The effects of inter-row spacing of Leucaena leucocephala (Lam.) de Wit in an alley cropping system on the incidence and severity of rust (Uromyces appendiculatus (Pers.) Unger) on intercropped beans (Phaseolus vulgaris L.) and their yield were examined over 2 years (1993 and 1994) at Chepkoilel Campus in Kenya. Each experiment consisted of three randomized blocks with treatments of three alley widths (2 m, 4 m and 8 m) and a treeless control with two intra-row spacings of Leucaena (0.5 m and 1.0 m). Hedgerows were coppiced at 1.0 m height and pruned subsequently at 2–3 months intervals. No fertilizer was applied but Leucaena loppings were incorporated as green leaf manure. Rust on beans was assessed at three growth stages in each season, using the Centro International de Agricultura Tropical (CIAT) scales. Microclimate was monitored in treatments, in 1994. Bean growth and yield were also measured. Rust increased with increasing alley width and was less severe in bean rows adjacent to hedgerows. Bean yield was highest in the treeless control plots and declined with decreasing alley width. Beans in 2 m alleys had significantly lower (p < 0.05) yields than 8 m alleys and treeless control plots. Bean growth was greatly modified in 2 m alleys and close to hedgerows. Light availability and diurnal temperature increased with alley width but relative humidity and leaf wetness duration decreased. Proximity to hedgerows also had marked effect on microclimate. The changes in yield, rust incidence and severity were examined in relation to microclimate, inoculum survival and dispersal.

The effects of inter-row spacing of Leucaena leucocephala in an alley cropping system on the incidence and severity of diseases on intercropped beans ( Phaseolus vulgaris L.) and their yield were examined over two years (1993 and 1994) at Chepkoilel Campus in Kenya. Each experiment consisted of three randomized blocks with treatments of three alley widths (2 m,4 m and 8 m) and a treeless control with two intra-row spacings of Leucaena (0.5 m and 1.0 m). Hedgerows were coppiced at 1.0 m height and pruned subsequently at two-to-three months intervals. No fertilizer was applied but Leucaena loppings were incorporated as green leaf manure. Incidence of angular leaf spot ( Phaeoisariopsis griseola ) and anthracnose ( Colletotrichum lindemuthianum ) on beans were assessed at three growth stages in each season, using the Centro International de Agricultura Tropical (CIAT) scales. Microclimate was monitored in treatments, in 1994. Angular leaf spot and anthracnose decreased with increasing alley width and were more severe in bean rows adjacent to hedgerows. Light availability and diurnal temperaturereaching the bean canopy increased with alley width but relative humidity and leaf wetness duration decreased. Proximity to hedgerows also had markedly reduced light levels, lower temperatures and higher relative humidity. Higher incidence and severity of angular leaf spot and anthracnose on beans in alleys than on beans in treeless plots were examined in relation to microclimate, inoculum survival and dispersal. The pattern of the diseases was best explained by microclimate changes induced by Leucaena hedgerows, especially effects of humidity.

Although there was no difference in the percentage of powdery mildew conidia that germinated on the second leaf of barley plants grown in either 350 or 700 ppm CO2, the percentage of conidia that progressed to produce colonies was lower in plants grown in 700 than in 350 ppm CO2. The lower percentage of conidia producing hyphae in 700 ppm CO2 was due to a higher proportion of the spores being arrested at the appressorial stage. The reduction in penetration of spores in 700 ppm CO2 was due neither to 700 ppm CO2 per se, nor to ontogenetic changes in the host tissue. Removing the epicuticular waxes from the surface of the leaf had no effect on the development of conidia on the surface of leaves in 350 or 700 ppm CO2, showing that increased epicuticular waxes were not causing the increased resistance to primary penetration of powdery mildew in 700 ppm CO2. We relate reduced rates of primary penetration in barley grown in 700 ppm CO2 to higher rates of net photosynthesis allowing increased mobilisation of resources into resistance including the production of papillae and accumulation of silicon at the sites of appressorial penetration. Established colonies of powdery mildew grew faster in 700 ppm CO2 than in 350 ppm CO2, coincident with accumulation of host carbohydrate in the source leaf.

