Factors Affecting the Vertical Progression of Septoria Leaf Blotch in Short-Statured Wheats

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Abstract
The meteorological factors affecting the development and vertical progress of Septoria leaf blotch of wheat were assessed for equally susceptible dwarf (70-80 cm) and semi-dwarf (100-120 cm) spring wheat [Triticum aestivum] cultivar pairs of different maturity in both an arid and a rainy region in Israel. In the dwarf cultivars, pycnidia of S. tritici were found immediately after leaf emergence; in the semi-dwarf cultivars, there was a 10-20 day lag between the emergence of the 4 upper leaves and pycnidia formation on those leaves. The time lag increased for plants of both dwarf and semi-dwarf cultivars in the rain-sparse region. The verticial progress of the pathogen from lower to higher leaves was affected by the distances between consecutive leaves; the ladder effect. The rate of vertical progress on the dwarf wheats under the severe epidemics was similar to the rate on the equally receptive semi-dwarf cultivars despite the difference in plant architecture and maturity. Functions were developed to analyze the net contribution of climatological factors on the progress of the disease within the temperature range of 10-25.degree. C. The vertical progress of the disease was correlated with the number of rainy and dewy days and temperature indices 7-21 days prior to disease observation and disease severity was correlated mainly with the number of dewy days and temperature indices 7-21 days prior. There were lower correlations in the arid region which was characterized by less rainfall, prolonged rainless periods and hot spells toward the end of the growing season than in the rainy coastal plains.

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