Effects of Cereal Cyst Nematode Infection on Resistant and Susceptible Barley
Date
2021
Authors
Adu-Gyamfi, Monica Ode
Editors
Advisors
Mather, Diane E.
Tyerman, Steve
Khoo, Kelvin
Tyerman, Steve
Khoo, Kelvin
Journal Title
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Thesis
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Abstract
Cereal cyst nematodes (CCN) are obligate biotrophs that affect the yield of cereals including barley. This parasite is one of the biotic factors that affect plant-water relations and imposes early stress that reduces yield irrespective of the availability of water and nutrient. Invasion, migration, feeding site formation, and feeding by this nematode alter host root anatomy and interfere with water and nutrient transport in the plant. To better understand the effects of CCN infection on water transport, susceptible and resistant barley cultivars were studied using exudation and suction methods to measure hydraulic conductivity (Lpr). Hydrostatic Lpr obtained using the suction method was assessed in the presence of xylem tension which was exerted at the shoot base using a vacuum while osmotic Lpr obtained using the exudation method was determined in the existence of osmotic gradient and water flow. Control plants showed higher hydraulic conductivity in the suction experiment (mean 5.47 ± 0.8 ×10⁻⁷ ms⁻¹MPa⁻¹) than in two exudation experiments (mean 2.99 ± 0.2 ×10⁻⁷ ms⁻¹MPa⁻¹ and 1.46 ± 0.06 ×10⁻⁷ ms⁻¹MPa⁻¹). CCN infection reduced growth, exudation flow rate, hydraulic conductance, and hydraulic conductivity of both resistant and susceptible barley. Both techniques showed the effect of CCN infection on hydraulic properties, but the effect was more evident in the suction experiment (70.1% reduction in Lpr in inoculated plants) than in the exudation experiments (21.5% and 19% reduction in Lpr in inoculated plants). To further investigate how water and solutes travel through seminal roots of barley that are parasitised by CCN, 8-hydroxyprene-1, 3, 6-trisulfonic acid trisodium salt (HPTS) was used as an apoplastic tracer dye. The flow of HPTS (presumably carried with water) through seminal roots was temporarily interrupted in infected regions. The duration of this interruption was longer in a CCN-susceptible cultivar Sloop than in its CCN-resistant derivative Sloop SA. Another CCN-resistant cultivar, Galleon for which resistance is conferred by the Rha4 locus on chromosome 5H, was confirmed to exhibit more robust seedling growth in hydroponics than the CCN-susceptible cultivar Sloop. Similar differences were also observed between resistant and susceptible early-generation Galleon × Sloop backcross families, making it seem possible that seedling vigour plays a role in CCN resistance. However, comparisons of seedling vigour between resistant (Rha4+) and susceptible (Rha4-) progeny within advanced generation backcross families revealed no significant differences. It was concluded that the CCN resistance locus Rha4+ is not the cause of the seedling vigour
School/Discipline
School of Agriculture, Food and Wine
Dissertation Note
Thesis (MPhil) -- University of Adelaide, School of Agriculture, Food and Wine, 2021
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