Population Dynamics of Colletotrichum Gloeosporioides on Different Parts of an Avocado (Persea Americana) Tree (original) (raw)
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Specialization of a fungal pathogen on host tree species in a cross-inoculation experiment
Journal of Ecology, 2011
1. In forest communities, the Janzen-Connell (J-C) model proposes that species diversity is maintained by noncompetitive distance-or density-dependent seedling mortality caused by host-specific natural enemies. Host specificity, however, has not been fully elucidated. 2. We conducted a cross-inoculation experiment to evaluate the host specificity of a pathogenic fungus, Colletotrichum anthrisci. The fungus was isolated from seedlings of four tree species (Prunus grayana, Fraxinus lanuginosa, Cornus controversa and Magnolia obovata), all of which were killed by damping-off disease beneath conspecific adults. Each fungal isolate was then inoculated into seedlings of P. grayana and F. lanuginosa. Molecular identification [internal transcribed spacer (ITS) sequences] also confirmed that all isolates (strains) showed 99-100% similarity with C. anthrisci, irrespective of their origin. 3. In both P. grayana and F. lanuginosa seedlings, all isolates of the pathogen caused damage, irrespective of origin, but the damage was more severe with the isolate from conspecifics rather than from any of the three heterospecifics. 4. In response to infection, callose papillae were deposited on the inner side of the leaf cell wall of seedlings in P. grayana; then, circular abscission layers formed between two layers of leaf cells surrounding the locus of infection. The central area of the infection was completely cut off from the rest of the leaf. In F. lanuginosa, infected leaves of seedlings were shed immediately after inoculation. This defensive behaviour, which may prevent further pathogen invasion, was more frequent in seedlings inoculated with isolates from conspecifics than from heterospecifics in both species. 5. Synthesis. Although the pathogenic fungus C. anthrisci is ubiquitous and attacks a wide range of host species, virulence was much stronger for strains derived from conspecifics rather than from heterospecifics, suggesting local adaptation and development of host specificity. If host specificity is common for several pathogens within a microbial community in a given area occupied by an adult, and the trait is also common for multiple tree species co-occurring within a forest community, the J-C model would be applicable to explain tree species diversity.
Pathogens of forrest trees in nurseries –a minireview
JOURNAL OF ADVANCES IN AGRICULTURE
The forest trees nurseries are attacked by different pathogens which are causing important damages and economic loss in forest commercial exploitations. One of the most important losses are in the tree nurseries, damaging the trees in their first stages of life Main pathogens for roots and stems are shown in this work. The fungi described may atack many agricultural cultures, and only some of them are specific for forest trees. The economic damages can be semnificatives. Some solutions for prevention and treatment of fungal pathogens attack are discussed further.
Fungal Ecology, 2016
We report an endemic entomopathogenic fungus, known in Brazil as the 'salmão' fungus and identified here as Colletotrichum nymphaeae (Sordariomycetes: Glomerellales), infecting populations of citrus orthezia scale, Praelongorthezia praelonga. The seasonal prevalence of this pathogen in P. praelonga populations was investigated in three commercial citrus groves maintained under different pesticide regimes. Two citrus groves included inundative releases of another insect pathogenic fungus, Lecanicillium longisporum. Natural epizootics were consistently observed, with up to 84% infection rates being recorded during the warm rainy season. Temporal progression of C. nymphaeae-induced disease varied among the three pesticide regimes. Low infection levels from C. nymphaeae were associated with intensive application of broad spectrum pesticides. However, the prevalence of C. nymphaeae followed a density-dependent pattern with insect host abundance, irrespective of the pesticide regime. High proportions of Lecanicillium-infected insects were observed following infection peaks of C. nymphaeae and both fungi together contributed to 95% overall mortality of citrus orthezia during the wet season. Hence, the combined effect of both fungi considerably improves the biological control of citrus orthezia. We also surmise that the host abundance, environmental conditions, and application frequency of chemical pesticides in citrus groves exert a great influence in the seasonal prevalence of C. nymphaeae-induced disease. Altogether, these results suggest that C. nymphaeae is an important pathogen of P. praelonga and indicate that frequent use of synthetic pesticides may delay or reduce fungal epizootics.
