Actinidia seed-borne latent virus (ASbLV, Betaflexiviridae, genus Prunevirus) was detected at hig... more Actinidia seed-borne latent virus (ASbLV, Betaflexiviridae, genus Prunevirus) was detected at high frequency in healthy seedlings grown from lines of imported seed in a New Zealand post-entry quarantine facility. To determine the route and efficiency of transmission of ASbLV in this dioecious crop species, we developed a rapid molecular protocol and identified a reliable progeny plant tissue to determine paternal and maternal transmission rates. The virus was detected at a high incidence (98%) in individual seeds, but cotyledon testing of seedlings from selected crosses confirmed staminate (male) transmission at high frequency (~ 60%), and pistillate (female) transmission at even higher frequency (~ 80%). The use of cotyledons allows non-destructive detection of ASbLV in very young seedlings that enables early screening of kiwifruit plants in nurseries to manage its spread to orchards. The high ASbLV transmission rates, whether from infected pollen or ovules, facilitate bulk testing...
European canker pathogen caused by the fungus Neonectria ditissima could not be isolated when inf... more European canker pathogen caused by the fungus Neonectria ditissima could not be isolated when infected woody tissues were plated directly onto potato dextrose agar (PDA) malt extract agar (MEA) or acidified PDA (pH 45) However the alternative media water agar (WA) and apple sapamended water agar (ASAWA) were successfully used to isolate the pathogen In the preparation of ASAWA green shoots of 1yearold fresh Scilate apple were frozen overnight then allowed to thaw The tissues were then centrifuged and the sap collected to prepare the medium Neonectria ditissima could be isolated from both symptomatic and asymptomatic apple tissues on both WA and ASAWA Both media supported the production of large numbers of conidia in vitro with more conidia being produced on ASAWA than on WA The conidia produced in vitro had morphological characteristics and pathogenicity similar to those produced in the field
Neonectria ditissima is a serious pathogen of apple. Low-virulent cultures of this fungus have be... more Neonectria ditissima is a serious pathogen of apple. Low-virulent cultures of this fungus have been isolated from cankers, but how and why low-virulent isolates can infect apple is unknown. Rasp wounds on ‘Royal Gala’ trees were inoculated with agar plugs from six low-virulent N. ditissima isolates in a glasshouse. Neonectria ditissima was re-isolated 10 weeks after inoculation. Agar plugs from the re-isolated cultures were used to inoculate ‘Royal Gala’ trees again. After the second re-isolation, conidial suspensions of the original cultures and the 2 x 6 re-isolates were used to determine the virulence on ‘Royal Gala’ compared with field-collected conidia. Three cultures did not cause any lesions; neither did their re-isolates. The re-isolates of two cultures did not differ in virulence compared with the originals. However, the virulence of one isolate increased with each re-isolation, with the second re-isolation causing significantly more lesions, lesion development occurring fa...
Bundles of dormant wood were submerged in water (45˚C for 45 min or 50˚C for 15 min), or were wra... more Bundles of dormant wood were submerged in water (45˚C for 45 min or 50˚C for 15 min), or were wrapped in moist cloth, placed inside zip-locked bags and submerged for 3—6 h or treated with one of three GRAS chemicals or untreated (two bundles per treatment). Scion wood was grafted onto ‘M9’ rootstocks then planted in a randomised order, with growth assessed after 16 weeks. Two of the GRAS treatments and submersion at 45˚C for either 45 min or 3 h in a bag did not significantly affect viability compared with the untreated control (83—95% viable). Submersion at 50˚C for 15 min reduced viability significantly (70%). Scions did not survive exposure to 50˚C for 3—5 h in bags…
Monitoring of disease progression by microscopy is an important component of the study of host-pa... more Monitoring of disease progression by microscopy is an important component of the study of host-pathogen interactions. The aim of this research was to investigate infection processes and the progression of Neofusicoccum luteum infection of grapevine leaves and shoots. Conidial suspensions (104 conidia mL-1) were inoculated onto wounded or non-wounded leaves and shoots of 18- month-old potted Pinot Noir vines growing in a shade house. The tissues remained attached, or were detached and incubated under high relaive humidity (RH) after inoculation. Scanning electron microscope (SEM) observation and pathogen re-isolation from the leaves at 24 to 72 h after inoculation and with the shoots at monthly intervals for 4 months. Results showed no infection in any non-wounded shoots or leaves. In wounded attached shoots and leaves, SEM at 24 h after inoculation, showed that conidia had germinated and germ tubes penetrated into the tissue. However, on the detached wounded shoots and leaves, the 2...
The mechanisms for dispersal of Botryosphaeria conidia,which can infect grapevines through wounds... more The mechanisms for dispersal of Botryosphaeria conidia,which can infect grapevines through wounds, were investigated to determine their seasonal prevalence in a New Zealand vineyard and to further develop control strategies. Airborne dispersal was investigated in April 2008 in four vineyards using Vaseline®-coated slides which were collected and replaced weekly. Inspection with a light microscope for characteristic Neofusicoccum and Diplodia conidia, distinguishable by their morphology and colour, found no conidia characteristic of the Botryosphaeriaceae although spores of other fungi were collected. Waterborne conidia were trapped by collecting rainwater that ran off the vines during May 2008–April 2009. The continuously collected rainwater suspensions were examined for characteristic conidia after every significant rainfall event. The rainwater suspensions yielded conidia of the Botryosphaeriaceae, with 59.8% of the conidia caught being Neofusicoccum spp. and 40.2% being Diplodia ...
