Field screening for resistance to barley net blotch

Abstract

S U M M A R YInoculation with barley net blotch from infested straw debris was compared with that from diseased plants after sowing infected grains. The straw debris had a high, uniform inoculation potential which gave an early, continuing infection and easily reproducible results that were effective for screening barley cultivars in the field for resistance against a natural population of the pathogen. Further, it minimises an eventual influence from other leaf pathogens coming from the surroundings.Irrigation was decisive for the success of the methodespecially in the initial phase. Ten m separation with an immune crop was insufficient to completely prevent infection in the uninoculated plots.The tested 25 cvs were differentiated in six categories of resistant and susceptible on the basis of disease development and final level of attack. None of them was free of symptoms. The most resistant cvs kept a constant, low level of attack during the whole growing season, whereas the most susceptible cvs showed an early and rapidly increasing attack. Intermediate cvs were characterised with more or less slow increase of the attack. The size and proportion of the brown necrotic spots and the surrounding yellow halo varied greatly from one cultivar to the other.The grain yield reduction was due solely to an effect on the thousand grain weight which decreased linearly with the squared point score for net blotch. Further, the disease affected the quality of the grains as less nitrogen was transported from straw to grain in the severely diseased plants.

Genetic Variability for Grain Yield and Protein Content in Barley and Its Modification by Net Blotch

“…The yield reduction could be explained as an effect of net blotch on 1000-grain weight. 1000-grain weight reduction in inoculated plants might be due to a reduction in photosynthetic activities and disturbance of the translocation of photosynthate from leaf and stem to the kernels (SKOU and HAAHR 1987). BUCHANNON and WALLACE (1962) also demonstrated that the yield reduction of barley by net blotch is caused by the effect of net blotch on 1000grain weight and the number of grains per plant, whereas JORDAN (1981) found that the 1000-grain weight was the most-affected component.…”

Reação de cultivares de cevada a Drechslera teres, e variabilidade patogênica de isolados do Sul do Brasil

“…Fatores genéticos e de ambiente, ligados ao patógeno, podem influenciar a reação do hospedeiro. Skov & Haahr (1987) mostraram que populações naturais de D. teres variam quanto à virulência, de uma região para a outra, ou em freqüência de ano para ano. Shipton et al (1973) relataram também que a progênie de um conídio de D. teres permanece segregando em características culturais e patogênicas por, no mínimo, seis gerações.…”