Greater Yield Reduction Research Articles

Genotypic variation in grain cadmium concentration in wheat: Insights into soil pollution, agronomic characteristics, and rhizosphere microbial communities

Soil cadmium (Cd) pollution poses a serious threat to both the productivity and quality of wheat. This study aimed to investigate the genotypic variation in grain Cd concentration in wheat through field and pot experiments. Among 273 wheat genotypes, a significant genotypic difference was found in grain Cd concentration, ranging from 0.01 to 0.14 mg kg−1. Two contrasting genotypes, X321 (a low grain Cd accumulator) and X128 (a high grain Cd accumulator), were selected for pot experiments. X321 exhibited a 17.9% greater reduction in yield and a 10.2% lower shoot-to-grain Cd translocation rate than X128 under Cd treatment. Grain Cd content showed a positive correlation with soil available Cd content and a negative correlation with Cu content. Soil catalase activity significantly decreased in X128 under Cd stress, whereas no difference was found in X321. The grains of X321 exhibited a more compact spatial distribution of starch grains and protein matrix than those of X128. Moreover, the size of A-type starch in X128 was larger than in X321. Meanwhile, X128 contained much B-type starch, with some surface pits observed on A-type granules under Cd stress. Cd treatment increased the abundance of rhizosphere microorganism communities, with Ellin6067 and Ramlibacter being enriched in X128 under Cd treatment, which might facilitate Cd uptake. The accumulation of Cd in grains demonstrated a strong positive correlation with the rhizosphere bacterial diversity (correlation coefficient = 0.78). These findings provide new insights into the basis of grain Cd accumulation in wheat and have potential implications for developing new verities with low Cd accumulation to ensure food safety and minimize human exposure.

Quantitative responses of tomato yield, fruit quality and water use efficiency to soil salinity under different water regimes in Northwest China

Reduced irrigation and high soil salinity are widely recognized to decrease tomato yield, but they can improve fruit quality and water use efficiency (WUE) when imposed appropriately. However, the response of plant to their interaction is still unclear, and the quantitative relationship of WUE and fruit quality with salinity under different water regimes is also lacking. This study investigated the responses of tomatoes in terms of yield, fruit quality, and WUE based on yield (WUEy), biomass (WUEb), and leaf (iWUE) to twelve treatments, consisting of combinations of three water regimes relative to the field capacity (FC) (W0, W1, and W2 refer to 95 % FC, 75 % FC, and 60 % FC, respectively) and four soil salinity levels (0 g, 2 g, 4 g, and 6 g salt mixtures added to 1000 g air-dried soil, respectively). Results showed that WUEy and WUEb had a negative correlation with salinity under different water regimes. Salinity resulted in a greater reduction in yield and biomass than water consumption compared to the control treatment. Therefore, lower water consumption of plants under W2 treatment alleviated the decrease of WUEy induced by salinity to a certain extent. From the leaf scale, iWUE was positively and linearly related with salinity, indicating that stomatal regulation was more prone to reduced stomatal conductance than the net photosynthetic rate under W0 and W1. Whilst it showed a quadratic relationship under W2, the results supported that a highly salinity-induced iWUE was dependent on water supply. In addition, although salinity had a negative correlation with fruit fresh mass (FM), dry matter content, and water content (WC) under W0 and W1, fruit titratable acidity (TA) and total soluble solids (TSS) were proportional to salinity regardless of water regimes. The results also showed that W1 increased the sensitivity of TA and TSS to salinity, but W2 resulted in weak sensitivity of FM and WC to salinity. Thus, we deduced that mildly reduced irrigation was an appropriate strategy to regulate iWUE and fruit quality under high salinity conditions. This study provides a water regime management basis for comprehensive changes in yield, WUE, and fruit quality of tomatoes grown in saline soils.

Pastures and Climate Extremes: Impacts of Cool Season Warming and Drought on the Productivity of Key Pasture Species in a Field Experiment.

