Photosynthetic Area Research Articles

Biology and Nutritional Indexes of Spodoptera frugiperda (Lepidoptera: Noctuidae) in Saccharine Sorghum

Saccharine sorghum has been analyzed as a supplementary prime matter for ethanol production, especially during the sugarcane off-season period. However, it has proven to be highly susceptible to insect attacks during the cultivation cycle. The fall armyworm should be emphasized due to its voracity and high damage capacity enhanced by feeding-caused decrease in photosynthetic area. Current analysis studies the biology and determines the nutritional indexes of Spodoptera frugiperda in saccharine sorghum. Cultivars of saccharine sorghum BRS 506, BRS 509 and BRS 511were evaluated. Duration and survival of the egg, caterpillar, pre-pupal and pupal phases were determined, coupled to weight of pupae and caterpillar, life span, fecundity and pre-egg laying period. Although S. frugiperda completed its life cycle on cultivars BRS 506 and BRS 511, egg-laying and egg feasibility rates were low, whereas insects did not lay eggs on cultivar BRS 509. There was no significant difference in feeding intake by S. frugiperda among these three sorghum cultivars. Results suggest that saccharine sorghum is not a suitable host for S. frugiperda. Biological data reveal that the three saccharine sorghum cultivars are recommended for the grain production system since the number of specimens of the next generation is low or null.

Low-cost assessment of grain yield in durum wheat using RGB images

The pattern of photosynthetic area of the canopy throughout the crop cycle is an important factor for determining grain yield in wheat. This work proposes the use of zenithal RGB images of the canopy taken in natural light conditions to derive vegetation indices as a low-cost approach to predict grain yield. A set of 23 varieties of durum wheat was monitored in three growing conditions (support irrigation, rainfed and late planting) and two sites (Aranjuez and Valladolid, Spain), totalling 6 field trials. For each plot, digital RGB images were taken periodically from seedling emergence to late grain filling. RGB-based Green Area (GA), Greener Area (GGA), Normalized Green Red Difference Index (NGRDI), Triangular Greenness Index (TGI) and a novel photosynthetic area index based on the CIE L*u*v* colour space (u*v*A) were compared to handheld spectroradiometer Normalised Difference Vegetation Index (NDVI) for reference. In the case of the irrigated and late planting trials the best phenotypic predictions of grain yield were achieved with the vegetation indices measured during the last part of the crop cycle (i.e. grain filling). For the rainfed trials the best phenotypic predictions were achieved with indices measured earlier (around heading). Among all the evaluated indices, the novel index performed the best. Considering the heritabilities of the evaluated RGB indices and their genetic correlations with grain yield, index-based predictions of grain yield were best in the early crop stages for both rainfed and irrigated conditions, while for late planting indices measured at different crop stages performed equally well.

Geostatistical stationary space-time covariance functions modeling of Yellow Sigatoka progress in banana crop

Banana production is affected by Yellow Sigatoka, one of the causes of leaf lesions, which causes the reduction of the photosynthetic area of the plant and, consequently, the quality of the fruit and the production. The objective of this study was to analyze using geostatistics and comparing separable and non-separable spatio-temporal covariance models with different adjustment methods. The experiment was carried out in a banana plantation of the Prata-Ana variety, which presented high severity of the disease, without any control measures, which allowed the study of behavior under natural conditions. The Separable Doubly Exponential and the non-separable model of Gneiting were tested with the Weight Least Squares (WLS), Restricted Maximum Likelihood (REML) and Likelihood Pairwise estimation methods. The Gneiting model, WLS curve-fitting methods for estimatives space-time covariance structure, allowed to reduce the uncertainties of the spatial and temporal prediction of the disease, as well as to characterize the spatio-temporal pattern of the disease.

The spike weight contribution of the photosynthetic area above the upper internode in a winter wheat under different nitrogen and mulching regimes

Besides leaves, non-foliar green organs such as stem and spike are also considered photosynthetic organs. To assess the photosynthetic contributions of these organs, the correlations between these photosynthetic areas and single-spike weight were investigated in a winter wheat (Triticum aestivum L.) under four nitrogen and mulching treatments: N120, N150, N195, and N195 + M. Two-year repeated field experiments were conducted on the Loess Plateau of China. Non-foliar photosynthetic area, grain-filling ratio and duration, grain yield, and in particular, single-spike weight, were measured, recorded and analyzed. Under the N195 + M treatment, plants showed the largest area of photosynthetic organs (flag leaf and non-foliar organs) and the highest grain yield and single spike weight. Single-spike weight was positively correlated with the areas of all examined non-foliar photosynthetic organs, in particular with the area above the flag leaf node (R2 = 0.761⁎) and the area above the exposed part of the peduncle (EXP) (R2 = 0.800⁎⁎). In addition, single-spike weight was highly correlated with average grain-filling ratio (R2 = 0.993⁎⁎), whereas it was less highly correlated with grain-filling duration (R2 = 0.533). The morphological traits of non-foliar photosynthetic organs were also more highly correlated with average grain-filling ratio than with average grain-filling duration. The significant correlation between each of the morphological traits (area, length and width) of EXP and single-spike weight indicates that morphological traits of EXP are important in determining spike weight in the Loess Plateau environment.

