Induced Resistance: Potential for Control of Postharvest Diseases of Horticultural Crops

Fortunately, plants have developed highly effective mechanisms with which to defend themselves when attacked by potentially disease-causing microorganisms. If not, then they would succumb to the many pathogenic fungi, bacteria, viruses, nematodes and insect pests, and disease would prevail. These natural defence systems of plants can be deliberately activated to provide some protection against the major pathogens responsible for causing severe yield losses in agricultural and horticultural crops. This is the basis of what is known as ‘induced’ or ‘acquired’ disease resistance in plants. Although the phenomenon of induced resistance has been known amongst plant pathologists for over 100 years, its inclusion into pest and disease management programmes has been a relatively recent development, ie. within the last 5 years. This review will discuss very briefly some of the characteristics of the induced resistance phenomenon, outline some of the advantages and limitations to its implementation and provide some examples within a postharvest pathology context. Finally some approaches being investigated by the fruit pathology team at DPI Indooroopilly and collaborators will be outlined.

Sustained genetic control of wheat rust diseases in north-eastern Australia

Control of wheat rusts in north-eastern Australia has been based on resistance breeding since the early 1920s. It has been an enduring journey of discovery, disappointment, and achievement, which has culminated in a pool of knowledge and expertise upon which today's plant breeders can efficiently target durable resistance to the major rust diseases. This paper outlines significant advances in genetic control of rusts in the region, with particular emphasis on the invaluable role played by the University of Sydney rust control program and its influence on wheat breeding in the region and throughout Australia. This paper is part of ‘Global Landscapes in Cereal Rust Control’, see Aust. J. Agric. Res. Vol. 58, no. 6.

Evaluation of the use of prochloraz in the control of postharvest diseases of papaya in Australia

Prochloraz as Sportak at 450 g a.i./L is registered for the control of postharvest diseases in papaya in Australia. A project in far north Queensland in 2011, examined the use patterns of postharvest treatments, evaluated treatment dips and sprays for prochloraz concentrations and evaluated the efficacy of prochloraz at 0, 20, 40, 55 and 70 ml/100 L, fludioxonil as Scholar at 260 ml/100 L and azoxystrobin as Amistar at 50 ml/100 L. Results showed that packing shed use of Sportak varied with recycled and stored solutions showing a depletion of the active ingredient. Measured prochloraz in solution was highly pH dependent with nominal solution values only being measured when the pH was less than 3.0. In the fungicide efficacy trial Sportak at the label rate of 55 ml/100 L provided more effective disease control than fludioxonil and azoxystrobin. The trial also suggested that fruit from older trees showed a high degree of disease incidence relative to fruit from young trees.

Comparison of fungicide dips efficacies for the control of mango postharvest diseases

The shelf-life of mangoes is limited by two main postharvest diseases when not consistently managed. These are anthracnose ( Colletotrichum gloeosporioides) and stem end rots ( Neofusicoccum parvum). The management of these diseases has often relied mainly on the use of fungicide applications either as field spray treatments and/or postharvest dips. Current postharvest dips are under continuous threats because of health concerns and the maximum residue levels allowed on treated fruit continuous to be reviewed and re-assessed. Research needs to keep up with the rate at which changes are occurring following some of these reviews. The recent withdrawal of carbendazin (Spinflo), as a postharvest dip being used to manage stem end rots necessitated the urgent search for a replacement fungicide to manage this disease. A study was therefore undertaken to compare the efficacy of current and potential products that could be used to fill the gap. The following products were evaluated: Carbendazin (Spinflo), Prochloraz (Sportak), Thiobendazole (TBZ) and Fludioxonil (Scholar). These products were tested both under ambient temperatures and as hot dips to identify one that was most effective. Scholar as a hot dip was the most effective product among the ones compared. It effectively controlled both anthracnose and stem end rots at highly significant levels when compared to the untreated control and even Spinflo which is being replaced. As a cold dip, it had some limited effect on anthracnose but had virtually no effect on stem end rots. Based on its performance in these experiments, the product has been recommended for rates and residue studies so that it can be registered as a hot dip for use in controlling postharvest diseases of mangoes.

Cucumber mosaic virus infection of kava (Piper methysticum) and implications for cultural control of kava dieback disease

Cucumber mosaic virus (CMV) was found by reverse transcription polymerase chain reaction (RT-PCR) to be not fully systemic in naturally infected kava (Piper methysticum) plants in Fiji. Twenty-six of 48 samples (54%) from various tissues of three recently infected plants were CMV-positive compared with 7/51 samples (14%) from three long-term infections (plants affected by dieback for more than 1 year). The virus was also found to have a limited ability to move into newly formed stems. CMV was detected in only 2/23 samples taken from re-growth stems arising from known CMV infected/dieback affected plants. Mechanical inoculation experiments conducted in Fiji indicate that the known kava intercrop plants banana (Musa spp.), pineapple (Ananas comosus), peanut (Arachis hypogaea) and the common weed Mikania micrantha are potential hosts for a dieback-causing strain of CMV It was not possible to transmit the virus mechanically to the common kava intercrop plants taro (Colocasia esculenta), Xanthosoma sp., sweet potato (Ipomoea batatas), yam (Dioscorea alata), papaya (Carica papaya) or the weed Momordica charantia. Implications of the results of this research on a possible integrated disease management strategy are discussed.

