2.1. Identification,characterisation and ecology of pathogens, pests and their natural enemies
In vineyards, a general assessment of key pest problems was regularly made through weekly visual observations in three demonstrative fields. Grape berry moths and vineyard leafhopper populations were carefully monitored using different trapping devices including pheromone and yellow sticky traps as well as beneficials involved on their natural control (spiders and other arthropods). Distribution patterns of those pests were followed inside the canopy in relation with risk assessment methodologies.
Some forms of decline are responsible for the short life of vine plants. Both abiotic and biotic factors are involved in this decline. Among biotic factors, crown-gall, caused by Agrobacterium vitis, and some fungal diseases are associated with the decline of young vines. Up to 1998, our studies were mainly directed to A. vitis, due to several important outbreaks, which were recorded in Portugal. The spread of the disease in the country, the development of more accurate and fast diagnosis methods, the release of preventive control measures, and some legislative rules imposed to nursery growers contributed to the decreasing of crown-gall incidence.
In what concerns the involvement of fungi with young vine decline, a study was carried out in rootstock nurseries and in young vineyards during the last two years. Rootstock nurseries, located in the most important production areas of Portugal (Ribatejo-Oeste and Beira Litoral), were surveyed. The fungi most frequently isolated from discoloured wood at the base of the stem were Cylindrocarpon destructans and Phaeoacremonium chlamydosporum. Acremonium sp., Phomopsis sp., Fusarium spp., Fusicoccum sp., Gliocladium sp., Phoma sp. and Sphaeropsis sp. were also present. Young vines (2-8 years old) showing decline symptoms were collected from various vine-growing regions of Portugal. Disease incidence was variable but decline symptoms were present in several wine and table grapevine cultivars grafted onto different rootstocks (99R, 110R, 1103P, 101-14, 140Ru, 5BB and 161-14). Isolates from symptomatic internal tissues revealed that C. destructans and P. chlamydosporum were also the predominant fungi associated with the basal end of the rootstocks and grafting tissues. In the pathogenicity tests carried out with C. destructans isolates, the pathogen was reisolated from inoculated plants showing black-foot symptoms but never from the controls. Our results suggest that both C. destructans and P. chlamydosporum are involved in young grapevine decline in Portugal.
In protected crops, species identification of pests, their incidence along season as well as the identification and seasonal occurrence of their natural enemies were performed. The first results obtained were published on a Technical Manual on May 1999.Species identification of natural control agents continued for mirids, chrysopids, cecidomids and parasitoids of leafminers, whiteflies, aphids and noctuid larvae.
In maritime pine stands, the flight pattern of the maritime pine bast scale, Matsucoccus feytaudi, males and two predator species that show a strong kairomonal response to the pheromone of M. feytaudi, i.e., Elatophilus crassicornis and Hemerobius stigma, was monitored. The results suggest that the phenology of portuguese populations of M. feytaudi may be different from that observed in other regions, e.g., France, where the species is reported to be univoltine.
In pear orchards, acarofauna was studied in 50 different locations of Oeste Region. Results showed the dominance of the eryophid mite Epitrimerus pyri among the phytophagous species and very low levels of predator mite species.
In apple orchards, soilborne pathogens (fungi and bacteria) were studied in order to identify the species involved with apple replant disease. Fungi such as Fusarium spp. and Cylindrocarpon spp. were frequently isolated from discoloured tissues from crown and roots of young trees showing poor growth of replanted orchards. Pathogenicity tests carried out with fungi isolates on apple seedlings (cultivars Bittenfelder and Granny Smith) revealed that they are involved in the disease. Inoculated seedlings showed root necroses and reduced growth when compared with noninoculated plants. High populations of Fusarium oxysporum and F. solani were also detected in some soil samples, randomly collected from the above referred orchards. When apple seedlings were grown in pots containing soil samples of each orchard amended with Fusarium selective chemicals (glucose, pentachloronitrobenzene, rose bengale), seedlings also showed reduced growth, when compared with raw or steamed soil samples. This selective technique, first described by D. Bouhot for F. oxysporum f. sp. melonis could be useful for estimating the inoculum potential of soils infested by Fusarium oxysporum and used in combination with other selective treatments in pot tests to predict and diagnose replant diseases. Crown-gall disease was not recorded on the sampled orchards.
In citrus groves, The flight pattern of citrus mealybug, Planococcus citri, was monitored. This seasonal flight activity observed is consistent with previous observations and with a multivoltine cycle: Planococcus citri is reported to present between three and five generations per year on citrus in Portugal.
In Luppin spp., lupin anthracnose, a fungal disease caused by species of Colletotrichum, poses significant constraints to the lupin crop development. Currently, the causal agent of the disease is considered as C. gloeosporioides, but the adoption of molecular criteria is suggesting that a number of isolates causing lupin anthracnose are likely to belong to the species C. acutatum. Moreover, genetic variability is known to exist within lupin anthracnose agents. The studies are being performed in the following directions:
1) screening the germplasm collections of Lupinus albus and L. angustifolius in the ISA genebank for anthracnose resistance; 2) evaluation of genetic variability among the lupin anthracnose agents and clarification of their taxonomy and phylogeny.
The main objective of item 1) is the identification of resistant and moderately resistant lines, in such a way that future crosses between them will allow the production of more resistant lines. Results showed the existence of important differences between accessions, in both species, concerning the resistance score. However, differences between L. angustifolius lines were more important than those between L. albus lines. Some wild germplasm accessions of L. angustifolius were distinguished by appreciable resistance to the isolate used and will be investigated further. Three of the best lines came from a single geographic location. Domesticated or semi domesticated lines were more susceptible.
In what concerns gardens and urban trees, a sanitary survey of conifer and broadleaves was carried out in the Lisbon area and several diseases were found to be the cause of premature leaf fall of shade and amenity trees. The diseases found were: anthracnosis in Arecastrum romanzoffianum, Citrus aurantium, Phytolacca dioica and Platanus spp., leaf spots in Aesculus spp., Cercis siliquastrum and Populus spp., powdery mildews of Quercus spp. and Platanus spp., leaf blister in Populus deltoides and P. nigra and graphiola disease of Phoenix canariensis.
An increase in cypress canker incidence was registered in urban areas. Control methods have been suggested to local authorities in order to avoid disease dissemination.
Surveys of diseases affecting lawns in gardens, landscape, golf and football fields were continued and several diseases were identified and studied: Bipolaris and Exserohilum diseases, anthracnose, rusts, gray leaf spot, septoria leaf spot, Leptosphaerulina leaf blight and slime mould.
An experimental field was established using a seed progeny of different Proteaceae fynbos species (as a basis for field research in the new future) aiming to study the adaptability of the different species and/or individuals to the particular ecological conditions of the Southwest region of Portugal and to choose the best performance for further vegetative propagation. At the same time the studies took in consideration the definition of the key-pests (Sesamia nonagrioides and Helicoverpa armigera) and disease problems affecting these plants and the development of an IPM programme for the region.
Protecção das Plantas
e dos Produtos Agrícolas Armazenados