African Entomology, 2023
Entomopathogenic fungi (EPF) are cosmopolitan soil borne pathogens that cause epizootics in various insect orders. EPF isolates of Metarhizium brunneum and M. pinghaense have shown the potential for use as biological agents of important agricultural insect pests. The aim of the current study was to test for the persistence of M. brunneum and M. pinghaense on apple bark over a period of three weeks, under laboratory conditions. Apple bark was sprayed with conidial suspensions of both fungi, at a standard infective conidial concentration of 10 7 conidia/ml. The persistence, or survival, of the conidia on apple bark was measured using codling moth larvae (CM) (Cydia pomonella) and females of woolly apple aphid (WAA) (Eriosoma lanigerum) as indicator species. The results showed that conidia of M. pinghaense can induce mortality of insect pests through contact with an EPF-treated substrate, with mortality of 39% to 82% for WAA over a period of 10 days post application, and with mortality of 3% to 68% for CM over a period of 7 days, after application to apple bark. Further evaluation showed that the conidia of M. pinghaense persisted longer on apple bark, up to 63%, than did M. brunneum, up to 11%, three weeks post application of the conidial suspensions. The study provides insights into the potential persistence of fungal isolates on apple bark over time post application. Further evaluation of the persistence of the isolates on apple bark under both glasshouse and field conditions should be conducted.
Annals of Applied Biology, 1980
Phytophthora colocasiae was successfully isolated by baiting with detergenttreated taro leaf discs 8 cm diameter placed on water slurries of soil, on suspensions of macerated infected leaf lesions or on the washings from petioles of harvested plants. Taro root tips, detached or left on corms, were not susceptible to zoospores of P. colocasiae nor were detached root tips of Lupinus angustifolius. Cubes o f taro corm used as baits, and agar selective for Phycomycetes which was inoculated directly with soil, both became too heavily overrun by Phythium splendens to allow detection of P. colocasiae. Investigations indicated that inoculum on lesions of detached leaves and in soil remains viable for only a few days. Petiole bases which comprise the bulk of the 'tops' used for vegetative propagation, lost detectable natural inoculum rapidly (2 days) if stored dry, but less rapidly (14 days) if planted immediately in the field. Artifically augmenting surface inoculum with naturally produced sporangia considerably extended the periods of detectability, probably by increasing the chances that a few propagules would survive, especially during dry storage. Incubation of inoculated tops in high humidity led to active infection and sporulation on petioles, especially on cut ends, a situation that might be paralleled under suitable moisture conditions in the field. Of several aroid species tested by artificial inoculation only Alocasia macrorrhiza was susceptible. Natural infection of this plant has not been seen, making it an unlikely alternate host of P. colocasiae under field conditions. Thus perennation between taro crops is effected by shortlived surface propagules and possibly also by mycelium within lesions on petioles. Reduction of the former and prevention of the latter might be achieved by dry storage of tops for 2 to 3 wk.
American Journal of Botany, 2001
This study assessed the levels of damage by leaf pathogens and their variability in terms of host species, space (four mature forest sites) and season of the year (dry and rainy), and the mechanisms of infection in the understory of the Los Tuxtlas tropical rain forest. Sixty-five percent of the species surveyed in the dry season (N ϭ 49) and 64.9% of those surveyed in the rainy season (N ϭ 57) were damaged by fungi. Leaf area damaged per plant, on average, was Ͻ1% (range: 0.25-20.52%). There was considerable variation in the degree of infection among species, but not among sites and seasons. The survey showed that 43% of the leaves were damaged by herbivores and pathogens concurrently, 16% showed damage by insect herbivory alone, and only 1.4% of the sampled leaves showed damage by pathogens alone. Pathogenicity assays experimentally confirmed that the predominant mechanism of fungal establishment was wounding, such as that caused by herbivory (or other similar sources), and only rarely did infection occur through direct contact (without wounds). The results revealed the omnipresence of leaf fungal infection, although with low damage per plant, and the importance of herbivorous insects in the facilitation of fungal infection in tropical understory plants.