Long-term deep-freeze storage of Neonectria ditissima conidium suspensions does not reduce their ability to infect apple trees
Fresh, wild-type conidium suspensions of Neonectria ditissima prepared from sporulating European canker lesions for use in field inoculation trials are not always readily available. The effect of freezing inoculum on the viability of spores and their ability to cause infection in situ was assessed using 15—19 frozen N. ditissima conidium suspensions during 2015—2017. Freshly prepared inoculum and water only were used to inoculate rasp wounds on ‘Braeburn’ (2015), ‘Scilate’/Envyâ„¢ (2016) and ‘Royal Gala’ and ‘Braeburn’ (2017) along with frozen inoculum ranging in age from 1—462 days at concentrations >104 conidia/mL. Lesion development was assessed at approximately monthly intervals. In all experiments, there was no substantial effect of storage time on lesion development although germination in droplets may have decreased during storage. As expected, there was a cultivar effect (2017 data only), with fewer lesions on ‘Braeburn’ compared with ‘Royal Gala’. Long-term deep-freeze storage up to 462 days of N. ditissima conidium suspensions (>104 conidia/mL) did not affect the ability of spores to infect apple trees. Therefore, spore suspensions can be batch-prepared and stored frozen for future experimental use.
Gomez-Cortecero A, Saville RJ, Scheper RWA, Bowen JK, De Medeiros HA, Kingsnorth J, Xu XM, Harrison RJ 2016. Variation in host and pathogen in the Neonectria/Malus interaction; toward an understanding of the genetic basis of resistance to European canker. Frontiers in Plant Science 7: 1365. https://doi.org/10.3389/fpls.2016.01365
Latorre BA, Rioja ME, Lillo C, Munoz M 2002. The effect of temperature and wetness duration on infection and a warning system for European canker (Nectria galligena) of apple in Chile. Crop Protection 21: 285–291. https://doi.org/10.1016/S0261-2194(01)00099-0
McCullagh P, Nelder JA 1989. Generalized Linear Models. 2nd ed. London, Chapman & Hall. 511+xix p. https://doi.org/10.1007/978-1-4899-3242-6
Scheper RWA, Frijters L, Fisher BM, Hedderley DI 2015. Effect of freezing of Neonectria ditissima inoculum on its pathogenicity. New Zealand Plant Protection 68: 257-263.
Walter M, Stevenson OD, Amponsah NT, Scheper RWA, Rainham d, Hornblow C, Kerer U, Dryden G, Latter I, Butler RC 2015. Control of Neonectria ditissima with copper based products in New Zealand. New Zealand Plant Protection 68: 241-249.
Walter M, Roy S, Fisher BM, Mackle L, Amponsah NT, Curnow T, Campbell RE, Braun P, Reineke A, Scheper RWA 2016. How many conidia are required for wound infection of apple plants by Neonectria ditissima? New Zealand Plant Protection 69: 238-245.
Xu X, Butt DJ, Ridout MS 1998. The effects of inoculum dose, duration of wet period, temperature and wound age on infection by Nectria galligena of pruning wounds on apple. European Journal of Plant Pathology 104: 511–519. https://doi.org/10.1023/A:1008689406350