The effect of take-all disease on gas-exchange rates and biomass in two winter wheat lines with different drought response

Abstract

There have been no studies of the effect of take-all on leaf gas-exchange rates, despite the fact that take-all severely restricts plant water and nutrient uptake, which results in significant biomass and grain yield reduction. Here we describe the effect of inoculation with Gaeumannomyces graminis (Sacc.) var. tritici (Ggt) on carbon assimilation rate (A) and biomass production of wheat plants grown under two water regimes. We show that the impact of Ggt inoculation on plant growth and leaf A may be through reduced photosynthetic capacity of the leaves and not water stress per se. The nature of this reduced photosynthetic capacity remains uncertain but may involve nutrient deficiency and different enzymes produced by the fungus. In each of the 3 years the experiment was conducted, Ggt significantly reduced A, i.e. at anthesis by 18% in 2000, 15% in 2001, and 12% in 2002. In agreement with other field studies, Ggt reduced tiller number and production of all plant components, mostly root dry mass and grain mass per plant. Highly significant negative correlations were found between disease rating and A in all years, showing that at disease ratings equal or higher than 3 (on a scale from 1 to 4) A could practically be zero. While A decreased, intercellular CO 2 concentration increased or did not change, and stomatal conductance was relatively high. In addition, A was more reduced under high than under low soil moisture content. These results support the idea that water stress per se did not contribute to the observed reduction of A. The mechanism of photosynthetic capacity reduction due to the Ggt root-rotting fungus is of interest as it may lead to the molecular mechanisms of plant resistance and ultimately to the development of take-all resistant plants.

Effects of Pythium irregulare and Root Pruning on Water‐Use Efficiency of Hydroponically Grown Wheat under PEG‐Induced Drought

“…The stable [CO 2 ] i under Pythium inoculation while photosynthesis decreased indicated that photosynthesis was not limited by stomatal control but possibly by reduction in photosynthetic capacity of the leaves. Similar findings were obtained by Balota et al (2005) for the effect of take-all disease on gas-exchange of wheat grown in soil in pots. Ayres (1978) indicated that plant pathogens may prevent stomatal closure or lower stomatal resistance resulting in lower WUE of the plant.…”

“…When compared with the results of Kirkegaard et al. (1999) and Balota et al. (2005), this suggests that moderate root damage by pathogens may have only a modest effect on water relations of wheat.…”

“…This can be expressed as water-use efficiency (WUE), which is the ratio of biomass produced to water used, typically measured at the whole-plant or area level, or as instantaneous WUE that is the ratio of carbon assimilation to transpiration, typically measured at the leaf level. Balota et al (2005) reported a reduction in instantaneous WUE of wheat infected with take-all, with a greater effect at higher disease ratings. Similarly, Martin et al (1986) reported a reduction in whole-plant WUE in wheat infected with Cephalosporium gramineaum, but this causes a vascular wilt disease rather than a root rot and its effects on host physiology could be different from other soilborne diseases.…”

“…This can be expressed as water‐use efficiency (WUE), which is the ratio of biomass produced to water used, typically measured at the whole‐plant or area level, or as instantaneous WUE that is the ratio of carbon assimilation to transpiration, typically measured at the leaf level. Balota et al. (2005) reported a reduction in instantaneous WUE of wheat infected with take‐all, with a greater effect at higher disease ratings.…”

“…Reduced carbon assimilation, growth and yield were correlated with reduced transpiration in wheat inoculated with Heterodera avenae (cereal cyst nematode) (Amir and Sinclair 1996) supporting a direct link between root damage, water uptake and growth depression. On the other hand, Balota et al (2005) reported a relatively small effect of inoculation with Gauemannomyces graminis var. tritici (take-all) on transpiration in wheat and suggested that the large effects of disease on carbon assimilation and growth rate were not directly due to water stress.…”