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The pathogenicity of Alternaria spp. on Malus × domestica in New Zealand has not been investigated fully. Alternaria spp. were isolated from necrotic spots on leaves and fruit rots from various apple cultivars. Pathogenicity of 31 Alternaria spp. isolates was tested on excised ‘Royal Gala’, ‘Golden Delicious’ and ‘Scifresh’ leaves (wounded and unwounded) by measuring lesion diameters. Viability of Alternaria spp. grown from infected leaf material was assessed to compare various storage conditions. Alternaria spp. were consistently isolated from the central brown area of leaf lesions but could not be isolated from outside the leading edge or from the purple region surrounding the lesion. All isolates produced lesions on wounded leaves. Most isolates showed some pathogenicity on at least one cultivar, with lesions on unwounded leaves. Lesions on leaf material caused by Alternaria spp. can be stored for at least 11 weeks by freeze-drying or air-drying leaf material and storing at 0.5˚C or room temperature. Some New Zealand Alternaria spp. isolates on Malus × domestica are pathogenic on fruit and leaves. Further studies are needed to better understand the biology of this pathogen in New Zealand and determine a suitable control programme.

Experiments were carried out to compare fire blight resistance screening methodologies used in the German and New Zealand pipfruit breeding programmes. The small differences between the respective screening methodologies did not result in significant differences in the incidence of fire blight infection or the amount of resistance observed in plants. Differences in bacterial growth media, inoculum suspension and inoculation technique did not have a significant effect on the incidence of fire blight infection or the extent of resistance expression in various apple cultivars. Some of the Erwinia amylovora isolates had a significant effect on the level of disease expression on different cultivars. These differences can be used as tools to identify resistance quantitative trait loci in different cultivars. Results from these experiments have led to standardisation of screening methods between the two countries and provided confidence in comparing the findings of the New Zealand/German collaborative resistance research programme.

Several Actinidia spp. genotypes exhibit crown gall-like symptoms in both roots and canes. Galls form on roots and pruning wounds of canes. Investigations were undertaken to determine if an Agrobacterium species was responsible for gall formation in the Actinidia spp. material. Macerated galls were plated onto King’s B and various selective Agrobacterium agars, e.g. 1A and Roy & Sasser media. Bacterial isolates were tested by PCR for the presence of tumour-inducing (Ti) plasmids. Isolates that tested positive for the Ti plasmid were subsequently tested for pathogenicity by inoculation onto cut carrot discs, Nicotiana glutinosa and Solanum lycopersicum, and assessed for gall formation. Bacterial isolates that tested positive by PCR for the Ti plasmid were an orange tan colour on selective medium 1A, and clear with a red centre on the Roy & Sasser medium. Galls formed on cut carrots, S. lycopersicum and N. glutinosa after inoculation of Ti-positive bacterial isolates. Initial results indicate that an Agrobacterium species is associated with the formation of galls in Actinidia seedlings. However, biochemical characterisation and confirmation of Koch’s postulates using Actinidia species are needed for verification of this result.

Fire blight a bacterial disease caused by Erwinia amylovora is an ongoing problem for pipfruit growers with few control options available Most commercial cultivars and rootstocks are highly susceptible to the disease Breeding of fire blightresistant scions and rootstocks to manage the disease is a major goal of the New Zealand apple breeding programme The main mode of disease establishment is through flowers However the breeding programme currently evaluates disease resistance through shoot inoculations This study compared the degree of resistance in 109 progeny from a Royal Gala times; Malus robusta Robusta 5 family assessed by shoot inoculation and by floral inoculations Results indicate that the two measures of resistance do not correlate well and that different quantitative trait loci may be involved in flower and shoot resistance Management of fire blight through the implementation of resistant cultivars will require resistance screening on both shoot and flower assessments

Herbaceous indicator bioassays are used to screen for unwanted plant viruses on imported plant material To optimise virus detection the effect of plant nutrition was investigated to determine whether this plays a role in virus symptom expression and severity Apple stem grooving virus and Tobacco ringspot virus were inoculated onto a range of herbaceous indicator species grown in potting mix supplemented with differing rates of slowrelease fertiliser Higher rates of fertiliser resulted in better plant nutrition and a greater incidence of virus expression and more severe expression of disease in the seven indicator plant species Overall disease assessments indicated that plant nutrition affects plant growth virus infection rate and virus symptom expression As virus infection affects plant growth and leaf colour good plant nutrition is important to avoid masking virus symptoms and to optimise the detection of viruses in postentry quarantine facilities

