Infection of wheat kernels by Pyrenophora tritici-repentis (Ptr) causes different types of discoloration. The symptom most commonly associated with kernel infection by this fungus is a reddish/pinkish discoloration known as red smudge, but dark smudge/specks and black point are also common. Other fungi, mostly Alternaria spp. and Cochliobolus sativus, have been more frequently isolated than Ptr from black-pointed durum wheat kernels in southern Saskatchewan. All wheat cultivars currently registered for use in western Canada are susceptible to Ptr-kernel infection. There is no correlation between susceptibility of leaves and of kernels to Ptr. There are differences among cultivars in incidence and severity of infection, and in the prevalent type of symptom developed. The intensity, incidence, and extent of kernel discoloration is partially related to seed color. The reddish discoloration was more apparent in white than in red seeds, and percent and severity of Ptr infection were generally higher in white seeded wheats than in red seeded wheat cultivars. Black point in Ptr-infected kernels was observed in all wheat classes. Its development was genotype-dependent, although it also appeared to be related to infection severity. The effect of red smudge infection of durum wheat seed on the health of the subsequent plants was examined in controlled-environment and field studies. Percent germination was lower for naturally infected red smudged seed than for uninfected seed, whereas germination rate was higher for artificially infected red smudged seed than for uninfected seed. The observation that red smudge speeds up germination of seeds was confirmed in common wheat. Growth of the coleoptile and primary roots, and number of roots were also depressed in red smudged seeds, indicating that Ptr-infection has a negative effect on seed vigor. Afield study designed to examine the effect of red smudge on seedling emergence, plant growth, and yield using three red smudge treatments (0%, 50%, and 100%) showed that percent emergence of seedlings declined with increasing proportion of red smudged seeds. This resulted in poor stands and lower yields per unit area in the field. Rate of seedling emergence and time to heading were also lower for red smudge treatments than controls; however, grain weight and yield per plant were not significantly affected. In none of the experiments was transmission of Ptr to durum wheat seedlings observed, but only to the coleoptile under controlled conditions.

English

9806|AGRIS 9802

Jose Juan Caballero

I1705031

CIMMYT Publications Collection