Shifts in the timing, intensity and/or frequency of climate extremes, such as severe drought and heatwaves, can generate sustained shifts in ecosystem function with important ecological and economic impacts for rangelands and managed pastures. The Pastures and Climate Extremes experiment (PACE) in Southeast Australia was designed to investigate the impacts of a severe winter/spring drought (60% rainfall reduction) and, for a subset of species, a factorial combination of drought and elevated temperature (ambient +3°C) on pasture productivity. The experiment included nine common pasture and Australian rangeland species from three plant functional groups (C3 grasses, C4 grasses and legumes) planted in monoculture. Winter/spring drought resulted in productivity declines of 45% on average and up to 74% for the most affected species (Digitaria eriantha) during the 6-month treatment period, with eight of the nine species exhibiting significant yield reductions. Despite considerable variation in species’ sensitivity to drought, C4 grasses were more strongly affected by this treatment than C3 grasses or legumes. Warming also had negative effects on cool-season productivity, associated at least partially with exceedance of optimum growth temperatures in spring and indirect effects on soil water content. The combination of winter/spring drought and year-round warming resulted in the greatest yield reductions. We identified responses that were either additive (Festuca), or less-than-additive (Medicago), where warming reduced the magnitude of drought effects. Results from this study highlight the sensitivity of diverse pasture species to increases in winter and spring drought severity similar to those predicted for this region, and that anticipated benefits of cool-season warming are unlikely to be realized. Overall, the substantial negative impacts on productivity suggest that future, warmer, drier climates will result in shortfalls in cool-season forage availability, with profound implications for the livestock industry and natural grazer communities.

How Does the Waterlogging Regime Affect Crop Yield? A Global Meta-Analysis.

Waterlogging, an abiotic stress, severely restricts crop yield in various parts of the world. Thus, we conducted a meta-analysis of 2,419 comparisons from 115 studies to comprehensively evaluate the overall change in crop yield induced by waterlogging in the global region. The results suggested that waterlogging obviously decreased crop yield by 32.9% on average, compared with no waterlogging, which was a result of a reduced 1,000-grain weight (13.67%), biomass (28.89%), plant height (10.68%), net photosynthetic rate (Pn, 39.04%), and leaf area index (LAI, 22.89%). The overall effect of a waterlogging regime on crop yield is related to the crop type; the crop yield reduction varied between wheat (25.53%) and cotton (59.95%), with an overall average value of 36.81% under field conditions. In addition, we also found that compared with no waterlogging, waterlogging in the reproductive growth stage (41.90%) caused a greater yield reduction than in the vegetative growth stage (34.75%). Furthermore, decreases in crop yield were observed with an extension in the waterlogging duration; the greatest decreases in crop yield occurred at 15 < D ≤ 28 (53.19 and 55.96%) under field and potted conditions, respectively. Overall, the results of this meta-analysis showed that waterlogging can decrease crop yield and was mainly affected by crop type, growth stage, and experimental duration.

Effects of Soybean Planting Date on Yield Loss From Defoliation

Soybean, Glycine max (L.) Merr., is planted during 3.5-4 mo across the Mid-South United States. Currently, no information exists regarding the effects of planting date on soybean yield loss from early season defoliation. In 2015 and 2016, to evaluate the effects of planting date on yield loss from defoliation, soybean were planted in field plots 2 wk apart from early April to mid-June, for a total of six planting dates. Each planting date included a nondefoliated control and a 100% defoliation treatment where leaves were manually excised at the V4 growth stage. Mean yield loss from defoliation varied across planting dates, with mid-April plantings having the least amount yield reduction, 573 kg/ha, and early-June plantings having the greatest yield reduction, 904 kg/ha. Percent yield reduction from defoliation increased as planting was delayed, suggesting that defoliation thresholds might need adjustment based on planting date and yield potential. However, more research is needed at lower levels of defoliation to accurately delineate such thresholds.

Field Performance and Susceptibility to Fungal Pathogens of Eleven Blackberry Cultivars

ABSTRACT Horticultural performance of eleven blackberry cultivars, including two primocane-fruiting cultivars, was evaluated over three years after fruiting began at the Musser Fruit Research Center in South Carolina, United States. Results showed differences in yield between cultivars for each year of the study. ‘Natchez’ had the highest cumulative yield after three years, followed by ‘Navaho’, ‘Von’, and ‘Osage’, whereas ‘Prime-Ark® Traveler’ produced significantly less than these four cultivars. Yield steadily declined for all cultivars over the three years, except for ‘Osage’, which remained consistent. ‘Prime-Ark® Freedom’ always had the largest fruit, although it had the greatest yield reduction after the second year. Multiple factors may explain yield decline for the majority of the cultivars studied, including freeze damage and tip dieback. Tip dieback was observed in 2016 in multiple cultivars, but dieback incidence was highest on ‘Prime-Ark® Traveler’. The dieback was associated with an outbreak of broad mites and thrips in the experimental block and with secondary pathogens isolated from the decaying tissues primarily Fusarium spp. and Alternaria spp. Cultivar differences in susceptibility to Alternaria spp. were confirmed in laboratory studies.

