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Effect of Pasmo Disease on Flower Production and Yield Components of Flax. M. W. Ferguson, Associate professor, Department of Plant Science, South Dakota State University, Brookings 57007; C. L. Lay, and P. D. Evenson. Professor, and Associate professor, respectively, Department of Plant Science, South Dakota State University, Brookings 57007. Phytopathology 77:805-808. Accepted for publication 10 October 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-805.

Petals of flax (Linum usitatissimum) flowers abscise and drop off 4–6 hr after full expansion of the flower. Therefore, daily flower counts can be taken without having to mark or account for the previous day’s flowers. This characteristic was used in making daily counts of flowers of plants in field plots to determine what effect pasmo (caused by Mycosphaerella linorum) has on the flowering process and subsequent yield parameters of flax. The flower counts were fitted to a curve using the NLIN procedure of Statistical Analysis Systems Institute and the logistic function CUMF = a/[l + exp(b + c* days)], where a = final cumulative number of flowers, b = arbitrary constant, c = proportionality constant, and days = date of count. Flowering curve parameters derived from this equation included maximum rate of flowering (s = (– ca)/ 4), date at which maximum flowering occurred (sd = b/–c), and period over which maximum linear daily flower production occurred (d = 4/–c). Several fungicides, timings of application, and maturity dates of varieties were used to determine their effect on the disease and the interaction of the disease with flowering parameters and yield components. Both benomyl and mancozeb significantly reduced the severity of pasmo (P = 0.05), whereas cultivar and timing did not. Fungicide treatments resulted in increased yield but did not significantly alter any of the flowering parameters. Pasmo was correlated with sd (1982) and d (1983) (P = 0.01, df = 70). In both years, pasmo was negatively correlated with yield (1982, r = –0.243; 1983, r = –0.332). In 1982, disease severity was negatively correlated with number of seeds per boll (r = –0.241) and in 1983 with seed weight (r = –0.263). Yield in both years was significantly correlated (P = 0.05) with seed weight (1982, r = 0.310; 1983, r = 0.371) and in 1982 negatively correlated with seeds per boll (r = –0.252). The flowering parameter sd was correlated (P = 0.01) with yield (1982, r = 0.233; 1983, r = 0.288).