Evolution of the population structure of Venturia inaequalis,the apple scab fungus,associated with the domestication of its host

Evaluating the impact of plant domestication on the population structure of the associated pathogens provides an opportunity to increase our understanding of how and why diseases emerge. Here, we investigated the evolution of the population structure of the apple scab fungus Venturia inaequalis in response to the domestication of its host. Inferences were drawn from multilocus microsatellite data obtained from samples collected on (i) the Central Asian Malus sieversii, the main progenitor of apple, (ii) the European crabapple, Malus sylvestris, a secondary progenitor of apple, and (iii) the cultivated apple, Malus×domestica, in orchards from Europe and Central Asia. Using clustering methods, we identified three distinct populations: (i) a large European population on domesticated and wild apples, (ii) a large Central Asian population on domesticated and wild apples in urban and agricultural areas, and (iii) a more geographically restricted population in M. sieversii forests growing in the eastern mountains of Kazakhstan. Unique allele richness and divergence time estimates supported a host‐tracking co‐evolutionary scenario in which this latter population represents a relict of the ancestral populations from which current populations found in human‐managed habitats were derived. Our analyses indicated that the domestication of apple induced a significant change in the genetic differentiation of populations of V. inaequalis in its centre of origin, but had little impact on its population dynamics and mating system. We discuss how the structure of the apple‐based agrosystem may have restricted changes in the population structure of the fungus in response to the domestication of its host.     

Small‐plot studies comparing pheromone and juice baits for mass‐trapping invasive Synanthedon myopaeformis in Canada

Recent introduction of Synanthedon myopaeformis (Borkhausen) (Lepidoptera: Sesiidae) into organic apple‐growing areas of Canada has stimulated research on semiochemical‐based management of this European pest. Replicated, small‐plot (0.16 ha) experiments were conducted to compare sex pheromone, 3Z,13Z‐octadecadienyl acetate (10 mg), Concord grape juice (300 ml), or their combination, as mass‐trapping lures at trap densities equivalent to 12.5, 25, 50, and 100 traps ha^?1. Total numbers of male and female moths removed from test plots increased significantly with trap density in all juice‐based mass‐trapping experiments. In pheromone mass‐trapping experiments, however, total catches of males did not increase significantly as trap densities were increased and catches appeared to plateau with 25–50 traps ha^?1. With pheromone‐based mass‐trapping, significantly fewer males were caught in pheromone‐baited assessment traps at the centre of each mass‐trapping plot than in identical traps in untreated plots. This reduction is indicative of significant trap interference or trap ‘shut‐down’. Increasing the density of juice‐based mass‐trapping had no effect on catches of male or female moths in juice‐baited assessment traps, indicating a short range of attraction and lack of interference between juice traps. Pheromone‐ and juice‐based mass trapping removed similar numbers of males at each trap density tested, respectively, but summed catches of males and females were greatest with juice baits. Combining pheromone and juice into a single mass‐trapping treatment (50 traps ha^?1) did not significantly increase catches of males or females relative to either treatment alone. If a practical bisexual mass‐trapping system is going to be developed for S. myopaeformis, then identification of volatile kairomones in Concord grape juice may be useful.     

Resistance to the pink potato aphid, Macrosiphum euphorbiae, in two accessions of Lycopersicon hirsutum f. glabratum

