PERSONAL DE APOYO
ANDERSON Freda Elizabeth
congresos y reuniones científicas
Título:
Biological control of Chilean needle grass (Nassella neesiana, Poaceae) in Australia. Application to release.
Autor/es:
ANDERSON, F.E. ; GALLEGO L., ; SÁNCHEZ, RM; BARTON, J.; MCLAREN DA
Lugar:
Melbourne
Reunión:
Congreso; !8th Australasian Weeds Conference; 2012
Institución organizadora:
Council of Australasian Weed Societies Inc.
Resumen:
Nassella neesiana (Chilean needle grass) is a significant agricultural and environmental weed in Australia and New Zealand and the two countries have worked together for ca. ten years to find a suitable biological control agent to use against it. The only suitable agent found in the home range of the weed (South America), and the subject of this paper, is the rust fungus Uromyces pencanus.  Most of the pathogens that have been used for classical biocontrol of weeds world-wide have been rusts, and they have never caused unpredicted non-target damage in the field. Uromyces pencanus has been observed killing infected leaves, and reducing seed production, of N. neesiana in the field in Argentina. The rust is particularly damaging in dry weather. Laboratory experiments have confirmed the rust can reduce the growth of infected plants. Rusts have complicated life-cycles that include up to five different types of spores A rust may complete its life cycle on only one host, or it can form some sporetypes on one host and other types on another (not closely related) host. Uromyces pencanus has been reported in the literature to form three types of spores on N. neesiana: urediniospores, teliospores and aeciospores. We have previously shown that aeciospores often found on N. neesiana belong to the life cycle of another rust (Puccinia graminella). Teliospores of U. pencanus appear to have lost the ability to produce basidiospores and  therefore, the nature of its life cycle can not be categorically proven. It is believed to cycle as urediniospores on its grass host. Mycoparasites that exist in Australia are similar to those that exist in Argentina, so there is no reason to believe they will significantly hamper the activity of the rust here. It is extremely unlikely that the introduction of U. pencanus would lead to adverse impacts on native rusts through hybridization. Extensive host range testing has been conducted with a single strain of U. pencanus (UP 27). It was applied to 79 taxa including 14 populations of N. neesiana, 2 populations of the weed serrated tussock and 7 cultivars of wheat (in total, 60 species were tested). UP 27 was shown to be highly host specific, however it did form pustules on two Austrostipa species, A. compressa and A. macalpinei.  On these species, spore formation was 30  and 10 times less respectively  than on the target plant. When the U. pencanus spores collected from these Austrostipa compressa were applied to N. neesiana plants, no infection resulted.  Climatic isolation from current and future spread of N. neesiana makes it unlikely that Western Australian populations of A. compressa or A. macalpinei will ever be in close association with N. neesiana making it unlikely they would ever come into contact with spore concentrations capable of infection. The ephemeral biology of these Austrostipa species further reduces the likelihood of U. pencanus attack on these species. Development of intercellular mycelium and a few haustoria was also observed within leaves of Austrostipa eremophila, A. breviglumis, A. mollis, A. nitida, A. nullanulla, A. platychaeta, A. stuposa and Piptatherum miliaceum.  However, the rust did not develop further to form uredinia on these species. Since it is the formation of uredinia (and the resulting disruption to the leaf epidermis) that is the main cause of damage to the target weed  these plants would be unlikely to be significantly adversely affected by the rust if they were to encounter it in the field. Strain UP 27 will form pustules on 7 out of 9 N. neesiana populations collected from Australia. Therefore, other strains of U. pencanus in Argentina may be required in the future to control N. neesiana infestations. If so, there is no reason to believe these other strains would have a broader host range than UP 27. If U. pencanus were introduced to Australia, there is no reason to believe its host range would broaden over time through evolution. To conclude: The introduction of U. pencanus to Australia is unlikely to cause any significant negative impact on native or otherwise valued plants or fungi but host testing does show some risk to two closely related Austrostipa species.  The massive environmental and agricultural impacts being caused by N. neesiana to Australian grasslands outweighs the relatively small risk that there may be some off target damage to two Austrostipa species. The introduction and release of U. pencanus for biological control of N. neesiana was approved in New Zealand in June 2011.   We would recommend its introduction and release on N. neesiana in Australia as well.