Abstract
Six commercial biocontrol agents (BCAs: Aureobasidium pullulans, Bacillus amyloliquefaciens, B. amyloliquefaciens plantarum, B. subtilis, Metschnikowia fructicola, or Trichoderma atroviride) were applied to bunch trash that was then incubated at one of five temperatures (T, 15, 20, 25, 30, and 35 °C) and one of five relative humidity levels (RH, 60, 80, 90, 95, and 100%). After 1 to 13 days of incubation (BCA colonization period), the number of colony forming units (CFUs) was assessed. The colonization of bunch trash in response to T/RH conditions and BCA colonization period differed among the BCAs; the coefficients of variation among the BCAs ranged from 104.6 to 397.7%. Equations were developed that accounted for the combined effects of the T, RH, and BCA colonization period on BCA colonization of bunch trash. Assuming that the equations, which had an R2 > 0.87, correctly predict BCA growth under field conditions, they would help farmers select the BCA to be used for a specific application based on weather conditions at the time of treatment and in the following days. The equations would also help predict how long an early season BCA application remains effective and thereby help farmers decide whether and when a second BCA application may be needed.
Highlights
Botrytis bunch rot (BBR) is an economically important disease of grapevine (Vitis vinifera L.) and is caused by the fungus Botrytis cinerea Pers.:Fr (anamorph of Botryotinia fuckeliana Whetzel) [1].Botrytis cinerea can develop as a saprophyte, necrotroph, or parasite on multiple vine organs including leaves, green shoots and rachides, flowers and flowering residues, and berries
Grapevine bunch trash colonized by B. cinerea has been considered an important source of inoculum for infection from flowering to ripening [46,47,48,49] and has been related to the severity of BBR at harvest [50,51,52]
The reduction in B. cinerea inoculum on bunch trash from flowering to pre-bunch closure may contribute to BBR control, as shown in a meta-analysis of 116 studies [53,54] and in several field experiments [12,13,55]
Summary
Botrytis bunch rot (BBR) is an economically important disease of grapevine (Vitis vinifera L.) and is caused by the fungus Botrytis cinerea Pers.:Fr (anamorph of Botryotinia fuckeliana (de Bary) Whetzel) [1].Botrytis cinerea can develop as a saprophyte, necrotroph, or parasite on multiple vine organs including leaves, green shoots and rachides, flowers and flowering residues, and berries. B. cinerea has multiple infection pathways, with infections mainly occurring from flowering to fruit set and after veraison [1,2,3,4,5]. BBR control is traditionally based on the application of fungicides at four grape growth stages (GS): A, end of flowering (GS69; [6]); B, pre-bunch closure (GS77); C, veraison (GS83); and D, before harvest (before GS89) [7,8]. These routine applications of fungicides make it possible to control all B. cinerea infection pathways. Conidia germinate and infect the flower styles and ovules (infection pathway I of Elmer and Michailides [1]), stamens and petals (pathway IIa), or the fruit pedicel
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