Aetiology of barley net blotch caused by Pyrenophom teres and some effects on yield



Laboratory and glasshouse tests showed that seed from barley crops in south-west England with much net blotch was often infected with Pyrenophora teres Drecksler. After sowing, mycelium in the caryopsis grew to infect the developing coleoptile and hence was carried above ground. On the growing foliage the fungus multiplied by conidial infection and also formed perithecia in late summer. The perithecia persisted in debris and released many ascospores in autumn which may infect volunteer plants and newly emerging barley seedlings. Pycnidia also developed on debris but the pycnidiospores were non-infective.

Mycelial infection from seed often produced streaks on the coleoptile that quickly penetrated to the underlying leaves. This symptom was therefore often distinguishable from those resulting from air- or splash- dispersed conidia or from ascospores. In optimum weather (20°C, 100 per cent r.h.) net blotch lesions developed and sporulated within five days from inoculation and if suitably positioned could kill a leaf within 15 days.

Severe leaf infection during tillering of winter barley (cv. Sonja) grown in pots outdoors significantly decreased yield both by decreasing the number of grains per ear and the thousand grain weight. In a fungicide trial on winter barley (cv. Hoppel) field plots sprayed with propiconazole yielded 23 per cent more than untreated plots, mostly because individual grains were larger.