The resistance of 11 olive cultivars to Verticillium dahliae was assessed in two experimental field trials. One-year-old rooted olive cuttings from the World Olive Germplasm Bank (IFAPA research center, Córdoba, Spain) were planted in a heavily infested field in Utrera (Sevilla province) and in a moderately infested field in Andújar (Jaén province) of southern Spain. Plants were assessed for Verticillium wilt resistance during 22 months based on disease severity and tree growth. Severe disease symptoms were observed 6 months after planting in both trials. Twenty months after planting in the heavily infested soil, V. dahliae had killed nearly all of the trees of ‘Bodoquera’, ‘Cornicabra’, ‘Manzanilla de Sevilla’, and ‘Picual’, demonstrating the elevated risk of planting susceptible cultivars in a soil heavily infested with V. dahliae. ‘Arbequina’, ‘Koroneiki’, ‘Sevillenca’, and especially ‘Frantoio’, ‘Empeltre’, and ‘Changlot Real’ showed a high level of disease resistance. However, all of them were affected by the disease. Although the field results confirmed the level of resistance previously obtained for these olive genotypes under controlled conditions, there were some discrepancies. This information will be useful in managing the disease and also in selecting new cultivars for the breeding of Verticillium wilt resistance.

This study investigated starch content, amount of pathogen DNA and density of occluded vessels in healthy and Verticillium dahliae infected olive shoots and stems. Starch hydrolysis is considered a mechanism to refill xylem vessels that suffered cavitation by either, drought conditions or pathogen infections. The main objective of this work was to evaluate this mechanism in olive plants subjected to V. dahliae infection or to drought conditions, in order to know the importance of cavitation in the development of wilting symptoms. In initial experiments starch content in the shoots was studied in trees of cultivars differing in the level of resistance growing in fields naturally infested with V. dahliae. The starch content, esteemed by microscopic observation of stem transversal sections stained with lugol, decreased with the level of symptom severity. Results were confirmed in a new experiment developed with young plants of cultivars ‘Picual’ (highly susceptible), ‘Arbequina’ (moderately susceptible) and ‘Frantoio’ (resistant), growing in pots under greenhouse conditions, either inoculated or not with V. dahliae. In this experiment, the pathogen DNA content, quantified by real-time PCR, and the density of occluded vessels, recorded by microscopic observations of transversal sections stained with toluidine blue, were related to the symptoms severity caused by the pathogen. Finally, a drought experiment was established with young plants of the cultivar ‘Picual’ grown in pots under greenhouse conditions in order to compare the effects caused by water deficit with those caused by the pathogen infection. In both cases, results show that starch hydrolysis occurred, what indirectly evidence the importance of xylem cavitation in the development of the symptoms caused by V. dahliae but in the water stressed plants no vessel occlusion was detected.

In May 2016, Fusarium crown rot (FCR) of wheat (Triticum aestivum) was identified in a commercial field located in Córdoba, Spain. Affected plants showed necrosis and dry rot of the crown and basal stems. Three foci and at least 10 plants per foci were surveyed. Necrotic tissues were washed under running tap water. Subsequently, they were surface-disinfested in a sodium hypochlorite solution (Cl at 5 g l–1) in sterile distilled water (SDW) for 1 min and washed twice with SDW. Small pieces from the basal stem were plated onto potato dextrose agar (PDA), acidified with 0.06% lactic acid and incubated at 25ºC in darkness for 7 days. According to the morphology of the colony, fungal species belonging to the Fusarium graminearum species complex were isolated, showing seven morphological types of colonies. All isolates were transferred onto PDA and carnation leaf agar (CLA) and incubated as described above. One of these isolates, ColPat-351, was first identified morphologically as F. pseudograminearum (Aoki and...