Pollen is traded internationally as a source of germplasm and for pollination. Thirty-nine viruses and five viroids are known to be pollen transmitted. We investigated whether reverse transcription-polymerase chain reaction (RT-PCR) could be used to detect viruses reliably in pollen. Four extraction methods yielded nucleic acid in appropriate quantity and quality from Tobacco ringspot virus (TRSV)-infected pollen for RT-PCR

Fire blight, caused by the bacterium Erwinia amylovora (Burrill) Winslow et al., is one of the most serious diseases of pear. The development of pear cultivars with a durable resistance is extremely important for effective control of fire blight and is a key objective of most pear breeding programs throughout the world. We phenotyped seedlings from the interspecific pear population PEAR3 (PremP003, P. × bretschneideri × P. communis) × ‘Moonglow’ (P. communis) for fire blight resistance at two different geographic locations, in France and New Zealand, respectively, employing two local E. amylovora isolates. Using a genetic map constructed with single nucleotide polymorphism (SNP) and microsatellite (SSR) markers previously developed for this segregating population, we detected a major quantitative trait locus (QTL) on linkage group (LG)2 of ‘Moonglow’ (R 2 = 12.9–34.4 %), which was stable in both environments. We demonstrated that this QTL co-localizes with another major QTL for fire blight resistance previously detected in ‘Harrow Sweet’ and that the two favorable (i.e., resistant) alleles were not identical by descent. We also identified some smaller effect (R 2 = 8.1–14.8 %) QTLs derived from the susceptible parent PEAR3. We propose SNP and SSR markers linked to the large effect QTL on LG2 as candidates for marker-assisted breeding for fire blight resistance in pear.

Ascospore production from pseudothecia in apple leaf litter in the spring is a critical step in the disease cycle of Venturia inaequalis Leaf litter management is potentially an important component of an integrated pest and disease management strategy An orchard study was carried out in Hawkes Bay to investigate the relationships between the incidence of black spot on leaves in autumn the density of apple leaf litter on the orchard floor in spring and the number of ascospores produced in spring A total of 22 blocks on eight orchards were surveyed for black spot incidence in autumn 2000 The following spring remaining leaf litter was measured and ascospore production was quantified using spore traps Autumn black spot levels and spring litter levels were accurate predictors of spring ascospore production Management strategies employed on different blocks influenced spring leaf litter and ascospore levels Blocks with high autumn black spot generally had high spring ascospore production Management practices that substantially reduced litter levels resulted in reduced V inaequalis inoculum

Helicobasidium purpureum (anamorph Rhizoctonia crocorum) is the causal organism of the carrot disease violet root rot, common in the Ohakune region of New Zealand. Helicobasidium purpureum has proven a difficult organism to isolate and grow in culture, confounding diagnosis of early infections. To enable early diagnosis of the disease, a conventional PCR assay was developed with the primer sequences (HelicoPurp1 and HelicoPurp2, 101bp amplicon) targeting part of the internal transcribed spacer (ITS) region of the organism. The assay detected all 15 H. purpureum isolates collected and maintained by our laboratory in pure culture. The assay was also robust enough to detect the fungi’s full range of inoculum types from the field (sclerotia, hyphae, mycelial mats and ‘black sheaths’), and was also able to detect the fungus when it was in association with plant tissues. Samples required washing, as soil inhibited this assay.

Violet root rot (VRR), caused by the fungus Helicobasidium purpureum (anamorph Rhizoctonia crocorum), is a common problem for carrot growers in the Ohakune region of New Zealand. VRR can still be problematic even after many years of fallow, suggesting that alternative hosts may be maintaining and harbouring the disease. Seeds from a selection of common weed and pasture (ryegrass, clover and plantain) species sourced from the Ohakune area were planted into pots of steam-sterilised Ohakune soil and grown in the glasshouse. Following seedling establishment, pots were inoculated with H. purpureum. Four and a half months post inoculation, all plants were assessed visually, and then well-rinsed root samples were taken for DNA extraction and PCR testing. Of the nine weed species assessed, all tested positive for H. purpureum by PCR, and seven had visual symptoms on plants. For the twelve pasture species assessed, ten tested positive for H. purpureum by PCR, while eight had visual symptoms on plants. Some plants, in particular various clovers, plantain and dock, had numerous sclerotia on the outside of roots. These results indicate that alternate hosts in pasture or fallowed fields are capable of harbouring H. purpureum.