Effect of micronutrient and bioactive compounds fortified organic manure on the growth and yield of blackgram in coastal saline soil

The micronutrients availability especially Zn and Fe is low in coastal saline soils due to soil characters such as poor texture, organic matter, leaching and chemical reaction involving precipitation and fixation at high pH and salinity. This results in greater yield reduction in such soil. To evaluate the influence of fortified organic manures on the growth and yield of blackgram in coastal saline soil, one field experiment was conducted in a farmer's field at Arunmozhidevan village, Parangipettai Block, of Tamil Nadu state during January-March 2018. The texture of the soil was sandy loam and taxonomically classified as Typic Ustifluvent. The soil analyzed pH 7.93, EC 2.03 dS/m and represented low status of organic carbon (0.44%). The soil had low alkaline KMnO4-N (120.21 kg/ha), Olsen-P (7.18 kg/ha) and NH4OAc-K (275.70 kg/ha). The following treatments, namely, T1-Control (recommended NPK), T2-NPK+ZnSO4 @ 25 kg/ha+FeSO4 @ 25 kg/ha, T3-NPK+100% Zn and Fe fortified organic manure @ 5 t/ha, T4-NPK+100% Zn and Fe+bio-active compounds fortified organic manure @ 5 t/ha, T5-NPK+75% Zn and Fe fortified organic manure @ 5 t/ha, T6-NPK+75% Zn and Fe+bio-active compounds fortified organic manure @ 5 t/ha, T7-NPK+50% Zn and Fe fortified organic manure @ 5 t/ha and T8-NPK+50% Zn and Fe+bio-active compounds fortified organic manure @ 5 t/ha were studied in RBD with three replications. Blackgram variety ADT 3 was cultivated. The results of the field experiment showed that all the growth characters like plant height, DMP, LAI, number of branches and yield components viz., number of pods per plant, number of flowers and 100-seed weight and seed and haulm yield were significantly influenced by the fortified manure application. Among the treatments, T6-NPK+75% Zn and Fe+bio-active compounds fortified organic manure @ 5 t/ha was superior in significantly increasing the growth and yield of blackgram. This treatment recorded a seed and haulm yield of 763 and 1314 kg/ha, respectively.

Effect of Abiotic Stress on Irrigated Maize Forage Yield as Compared to Sorghum

A study was conducted in Sudan (Africa) during the summer and winter seasons (2013 – 2014) at two locations: Shambat (normal soils) and Soba (salt affected soils). Nine maize (ZeamaysL.) and sorghum (Sorghum bicolor(L.) Moench) cultivars were studied under two watering regimes arranged in split plot experiment in randomized complete block design. The eight test-environments created by the combination of locations, seasons and watering regimes were used to investigate the effect of salt, water and heat stresses on forage yield and some related traits. The results showed that separate and combined stress factors significantly reduced forage yield. The greatest reduction in dry matter yield caused by one factor was shown by salt stress (29.6%) and the least reduction was caused by heat stress (3.9%). Water stress coupled with either heat or salt stress caused the greater reduction in yield (37.0%-43.3%) than the combination of the other factors. Full stress caused 53.8% yield reduction. Days to tasseling was significantly reduced by heat stress whereas water and salt stress showed no significant effect on tasseling duration. Full stress caused the greatest effect on days to tasseling. Plant height and stem diameter were significantly reduced by salt and water stress. Two hybrids kept top rank in yield through most abiotic stress levels showing resilience to unfavorable environments. All maize genotypes significantly outyielded the sorghum check under no heat stress (winter sowing) regardless the effect of salt and water stresses while the opposite is true under the heat stress (summer sowing). It was concluded that salt and water stress are the major abiotic stresses limiting forage maize production. Maize tolerate better reduction in temperature than dose sorghum while the latter tolerate better salt and water stresses than dose maize. Forage maize could be competitively grown during summer if water and salt stresses are avoided

Artificial Defoliation to Simulate Losses on Production of Bean (&amp;lt;i&amp;gt;Phaseolus vulgaris&amp;lt;/i&amp;gt; L. cv. Goytacazes)

