Relative significance of nursery infections and orchard inoculum in the development and spread of apple canker (Nectria galligena) in young orchards

Abstract

Three nurseries produced apple rootstocks (M9) and budwood (cv. Royal Gala), which they exchanged at the end of the first year. Each nursery then budded its own budwood onto the rootstocks it had produced and that from the other two nurseries. Budded trees were grown on for a further year before being planted at HRI, East Malling in southern England; NIHPBS, Loughgall in Northern Ireland; and ADAS, Rosemaund in the West Midlands of England. Canker development was monitored twice a year. The position of the infected trees within the orchard was recorded, as was the position of the canker on each tree (main-stem or peripheral). Nectria galligena was isolated from representative cankers and analysed using molecular techniques. At the sites in Northern Ireland and HRI there was a strong positional effect, especially of peripheral cankers, indicating that most of the inoculum was external and had been spread from neighbouring orchards. There was little or no positional effect on main-stem cankers at any of the three sites. The proportions of different isolates taken from peripheral cankers was different in Northern Ireland from that in England, suggesting different populations associated with the geographic areas. In contrast, the populations of N. galligena obtained from main-stem cankers were very similar in England and Northern Ireland. It was concluded that a small proportion of trees developing canker were infected during propagation, with no symptom development until after planting. In a second trial it was demonstrated that trees infected during the propagation phase, and particularly at budding and heading back, could develop canker up to 3 years later. While it is clear that some canker developing in the orchard can be associated with the nursery of production, in climatic conditions conducive to the formation and dissemination of conidia, inoculum from surrounding infected orchards is the primary source of the pathogen. Aerial spread is therefore an essential element of the epidemiology of N. galligena , and its control is a crucial part of any canker-control programme.

Evaluation of biological and agrichemical products for control of <i>Neonectria ditissima</i> conidia production

“…The larger the wound and the higher the number of spores reaching the wound, the shorter the latent period from infection to symptom expression (Amponsah et al 2015;Walter et al 2016). Depending on wound size and spore load, a latency period as brief as 2-4 months is common (Walter et al 2016;Amponsah et al 2015); however, latent periods greater than three years have been reported (McCracken et al 2003). Inoculum control is a very important aspect in European canker disease control.…”

Development of a method for detection of latent European fruit tree canker (Neonectria ditissima) infections in apple and pear nurseries

“…It is suggested that the major source of infection by N. ditissima in newly planted orchards was brought in with the introduction of trees from nurseries, because significant numbers of young trees developed large cankers along the main stem. Since the trees did not show symptoms at the time of planting in the orchards, they likely became infected during propagation without showing symptom development (Brown et al 1994;McCracken et al 2003;Weber 2014). Several molecular tools have been developed to detect N. ditissima (Langrell and Barbara 2001;Langrell 2002;Ghasemkhani et al 2016).…”

Pathogenicity of Neonectria fuckeliana on Norway Spruce Clones in Sweden and Potential Management Strategies

“…Latent infections are also reported for N. ditissima [32][33][34] and the latent period varies with wound size and spore concentration. Larger wounds and higher spore concentration shorten the latent period.…”

“…Latent natural infections are widely reported in literature where N. fuckeliana has been isolated from wounded and healthy looking stems of Norway spruce [5,12,13,35]. Furthermore, a light rain occurred during part of the inoculation process and the temperature was under 20 • C. Mild and wet weather conditions are favorable for pathogen sporulation, dispersal, and infection of N. ditissima [33,36,37] and likely also for N. fuckeliana. If the trees in the field trial received the same background inoculum level, then the larger lesion length under bark (approximately 12 mm or 46%) for the inoculated trees was likely due to the additional inoculum of N. fuckeliana mycelial plugs.…”