Biologia i epidemiologia de fongs patògens de la fusta de la vinya i noves perspectives en el seu control = Biology and epidemiology of grapevine trunk pathogenic fungi and new perspectives on their control

Laburpena

Over the past few decades, the incidence of grapevine trunk diseases has increased worldwide and has become a serious concern for the scientific community and grape and wine producers. Therefore, the main objective of this thesis has been to provide new background knowledge about the biology and epidemiology of these diseases as well as to apply new insights into disease control methods. Some of the most significant pathogenic fungi involved in grapevine trunk diseases include Botryosphaeriaceae (which include Diplodia seriata), Phaeomoniella chlamydospora and Eutypa lata. Eighty-three isolates of D. seriata were characterized with respect to their genetic, phenotypic (conidial size, mycelial growth and vegetative and sexual compatibility) and pathogenic features. Molecular analyses showed 88 % polymorphism among isolates. These were grouped into two distinct genetic clusters. No relationships were found between the clustering results and the results of the remaining analyses, thus revealing the high intraspecific variability of D. seriata. However, this species was confirmed as pathogenic on grapevines. In order to optimize the inoculum potential that was to be used in artificial inoculations with D. seriata, E. lata and P. chlamydospora, pruning wounds were inoculated with different spore concentrations. Infection percentages between 50-70 % were achieved when wounds were inoculated with 100-1000 conidia of D. seriata per wound, 1000-2000 conidia of P. chlamydospora and 100-500 ascospores of E. lata.The release of D. seriata conidia in pruning debris was also studied within the period 2-3.5 years after canes were pruned. A progressive reduction in the inoculum pressure was recorded, as indicated by a decrease in pycnidia which contained conidia, the mean amount of conidia per pycnidia, and the percentage of viable conidia. However, 3.5 years after pruning, conidia which were still able to germinate were detected, thus showing that pruning debris left in the vineyards becomes an important long-lasting inoculum source. Micoflora resulting from the natural infection of pruning wounds was evaluated in a 4-year study. The pathogenic fungi identified in this study were, in order of descending frequency, D. seriata, P. chlamydospora, Cryptovalsa ampelina and E. lata. Infection rates were generally higher after late pruning carried out in winter, as compared with early pruning done in autumn. Accumulated rainfall up to 3 months after pruning and temperatures recorded during the same period showed a positive correlated with infection rates. The susceptibility of pruning wounds to D. seriata and P. chlamydospora decreased as the time between prunings and the infection of wounds increased. Pruning wounds remained susceptible for a longer period when infection with D: seriata was carried out after late pruning in winter. However, no overall seasonal changes in susceptibility were detected for Phaeomoniella chlamydospora. The length of the pruned internode did not make it difficult for D. Seriata to colonize the cane. However, the colonization of the cane decreased for P. chlamydospora when internodes were longer. The effect of hot water treatment on the viability of eight Botryosphaeriaceae species was also studied. In an in vitro assay, survival of fungi and their mycelial growth were evaluated after various treatments where different combinations of temperature and time exposures were used in a water bath. In the in planta experiment, Richter rootstock canes which had been previously colonized with the fungi were subjected to a water bath within a range 50 53 °C for 30 minutes and their survival was further assessed. In the in vitro assay it was observed that D. seriata, Dothiorella viticola, Neofusicoccum luteum and N. parvum were the most susceptible species, whereas N. vitifusiforme and Lasidiplodia theobromae were the most tolerant. In the in planta assay, all the viability of isolates was dramatically reduced after 30 minutes at 51 °C and higher temperatures, thus showing the feasibility of this technique as a means of control in the grapevine propagation process.