summaryThe dry weight of barley plants in 700 μmol mol−1CO2 was increased by 19 d after planting relative to plants grown in 350 μmol mol−1CO2. Infection of the second leaf by powdery mildew led to reduced growth rates in both 350 and 700 μmol mol−1CO2, but the reduction in growth was transitory in 350 μmol mol−1CO2. Neither the allometric coefficient k between shoot and root, nor the leaf weight ratio, was altered by growth in 700 μmol mol−1CO2 or by infection with powdery mildew. The number of tillers produced increased per plant but not per unit d. wt in 700 μmol mol−1CO2. The growth response of barley to increased concentrations of CO2 and/or to infection with powdery mildew was not associated with alterations in net carbon partitioning, so a change in the ratio of photosynthetic to non‐photosynthetic tissue, contributed to neither the growth response of barley to 700 μmol mol−1CO2 nor to infection with powdery mildew. The increase in the growth rate of barley in 700 μmol mol−1CO2 and the reduction in the growth rate after infection occurred at the same time as increased and reduced rates of net photosynthesis respectively.

Although there was no difference in the percentage of powdery mildew conidia that germinated on the second leaf of barley plants grown in either 350 or 700ppm CO2, the percentage of conidia that progressed to produce colonies was lower in plants grown in 700 than in 350ppm CO2. The lower percentage of conidia producing hyphae in 700ppm CO2was due to a higher proportion of the spores being arrested at the appressorial stage. The reduction in penetration of spores in 700ppm CO2was due neither to 700ppm CO2per se,nor to ontogenetic changes in the host tissue. Removing the epicuticular waxes from the surface of the leaf had no effect on the development of conidia on the surface of leaves in 350 or 700ppm CO2, showing that increased epicuticular waxes were not causing the increased resistance to primary penetration of powdery mildew in 700ppm CO2. We relate reduced rates of primary penetration in barley grown in 700ppm CO2to higher rates of net photosynthesis allowing increased mobilisation of resources into resistance including the production of papillae and accumulation of silicon at the sites of appressorial penetration. Established colonies of powdery mildew grew faster in 700ppm CO2than in 350ppm CO2, coincident with accumulation of host carbohydrate in the source leaf.

summaryThe rate of net photosynthesis in the second leaf of barley was higher in 700 than 350 μmol mol−1CO2, when measured in the CO2 concentration in which the plants were grown, but the magnitude of this difference decreased as the leaf aged. Infection by powdery mildew accelerated the decline in net photosynthesis of leaves grown in either 350 or 700 μmol mol−1CO2. A/Ci curves allowed the reduction in net photosynthesis of plants exposed to 700 μmol mol−1CO2 or after infection by powdery mildew to be related to changes in the carboxylation efficiency or in the regeneration of ribulose 1,5‐bisphosphate. The carboxylation efficiency declined in plants exposed to 700 μmol mol−1CO2. In plants infected with powdery mildew, the reduction in net photosynthesis was associated with both reduced carboxylation efficiency and reduced ability to regenerate ribulose 1,5‐bisphosphate. Reduced carboxylation efficiency of the second leaf of plants grown in 700 μmol mol−1CO2, was not associated with a reduction in the concentration of rubisco within the leaf. In contrast to the presence of a close exogenous sink, leaf age had large effects on the acclimation of photosynthesis to 700 μmol mol−1CO2.

