Barrier effects on the spatial distribution of Xylella fastidiosa in Alicante, Spain

Spatial models often assume isotropy and stationarity, implying that spatial dependence is direction invariant and uniform throughout the study area. However, these assumptions are violated when dispersal barriers are present in the form of geographical features or disease control interventions. Despite this, the issue of non-stationarity has been little explored in the context of plant health. The objective of this study was to evaluate the influence of different barriers in the distribution of the quarantine plant pathogenic bacterium Xylella fastidiosa in the demarcated area in Alicante, Spain. Occurrence data from the official surveys in 2018 were analyzed with four spatial Bayesian hierarchical models: i) a stationary model representing a scenario without any control interventions or geographical features; ii) a model with mountains as physical barriers; iii) a model with a continuous or iv) discontinuous perimeter barrier as control interventions surrounding the infested area. Barriers were assumed to be totally impermeable, so they should be interpreted as areas without host plants and in which it is not possible for infected vectors or propagating plant material to pass through. Inference and prediction were performed through the integrated nested Laplace approximation methodology and the stochastic partial differential equation approach. In the stationary model the posterior mean of the spatial range was 4,030.17 m 95% CI (2,907.41, 5,563.88), meaning that host plants that are closer to an infected plant than this distance would be at risk for X. fastidiosa. This distance can be used to define the buffer zone around the infested area in Alicante. In the non-stationary models, the posterior mean of the spatial range varied from 3,860.88 m 95% CI (2,918.61, 5,212.18) in the mountain barrier model to 6,141.08 m 95% CI (4,296.32, 9,042.99) in the continuous barrier model. Compared with the stationary model, the perimeter barrier models decreased the probability of X. fastidiosa presence in the area outside the barrier. Differences between the discontinuous and continuous barrier models showed that breaks in areas with low sampling intensity resulted in a higher probability of X. fastidiosa presence. These results may help authorities prioritize the areas for surveillance and implementation of control measures.

Effectiveness of herbicides on Lysimachia vulgaris: a 17-year case study

Garden loosestrife (Lysimachia vulgaris L.), is an invasive wetland plant that is subject to management in King County, WA, USA. Large-scale management efforts are generally conducted using herbicides. In this case study, we analyzed 17 yr of monitoring and treatment data in four riparian areas in King County to estimate the rate of spread of L. vulgaris and the efficacy of herbicidal treatments against L. vulgaris populations. In each area, herbicide treatments were applied annually. In three of the areas, the area infested with L. vulgaris did not change over time, while in the fourth area populations of L. vulgaris were spreading at a rate of 0.79 m2 yr−1. There were a greater number of sampled locations infested with L. vulgaris over the 17-yr period, and because populations were either not spreading or spreading slowly, it is possible that populations were becoming more fragmented. There was no relationship between the percentage of the infested area treated with herbicides and the area infested in the following year. However, there was a negative relationship between the area treated and the percent change in the invaded area; specifically, in years when <80% of the infested area was treated, there was an increase in the percent change of the invaded area between the year of treatment and the following year. The results of this study suggest that at the current level of management effort, the spatial extent of L. vulgaris did not retract over the 17-yr study period.

TINGKAT DAN POLA DISTRIBUSI INFESTASI PENGGEREK BATANG JAGUNG OSTRINIA FURNACALIS (LEPIDOPTERA: CRAMBIDAE) DI PADANGSIDIMPUAN

Ostrinia furnacalis Guenee as known as Asian corn stem borer is one of the main pests in corn cultivation practices in Indonesia. Besides Indonesia, these pests attack in other Asian regions such as Central Asia, East Asia, and also Australia. This study was aimed to measure the intensity of infestation and to analyze patterns of distribution of O. furnacalis in corn field. The observations of intensity and infestation distribusiton were held on 12 corn plantations owned by farmers in six sub-districts of Padangsidimpuan. Results showed that The lowest infested area of O. furnacalis larvae was 1.1%, while the highest was 4.31%. O. furnacalis larvae infestations at each plant in each plantations has a random distribution and the distribution was varies among corb fields.

Effect of the media on morphology of Cryphonectria parasitica (Murr.) Barr isolates and their Vegetative Compatibility Groups

The most dangerous pathogen for the European and American chestnuts is the blight fungus Cryphonectria parasitica (Murrill) Barr. Short after its introduction a big number of chestnut trees were destroyed on the infested area. The control could be really complicated, because of the numerous vegetative compatibility groups of the fungus. There is a type that carries a mycovirus viz. hypovirus in the cytoplasm. We are able to control effectively this pathogen by using mycovirus-carrying strains (called hypovirulent fungal strains also). In laboratory it is easy to multiply the virulent and the hypovirulent strains of the fungus but do not easy to differentiate colonies visually on simple PDA medium. During our research, we tested different types of media, based on potato and chestnut bark extract respectively. It was observed that on potato medium the virulent strains produce more orange pigments. So it is more easy to differentiate virulent or hypovirulent isolates of chestnut blight fungus based on colony colour and morphology.