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ARS Home » Southeast Area » Poplarville, Mississippi » Southern Horticultural Research Unit » Research » Publications at this Location » Publication #327868
Title: Effects of Phytophthora cinnamomi isolate, inoculum delivery method, flood, and drought on vigor, disease severity and mortality of blueberry plants

Author
item Smith, Barbara
item Miller Butler, Melinda
item CURRY, KENNETH - University Of Southern Mississippi
item Sakhanokho, Hamidou

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2016
Publication Date: 11/1/2017
Citation: Smith, B.J., Miller Butler, M.A., Curry, K.J., Sakhanokho, H.F. 2017. Effects of Phytophthora cinnamomi isolate, inoculum delivery method, flood, and drought on vigor, disease severity and mortality of blueberry plants. Acta Horticulturae. 1180/93-104.

Interpretive Summary: Phytophthora root rot is a major disease of blueberries grown in the southeastern US. Southern highbush cultivars are particularly susceptible to this disease. Disease management strategies include cultural practices and chemical applications, but neither approach will eliminate the pathogen from infested fields. The goal of these studies was to develop a protocol that could be used to evaluate blueberry germplasm for tolerance to root rot, to test potential chemical, natural and biological products for efficacy to control this disease, and to study interactions between the environment, pathogen, and host of infection and disease development. Through a series of studies we determined that young southern highbush plants grown in potting media infested with the pathogen grown on rice grains developed root rot symptoms within six weeks. Disease development was enhanced when pots containing the plants were immersed in water for 48 hours every six weeks. This use of this protocol will allow researchers to develop better root rot disease management strategies and to gain a better understanding of the effect of the environment on disease development. Ultimately control of this disease will result in a more abundant supply of high quality blueberries to the American consumer at an affordable price.

Technical Abstract: Four studies evaluated the effect of Phytophthora cinnamomi isolates, inoculum delivery methods, and flood and drought conditions on vigor, disease severity scores, and survival of blueberry plants grown in pots in the greenhouse. Phytophthora cinnamomi isolates were obtained from blueberry plants or the root zone of plants with symptoms of Phytophthora root rot. Rabbiteye ‘Tifblue’ and southern highbush ‘Biloxi’ and ‘Star’ blueberry plants were grown in a potting medium infested with five isolates of P. cinnamomi using four inoculum preparation and delivery methods. Inoculum was prepared as a mycelial slurry, zoospore suspension, or grown on rice grains or vermiculite. The effect of flood treatments on root rot symptom development was investigated by immersing the pots containing plants grown in a potting medium infested P. cinnamomi isolate for 24 or 48 hours at 3 or 6 week intervals. The effect of drought was investigated by watering plants 4, 5 or 7 days each week. Plants were assessed for plant vigor and disease severity at regular intervals. Based on the results of the four studies the following protocol was developed to achieve rapid, consistent root rot symptom development. Blueberry potting medium should be infested with a virulent isolate of P. cinnamomi using the rice grain inoculum delivery method. Rooted cuttings of germplasm to be tested are then transplanted into the infested medium, and the pots containing the plants are flooded for 48 hours every 6 weeks to allow rapid infection of the root systems. Disease evaluations based on above-ground symptoms should be made beginning six months after transplanting the cuttings into the infested potting medium. Rooted cuttings of a susceptible southern highbush cultivar should be used as the assay plant when evaluating chemical or biological control products or when studying environmental effects. We will use this protocol to study environmental effects on the development of Phytophthora root rot of blueberries and to evaluate blueberry germplasm for tolerance to root rot, and to determine the efficacy of chemical and biological products for root rot control.