Control of Burrowing Nematodes

Control of Burrowing Nematodes.

A review of the biology, ecology, distribution and control of Mozambique tilapia, Oreochromis mossambicus (Peters 1852) (Pisces: Cichlidae) with particular emphasis on invasive Australian populations

Oreochromis mossambicus (Peters 1852) are native to the eastward flowing rivers of central and southern Africa but from the early 1930s they have been widely distributed around the world for aquaculture and for biological control of weeds and insects. While O. mossambicus are now not commonly used as an aquaculture species, the biological traits that made them a popular culture species including tolerance to wide ranging ecological conditions, generalist dietary requirements and rapid reproduction with maternal care have also made them a 'model' invader. Self-sustaining populations now exist in almost every region to which they have been imported. In Australia, since their introduction in the 1970s, O. mossambicus have become established in catchments along the east and west coasts and have the potential to colonise other adjacent drainages. It is thought that intentional translocations are likely to be the most significant factor in their spread in Australia. The ecological and physical tolerances and preferences, reproductive behaviour, hybridization and the high degree of plasticity in the life history traits of O. mossambicus are reviewed. Impacts of O. mossambicus on natural ecosystems including competitive displacement of native species, habitat alteration, predation and as a vector in the spread of diseases are discussed. Potential methods for eradicating or controlling invasive populations of O. mossambicus including physical removal, piscicides, screens, environmental management and genetic technologies are outlined.

The potential for monitoring and control of insect pests in Southern Hemisphere forestry plantations using semiochemicals

Southern Hemisphere plantation forestry has grown substantially over the past few decades and will play an increasing role in fibre production and carbon sequestration in future. The sustainability of these plantations is, however, increasingly under pressure from introduced pests. This pressure requires an urgent and matching increase in the speed and efficiency at which tools are developed to monitor and control these pests. To consider the potential role of semiochemicals to address the need for more efficient pest control in Southern Hemisphere plantations, particularly by drawing from research in other parts of the world. Semiochemical research in forestry has grown exponentially over the last 40 years but has been almost exclusively focussed on Northern Hemisphere forests. In these forests, semiochemicals have played an important role to enhance the efficiency of integrated pest management programmes. An analysis of semiochemical research from 1970 to 2010 showed a rapid increase over time. It also indicated that pheromones have been the most extensively studied type of semiochemical in forestry, contributing to 92% of the semiochemical literature over this period, compared with research on plant kairomones. This research has led to numerous applications in detection of new invasions, monitoring population levels and spread, in addition to controlling pests by mass trapping or disrupting of aggregation and mating signals. The value of semiochemicals as an environmentally benign and efficient approach to managing forest plantation pests in the Southern Hemisphere seems obvious. There is, however, a lack of research capacity and focus to optimally capture this opportunity. Given the pressure from increasing numbers of pests and reduced opportunities to use pesticides, there is some urgency to develop semiochemical research capacity.

Biological control of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in gerberas, chrysanthemums and roses

Frankliniella occidentalis (Pergande), western flower thrips (WFT), is a major worldwide pest of vegetables and ornamental crops. The biology of WFT was examined on gerberas, chrysanthemums and roses in relation to plant stage (flowering and non-flowering), pupation site, soil moisture and plant parts often inhabited by adult and immature thrips. Four foliage thrips predators ( Transeius montdorensis (Schicha), Orius armatus (Gross), Mallada signata (Schneider) and Neoseiulus cucumeris (Oudemans)) and three soil predators ( Geolaelaps aculeifer (Canestrini), Steinernema feltiae (Filipjev) and Dalotia coriaria (Kraatz)) were studied to determine their ability to reduce the numbers of WFT on gerberas, chrysanthemums and roses. There was no difference in the number of adults that emerged from growing media of high or low moisture content on any host plant. There were also no differences in the total numbers of WFT recaptured from flowering gerberas, chrysanthemums or roses. However, about seven times the number of thrips were collected from flowering chrysanthemums compared with non-flowering chrysanthemums, indicating that the flowering plants were more suitable hosts. Of all thrips recollected, the greatest percentage was immature (larval and pupal) thrips (70%, 71% and 43%) on the flowers for gerberas, chrysanthemums and roses, respectively. The mean percentage of thrips that emerged as adults from the soil was very low (5.31.2, 8.52.9, 20.59.1 and 28.25.6%) on gerberas, flowering and non-flowering chrysanthemums, and roses, respectively. Simultaneous release of foliage and soil predators did not reduce the number of thrips beyond that caused by foliage predators alone. Of the foliage predators, T. montdorensis, O. armatus and N. cucumeris performed best, significantly reducing the numbers of adult and immature thrips on flowers and foliage by 30-99%. Further research is required to determine the most cost-effective rates of release in cut flower crops.

