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.
Influences of Northern Leaf Blight on corn silage fermentation quality, nutritive value and feed intake by sheep.
This study examined the differences between non-inoculated (control) corn and Northern Leaf Blight (NLB)-damaged corn (inoculated corn); dry matter (DM) yield, silage fermentation quality, nutritive value and feed intake by sheep were compared. Leaf, stem and grain dry weights and gross yield of inoculated corn were significantly (P < 0.05) decreased compared with control corn. The contents of water-soluble carbohydrate and nitrogen-free extract (NFE) were decreased in inoculated corn compared with control corn. Silage made from both inoculated and control corn showed good fermentation quality. The digestibility of DM, organic matter, ether extract, NFE, and energy of silage made from inoculated corn were significantly (P < 0.05) lower, and contents of total digestible nutrients (TDN) and digestible energy (DE) were also significantly (P < 0.05) lower compared with silage made from the control corn. DM intake showed no significant discrepancy between the two types of silage. TDN and DE intakes from inoculated silage were significantly (P < 0.05) lower compared with control silage. From the above results it was shown that NLB caused a decrease in DM yield and NFE content in corn and a decrease in the nutritive value and feed intake of silage.
Influence of photoperiod on sporulation of and infection by Helminthosporium turcicum on Zea mays
The influence of photoperiod on sporulation of and infection by Helminthosporium turcicum Pass. (Trichometasphaeria turcica Luttrell), the causal agent of northern leaf blight of corn (Zea mays L.), was studied in growth chambers simulating normal, field weather conditions. The results were compared to an epidemic of the disease on sweet corn in Kent County, Ontario, in 1972 during a period of unusual weather conditions. An 8-h photoperiod was required to maintain both the diseased plants in a state of survival and the fungus in a state of repeated sporulating cycles on the plants in the growth chambers. The specific climatic component which could be correlated with growth chamber data was the photoperiod. Extremely wide temperature and rainfall variations from their long term means, and a low average exposure to light, contributed to the progress of the disease.