Actinidia seed-borne latent virus (ASbLV, Betaflexiviridae, genus Prunevirus) was detected at hig... more Actinidia seed-borne latent virus (ASbLV, Betaflexiviridae, genus Prunevirus) was detected at high frequency in healthy seedlings grown from lines of imported seed in a New Zealand post-entry quarantine facility. To determine the route and efficiency of transmission of ASbLV in this dioecious crop species, we developed a rapid molecular protocol and identified a reliable progeny plant tissue to determine paternal and maternal transmission rates. The virus was detected at a high incidence (98%) in individual seeds, but cotyledon testing of seedlings from selected crosses confirmed staminate (male) transmission at high frequency (~ 60%), and pistillate (female) transmission at even higher frequency (~ 80%). The use of cotyledons allows non-destructive detection of ASbLV in very young seedlings that enables early screening of kiwifruit plants in nurseries to manage its spread to orchards. The high ASbLV transmission rates, whether from infected pollen or ovules, facilitate bulk testing...
European canker pathogen caused by the fungus Neonectria ditissima could not be isolated when inf... more European canker pathogen caused by the fungus Neonectria ditissima could not be isolated when infected woody tissues were plated directly onto potato dextrose agar (PDA) malt extract agar (MEA) or acidified PDA (pH 45) However the alternative media water agar (WA) and apple sapamended water agar (ASAWA) were successfully used to isolate the pathogen In the preparation of ASAWA green shoots of 1yearold fresh Scilate apple were frozen overnight then allowed to thaw The tissues were then centrifuged and the sap collected to prepare the medium Neonectria ditissima could be isolated from both symptomatic and asymptomatic apple tissues on both WA and ASAWA Both media supported the production of large numbers of conidia in vitro with more conidia being produced on ASAWA than on WA The conidia produced in vitro had morphological characteristics and pathogenicity similar to those produced in the field
Neonectria ditissima is a serious pathogen of apple. Low-virulent cultures of this fungus have be... more Neonectria ditissima is a serious pathogen of apple. Low-virulent cultures of this fungus have been isolated from cankers, but how and why low-virulent isolates can infect apple is unknown. Rasp wounds on ‘Royal Gala’ trees were inoculated with agar plugs from six low-virulent N. ditissima isolates in a glasshouse. Neonectria ditissima was re-isolated 10 weeks after inoculation. Agar plugs from the re-isolated cultures were used to inoculate ‘Royal Gala’ trees again. After the second re-isolation, conidial suspensions of the original cultures and the 2 x 6 re-isolates were used to determine the virulence on ‘Royal Gala’ compared with field-collected conidia. Three cultures did not cause any lesions; neither did their re-isolates. The re-isolates of two cultures did not differ in virulence compared with the originals. However, the virulence of one isolate increased with each re-isolation, with the second re-isolation causing significantly more lesions, lesion development occurring fa...
Bundles of dormant wood were submerged in water (45˚C for 45 min or 50˚C for 15 min), or were wra... more Bundles of dormant wood were submerged in water (45˚C for 45 min or 50˚C for 15 min), or were wrapped in moist cloth, placed inside zip-locked bags and submerged for 3—6 h or treated with one of three GRAS chemicals or untreated (two bundles per treatment). Scion wood was grafted onto ‘M9’ rootstocks then planted in a randomised order, with growth assessed after 16 weeks. Two of the GRAS treatments and submersion at 45˚C for either 45 min or 3 h in a bag did not significantly affect viability compared with the untreated control (83—95% viable). Submersion at 50˚C for 15 min reduced viability significantly (70%). Scions did not survive exposure to 50˚C for 3—5 h in bags…
Monitoring of disease progression by microscopy is an important component of the study of host-pa... more Monitoring of disease progression by microscopy is an important component of the study of host-pathogen interactions. The aim of this research was to investigate infection processes and the progression of Neofusicoccum luteum infection of grapevine leaves and shoots. Conidial suspensions (104 conidia mL-1) were inoculated onto wounded or non-wounded leaves and shoots of 18- month-old potted Pinot Noir vines growing in a shade house. The tissues remained attached, or were detached and incubated under high relaive humidity (RH) after inoculation. Scanning electron microscope (SEM) observation and pathogen re-isolation from the leaves at 24 to 72 h after inoculation and with the shoots at monthly intervals for 4 months. Results showed no infection in any non-wounded shoots or leaves. In wounded attached shoots and leaves, SEM at 24 h after inoculation, showed that conidia had germinated and germ tubes penetrated into the tissue. However, on the detached wounded shoots and leaves, the 2...
The mechanisms for dispersal of Botryosphaeria conidia,which can infect grapevines through wounds... more The mechanisms for dispersal of Botryosphaeria conidia,which can infect grapevines through wounds, were investigated to determine their seasonal prevalence in a New Zealand vineyard and to further develop control strategies. Airborne dispersal was investigated in April 2008 in four vineyards using Vaseline®-coated slides which were collected and replaced weekly. Inspection with a light microscope for characteristic Neofusicoccum and Diplodia conidia, distinguishable by their morphology and colour, found no conidia characteristic of the Botryosphaeriaceae although spores of other fungi were collected. Waterborne conidia were trapped by collecting rainwater that ran off the vines during May 2008–April 2009. The continuously collected rainwater suspensions were examined for characteristic conidia after every significant rainfall event. The rainwater suspensions yielded conidia of the Botryosphaeriaceae, with 59.8% of the conidia caught being Neofusicoccum spp. and 40.2% being Diplodia ...
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Papers by Nicholas Tabi Amponsah