CHANCRO RESINOSO DEL PINO (FUSARIUM CIRCINATUM) HISTORIA, EVOLUCIÓN, DISPERSIÓN Y ESTRATEGIAS DE MANEJO

La enfermedad denominada con el nombre de Chancro Resinoso del Pino es causada por el hongo ascomicete Fusarium circinatum Nirenberg et O’Donnell (teleomorfo= Gibberella circinata). Afecta numerosas especies de coníferas y a la fecha tiene presencia en todos los continentes del mundo, a excepción de la Antártida. Debido a las variaciones climatológicas y ambientales a nivel global que han favorecido el rango biológico de dispersión de la enfermedad, sumado al comercio internacional de madera y sus derivados con medidas cuarentenarias insuficientes, actualmente el hongo amenaza con expandirse a zonas libres de la infección. En las zonas donde ya se ha confirmado la presencia de la enfermedad se reportan importantes pérdidas económicas en viveros, semilleros forestales, plantaciones silvestres y comerciales de distintas especies de coníferas. No menos importante pérdida ecosistémica causada por la inestabilidad de los bosques y nichos ecológicos altamente sensibles a las variaciones florísticas. Actualmente es considerada la patología más importante a nivel mundial de las coníferas, tanto silvestres como comerciales, y no posee tratamiento curativo por lo que los esfuerzos están centrados en el tratamiento preventivo. Dentro del ámbito científico destacan las investigaciones en resistencia genética del hospedante y el uso de controladores biológicos que prometan resultados significativos.

Gibberella circinata. [Distribution map].

A new distribution map is provided for Gibberella circinata Nirenberg & O'Donell ex Britz, T.A. Cout., M.J. Wingf. & Marasas. Ascomycota: Hypocreales. Hosts: Pinus spp. and Douglas fir (Pseudotsuga menziesii). Information is given on the geographical distribution in Europe (France, Italy, Portugal, and Spain), Asia (Kyushu, Ryukyu Archipelago, Japan, and Korea Republic), Africa (South Africa), North America (Mexico, Alabama, Arkansas, California, Florida, Georgia, Louisiana, Mississippi, North Carolina, Tennessee, Texas, Virginia, USA), Central America & Caribbean (Haiti), South America (Chile and Uruguay).

First Report of Grass Species (Poaceae) as Naturally Occurring Hosts of the Pine Pathogen Gibberella circinata

Gibberella circinata (anamorph Fusarium circinatum) causes pitch canker in pines and is not known to have any hosts outside the Pinaceae. However, G. circinata is closely related to and interfertile with G. subglutinans, which is associated with grasses both as a pathogen and a commensal endophyte. Furthermore, studies under controlled conditions have shown that G. circinata can colonize corn (Zea mays) without inducing symptoms (4). To determine if G. circinata can also infect grasses under natural conditions, plants were collected in proximity to trees with symptoms of pitch canker in native stands of Pinus radiata (Monterey pine) on the Monterey Peninsula and P. muricata (bishop pine) at Pt. Reyes National Seashore on the California coast during July and August of 2011. Leaves and stems were rinsed in 0.1% Tween 20, immersed in 70% ethanol for 30 s followed by 1 min in 1% NaOCl, and placed on a Fusarium selective medium (FSM) (1). Single-spore subcultures of colonies growing from cultured plant material were transferred to 0.6% KCl agar and identified as G. circinata based on morphological criteria as described by Gordon et al. (2). G. circinata isolates were recovered from Holcus lanatus and Festuca arundinacea on the Monterey Peninsula and H. lanatus at Pt. Reyes National Seashore. Three isolates from each of these sources (nine total) and one known G. circinata isolate from pines (GL 17) were tested for virulence by inoculating 1-year-old, greenhouse-grown Monterey pine trees; three trees were inoculated, once for each isolate. Trees were inoculated by depositing 250 spores in a wound on the main stem by the method described by Gordon et al. (3). Two weeks later, all grass isolates had induced resinous branch cankers with lesions comparable in length (17 to 24 mm) and appearance to those caused by GL 17. Similar results were obtained when inoculations were repeated. One isolate from F. arundinacea and one from H. lanatus (collected at Pt. Reyes National Seashore) were tested and shown to be somatically compatible with tester strains for vegetative compatibility groups C6 and C1, respectively, both of which are associated with isolates previously recovered from diseased pines (2). GL 17 and one isolate each from F. arundinaceae and H. lanatus were tested for their ability to infect F. arundinaceae cv. Fawn. For each isolate, 20 14-day-old seedlings (10 pots with two plants per pot) were sprayed to runoff with an aqueous suspension of 106 spores per ml. All inoculations were repeated once. Two weeks after inoculation, leaves and stems were rinsed briefly in 0.1% Tween 20, immersed for 10 s in 70% ethanol, followed by 30 s in 1% NaOCl, and cultured on FSM. All tested isolates were recovered from at least some of the inoculated plants (range 20 to 100%), from living stems and leaves, as well as from senescing tissue. These results show that grass species can be symptomless hosts for G. circinata, constituting the first documentation of any host for this pathogen outside the Pinaceae. Studies are underway to further characterize the host range of G. circinata and assess the epidemiological implications of grasses as alternate hosts for the pitch canker pathogen. References: (1) B. J. Aegerter and T. R. Gordon. For. Ecol. Manag. 235:14, 2006. (2) T. R. Gordon et al. Mycol. Res. 100:850, 1996. (3) T. R. Gordon et al. Hortscience 33:868, 1998. (4) C. L. Swett and T. R. Gordon. Phytopathology (Abstr.) 89:S126, 2009.

Limiting Effects of Low Temperature on Growth and Spore Germination in Gibberella circinata, the Cause of Pitch Canker in Pine Species

Pitch canker, caused by Gibberella circinata (anamorph = Fusarium circinatum), causes canopy dieback and mortality in susceptible pine species in many parts of the world. Pitch canker is most problematic in areas with a relatively warm climate, suggesting a possible limitation on disease development imposed by low temperatures. To test this hypothesis, the effect of temperature on radial growth was examined in isolates of G. circinata of diverse geographic origin. All isolates grew most rapidly at 25°C and progressively more slowly at 20, 15, and 10°C. Spore germination occurred most rapidly at 20°C and was slowest at 10°C. To determine if the time required for spore germination might influence the likelihood of infection, the duration of wound susceptibility was examined by inoculating branches of susceptible Monterey pines (Pinus radiata). In each of six field trials, branches were wounded and then inoculated immediately or at 2, 6, or 9 days after wounding. The results indicated that wounds inoculated immediately became infected at a significantly higher rate than those inoculated 2 days later. Thus, if low temperatures extend the time required for germination beyond this period, a reduced infection frequency would be expected. Such a limiting effect of temperature could help to explain the current distribution of pitch canker.