TITLE:
Ambient Stresses Regulate the Development of the Maize Late Wilt Causing Agent, Harpophora maydis
AUTHORS:
Ofir Degani, Yuval Goldblat
KEYWORDS:
Acremonium maydis, Black Bundle Disease, Cephalosporium maydis, Environment Stress, Fungus, Harpophora maydis, Late Wilt
JOURNAL NAME:
Agricultural Sciences,
Vol.5 No.7,
June
9,
2014
ABSTRACT: Late wilt, a severe
vascular disease of maize caused by the fungus Harpophora maydis, is
characterized by relatively rapid wilting of maize plants before tasseling and
until shortly before maturity. In Egypt and Israel, the disease is considered
to be a major problem. The pathogen is currently controlled using cultivars of
maize having reduced sensitivity, but the fungi can undergo pathogenic variations
and become a threat to resistance cultivars as well. The abiotic and biotic
factors influencing the infection and disease development are not fully
determined. To impose stress in a uniform and chronic manner, we expose the
Israeli H. maydis isolates colonies or spores to light, different pH,
ionic and hyperosmotic pressures (induced with KCl or sorbitol) or
oxygen-related stresses (induced with oxygen enrichment, menadione or
peroxide). The optimum pH for both hyphal development and spore germination was
pH = 5 - 6, similar to reports for the Egyptian, Indian and Hungarian isolates
of H. maydis. In the hyperosmotic regime, hyphal growth was affected in
a dosage-dependent curve. Although inoculation under high salt stress also
inhibited spore germination, the spores were relatively resistant to this
stress in comparison to the hypha. An opposite picture was revealed under
menadione/peroxide stress: under high dosage of these compounds, the spore
germination was virtually abolished while the colony growth was moderately
affected. A daily oxygen enrichment of liquid medium cultures caused an
increased growth in the pathogen wet and dry biomass, but daily double
treatments led to growth suppression. These findings are a preliminary step
towards the inspection of the fungal-host interaction under these different
stressful environments. This is important for the future development of new
strategies to restrict the disease burst and to protect field corps.