The plant trade is unwittingly accelerating the worldwide spread of well-known and new or undescribed Phytophthora species and creating novel niches for emerging pathogens. The results of a survey carried out from 2001 to 2006 in garden centres and nurseries of the Balearic Islands and eastern Spain combined with the analysis of samples received from ornamental nurseries from northern Spain reflected the extent of this global issue at the local scale. A total of 125 Phytophthora isolates were obtained from 37 different host species and 17 putative species identified on morphological features and direct sequencing of the internal transcribed spacer and four mitochondrial and nuclear genes. Five species, P. ramorum , P. hedraiandra , P . 'niederhauserii', P . 'kelmania' and P . 'taxon Pgchlamydo' were formally unknown to science prior to 2001. In addition, 37 new host/pathogen combinations were first records for Spain, highlighting the risk of non-coevolved organisms from different biogeographic origins coming into contact under managed environments. The problem generated by new or rare taxa of Phytophthora found in nurseries for which no prior information on natural habitat and ecology is available for pest risk analysis is discussed.

Considerable losses of citrus trees have been observed in the major citrus-growing areas of Spain. Samples were collected from 132 orchards, and isolations and pathogencity tests were conducted to determine the aetiology of a serious canker disease. Affected trees showed cankers on the scion that frequently began on the branches. Three Phytophthora species were identified based on their morphological, cultural, physiological and molecular profiles. Phytophthora citrophthora was the main species associated with this new syndrome in 114 orchards. Phytophthora nicotianae (syn. P. parasitica ) was isolated from nine orchards as the sole Phytophthora species and in coinfection with P. citrophthora from another nine orchards. Phytophthora citricola was isolated only from one orchard. In stem-inoculation studies conducted under greenhouse conditions, clementine mandarin cv. Hernandina and sweet orange cv. Navel Late were more susceptible to P. citrophthora than sour orange and Carrizo citrange rootstocks. Clementine cv. Hernandina was also highly susceptible in field inoculation experiments. In agreement with field surveys, clementine mandarin cultivars were the most affected, their rootstocks remaining healthy. Phytophthora citrophthora was found to be the predominant species in orchard soils; however, P. nicotianae was also isolated. This information changes the scenario of diseases caused by Phytophthora spp. in Spain and consequently, the present knowledge of epidemiology and the effectiveness of the current control measures should be reassessed.

Considerable tree losses have been observed during the past few years in Spain due to Phytophthora branch canker of clementines caused by Phytophthora citrophthora. The emergence of this disease led to the speculation that either the pathogen has evolved increasing its aggressiveness or specificity to clementines. A total of 134 isolates of P. citrophthora collected from 2003 to 2005 in 135 citrus orchards in Spain and 22 reference isolates were analyzed genotypically and phenotypically to determine the structure of the population. Genotypic diversity was evaluated by means of Inter-Simple Sequence Repeat (ISSR) markers. Among the phenotypic characteristics examined, sporangial characters, sexual behavior, growth rates and colony morphology of the isolates at different temperatures were studied. The aggressiveness and host-specificity of selected isolates were evaluated by pathogenicity tests on sweet oranges and clementines under field conditions. Phytophthora branch canker of clementines was associated mainly with one genotype (P-1), which included 88% of the isolates obtained from branches. Strains isolated years before the first disease outbreak clustered also with this major genotype, thus it may be considered as a predominant population. Thirteen other minor genotypes were determined, but most contained only one isolate. Although there was wide variation in the morphological and physiological characters, all Phytophthora isolates obtained from branch cankers were sexually sterile and showed a characteristic petalloid colony pattern. As in previous greenhouse studies, pathogenicity tests under field conditions demonstrated that clementines and their hybrids were more susceptible to P. citrophthora than sweet oranges. However, no evidence was found to support the hypothesis that the emergence of the disease was associated with more aggressive or host-specific forms of P. citrophthora.

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