Eucalyptus rust: epidemiology and genetic resistance / Epidemiologia da ferrugem do eucalipto e resistência genética

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Rust caused by Puccinia psidii is one of the most important diseases of eucalyptus in Brazil, Paraguay, Uruguay and Argentina. If this disease is introduced into other countries, such as Australia, it can pose a serious threat to its flora, in which species of the Myrtaceae family predominate, and South Africa, for its industrial eucalyptus plantations. Knowledge on the environmental conditions favorable to infection, inheritance of resistance mechanisms, and sources of genetic resistance is fundamental for an effective control of the disease. The objectives of present work were: a) to understand the reasons for which eucalyptus trees above 3 m high, at phonological stage C, escape the rust; b) determine the relationship among the micrometeorological factors; c) study the wind dispersion of urediniospores and disease progress; d) evaluate the resistance in different genetic materials derived from Australia; and e) study the probable genetic background effect on the resistance of progenies from a female parent that is dominant homozygous for resistance. The evaluation of the effect of height gradient on eucalyptus rust incidence, in relation to leaf wetness duration and number of urediniospores suspended in air, showed that rust incidence was reduced with increase in height. It was found positive correlation (P <0.05) of the area below the curve of disease progress and percentage of leaves with rust with the leaf wetness period and mean number of urediniospores, and negative correlation of disease with height. The number of P. psidii urediniospores (SP) was quantified by using a Burkard trap in the period from July 2004 to June 2005. Spores were captured in 77% of the sampled days. Larger mean SP (3.21 spore/m3 of air/2h) was found between July and November. In this period, 58% of SP were captured during the night and SP was negatively related to minimum, average (AT) and maximum temperatures, and with wind speed (WS). There was positive correlation among SP, duration of leaf wetness (LW) and relative humidity (RH). A larger number of urediniospores was recorded for the combination of low average temperature, low light intensity, low wind speed, and high relative humidity and long period of leaf wetness, conditions more frequently found during the night period. The resistance to rust of different Myrtaceaes originated from of Australia was shown independent of the provenance. The most resistant species were: Corymbia calophylla rosea , Corymbia tesselaris, Melaleuca ericifolia, Eucalyptus tereticornis, E. resinifera, E. scias spp. scias, E. paniculata, E. pellita and C. intermediata; and the most susceptible were: M. nesophila, M. alternifolia, M. cajuputi spp. cajuputi, M. leucadendra, M. quinquenervia, E.cloeziana, E. diversicolor, E. regnans, and E. grandis. The existence of susceptible individuals, most probably derived from the G26 matrix of E. grandis, dominant homozygous for resistance, was not related to the genetic background effect, but due to operational flaws, probably during seed processing and/or seedling production.

ASSUNTO(S)

marcadores genéticos puccinia psidii epidemiology puccinia psidii ferrugem do eucalipto fitopatologia eucalyptus rust resistance molecular markers resistência epidemiologia

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