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Abstract

Fungi of the genus Mycosphaerella is one of the
major leaf disease of Eucalyptus globulus
worldwide. The main species that infect E.
globulus in southern Australia are M. cryptica
and M. nubilosa. M. nubilosa is mainly confined
to the juvenile foliage whereas M. cryptica may
occur on both foliage types. Mycosphaerella
damage to E. globulus plantations can be severe
and the risk of disease damage is one of the
main reasons for the shift towards planting the
more resistant E. nitens in northern Tasmania.
We examined the quantitative genetic variation
in susceptibility to infection by M. nubilosa in a
genetically diverse population of E. globulus
families growing in a field trial in north-west
Tasmania. The trees were two years old and
still entirely in the juvenile foliage stage when a
heavy epidemic of M. nubilosa occurred.
Disease incidence was uniform across the trial
and the mean leaf area damage (severity
assessed as % of necrotic of lost leaves on
whole tree basis) was very high at 34%.
Significant genetic variation for susceptibility was
detected with a narrow-sense heritability of
disease severity of 0.6 being the highest yet
reported for a Mycosphaerella disease of
eucalypts. We followed the effects of this
disease outbreak on growth up to age 7 years
and found that M. nubilosa damage had a
significantly deleterious impact on tree growth at
both the phenotypic and genetic level. At age 7,
the top 10% of families had a mean DBH 20.8%
greater than the trial mean. Approximately half of
this gain would have been achieved by early
selection for disease resistance (9.1%) or height
(11.0%) at age 2, with a time advantage of 5
years. This is similarly the case for selection of
above average families. It is likely such gains
would be reduced in homogenous plantings of
resistant genotypes, or if genotype x
environment interactions are significant.
Nevertheless, a large component of this gain is
likely to be due to disease resistance per se, and
collection of seed from resistant seed orchard
parents offers the potential for rapid gains in
productivity in plantations at risk of
diseaseAbstract
Fungi of the genus Mycosphaerella is one of the
major leaf disease of Eucalyptus globulus
worldwide. The main species that infect E.
globulus in southern Australia are M. cryptica
and M. nubilosa. M. nubilosa is mainly confined
to the juvenile foliage whereas M. cryptica may
occur on both foliage types. Mycosphaerella
damage to E. globulus plantations can be severe
and the risk of disease damage is one of the
main reasons for the shift towards planting the
more resistant E. nitens in northern Tasmania.
We examined the quantitative genetic variation
in susceptibility to infection by M. nubilosa in a
genetically diverse population of E. globulus
families growing in a field trial in north-west
Tasmania. The trees were two years old and
still entirely in the juvenile foliage stage when a
heavy epidemic of M. nubilosa occurred.
Disease incidence was uniform across the trial
and the mean leaf area damage (severity
assessed as % of necrotic of lost leaves on
whole tree basis) was very high at 34%.
Significant genetic variation for susceptibility was
detected with a narrow-sense heritability of
disease severity of 0.6 being the highest yet
reported for a Mycosphaerella disease of
eucalypts. We followed the effects of this
disease outbreak on growth up to age 7 years
and found that M. nubilosa damage had a
significantly deleterious impact on tree growth at
both the phenotypic and genetic level. At age 7,
the top 10% of families had a mean DBH 20.8%
greater than the trial mean. Approximately half of
this gain would have been achieved by early
selection for disease resistance (9.1%) or height
(11.0%) at age 2, with a time advantage of 5
years. This is similarly the case for selection of
above average families. It is likely such gains
would be reduced in homogenous plantings of
resistant genotypes, or if genotype x
environment interactions are significant.
Nevertheless, a large component of this gain is
likely to be due to disease resistance per se, and
collection of seed from resistant seed orchard
parents offers the potential for rapid gains in
productivity in plantations at risk of
diseaseAbstract
Fungi of the genus Mycosphaerella is one of the
major leaf disease of Eucalyptus globulus
worldwide. The main species that infect E.
globulus in southern Australia are M. cryptica
and M. nubilosa. M. nubilosa is mainly confined
to the juvenile foliage whereas M. cryptica may
occur on both foliage types. Mycosphaerella
damage to E. globulus plantations can be severe
and the risk of disease damage is one of the
main reasons for the shift towards planting the
more resistant E. nitens in northern Tasmania.
We examined the quantitative genetic variation
in susceptibility to infection by M. nubilosa in a
genetically diverse population of E. globulus
families growing in a field trial in north-west
Tasmania. The trees were two years old and
still entirely in the juvenile foliage stage when a
heavy epidemic of M. nubilosa occurred.
Disease incidence was uniform across the trial
and the mean leaf area damage (severity
assessed as % of necrotic of lost leaves on
whole tree basis) was very high at 34%.
Significant genetic variation for susceptibility was
detected with a narrow-sense heritability of
disease severity of 0.6 being the highest yet
reported for a Mycosphaerella disease of
eucalypts. We followed the effects of this
disease outbreak on growth up to age 7 years
and found that M. nubilosa damage had a
significantly deleterious impact on tree growth at
both the phenotypic and genetic level. At age 7,
the top 10% of families had a mean DBH 20.8%
greater than the trial mean. Approximately half of
this gain would have been achieved by early
selection for disease resistance (9.1%) or height
(11.0%) at age 2, with a time advantage of 5
years. This is similarly the case for selection of
above average families. It is likely such gains
would be reduced in homogenous plantings of
resistant genotypes, or if genotype x
environment interactions are significant.
Nevertheless, a large component of this gain is
likely to be due to disease resistance per se, and
collection of seed from resistant seed orchard
parents offers the potential for rapid gains in
productivity in plantations at risk of disease

Item Type:	Conference or Workshop Item (Paper)
Authors/Creators:	Potts, BM and Milgate, AW and Joyce, K and Mohammed, CL and Vaillancourt, RE and Dutkowski, GW
Keywords:	Quantitative Genetics Mycosphaerella genetic resistance
Publisher:	RAIZ, Instituto Investigação de Floresta e Papel, Portugal
Additional Information:	BM Potts. IUFRO -International Union of Forest Research Organzation.
Item Statistics:	View statistics for this item

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