An integrated programme of pheromone-mediated mating disruption using Isomate-C®, post-harvest removal of fruit, and trapping overwintering larvae with cardboard tree bands, was used to control codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), in four commercial organic apple orchards in Cawston, British Columbia during 1989–1992. One application of 1000 dispensers ^{– 1} on May 1 delivered estimated seasonal totals of 16.6, 16.5 and 19.9 g of E,E-8,10-dodecadien-1-ol [=codlemone] ^{– 1}in 1990, 1991 and 1992, respectively, at median rates of 8.4, 8.3, and 13.3 mg · < ha^–1 · ha^–1 during dusk flight periods of first brood and 5.3, 4.7 and 4.6 mg · ^{– 1}· ha^–1 in second brood, respectively. Over this 3-year period damage from codling moth at harvest ranged from 0.08 to 2.4%, and averaged 60.7% in these four organic orchards, while damage in five conventional orchards receiving sprays of azinphosmethyl ranged from 0.02 to 1.85%, and averaged 0.5%. Damage in an experimental orchard that was banded only, ranged from 43.5 to 56.7%, and averaged 48.9%. Between 1990 and 1992 cumulative male catches in Pherocon 1-CP wing traps baited with 10 mg of codlemone declined by 52% and densities of overwintering codling moth larvae declined an average of 49.5% in all organic orchards. Overwintering populations in the banded experimental orchard showed an increase of 57.7% during this study period. We conclude that an integrated programme of pheromone-mediated mating disruption, post-harvest fruit removal and tree banding, controls codling moth effectively enough to make organic apple production viable in British Columbia.     

Factors affecting the presence of Typhlodromusspp. (Acarina: Phytoseiidae) in the calyx cavities of apple fruits and implications for integrated pest management

Predatory mites of the family Phytoseiidae include several species of importance as biological control agents of phytophagous mites in various crops including apples. We report on the post-harvest presence of the motiles of two species, Typhlodromus occidentalis and Typhlodromus pyri, in the calyx cavities of apple fruits of three cultivars. The mean numbers of motiles per fruit were as high as 6.10. The phytoseiid densities were lowest in cv. Bonza and tended to be greater in samples taken in late autumn, particularly in cv. Red Delicious. No significant effect (p > 0.05) was observed for different insecticide treatments. Phytoseiids remained present within fruits of cv. Granny Smith left on the orchard floor in winter. Together with an observed reduction in the numbers of T. occidentalis in the early spring, this suggests that fruits constitute an overwintering refuge. The findings are discussed in relation to the implications for biological control, in particular the minimization of the removal of natural enemies from orchards. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microbial population dynamics on Golden Delicious apples from bud to harvest and effect of fungicide applications

The microbial population dynamics on apples cv. Golden Delicious were analysed every 15 days between bud and harvest in a fully replicated experiment in northern Spain in 1994 and 1995. The total microbial populations varied with developmental stage, and with prevailing climatic conditions. The predominant mycroflora were the filamentous fungi Cladosporium and Alternaria spp. and white and pink yeasts. Other genera isolated included mainly species of Epicoccum, Fusarium and Acremonium. However, the most important post-harvest pathogens Penicillium expansum and Botrytis cinerea were seldom isolated from ripening apples. Maximum total filamentous fungal populations occurred after fruit set and during early ripening [2 × 10⁴cfu (colony-forming units) g^-1 approximately] while those of bacteria were maximum at bud stage (3.5 × 10⁵and 3.0 × 10⁴ cfu g^-1 in 1994 and 1995 respectively). White yeasts were more numerous than pink yeasts. Endophytic infection of apple buds by Alternaria spp., responsible for core rot, was found in almost all bud tissue. By contrast, Cladosporium spp. were initially isolated later from 12.5–50% of tissue samples during blooming and fruit set. The impact of a four-spray fungicide regime during apple development significantly decreased the total filamentous fungal populations in both years, and that of Cladosporium spp. in 1994. However, bacterial populations were often higher on apples from fungicide-treated plots. Fungicide sprays decreased populations of Cladosporium, Alternaria and white yeasts for a maximum of up to 15–30 days after application. Fungicide application had little effect on endophytic infection of apples by Alternaria spp. between bud and harvest.     

