Alicia Lorenzana

Influence of Rhizoctonia solani and Trichoderma spp. in growth of bean (Phaseolus vulgaris L.) and in the induction of plant defense-related genes

Many Trichoderma species are well-known for their ability to promote plant growth and defense. We study how the interaction of bean plants with R. solani and/or Trichoderma affect the plants growth and the level of expression of defense-related genes. Trichoderma isolates were evaluated in vitro for their potential to antagonize R. solani. Bioassays were performed in climatic chambers and development of the plants was evaluated. The effect of Trichoderma treatment and/or R. solani infection on the expression of bean defense-related genes was analyzed by real-time PCR and the production of ergosterol and squalene was quantified. In vitro growth inhibition of R. solani was between 86 and 58%. In in vivo assays, the bean plants treated with Trichoderma harzianum T019 always had an increased size respect to control and the plants treated with this isolate did not decrease their size in presence of R. solani. The interaction of plants with R. solani and/or Trichoderma affects the level of expression of seven defense-related genes. Squalene and ergosterol production differences were found among the Trichoderma isolates, T019 showing the highest values for both compounds. T. harzianum T019 shows a positive effect on the level of resistance of bean plants to R. solani. This strain induces the expression of plant defense-related genes and produces a higher level of ergosterol, indicating its ability to grow at a higher rate in the soil, which would explain its positive effects on plant growth and defense in the presence of the pathogen.

Thresholds for management of Phorodon humuli (Hemiptera: Aphididae) on hops.

The hop aphid, Phorodon humuli (Schrank), is one of the main hop, Humulus lupulus L. (Cannabaceae), pests in the world. The aim of this work was to determine (1) the yield loss function in hops bas...

Investigations of Trichoderma spp. and Beauveria bassiana as biological control agent for Xylotrechus arvicola, a major insect pest in Spanish vineyards

Xylotrechus arvicola (Olivier) (Coleoptera: Cerambycidae) is an important pest in vineyards (Vitis vinifera) in the main wine-producing regions of Spain. Effective control of this pest is difficult due to the biology of this pest. Biological control agents (BCAs) have proven to be an effective tool in controlling and preventing the spread of a variety of plant pests and diseases. Consequently, the aim of the present study was to assess the capacity of different Trichodema spp., isolated from various vineyards and one commercial isolate of Beauveria bassiana Vuillemin (Hypocreales: Cordycipitaceae), as BCAs of X. arvicola. Isolates of Trichoderma spp. and one isolate of B. bassiana were evaluated against X. arvicola eggs, larvae and adults. Trichoderma harzianum and Trichoderma gamsii demonstrated a good ovicidal control, 100.0% with T. harzianum and over 92.0% with T. gamsii. These Trichoderma strains achieved an over 65.0% larval mortality and 87.5% adult mortality. B. bassiana was the most effective treatment against X. arvicola larvae. These results confirm that Trichoderma spp. can be used to inhibit egg development. In addition, Trichoderma spp. and B. bassiana can help to prevent larvae boring into vines and to kill adults. Therefore, Trichoderma spp., especially T. harzianum and T. gamsii, and B. bassiana can be considered as highly effective BCAs of X. arvicola in vineyards.

Within-plant distribution of Phorodon humuli (Hemiptera: Aphididae) and natural enemies on hops with implications for sampling and management

A field trial was performed on a hop yard throughout 2006, 2007 and 2008 in order to analyze the within‐plant distribution of Phorodon humuli (Schrank) and its natural enemies. The aphid population was higher on the leaves of the middle section of the main stem. Specifically, the population was significantly higher at 2 and 3.25 m than at 6 m during the three years. Natural enemies consisted of aphidophagous predators of which Coccinella septempunctata was recorded in the highest number. Its number was greater where the aphid population was higher, with a significantly higher number of eggs, larvae and adults at 2 and 3.25 m than at 6 m. Lacewing eggs were also frequently observed, with a significantly higher population where the number of aphids was higher. The number of winged aphids was higher at 3.25 m than at 2 m within a plant. Understanding hop aphid distribution within the hop canopy is important in developing sampling programs, in evaluating injury and helps the development of sustainable management practices.

Estimating hop parameters prior to calculating economic thresholds of intervention against Phorodon humuli (Hemiptera: Aphididae)

Summary Economic thresholds of intervention against the hop aphid, Phorodon humuli, can be expressed using different parameters. Some of these parameters are calculated using measurements which are not easy to record directly, but which can be obtained from simpler measurements. In this paper, the functions relating two simple measurements to two more complex ones were obtained from two hop plots in León, Spain, in 2002 and 2004. The function relating the area of the hop leaf (y) to its length (x) is obtained by y = 1.13 (± 0.10) x2 – 3.55 (± 1.91) x + 3.64 (± 8.25). The functions relating the number of leaves (y) in the canopy volume formed by the area (x) of the bine section of the hop plant (which normally had two strings per rootstock and three bines trained per string) as a base and a height of 20 cm, to this area (x) are y = 0.020 (± 0.002) x + 5.291 (± 2.278), at heights of 2 m and 3.25 m from ground level, and y = 0.034 (±0.004) x – 0.419 (± 4.310), at a height of 6 m above ground level.