The overwintering ofExserohilum turcicum in Israel
Exserohilum turcicum (Pass.) Leonard and Suggs, the causal agent of northern leaf blight of corn, overwinters onSorghum halepense L. plants and on corn debris (dead leaves). Spqrulating lesions ofE. turcicum were observed on sorghum plants in the winter (February). Spores from these lesions were pathogenic to susceptible sweet corn plants cv. ‘Jubilee’. Infected sporulating leaves of corn were stored for 1 year at 20°C (40-60% relative humidity), at 5°C (60% relative humidity), or buried 5 cm underground. During the storage period, 32% and 22% of the spores formed chlamydospores, at 20° and 5°C, respectively. Leaves buried 5 cm underground were totally decomposed after 6 months. After 4 months, 25% of the spores in the buried leaves had formed chlamydospores. Spores with chlamydospores were pathogenic to corn plants. The viability of spores without chlamydospores stored at 20°, 5°C or buried underground was 0, 60 and 0%, respectively. In a parallel experiment infected leaves were stored under similar conditions and allowed to sporulate. No sporulation occurred on infected leaves buried in soil. Spores produced on infected leaves stored at 20° and 5°C were highly pathogenic to corn plants. In leaves treated with 0.1N glucose, chlamy dospore formation was significantly inhibited.
Sporulation of Helminthosporium turcicum on sweet corn: effects of light and sugars
Conidial formation, but not conidiophore growth, at Helminthosporium turcicum Pass, on detached blighted leaves of corn was greatly inhibited by blue light. Percentage inhibition of conidial production increased with increasing leaf temperature and light level. With 8 μE m−2 s−1 of blue light, spore production was reduced by 30, 87 and 96% at 15, 20 and 25°C, respectively, compared to the respective dark controls. Light exerted no inhibitory effect on spore formation if conidiophore-bearing leaves were first kept for 2 and 3 h in the dark at 15 and 20°C, respectively, or for 1 h at 10°C in either dark or light conditions. Sucrose had a great enhancing effect on conidial production in the dark, but could not counteract the inhibitory effect of light. Prolonged incubation of intact infected plants in darkness favoured subsequent sporulation. A suggestion is made that a single photoreceptor pigment system operates the synthesis or activation of antisporulants which may act directly or may counteract the activity of chemicals essential for spore production.
Analysis of Macro and Micronutrients in Soils from Palestine Using Ion Exchange Membrane Technology
Ion Exchange membrane technology (IEM) is a method that allowed a single extraction process and a single subsequent measurement of different elements that are available in soil. The values of the available forms of the different macro- and micronutrients obtained by IEM extraction were compared with the values of the soluble form obtained by conventional extraction methods. In surface soil sample, the concentrations of available potassium, nitrate, phosphate, iron and boron were 37.7 mg kg–1, 17.5 mg kg–1, 3.6 mg kg–1, 171.0 μg kg–1, and 4.2 μg kg–1 respectively were greater than that of soluble forms of the same elements which were 7.0 mg kg–1, 9.2 mg kg–1, 0.4 mg kg–1, 109.0 μg kg–1, and 1.9 μg kg–1 respectively.