The reduction of foliar area can cause yield reduction in common bean crops. The objective of this work was to verify which is the effect of different defoliation levels realized in several development stages of common bean (Phaseolus vulgaris L. cv. Goytacazes) over yield, weight of 100 seeds and number of pods per plant. The experimental design was randomized blocks, in a split-plot arrangement with five replications. The plot corresponded to the five defoliation epochs (first trifoliate leaf, flowering, pods formation, pods filling, and dry pods). In each plot, the split plot was represented by the four defoliation levels (0%, 33%, 67% and 100%). It was observed a decrease of yield for all levels defoliation considering all development stages, except for dried pods. The highest decrease was detected for flowering and pods formation. Through the regression analysis got a greater reduction in yield with 100% defoliation made at 42 days after emergence. The evaluation parameter that showed better relation with yield was a number of pods per plant.

Effects of drought stress at different growth stages on photosynthetic efficiency and water consumption characteristics in sweet potato.

To investigate the effects of drought stress on the growth of sweet potato, photosynthesis, yield, and water consumption characteristics were investigated in field-grown sweet potato plants (Jishu 21, a drought-tolerant cultivar) at different growth stages in 2014-2015. There were five drought treatments, including the whole growth period (DS), the early stage of growth (rooting and branching period, DS1), the middle stage of growth (storage root initiation period, DS2), and the late stage of growth (storage root bulking period, DS3), and a normal irrigation treatment (WW) as control. The results showed that sweet potato plants in DS significantly decreased in dry mass, biomass, and harvest index during two years. The biomass of sweet potato under DS, DS1, DS2 and DS3 was decreased by 31.3%, 21.2%, 19.6% and 7.7%; the harvest index was decreased by 19.9%, 14.5%, 14.1% and 6.5%, and the dry mass was decreased by 45.3%, 33.1%, 31.3% and 14.2%, respectively. The leaf area index in DS, DS1, DS2 and DS3 was decreased by 77.1%, 60.1%, 39.2% and 17.1% at 100 days after transplanting (DAT), and the net photosynthesis was decreased by 56.7%, 26.6%, 18.7% and 9.5% at 90 DAT, respectively. Plants under drought stress reduced diurnal evaporation, transpiration rate, water consumption, daily water consumption, and soil water use efficiency, but increased irrigation water use efficiency. Drought stress decreased leaf area index, Pn, biomass and the allocation of biomass to storage root, resulting in a significant reduction of yield. The early drought and the long stress duration had significant impacts on leaf area index, Pn, biomass and harvest index, leading to a greater reduction in yield and water use efficiency. Therefore, drought stress at the early growth stages of sweet potato should be avoided during cultivation.

Combined effects of ocean acidification and nutrient levels on the photosynthetic performance of Thalassiosira (Conticribra) weissflogii (Bacillariophyta)

:The purpose of this study was to investigate the effects of ocean acidification and nutrient level on the growth and photosynthetic performance of the diatom Thalassiosira (Conticribra) weissflogii. Cells were exposed to varying levels of CO2 [current CO2 (LC), 400 μatm; high CO2 (HC), 1000 μatm] and nutrients, with NO3− and PO43− concentrations enriched, respectively, at 50 μmol l−1 and 5 μmol l−1 [high nutrient (HN)], 20 μmol l−1 and 2 μmol l−1 [mid-level nutrient (MN)] and 10 μmol l−1 and 1 μmol l−1 [low nutrient (LN)]. After acclimatization for over 20 generations, no significant differences in growth rates were observed between LC and HC cultures under both HN and LN conditions; whereas, HC significantly reduced the growth rate under MN conditions. Lower nutrient loading significantly inhibited the growth rates of both LC and HC cultures; whereas, HC (but not LC) significantly decreased chlorophyll a and carotenoid contents in LN treatments. HC conditions significantly increased maximum relative electron transport rates (rETRmax) and saturating light intensity (Ik) of HN cultures, with rETRmax showing a positive relationship with growth rates stimulated by nutrient enrichments. The maximum (Fv/Fm) and effective quantum yield (Yield) were all inhibited under LN conditions, with the greatest reduction in Yield observed under LC conditions, corresponding to the highest nonphotochemical quenching, lowest light use efficiency (α) and lowest rETRmax. Based on these results, ocean acidification and nutrient availability may influence photosynthetic performance in T. weissflogii individually or interactively, with the future growth of marine diatoms mediated by these codependent environmental drivers.

