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Potential contribution of selected canopy traits to the tolerance of foliar disease by spring barley

Bingham, I.J., Topp, C.F.E.
Plant pathology 2009 v.58 no.6 pp. 1010-1020
Hordeum vulgare, absorption, canopy, disease resistance, disease severity, foliar diseases, genetic variation, germplasm, leaf area index, leaves, models, photosynthesis, solar radiation, spring barley, temperature, Scotland
A model of canopy photosynthesis and above-ground growth rate was used to investigate the potential impact of several canopy traits on tolerance of foliar disease by barley. Disease tolerance was defined as the reduction in predicted crop dry-matter growth rate per unit of visible disease symptoms. The traits were canopy area (leaf area index, LAI), light extinction coefficient (k) and the ratio of virtual to visible lesion size (β). The effects of altering the area of the healthy flag leaf and its light-saturated rate of photosynthesis (Pmax) in response to disease elsewhere on the plant were also investigated. The model was parameterized for spring barley and run with a solar radiation and temperature regime typical of north-east Scotland. Predicted reductions in growth rate per unit increase in disease were greatest at high disease severity and when disease was distributed relatively uniformly through the canopy. Tolerance was increased by increasing LAI to >3 and k to >0·3, but the beneficial effects depended on the severity and, to a lesser extent, the distribution of disease. Tolerance was reduced by increasing β. A sensitivity analysis performed at a single disease severity and distribution showed that tolerance was most sensitive to variations in β and compensatory adjustments in area and Pmax of the flag leaf, and least sensitive to whole canopy LAI and k. Future research should quantify the genetic variation in these traits within barley germplasm to evaluate the scope for improving the disease tolerance of spring barley.