Effects of rust and post‐infection drought on photosynthesis, growth and water relations in groundsel

Abstract

Exchanges of CO2 and water vapour were examined in groundsel, Senecio vulgaris, grown and infected with rust, Puccinia lagenophorae, under laboratory conditions. The effects of drouglit were examined by withholding water from plants from 2 days until approximately 10 days after infection, after which further daily water losses were restored. Net photosynthesis was inhibited and dark respiration was stimulated in rust-infected leaves but, in young healthy leaves on the same plant, gross and net photosynthesis were stimulated and photorespiration was inhibited. The growth of plants was stunted 15 days after infection because the growth of leaf area was inhibited and, thereby, the photosynthetic capacity of the plant was reduced. Drought inhibited the growth of leaf area in both healthy and infected plants and, when combined with rust, had additive deleterious effects on net photosynthesis per plant and on growth. After sporulation, rusted plants transpired more rapidly than did healthy controls and leaf water potential fell to reach -0-95 and-1-92 MPa in well-watered and drouglit-stressed plants respectively, compared with -0-18 and -1 -2 MPa in healthy controls, 20 days after infection. Rust impaired the normal increase in Water-Use Efficiency in response to drought.

Interactive effects of drought and pathogens in forest trees

“…Since both infection and drought act as stressors, each reducing the plant's capacity for plastic response, it is likely that their combined occurrence has additive deleterious effects and may lead more rapidly to exhaustion [10]. Paul and Ayres [154,155] provided a nice illustrative example in a series of experiments with groundsel rust, showing that mechanisms of compensation for infection (principally higher leaf-to-root ratio) were much less effective during drought than in well-watered plants and even an aggravating factor of water stress. Mechanisms producing a synergistic effect between water deficit and infection in trees have been described in a study of Dutch elm disease (DED) in Ulmus minor [183].…”

WATER STRESS MODIFIES INTRASPECIFIC INTERFERENCE BETWEEN RUST (PUCCINIA LAGENOPHORAE COOKE)‐INFECTED AND HEALTHY GROUNDSEL (SENECIO VULGARIS L.)

“…The effects of such stress may differ from those occurring when comparatively mild water deficits develop relatively slowly and concurrently with plant growth, as may often occur in the field. Under such conditions total water loss from the whole plant may be little changed by rust, despite increased loss per unit leaf area, because of the inhibition of leaf growth which also results from disease (Paul & Ayres, 1984). However, the maintenance of water fiux depends upon the rusted plant having access to water as soil drying progresses.…”

“…On 21 July, plants were inoculated with an aqueous suspension of aeciospores oi Puccinia lagenophorae Cooke applied using a camel hair brush. After inoculation all populations were covered with black polythene sheet for 24 h to provide conditions of darkness and high humidity necessary for infection (Paul & Ayres, 1984). Inoculation was repeated on 29 July and 4 August to ensure high and uniform levels of infection.…”

Identification of powdery mildew (Erysiphe graminis sp. tritici) and take-all disease (Gaeumannomyces graminis sp. tritici) in wheat (Triticum aestivum L.) by means of leaf reflectance measurements

“…The different physiological effects of the fungus depend on the nature of the interaction with the host. Foliar pathogens affect their host in a number of ways, including reducing photosynthesis in infected leaves, increasing water loss through transpiration [21], and diminishing water uptake by the roots [22]. However, root-born or systemic pathogens are often much harder to detect [20].…”