Location: Horticultural Crops Disease and Pest Management Research Unit
Project Number: 2072-22000-045-034-G
Project Type: Grant
Start Date: May 1, 2023
End Date: Oct 31, 2025
Objective:
1. Determine susceptibility of different phenological stages of highbush blueberry flowers to Botrytis infection.
2. Investigate the role of dead petals attached to the developing fruits as possible infection courts for Botrytis infection.
3. Evaluate Botrytis latent infections in late-season disease development.
Approach:
Potted blueberry plants cv. ‘Draper’ growing in a greenhouse will be used for these experiments. Inoculations will use B. cinerea isolate NF-31C (previously characterized by ARS) obtained from a blueberry fruit, which exhibits resistance to fungicides in FRAC groups 7, 9, and 17 (boscalid, cyprodinil, and fenhexamid, respectively). Plants bearing flower clusters at different stages: corolla partly protruding from the calyx (F4), corolla half developed (F5), pink or white bud pre-bloom (F6), corolla fully open (F7), and senesced corolla (F8; Hildebrand et al. 2001) will be inoculated (106 conidia/mL) using a hand atomizer until run-off. Post inoculation, plants will be incubated in a dark moist chamber at 20°C for 24 h and placed in the greenhouse. Eight days post inoculation harvested flower clusters will be both surface and non-surface disinfested prior to recovery of Botrytis representing internal colonization and external colonization, respectively. Individual flowers will be dissected into carpels, stamens, sepals, petals, pedicel, and receptacle and plated on Botrytis selective medium (BSM; Edwards and Seddon, 2001). Colonization of each tissue by B. cinerea will be treated as a binary response and logistic regression analysis will be conducted to test the effect of different developmental stages on Botrytis infection.
Fruit clusters at different growth stages: early green (all berries small and light green color), late green (berries larger & may have red blush), 25% blue (25% of berries in a cluster are ripe), and 75% blue fruits (nearly all berries are ripe, often the timing of first machine harvest) that have either A) petals retained on the developing fruits or B) petals manually removed from the developing fruits will be inoculated with a drop of (50 µL) of B. cinerea isolate NF-31C inoculum (106 conidia/mL). For treatment A, inoculum will be placed on the petals ensuring there is a water film at the inoculation site. For treatment B, inoculum will be placed at the calyx end of the fruit without any wounding. Inoculated plants will be incubated in dark, moist chambers at 20°C for 24 h and placed in the greenhouse. Developing fruit will be monitored daily for the development of necrotic symptoms that typically initiate from the inoculation site. A week after inoculation, fruits will be harvested, surface disinfested and plated on BSM.
Plants bearing flower clusters at different stages (F4, F5, F6, F7, and F8; Hildebrand et al. 2001) and fruit clusters at different growth stages (early green, late green, 25% blue and 75% blue) will be inoculated and incubated as described in objectives 1 and 2. However, these experiments differ from the other two objectives in that repetitive sampling will be performed from the tissues that were inoculated at different growth stages. For example, flowers inoculated at F4 will be sampled at F5 stage until 75% blue stages and this process of repeated sampling will be followed on tissues inoculated at other growth stages. The sampled tissues will be surface disinfested to target latent infections and plated on BSM.