Maternal control of seed weight in rapeseed (Brassica napus L.): the causal link between the size of pod (mother, source) and seed (offspring, sink).

SummarySeed size/weight is one of the key traits related to plant domestication and crop improvement. In rapeseed (Brassica napus L.) germplasm, seed weight shows extensive variation, but its regulatory mechanism is poorly understood. To identify the key mechanism of seed weight regulation, a systematic comparative study was performed. Genetic, morphological and cytological evidence showed that seed weight was controlled by maternal genotype, through the regulation of seed size mainly via cell number. The physiological evidence indicated that differences in the pod length might result in differences in pod wall photosynthetic area, carbohydrates and the final seed weight. We also identified two pleiotropic major quantitative trait loci that acted indirectly on seed weight via their effects on pod length. RNA‐seq results showed that genes related to pod development and hormones were significantly differentially expressed in the pod wall; genes related to development, cell division, nutrient reservoir and ribosomal proteins were all up‐regulated in the seeds of the large‐seed pool. Finally, we proposed a potential seed weight regulatory mechanism that is specific to rapeseed and novel in plants. The results demonstrate a causal link between the size of the pod (mother, source) and the seed (offspring, sink) in rapeseed, which provides novel insight into the maternal control of seed weight and will open a new research field in plants.

One-step approach for estimating maize actual water use: Part I. Modeling a variable surface resistance

In a global scenario of climate change, water scarcity and population growth, it is imperative to optimize crop water management. One way is by calibrating a physically based crop evapotranspiration (ET) model, in the so-called one-step approach; as opposed to the two-step approach that uses reference evapotranspiration and crop coefficients. The Penman–Monteith (Symposium of the society for experimental biology, the state and movement of water in living organisms, Academic Press, Inc., New York; Monteith, Symposium of the society for experimental biology, the state and movement of water in living organisms, Academic Press, Inc., New York, 1965) ET model uses a bulk surface resistance (rs) term. This variable describes the resistance (stomatal, leaf, and canopy) to crop water transpiration and water evaporation from the soil surface. If the crop is not transpiring at a potential rate the rs resistance depends on the water status of the soil and vegetation. The stomatal resistance is influenced by climate and by water availability. However, this influence is different from crop to crop. The resistance increases when the crop is stressed and when the soil water availability limits ET. In this study, surface resistance was parameterized for grain maize considering a number of plant and environmental variables for water stressed and non-stressed conditions. The independent explanatory variables that facilitated a good calibration of rs, on a half-hourly basis, were: net radiation, photosynthetic active radiation, aerodynamic resistance, crop height, and leaf area index. The application of the obtained “rs” model (based on the variables mentioned above) resulted in maize ET (mm 30-min−1) estimation error of less than 1 ± 10% when evaluated with eddy covariance based ET data. This result is evidence that it is possible to calculate maize ET with a small associated error at very small time scales, for water deprived and advective conditions, using the one-step ET approach.

Monitoring and modelling of water and heat fluxes from asparagus fields

Precise estimates of evapotranspiration and other scalar fluxes of asparagus (Asparagus officinalis) crops are required for irrigation control, regional water budget projections or climate impact modelling studies. In Germany, asparagus fields are frequently quite extensive and enable the application of eddy covariance (EC) technique to measure the turbulent fluxes of CO(2), sensible and latent heat (H(2)O) and momentum. In this work we present results of two year EC measurements (2015-16) over an extended asparagus field with commonly used cultivars ('Backlim' and 'Grolim'). With supplementary collected seasonal data of fern area, fern height and several meteorological sensors combined with a sophisticated quality assessment and footprint analysis we are able to parameterize well established physical and physiological crop responses. These include the aerodynamic resistance with separate transfer terms above and within the canopy and the bulk stomatal resistance in a one-layer setting of energy balance formulation. The instantaneous fern canopy conductance is predicted by partial responses of photosynthetic active radiation and fern area, air temperature, air vapour pressure deficit, fern senescence state and the daily canopy to air temperature difference.

Socio-Economic Analysis of Hybrid Rice Variety “OPTIMA” Farming in District of Banyuwangi to Increase Income, Indonesia

In general, hybrid rice has a significant advantage over inbred rice, such as higher yields, more competitive harvesting, wider, shorter plant life, wider photosynthetic area, lower respiratory intensity and higher assimilation translocation . Although in Indonesia hybrid rice has been popularized since 1983, but the empirical facts show that few farmers are adopting new technology in this field of seed, although the price of production is more expensive than the price of the rice product inbrid. Therefore, this paper explains the following matters: 1) Socio-economic factors that influence farmers' decision to plant hybrid rice OPTIMA, 2) Level of profit of hybrid rice farming OPTIMA, and 3) Cost efficiency level of rice farming hybrid OPTIMA. The research method used is descriptive method of quantitative and qualitative techniques where census data information collected includes primary data and secondary data. The population in this research is farmers of hybrid rice varieties of OPTIMA in Banyuwangi. Data analysis techniques used are probability probability analysis of probit model function, cost efficiency analysis, and profit. Simultaneously there are several factors that are expected to significantly influence farmers' decision to plant hybrid rice optima at a 1% significance level. But partially only factor of production amount which have no significant effect to dependent variable (Farmer's Decision, while variable of output price and farmer perception about hybrid varieties of Optima hybrid is significant effect) Farm profit rate during second rainy season and drought in year 2013/2014 reach IDR 9.61.992,06 per hectare with average production of 5,9 tons and the farming efficiency level reached 1,5 or has reached the point of technical efficiency.