Historical tests of the toxicity of pesticides to Typhlodromus pyri (Acari: Phytoseiidae) and their relevance to current pest management in New Zealand apple orchards 2. Short-term field tests

A two-part review is presented relating historical tests of the toxicity of pesticides to Typhlodromus pyri and their relevance to modern pest management in New Zealand pome-fruit orchards. Over the past 30 years, the initial need for T. pyri to be resistant to broad-spectrum pesticides has substantially declined as a growing array of new selective chemicals have come into use. In Part 2, a short-term field test is described for determining the toxicity of single applications of pesticides at recommended rates to European red mite (ERM), Panonychus ulmi, and its predator, an organophosphate (OP)-resistant strain of T. pyri on apples in New Zealand. For each pesticide, changes in mite density were measured from pre-treatment to 2, 7 and up to 25 days post-treatment compared with a water-sprayed control. Density was recorded and analysed for live adult and immature ERM, and live and dead eggs, larvae, nymphs and adults of T. pyri. Fifteen acaricides, 17 fungicides and 17 insecticides were evaluated. Chemicals more toxic to T. pyri than ERM were aminocarb, amitraz, binapacryl, chlordimeform, etrimphos, fenvalerate + azinphos-methyl, mancozeb + dinocap, methidathion, methiocarb, omethoate, oxamyl, pirimiphos-methyl and pyrazophos. Chemicals equally or less toxic to T. pyri than to ERM were acequinocyl, azocyclotin, benzoximate, bromopropylate, chlorpyrifos, clofentezine, cycloprate, cyhexatin, dinocap, mineral oil, propargite, triazophos and vamidothion. The remaining 23 chemicals (primarily fungicides and OP insecticides) had slight or no toxicity to ERM and T.pyri. The short-term field tests provided a useful guide to the long-term effects on ERM and T. pyri populations of almost all the pesticides. However, the potential disruptive effect of pyrazophos was not found in long-term field trials, and conversely, the apparently harmless dithiocarbamate fungicides were later shown to be highly disruptive when repeatedly sprayed, as in commercial practice. Most of the chemicals tested are no longer used in commercial pome-fruit orchards in New Zealand, all of which now practise integrated fruit production or organic fruit production based on selective pest management methods. The tested pesticides of continuing importance are identified and discussed with special emphasis on the current need to retest for dithiocarbamate resistance in T. pyri, some populations of which have been exposed to these compounds for up to 40 years. This and the changes in pesticide use in New Zealand are paralleled by similar developments in most pome-fruit growing areas of the world.     

Aureobasidium pullulans as a biocontrol agent of postharvest pathogens of apples in Uruguay

Aureobasidium pullulans was the microorganism most frequently recovered from the surface of apple fruit (cv. Red Delicious) stored in commercial cold chambers for 6 months. In the present work, 10 isolates of Aureobasidium pullulans were assayed to determine if they could control blue and grey mold disease of apple during cold storage. Although nine of 10 isolates, significantly reduced the percentage of decayed wounds when compared to the control, one of them, designated isolate ApB, showed the highest levels of protection. ApB was able to grow in a wide range of temperatures lower than 35°C, which is an important human health safety factor. ApB was resistant to thiabendazole, iprodione and imazalil, the most commonly commercially applied fungicides in postharvest treatment of apples in Uruguay. Regarding the mechanisms of action of the selected biocontrol agent, lytic enzymes did not seem to play a central role. ApB depleted iron from nutrient media, which may be an important aspect of its ability to inhibit Botrytis cinerea. Further experiments are needed, however, to determine if the depletion of iron is caused by the production of siderophores, by the immobilization of iron in an insoluble pigment, or a combination of both.     

Investigation of the radiation effects on Brown Rot disease of Golden Delicious apples,inoculated with the fungus Monilinia fructigena

The effects of 0, 1.5 and 3 KGy gamma-irradiation on Brown Rot disease affecting Golden Delicious apples are investigated. The apples were artificially inoculated with Monilinia fructigena fungus before and after irradiation. Results show clearly that radiation induces a delay in fungus development, even when it is not directly affected. The effect of radiation on the apples' substrate seems to be considerable, being the main factor affecting fungal growth. Radiation doses of 1.5 and 3 KGy do not seem to produce strong differences in the fungal growth. Irradiation, however, is very effective, producing important changes of practical interest for apples infected before or after irradiation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Life history and mortality factors of Agrilus mali Matsumura (Coleoptera: Buprestidae) in wild apples in Northwestern China

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