summary Soluble carbohydrate accumulated faster in second leaf blades of barley when plants were grown in 700 μmol mol−1 CO2 rather than 350 μmol mol−1 CO2. Infection of the second leaf blade by powdery mildew had no effect on the concentration of soluble carbohydrate until 6 d after inoculation when it was lower than in controls. The accumulation of soluble carbohydrate in the second leaf of uninfected plants grown in 700 μmol mol−1 CO2 was due largely to earlier and faster accumulation of fructan. TLC showed that the series of fructan was not different in plants grown in 700 μmol μmol−1 CO2 relative to plants grown in 350 μmol mol−1 CO2, neither did infection by powdery mildew affect the series of fructan present in the second leaf blade. The rate constant for phloem loading obtained by compartmental analysis of 14C efflux from the leaf blade was not reduced in plants grown in 700 μmol mol−1 CO2, indicating that carbohydrate accumulation was not caused by reduced ability of the leaf to export carbon.

summaryWheat (Triticum aestivum L. cv. Longbow) was grown hydroponically with either 0, 0.33 or 3.3 mol Pi m−3 and, after 12 d, was infected with powdery mildew (Erysiphe graminis D.C. ex Merat f.sp. tritici). Fructan content of infected first leaves was increased by mildew infection but infection increased starch content only at 0 Pi. Photosynthetic 14CO2 fixation was reduced by infection, especially at 0 Pi. Accumulation of 14C in fructan rose with reduced Pi supply but was unaffected by mildew; accumulation of 14C in starch was lower in infected leaves. Pi deficiency increased the content of sugars in the apoplast, as did mildew infection, the greatest content being in infected leaves of low Pi status. Acid invertase activity was increased by infection but was not affected by Pi status. Thus P‐deficiency alone does not mimic the effects of mildew but Pi status and mildew interact in their effect on leaf carbohydrate metabolism.

summaryWheat grown hydroponically on three concentrations of inorganic phosphate (0, 0.33 and 3.30 mol m−3 P1) was infected with Erysiphe graminis when 12 d old. Large differences in P status, but small differences in growth due to Pi supply, were seen in uninfected controls 5 and 8 d later. Mildew, did not alter the P content of any part of the plants, but did increase the rate of respiration of infected leaves. Whilst mildew reduced the photosynthetic rate of leaves on plants grown at high Pi concentrations to about 50% of non‐infected controls, an interaction between the effects of mildew and Pi concentration resulted in a fall of photosynthesis to very low rates in plants grown on zero Pi.

Wild type (Rif−) and rifampicin resistant (Rif+) isolates of fluorescent Pseudomonads were grown in King’s B liquid medium in the presence and absence of iron and subcultured every 48 h for 12 days. Growth rates and the proportion of non-fluorescent colonies were measured. All Rif+ isolates when grown in the presence of iron produced a significantly higher proportion of non-fluorescent colonies. One Rif+ isolate had a reduced growth rate.

Methods are described for measuring the colonisation of a radish (Raphanus sativus) root system by seedlings with rifampicin resistant fluorescent pseudomonads by dilution plating, and which would take account of differences in root morphology. Differences in the levels of pseudomonad colonisation was highly dependent on the units in which surface areas was expressed. Population levels are expressed using estimates of surface area based on root length, tap-root length and root weight. The best estimate of surface area was root length, but the most practical method was surface area calculated as a function of dry weight. This method could differentiate differences in the levels of root colonisation independent of differences in root morphology and was efficient enough to allow the routine processing of a large number of replicate root samples.

The colonisation of a radish root system by strains ofPseudomonas fluorescens, selected for their ability to promote potato and radish growth under different environmental conditions is reported. In pot experiments colonisation of different parts of the root system was measured at different temperatures, in different watering regimes and in sterile and recropped soil. Root colonisation was extensive but populations were highest on the upper root system and their distribution throughout the root system was greatly affected by environmental factors. percolation of water through the soil and partial soil sterilisation enhanced colonisation but the effects of temperature and recropping were complex. Growth promotion was unpredictable and there was no simple relationship between PGPR colonisation and stimulation of plant growth.