Proline Content and Membrane Permeability Index in Response to Water Stress in Recombinant Inbred Lines of Lentil

Proline Content and Membrane Permeability Index in Response to Water Stress in Recombinant Inbred Lines of Lentil Proline content and membrane permeability index are important stress related parameters. Field experiments were conducted to examine the effect of proline and membrane permeability index on 135 recombinant inbred lines (RILs) under irrigated and rainfed conditions and to analyze their relationship with yield and its component traits in lentil. Higher content (1.89 ± 0.046 mg g-1 FW) of proline was found under rainfed conditions in comparison to irrigated (1.22 ± 0.040 mg g-1 FW). The membrane permeability index of lentil lines increased significantly under rainfed conditions from 63.17 to 84.32 percent. The seed yield was significantly higher in irrigated (122.88 g/plot) than in rainfed conditions (69.99 g/ plot). RILs were categorized in five subsets based on percent yield reduction due to water stress in rainfed conditions. It was found that RIL-23,-78,-86,-90,-95,-104,-109 and-111 recorded minimum yield reduction (15-30%) had higher proline accumulation (65.58%) while, RIL-51 with greater yield reduction (75-90%) showed only 7.92 percent increase in proline content under rainfed conditions thereby suggesting the role of proline as an osmoprotectant under stress conditions in lentil...

Tripartite interactions of Barley yellow dwarf virus, Sitobion avenae and wheat varieties.

The tripartite interactions in a pathosystem involving wheat (Triticum aestivum L.), the Barley yellow dwarf virus (BYDV), and the BYDV vector aphid Sitobion avenae were studied under field conditions to determine the impact of these interactions on aphid populations, virus pathology and grain yield. Wheat varietal resistance to BYDV and aphids varied among the three wheat varieties studied over two consecutive years. The results demonstrated that (1) aphid peak number (APN) in the aphid + BYDV (viruliferous aphid) treatment was greater and occurred earlier than that in the non-viruliferous aphid treatment. The APN and the area under the curve of population dynamics (AUC) on a S. avenae-resistant variety 98-10-30 was significantly lower than on two aphid-susceptible varieties Tam200(13)G and Xiaoyan6. (2) The production of alatae (PA) was greater on the variety 98-10-30 than on the other varieties, and PA was greater in the aphid + BYDV treatment on 98-10-30 than in the non-viruliferous aphid treatment, but this trend was reversed on Tam200(13)G and Xiaoyan6. (3) The BYDV disease incidence (DIC) on the variety 98-10-30 was greater than that on the other two varieties in 2012, and the disease index (DID) on Tam200(13)G was lower than on the other varieties in the aphid + BYDV and BYDV treatments in 2012, but not in 2011 when aphid vector numbers were generally lower. (4) Yield loss in the aphid + BYDV treatment tended to be greater than that in the aphid or BYDV alone treatments across varieties and years. We suggested that aphid population development and BYDV transmission tend to promote each other under field conditions. The aphids + BYDV treatment caused greater yield reductions than non-viruliferous aphids or virus treatment. Wheat varietal resistance in 98-10-30 affects the aphid dispersal, virus transmission and wheat yield loss though inhibits aphid populations from increasing.

Delaying Weed Control Lengthens the Anthesis-Silking Interval in Maize

Stress caused by early weed competition is known to delay the rate of maize development which may result in a decrease in kernel number. Kernel number in maize is correlated negatively with the length of the anthesis-silking interval (ASI). A short ASI has been identified as an easily measured, visual trait which may identify enhanced drought tolerance in maize. Field studies were conducted to test whether: (1) delaying weed control would result in a lengthening of ASI in both a drought tolerant and non-drought tolerant maize hybrid and (2) the presence of drought tolerance genetics comes at a physiological cost, resulting in a greater yield reduction under weedy conditions. In this study, the response of a drought tolerant hybrid with its non-drought tolerant near-isoline was compared to seven different timings of weed control using wheat as a surrogate competitor. Results confirmed that there was no treatment by hybrid interaction at any site–yr for any of the parameters evaluated. Delaying weed control reduced plant height, leaf tip number, shifted and reduced biomass accumulation, kernel number and grain yield and lengthened ASI for both hybrids. Although yield losses occurred with the delay in weed control timing, no yield differences were observed between hybrids suggesting that there was no additional physiological cost associated with the drought tolerant traits. The drought tolerant hybrid, however, was found to have a shorter ASI, lower kernel number and higher kernel wt compared to the non-drought tolerant hybrid. This study confirmed that delaying weed control can influence the length of ASI, which is an important drought tolerant trait. The lengthening of ASI by early weed competition resulted in a rate of yield loss of 0.13 T ha−1growing degree days (GDD)−1when averaged across both hybrids and all treatments.

