Damage components of powdery mildew in winter wheat

Abstract

The photosynthesis and transpiration rates of winter wheat leaves were measured at different developmental stages and at various levels of mildew infection. Even at low levels of infection, circa 40Jo leaf area being covered, both the assimilation and transpiration rates at light satiation were considerably reduced. Light use efficiency and dark respiration were not significantly affected. The physiological background of these effects was analysed by photosynthesis measurements at different external COz concentrations. It was shown that the carboxylation resistance was increased due to mildew infection and that stomatal resistance, boundary layer resistance and transport resistance in the mesophyll were only indirectly affected.A simulation model was used to compute the consequences of these effects on daily growth rate of a winter wheat canopy at different development stages and with different levels of mildew severity. These computations show that a low infection level may result in a considerable reduction of the crop growth rate. This effect was more pronounced when the sky was clear than overcast.

Genetic variation in partial resistance to leaf rust in winter wheat: disease progress, foliage senescence and yield reduction

“…The rust accelerated foliage senescence, reducing the cumulative light interception of the crop and so its total dry matter production, which was proportional to the light interception. The applicability of such a crop physiological analysis to disease or pest-induced yield losses was also demonstrated by, among others, Rossing et al (1989), Waggoner and Berger (1987), Johnson (1987), Van Roermund et al (1986), Rabbinge et al (1985). The results of photosynthesis measurements in the field support the hypothesis that leaf rust in winter wheat reduces crop photosynthesis by reducing the green, photosynthesizing area without affecting the photosynthetic rate per unit of remaining green surface.…”

“…96 (1990) estimate of the reduction in photosynthetic capacity of the foliage. The situation may be different for other diseases, as suggested, for instance, by the results of Rabbinge et al (1985) who found that a 40Jo coverage of powdery mildew in wheat reduced leaf photosynthesis by 50%.…”

Alterações na fotossíntese e na transpiração de folhas de milho infetadas por Phaeosphaeria maydis

“…No entanto, em outros, a taxa fotossintética é reduzida também no tecido verde, aparentemente sadio, ao redor das lesões (Rabbinge et al, 1985;Bastiaans, 1991;Goodwin, 1992;Shtienberg, 1992;Bassanezi et al, 1997). Para determinar o tipo de efeito causado pelo patógeno, Bastiaans (1991) estabeleceu a função matemática P x /P o =(1-x) β que relaciona severidade da doença (x) e taxa fotossintética líquida relativa da folha (P x /P o ), onde P x é a fotossíntese líquida da folha com severidade de doença x e P o é a fotossíntese líquida média de folhas sadias.…”

“…Esse mesmo efeito já foi constatado para patossistemas como Erysiphe graminis -trigo [Triticum aestivum (L.) Thell.] (Rabbinge et al, 1985;Shtienberg, 1992), Magnaporthe grisea (Hebert) Yaegashi & Udagawa -arroz (Bastiaans, 1991) (Shtienberg, 1992), Xanthomonas campestris pv. phaseoli (Smith) Dye -feijoeiro (Phaseolus vulgaris L.) (Goodwin, 1992) e o fato dos ensaios terem sido realizados no campo.…”

Effects of powdery mildew and weather on winter wheat yield. 2. Effects of mildew epidemics

“…Models of crop growth, which compute yield from temperature and radiation, provide another option to answer the question if they can be combined with models of the pathogen. Rabbinge et al (1985) quantified the effect of powdery mildew on photosynthesis of wheat leaves (Allen, 1942;Walters and Ayres, 1984). How these effects on photosynthesis measured in the laboratory may be used to estimate loss of kernel yield and to what extend they explain yield loss caused by mildew in the field remained to be answered.…”