Tesis doctoral de Carla Casals Rosell
Brown rot caused by monilinia spp. Is the main disease affecting peaches and nectarines. Fruit are infected basically in the field, but the disease development occurs generally during postharvest of fruit, where the economic losses can reach high values. In addition, there are not available chemical products authorised to be applied on postharvest of stone fruit in spain and then the disease control is mainly by fungicide spray programs applied in the field or by cultural practices. For this reason, the main objective of this thesis was to contribute in developing strategies for brown rot control in postharvest of peaches and nectarines. Firstly, the conditions of temperature and water activity (aw) where monilinia laxa, m. Fructigena and m. Fructicola are able to germinate were determined (chapter 1). Next, a wide range of postharvest treatments were evaluated. In the chapter 2, posthavest treatments based on the application of several biocontrol agents, different water bath temperatures and exposure times, and some sodium bicarbonate (sbc) concentrations, were evaluated. The most efficient conditions for controlling brown rot of each these treatments also were evaluated applying them separately or in combination. Radiofrequency (rf) postharvest treatment was evaluated in chapter 3. Finally, the curing treatment also was studied (chapter 4 and 5), likewise, its combination with a biological agent or a chitosan solution (chapter 6). from the results obtained in chapter 1, we concluded that temperature and aw are key factors for germination of monilinia spp. Conidia. In addition, the results showed that at 0 ºc, temperature that fruit are stored during postharvest, monilinia spp. Conidia are able to germinate, indicating that this pathogen could develop and cause brown rot on peaches and nectarines, even under low temperatures. The limit conditions of temperature and aw for germination of the three species of monilinia spp. Studied are 38 ºc and 0.87 aw, respectively. generally, the postharvest treatments evaluated are effective for brown rot control. Thereby, the biocontrol agent cpa-8 identified as a bacillus subtilis species complex applied at 107 cfu ml-1 is effective for controlling brown rot in a wide range of varieties of peaches and nectarines incubated at 20 ºc, in both, fruit artificially inoculated with m. Laxa or m. Fructicola and in fruit with natural inoculum. However, the efficacy of the biocontrol agent when fruit are incubated at 0 ºc is dramatically decreased, possibly because at 0 ºc it is not able to grow. The hot water treatment at 60 ºc for 40 s applied on peaches and nectarines, artificially inoculated with m. Laxa or fruit with natural inoculum, decreases significantly the incidence of brown rot. In contrast, the sbc treatment applied for 1 min does not show any effect. In general, the efficacy level for brown rot control provided by the biocontrol and hot water treatment fluctuate along the varieties evaluated. However, it is overcame when both treatments are applied in combination, first the hot water and then the biocontrol agent, since, the efficacy level is constant and in addition, there is an additive effect for controlling brown rot on peaches and nectarines incubated at 20 ºc. However, when fruit are incubated at 0 ºc this additional effect is not detectable. the rf treatment applied at 17 mm distance between top of fruit and upper electrode and 18 min exposure time is effective to control brown rot on peach varieties that are artificially inoculated with m. Fructicola or fruit with natural inoculum. The efficacy of the rf treatment is not affected by the inoculation time before the treatment, between 0 and 48 h. However, depending on the variety of peach fruit evaluated, the rf treatment is affected by the inoculum concentration of m. Fructicola when it is increased from 103 to 104 o 105 conidia ml-1. the study related to the curing treatment took an important part of this thesis. The curing treatment at 50 ºc for 2 h and 95-99 % relative humidity provides an important and even a total control of brown rot, in a wide range of varieties of peaches and nectarines artificially inoculated with m. Laxa o m. Fructicola or in fruit with natural inoculum. However, the efficacy of curing is compromised when the inoculum concentration, the level of fruit maturity and the infection time before treatment are increased. In addition, curing treatment does not provide preventive effect for controlling further infections after the treatment. However, our results indicated that this limitation could be overcome by combining curing with an application of the biocontrol agent cpa-8 after treatment, for fruit incubated at 20 ºc. Moreover, the 1 % of chitosan application after curing also reduces the incidence of future infections when fruit are incubated at 20 ºc. the results obtained in this thesis provide interesting information for postharvest sector of stone fruit, since it offers a wide range of possibilities that could be applied commercially, some of them early.
Datos académicos de la tesis doctoral «Control de la podridura marró causada per monilinia spp. en postcollita de fruita de pinyol«
- Título de la tesis: Control de la podridura marró causada per monilinia spp. en postcollita de fruita de pinyol
- Autor: Carla Casals Rosell
- Universidad: Lleida
- Fecha de lectura de la tesis: 06/05/2010
Dirección y tribunal
- Director de la tesis
- María Inmaculada Viñas Almenar
- Tribunal
- Presidente del tribunal: vicente Sanchis almenar
- lluís Palou vall (vocal)
- María isabel Abadias sero (vocal)
- antonieta De cal y cortina (vocal)