Simulation of Winter Wheat Yield in Response to Irrigation Level at Critical Growing Stages in the Huang-Huai-Hai Plain

Water deficiency is recognized as a major problem in winter wheat production in the Huang-Huai-Hai Plain. This study aimed to assess the impact of drought stress on winter wheat yield and raise irrigation proposals for water-saving production in this area. With reference to the fact of water deficits in major growth stages of wheat and the local irrigation practice, we input different irrigation levels(volumes) required by the DSSAT crop model to simulate yield variations in response to irrigation levels at critical growing stages in four typical sites during the past three decades. The cumulative probability for yield reduction was concluded based on irrigation at jointing–heading and filling stages. The greatest yield reduction was found under jointing–heading drought stress, and the relative change rate in yield was two folds to that under drought stress at filling stage. This relative yield change was primarily attributed to the relative change in grain number per square meter caused by water deficiency during jointing–heading stage. Under high-strength drought stress, medium yield reduction dominantly resulted from water deficiency during jointing–heading, with a two-fold probability to that under drought stress at filling stage(except for Yanzhou site); whereas, slight and severe yield reductions at Shijiazhuang and Tianjin sites resulted from early(jointing–heading) drought stress and those at Yanzhou and Xinxiang sites were attributed to either early(jointing–heading) or late(filling stage) drought stress. At Yanzhou and Xinxiang sites, the probabilities of slight yield reduction were similar under early and later drought stressed; however, water deficiency at filling stage resulted in severe yield reduction. These results indicate that irrigation is important not only from jointing to heading but also at filling stage of winter wheat in the southern area of the Huang-Huai-Hai Plain.

Effects of Machine-Induced Soil Compaction on Growth and Yield of Sugarcane

Problem statement: Sugarcane is one of the main economic crops in Thailand. After planting, it can be harvested annually for several successive ratoon crops. Recently, soil compaction due to mechanization has been recognized as a serious problem in sugarcane production. Therefore, this study aimed to clarify the effects of soil compaction on the growth and yield of sugarcane. Approach: The field experiments were conducted in loamy soil using a Randomized Complete Block Design (RCBD) with four treatments of soil compaction prepared by 0, 5, 15 and 20 numbers of wheel passages of a tractor. Results: The results showed that soil compaction had significant effects on both the growth and yield of sugarcane, with the exceptions of tillering and Brix. The greatest reduction in yield compared with the control field was 22.9%, which resulted from compacting with 15 tractor passages. The influence of block or furrow irrigation was indicated by the positive effect that higher watering had on minimizing the impact of soil compaction on the growth of sugarcane. Conclusion: Effects of soil compaction on growth and yield of sugarcane were clarified to some extent.

Comparison of pathogenicity of the Fusarium crown rot (FCR) complex (F. culmorum, F. pseudograminearum and F. graminearum) on hard red spring and durum wheat

Fusarium species involved in the Fusarium crown rot (FCR) complex affect wheat in every stage of development from seedling to grain fill. This study was designed to compare the aggressiveness of the FCR complex members including F. culmorum, F. pseudograminearum and F. graminearum in causing seedling blight, decreased plant vigour and crown rot. To assess their relative pathogenicity, two hard red spring wheat cultivars and two durum wheat cultivars were inoculated in the field with five isolates from each of the three species for two years. Significant differences in patterns of pathogenicity were identified. In particular, F. culmorum caused greater seedling blight while F. pseudograminearum and F. graminearum caused greater crown rot. Greatest yield reductions were caused by F. pseudograminearum. Cultivar differences were identified with respect to seedling disease and late season crown rot. No interactions were identified between cultivar performance and isolates or species with which they were challenged.