Comparisons are made of the aerodynamic drag coefficients measured on four truck models in four closed-jet wind tunnels and one three-quarter open-jet wind tunnel. Significant differences were found between the drag levels in the different tunnels, with the open-jet tunnel measuring lower drag levels than the closed-jet tunnels. The application of blockage corrections to all the measurements bring the data into closer, but not exact, agreement.

SummaryThe kinetics of ion efflux from leaf discs were used to show that there is no general increase in the permeability of plasmalemma or tonoplast resulting from infection of barley leaves by brown rust (Puccinia hordei Otth.). An assay of in vivo chlorophyll fluorescence showed that there were clear differences between chloroplasts in healthy and diseased tissue, but overall the thylakoid lamellae function well in rusted barley leaves. We conclude that in this biotrophic system there is no gross impairment of host membrane integrity, and show that delivery of host nutrients to the apoplast is at rates greatly in excess of those needed to accommodate fungal nutrient uptake. This does not preclude localized effects of the pathogen on host membranes.

SummaryThe movement of 32P, fractionation of 32P and unlabelled phosphorus, and efflux of 32P from leaf discs, in control and brown‐rust infected first leaf blades of barley are described for the day of sporulation, 7 d after infection. It is shown that P retranslocation is greatly reduced by disease, that the concentration of P in the infected leaf blade increases greatly and that the increase is probably largely in the fungus, and partly in the form of polyphosphate. The P content of fungal spores is derived largely from P currently entering the leaf in the xylem. The data are used to derive P budgets for control and infected leaf‐blades, and the significance of P to the diseased state is discussed.

SummaryTranslocation of14C from first leaves of barley is reduced by rust infection. Infection of the leaf base alone results in enhanced loss of14C from the leaf tip, whilst infected leaf tips show greatly reduced loss. Concentrations of soluble sugar are lower and those of storage polysaccharide higher in rusted leaves. Their amounts and the kinetics of flux of14C through them are used to validate a compartmental model of translocatory carbon flux derived from the pattern of14C‐effiux from the leaf. This model suggests that the major consequences of infection are reduced size of the sucrose transport pool and elimination of a phase of efflux with a half‐life of 2h.

The rate of net photosynthesis is reduced in leaves of barley infected with brown rust. This reduction is not due to reduced carbon dioxide fixation per chloroplast, but is ascribed to a decrease in the number of functional chloroplasts. Chloroplasts isolated from diseased leaves show increased contents of starch and phosphorus, and unaltered rates of ferricyanide-dependent oxygen evolution, as compared with controls. Fluxes through the phosphate translocator on the chloroplast inner envelope are shown to be higher in diseased leaves. The kinetics of in vivo chlorophyll fluorescence induction are described, and it is shown that whilst they change with leaf age in control leaves, in diseased leaves the juvenile kinetics are retained. These data are interpreted as showing that each surviving chloroplast in diseased leaves is functioning at least as well as those from healthy leaves.

Levels of calcium, magnesium, potassium, nitrogen and phosphorus have been measured in young barley plants with the first leaf infected with brown rust. The rate of uptake per unit of root was increased by disease for the cations and nitrogen but not for phosphorus. In infected leaves, potassium and phosphorus accumulated to above control levels. The behaviour of the cations can be entirely explained by relatively unaltered xylem import into diseased leaves, but reduced export of the phloem-mobile ions. Nitrogen and phosphorus show more complex behaviour. Nitrogen import into infected leaves was increased, whilst the increased level of phosphorus in diseased leaves is explicable by reduced retranslocation coupled with active accumulation within the infected leaf blade.

Barley plants infected with brown rust at the first leaf stage showed reduced growth over the following 16 days. This could be accounted for entirely by reduced net photosynthesis of, and transport from, the infected leaf. Diseased leaves had reduced net photosynthesis, increased dark and photo-respiration and slightly decreased stomatal resistance. A treatment of photosynthesis as a diffusion process showed a doubling of mesophyll resistance, calculated on a total leaf area basis, following disease. The utility of diffusion models in rusted leaves is discussed.