Spatial pattern of Bois noir: case study of a delicate balance between disease progression and recovery

Abstract

Bois noir (Bn) is the most important phytoplasma disease of euro-Mediterranean area and induces severe loss of production and even the death of vines. Understanding the delicate balance between disease progression and recovery of Bn infected plants over space and time is crucial to set up management tools. the data collected and analysed allowed to provide insights into dispersal pattern of the disease, caused by'Candidatus phytoplasma solani'. point pattern analysis (ppA) was applied to assess the spatial arrangement of symptomatic plants and the spatial correlation of disease levels in four vineyards. for spatio-temporal patterns of Bn, a mark-correlation function was applied. Spacetime PPA over multiple years (2011-2015) provided graphical visualisation of grapevines more severely affected by BN along the borders of the vineyards, mainly in 2011 when disease incidence was high. PPA across the symptomatic plants in the four vineyards confirmed this visual trend: an overall aggregated pattern at small (<10 m) spatial scales (2013) that were more evident later at all spatial scales (0-15 m). Application of this innovative spatial approach based on point and surface pattern analyses allowed the spread and severity of BN to be monitored, to define the dispersal routes of the pathogen. Such data will contribute to better understand the distribution of symptomatic plants over space and time and to define a model for preventive strategies to reduce future infections. Bois noir (BN) is one of the most important grapevine yellows in Europe 1 and phytoplasma related to 'stolbur group' are today emergent threats for the grapevine cultivation and for vegetable crops in South and East Asia 2,3. BN is generally considered less epidemic than Flavescence dorée (FD), although it is more difficult to manage, because no direct means are available for the pathogen and the main vectors 4. Over recent decades, frequent BN outbreaks have been recorded in the main viticultural areas 3,5-9 , which have led to dramatic losses in grape quality and quantity, most of all for highly susceptible grapevine cultivars such as 'Chardonnay' 1,10,11. The causal agent of BN is a phytoplasma that belongs to the stolbur group (16SrXII-A subgroup) and has been assigned to 'Candidatus Phytoplasma solani' ('Ca. P. solani') 12. It is transmitted mainly by the polyphagous planthopper Hyalesthes obsoletus (Sign., 1865, Hemiptera: Cixiidae) to a wide range of wild plants, such as Convolvulus arvensis, Calystegia sepium, Urtica dioica 13. However, several weeds were reported as hosts of 'Ca. P. solani' within and around infected vineyards and can therefore play a key role in the BN spreading 8,14-18. Thus, all of these hosts represent potential inoculum sources, while for grapevines, the occasional infections by H. obsoletus represent dead-end hosts for the stolbur phytoplasma. BN symptoms include abnormal lignification of canes, short internodes, flower abortion, and curling and discoloration of leaves, with intervein yellowing or reddening 1,10. These are ...

Molecular and spatial analyses reveal new insights on Bois noir epidemiology in Franciacorta vineyards

“…Considering that most symptomatic grapevines were not replaced throughout the years, it follows that many vines previously diseased did not show any symptoms in the following seasons. Such dynamics confirmed the existence of balanced equilibrium between driving forces acting on BN impact (Murolo, Garbarino, Mancini, & Romanazzi, 2020; Rotter et al, 2018). In particular, vector‐mediated CaPsol transmission to grapevines (new infections) and symptom remission were equally strong drivers in Erbusco, while the latter was prevalent in Corte Franca.…”

[Retracted] Spatial Pattern Evaluation of Rural Tourism via the Multifactor‐Weighted Neural Network Model in the Big Data Era

“…Firstly, the nearest neighbor distance index (NNI). The calculation result of the average distance between the closet attractions is compared with that between nodes in the random distribution to analyze the degree of deviation from the random distribution, so as to obtain the distribution type of rural tourism attractions [ 34 ]. The calculation can be written as …”

Differential Response of Grapevine to Infection with ‘Candidatus Phytoplasma solani’ in Early and Late Growing Season through Complex Regulation of mRNA and Small RNA Transcriptomes

“…The same grapevines were sampled again in the early growing season of 2020. In 2020, the grapevines did not develop symptoms over the summer, and phytoplasmas were not detected in samples from these grapevines later in the growing season, which suggested that these grapevines had already recovered from their previous infection or were in the recovery process [ 41 ]. Moreover, the RNA-Seq analysis of samples from these grapevines revealed that there was not even a single differentially expressed gene defined between the recovered and uninfected grapevines ( Table S1 ), which indicated that the recovery appeared to have occurred previously, in 2018 or 2019 [ 20 ].…”