Effects of two sediment types on the fluorescence yield of two Hawaiian scleractinian corals

This study used non-invasive pulse-amplitude modulated (PAM) fluorometry to measure the maximum fluorescence yield (F(v)/F(m)) of two Hawaiian scleractinian coral species exposed to short-term sedimentation stress. Beach sand or harbor mud was applied to coral fragments in a flow-through aquarium system for 0-45 h, and changes in F(v)/F(m) were measured as a function of sediment type and length of exposure. Corals were monitored for up to 90 h to document recovery after sediment removal. Sediment deposition significantly decreased F(v)/F(m) in both species and was a function of sediment type and time. Corals that received sediment for 30 h or more had the greatest reduction in yield and exhibited little recovery over the course of the experiment. Harbor mud caused a greater reduction in Porites lobata yield than beach sand, whereas both sediment types had equally deleterious effects on Montipora capitata. Colony morphology and sediment type were important factors in determining yield reduction--P. lobata minimized damage from coarse sand grains by passive sediment rejection or accumulation in depressions in the skeleton, and fluorescence yield decreased most in corals exposed to sticky harbor mud or in colonies with flattened morphologies. Species-specific differences could not be tested due to differences in colony morphology and surface area.

Resource competition in contour hedgerow intercropping systems involving different shrub species with mature and young tea on sloping highlands in Sri Lanka

Tea (Camellia sinensis) in Sri Lanka is grown predominantly on sloping highlands. Incorporating trees as hedgerows along contours is aimed at reducing erosion and improving soil fertility through addition of prunings as mulch. However, there could be significant competition for essential growth resources between the hedgerows and tea. The primary objective of this study was to determine the influence of six hedgerow species (Calliandra calothyrsus, Senna [Cassia] spectabilis, Eupatorium inulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) on mature (6-year-old) and young (6-month-old) tea. This study had three on-farm, long-term (from Nov 1998 to Dec 2002) field experiments. Experiment 1 had 12 treatment combinations with the six shrub species and two mulching treatments (i.e. hedgerow prunings added to the tea plot as a mulch, and unmulched) on mature tea plus a sole tea crop as control. The same was repeated on young tea in Experiment 2 to determine whether resource competition on young tea was greater than that on mature tea. Experiment 3 examined the effects of removing tree root competition on tea by cutting a 1-m deep trench between hedgerows and tea.In all experiments, total tea yields of hedgerow intercrops, cumulated over the 50-month experimental period, were significantly lower (by 3–50%) than sole tea crops, thus indicating significant resource competition except in the case of mulched hedgerow systems involving Eupatorium and mature tea (18% yield increase). Removal of below-ground competition significantly increased tea yields by 11–19%. Addition of hedgerow prunings as a mulch significantly increased yields of both mature and young tea by 13–21%. Tea yields of hedgerow systems with Calliandra, Flemingia and Eupatorium showed greater yield reductions in young tea than in mature tea, but the opposite was shown with other hedgerow species. There was a significant negative linear relationship between tea yield and pruned biomass of hedgerows. Tea yields of all experiments showed significant negative correlations with several hedgerow characters, which are indicators of their competitive ability. These included hedgerow root density, canopy lateral spread, height and cross-section. In a majority of hedgerow systems, the available phosphorus content of topsoil (0–20 cm depth) was up to 51% lower compared to sole crops. It is concluded that incorporation of contour hedgerows in to an existing tea crop could result in significant resource competition with tea and thereby cause tea yield to decrease. However, there is scope for selection of hedgerow species that minimize competition through spatial and temporal complementarity with tea in resource capture.

Cultivar and environment influence the development of lupin anthracnose caused byColletotrichum lupini

A series of experiments was conducted to assess the effect of different levels of initial anthracnose inoculum (as transplanted infected seedlings) on final infection and yield of lupins. The influences of environment and cultivar resistance on anthracnose infection were also examined. Anthracnose infection caused significant yield reduction at a range of sites. Disease incidence was higher and yield reduction greater when initial inoculum was increased. Yield reduction was less in cv. Wonga (resistant) than in either cv. Myallie (susceptible) or cv. Kiev Mutant (extremely susceptible). Stem tissue of Wonga was more resistant to infection than pods. Higher rainfall resulted in more anthracnose infection and greater yield reduction. Infection spread further with greater wind strength and was more severe in warmer temperatures. Cultivar resistance and environment influenced the effect of initial anthracnose inoculum on crop infection and yield.