A sensitive conventional RTPCR assay has been developed for an uncharacterised virus within the family Betaflexiviridae prompted by detection of the virus in Actinidia seedlings held in postentry quarantine that had been grown from openpollinated seed Infection is asymptomatic and presently assessed as lowtozero biosecurity risk The assay targets the RNAdependent RNA polymerase (RdRP) of the virus primer sequences (BetaF2 and BetaR2 278bp amplicon) being based on a partial RdRP sequence for the virus The assay detects the nine virus isolates found to date in a range of sample types (fresh leaf stem cambium archived RNA) The assay which includes a multiplexed internal control has been accredited by International Accreditation New Zealand for Actinidia testing To support management of the virus the assay and associated RNA extraction method have been applied to testing dried Actinidia seed directly They have been found sufficiently sensitive to detect the virus in individual seeds Initial results show efficient transmission of the virus from infected pollen to the seed

Current tools for the control of fire blight disease of apples caused by Erwinia amylovora have limitations, including the increasing pressure by markets against the use of streptomycin. Coast Manuka and Coast Lema ® Oil products have been previously shown to provide control against some bacterial, fungal and yeast diseases. Experiments were carried out to determine whether either of these products provided control against Erwinia amylovora. Coast Lema Oil (0.5, 1, 2, 3, 4% w/v) inhibited E. amylovora when added to a bacterial suspension. Coast Manuka Oil (0-4% w/v) failed to inhibit E. amylovora when added to the bacterial suspension. It was also demonstrated that Coast Lema Oil (0.5, 1, 2, 3, 4% w/v) and Coast Manuka Oil (0.5, 1, 2, 3, 4% w/v) inhibited E. amylovora replication when added to agar. Filter paper discs soaked in Coast Lema Oil (2, 3, 4% w/v) caused small inhibition zones around the product when placed directly onto E. amylovora. Coast Manuka Oil (0-4% w/v) was unsuccessful in causing inhibition zones around the discs when placed directly onto E. amylovora. These initial results indicate that Lema oil has the potential to control fire blight in pipfruit trees.

Surveys to determine the phytosanitary status of apple (Malus) and pear (Pyrus) trees in New Zealand were conducted from 2005 to 2006 A total of 188 symptomatic and nonsymptomatic trees from various geographical locations were tested for the presence of a number of viruses and viroids by RTPCR All Malus samples were tested for Apple chlorotic leaf spot virus (ACLSV) Apple stem grooving virus (ASGV) Apple stem pitting virus (ASPV) Apple mosaic virus (ApMV) Apple scar skin viroid (ASSVd) Apple dimple fruit viroid (ADFVd) Cherry rasp leaf virus (CRLV) and Tomato ringspot virus (ToRSV) ACLSV was detected in 48 ASGV in 36 ASPV in 61 and ApMV in 45 of samples tested ASSVd ADFVd CRLV ToRSV were not detected in any of the 165 sampled Malus plants which provides evidence that they are not present in New Zealand All Pyrus samples were tested for ACLSV ASGV ASPV ApMV Pear latent virus (PeLV) and Pear blister canker viroid (PBCVd) ACLSV was detected in 17 ASGV in 13 ASPV in 17 and ApMV in 4 of sampled Pyrus trees PeLV and PBCVd were not detected in any of the 23 sampled symptomatic Pyrus trees which provides evidence that PeLV and PBCVd are not present in New Zealand

In 2012, trials were established in four kauri forest sites severely affected by kauri dieback (Phytophthora agathidicida = P. taxon Agathis, PTA) to determine the potential of phosphorous acid (phosphite) as a control tool. Baseline assessments of 162 trial trees included canopy disease rating, trunk lesion dimensions and lesion activity (recent bleeding/ oozing). Phosphite (Agrifos®600) at concentrations of 7.5% or 20% was injected (20 ml) at 20-cm intervals around the trunk. Control trees were left untreated. After 1 year, half the previously injected trees were re-injected, in all cases with 7.5% phosphite. Phytotoxicity symptoms (leaf yellowing, browning or leaf/twig abscission) were noted in some phosphite- injected trees, particularly where the 20% concentration was used. After 3 years, many more trunk lesions remained active (expressing ooze, continued expansion) in untreated trees (58.5%) than in phosphite-treated trees (0.8%). Average lesion expansion after 3 years was 12.7 cm in untreated and 0.4 cm in phosphite-treated trees.