their physiological profiles obtained with Biolog EcoPlates, comparing the weed-free tree row with grass drive rows. Information on infection sources will inform cultural practices that reduce disease pressure and the need for heavy fungicide applications. Knowing the timing of critical infection periods will inform targeted and judicial applications of control products. This research will be combined with related studies on bitter rot fungal species and their fungicide sensitivity profiles to help northeastern apple growers improve their integrated management of bitter rot.

1. Determine the sources and major infection periods of Colletotrichum spp. (bitter rot fungi) in PA apple orchards. Determine if Colletotrichum spp. spore sources are on outer bud scales, in the tree canopy, splashed up from the orchard floor, or from nearby forested areas, and the timing and quantity of spore dispersal from those sources. Detect the timing and incidence of dormant infections in apples throughout the season.

2. Track the degradation of infected apples and reduction of Colletotrichum spp. on the orchard floor and the successional microbes driving that degradation. Quantify the reduction of bitter rot fungi in decaying apples on the orchard floor, comparing weed-free tree rows with grassed row middles. Determine successional fungal and bacterial species and physiological profiles in infected apples, comparing weed-free tree rows with grassed row middles.