Evaluation of chlorothalonil and paraffinic oil alone and in combinations with registered fungicides for the control of yellow Sigatoka (Mycosphaerella musicola) of bananas in Northern Queensland, Australia

The efficacy of chlorothalonil and paraffinic oil alone and in combinations with the registered fungicides propiconazole, tebuconazole, difenoconazole, epoxiconazole and pyrimethanil was evaluated in a field experiment over two cropping cycles in 2013 and 2014 in Northern Queensland, Australia, for control of yellow Sigatoka (caused by Mycosphaerella musicola) of banana. The predominantly applied by the banana industry treatment mancozeb with paraffinic oil was included for comparison. The results from the two cropping cycles suggested that all chemicals used with paraffinic oil were as effective or more effective than when applied with chlorothalonil, and chlorothalonil alone. Difenoconazole and epoxiconazole with paraffinic oil followed by propiconazole with paraffinic oil were the most effective treatments. Pyrimethanil and tebuconazole plus chlorothalonil were the least effective treatments. None of the chemical treatments was phytotoxic or reduced yield.

Potential of Trichoderma harzianum for control of banana leaf fungal pathogens when applied with a food source and an organic adjuvant

Trichoderma isolates were obtained from diseased leaves and fruit collected from plantations in the main banana production area in Northern Queensland. Phylogenetic analyses identified the Trichoderma isolates as T. harzianum and T. virens. The Trichoderma spp. were found to be antagonistic against the banana leaf pathogens Mycosphaerella musicola, Cordana musae, and Deight-oniella torulosa in vitro. Several products used by the banana industry to increase production, including molasses, Fishoil and Seasol, were tested as food source for the Trichoderma isolates. The optimal food substrate was found to be molasses at a concentration of 5 %, which when used in combination with a di-1-p-menthene spreader-sticker enhanced the survivability of Trichoderma populations under natural conditions. This formulation suppressed D. torulosa development under glasshouse conditions. Furthermore, high sensitivity was observed towards the protectant fungicide Mancozeb but Biopest oil (R), a paraffinic oil, only marginally suppressed the growth of Trichoderma isolates in vitro. Thus, this protocol represents a potential to manage banana leaf pathogens as a part of an integrated disease approach.

Control of grey mould and stem-end rot in strawberry plants growing in a subtropical environment

The effect of different fungicide programs on grey mould (caused by Botrytis cinerea) and stem-end rot (caused by Gnomoniopsis fructicola) affecting strawberry plants (Fragaria ×ananassa cv. Festival) was studied in subtropical Australia over three years. The treatments involved a range of different synthetic multi- and single-site fungicides with different modes of action, a plant-defence promoter, plant extracts (lupin and rhubarb), organic acids, fatty acids, a salt, two strains of Bacillus subtilis, and single strains of B. amyloliquefaciens, Streptomyces lydicus and Trichoderma harzianum. Standard programs based on captan and thiram alternated, and applied with iprodione, fenhexamid, cyprodinil + fludioxonil, and penthiopyrad resulted in 3–4 % of unmarketable fruit compared with 25–38 % in the water-treated controls. There was no difference in the level of disease suppression when five or thirteen applications of single-site fungicides were rotated with the two multi-site fungicides. The incidence of unmarketable fruit was similar to the standard programs using isopyrazam (in 1 year out of 2), or penthiopyrad, fluazinam, chlorothalonil or thiram alone (in 1 year out of 1). The other fungicide programs were generally less effective. There were strong relationships between marketable yield and the incidence of unmarketable fruit over the three years (R2s = 0.82–0.93). A strategy based on thiram and captan applied alternately, with reduced applications of single-site fungicides is recommended and should reduce the chance of resistance to single-site fungicides becoming widespread in populations of the grey mould fungus. Although the program based on thiram alone had a similar incidence of unmarketable fruit as the standard program, repeated weekly applications of thiram are not recommended as they may cause unacceptable residues in the fruit. There were issues with some of the other fungicides due to phytotoxicity, residues, or difficulties with registering new fungicides that are in the same chemical group as currently registered products.

A comparison of the performance and biological efficiency of new knapsack sprayers and a controlled droplet application (CDA) sprayer for the control of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae)

Field trials and laboratory bioassays were undertaken to compare the performance and efficacy (mortality of diamondback moth larvae) of insecticides applied to cabbages with three high volume hydraulic knapsack sprayers (NS-16, PB-20 and Selecta 12V) and a controlled droplet application (CDA) sprayer. In field experiments, the high volume knapsack sprayers (application rate 500-600 L ha-') provided better spray coverage on the upper and lower surfaces of inner leaves, the upper surfaces of middle and outer leaves, and greater biological efficacy than the CDA sprayer (application rate 20~40 L ha-'). The PB-20 provided better spray coverage on the upper surface of middle leaves and both Surfaces of outer leaves when compared with the Selecta I2V. However, its biological efficacy in the field was not significantly different from that of the other high volume sprayers. Increasing the application rate from 20 to 40 L ha - ' for the CDA sprayer significantly increased droplet density but had no impact on test insect mortality. Laboratory evaluations of biological efficacy yielded higher estimates than field evaluations and there was no significant difference between the performance of the PB-20 and the CDA sprayer. Significant positive relationships were detected between insect mortality and droplet density deposited for both the PB-20 and the CDA sprayers