Grain Biotech Australia
(GBA) General Manager and former CIMMYT wheat breeder, Paul
Fox has refuted Department of Agriculture suggestions that
newly released wheat variety GBA Ruby was as likely to need a
spray for rust as Wyalkatchem and EGA Bonnie Rock.
Dr Fox explained that GBA Ruby was
protected from leaf rust by a “slow rusting” genetic
background assembled by CIMMYT in Mexico and based on minor
genes expressed in adult plants, but not in seedlings.
University of Sydney studies
suggest the slow rusting gene Lr34 is functioning.
“Such a genetic background has
proved effective against major crop losses across the world
for many years,” he declared.
“Alarmingly, Australian wheat
varieties have generally been too dependent upon major genes
and the pitfalls have been seen with stripe rust in Western
Australia in 2002 and with the same pathogen again in eastern
Australia in 2003.
“Major genes confer ‘clean skin’
resistance and thus exert very strong pressure on the pathogen
for selection of a mutant to overcome the resistance gene.
“What this means is when major
genes go down, they go down hard,” Dr Fox said.
Because some rust was often
observed with slow rusting, or minor gene resistance, the
pathogen survived at a low level, without the huge pressure
for selecting a virulent mutant to overcome the gene, which is
what occurs with major gene resistance.
“With slow leaf rusting you get a
natural low level refuge for rust survival and only very
rarely see a major attack and even less rarely a mutation in
the rust.”
Dr Fox believed the real test for
GBA Ruby was the Disease Progress Nursery in 2003 at Gatton,
Queensland, where, for leaf rust, Ruby was scored as 10MR and
5MR.
“This means five to 10 per cent of
the leaf was affected with a moderately resistant or
restricted pustule type, compared to other wheats where up to
100 per cent of the leaf was covered with juicier, more
susceptible pustules,” he said.
Further, GBA asserts that the risk
of having to spray GBA Ruby for leaf rust is much lower than
the risk of having to spray Wyalkatchem for stem rust or EGA
Bonnie Rock for stripe rust. This related to the very nature
of the three rusts.
“The potential yield damage of leaf
rust is significantly lower than for stem rust or stripe
rust,” Dr Fox explained.