Effects of different densities of mixed-cropping on 13C-photosynthate distribution and grain yield of maize.

To explore the effects of different densities of mixed-cropping on 13C-photosynthate distribution and grain yield of maize, we measured photosynthetic characteristics, 13C-photosynthate distribution, dry matter accumulation, and grain yield under different planting densities (LD, 67500 plants·hm-2 and HD, 97500 plants·hm-2) under mixed-cropping (M, 1:1, 2:2) and monoculture of Zhengdan958 (ZD) and Denghai605 (DH). The results showed that with the increases of planting density, grain yield, 13C-photosynthate allocation to grain, dry matter accumulation, and leaf area index (LAI) increased, but the chlorophyll content and net photosynthetic rate decreased. No significant difference was observed between the monoculture and mixed-cropping at the density of 67500 plants·hm-2. However, at 97500 plants·hm-2, LAI, chlorophyll content, net photosynthetic rate and dry matter accumulation in mixed-cropping were higher than that in monoculture. Mixed-cropping promoted the transport of dry matter from the vegetative organs such as stem to the grain and the distribution of 13C-photosynthates to grain. Grain yield of summer maize significantly increased in mixed-cropping due to the increase of 1000-grain mass. Under high plant density, the mixed-cropping could enlarge photosynthetic area, maintain higher net photosynthetic rate, increase dry matter accumulation, improve the distribution of dry matter, promote the distribution of 13C-photosynthates to grains and thus increase the grain yield. Our results indicated that mixed-cropping could significantly increase the yield of close planting summer maize in Huang-Huai-Hai Plain.

Conserved thermal performance curves across the geographic range of a gametophytic fern.

Species-level responses to environmental change depend on the collective responses of their constituent populations and the degree to which populations are specialized to local conditions. Manipulative experiments in common-garden settings make it possible to test for population variation in species’ responses to specific climate variables, including those projected to shift as the climate changes in the future. While this approach is being applied to a variety of plant taxa to evaluate their responses to climate change, these studies are heavily biased towards seed-bearing plant species. Given several unique morphological and physiological traits, fern species may exhibit very different responses from angiosperms and gymnosperms. Here, we tested the hypothesis that previously detected population differentiation in a fern species is due to differentiation in thermal performance curves among populations. We collected explants from six populations spanning the species’ geographic range and exposed them to 10 temperature treatments. Explant survival, lifespan and the change in photosynthetic area were analysed as a function of temperature, source population and their interaction. Overall results indicated that explants performed better at the lowest temperature examined, and the threshold for explant performance reflects maximum temperatures likely to be experienced in the field. Surprisingly, explant fitness did not differ among source populations, suggesting that temperature is not the driver behind previously detected patterns of population differentiation. These results highlight the importance of other environmental axes in driving population differentiation across a species range, and suggest that the perennial life history strategy, asexual mating system and limited dispersal potential of Vittaria appalachiana may restrict the rise and differentiation of adaptive genetic variation in thermal performance traits among populations.

Variability examination of photosynthetic pigment content and specific leaf area in individual maize (Zea mays L.) plants

Currently, maize is one of the most important crops (Zea mays L.) both globally and in Hungary. We compared physiological parameters of a maize genotype – p9903 – at two different experimental sites in a field experiment. Furthermore, we examined these parameters’ variability in individual plants on the leaves with different ages. Absolute chlorophyll content of the leaves were analysed, separately that of chlorophyll a and chlorophyll b. We also measured the absolute carotenoid contents of leaves. Furthermore, we calculated these photosynthetic pigments’ content ratio. Specific leaf area (SLA) and dry matter weight were also measured in order to characterise plant production. The results obviously reflect the decreasing in the efficiency of photosynthetic apparatus on the low yield site. Otherwise, we identify significant differences only in certain cases of leaves.

Effect of row spacing on physiological characteristics and yield of intercropped peanut with wheat.

Using two peanut varieties Shanhua108 (early-maturing variety) and 780-15 (late maturing variety), a field experiment was conducted to investigate the influences of row-spacing of wheat (25 cm, 30 cm, 40 cm+20 cm) and two peanut cropping patterns (intercropped peanut with wheat, summer-sowing peanut) on yield components, photosynthetic characteristics, antioxidant system, and dry matter accumulation and transportation. The results showed that wide spacing form of wheat and wide-narrow row planting pattern increased the pod yield, kernel yield, leaf area index, total dry matter accumulation and photosynthetic capacity, as well as SOD, POD and CAT activities, but decreased the MDA content. There are no obvious differences of wheat yield between the two row-spacing. Intercropping system increased peanut yield compared with summer-sowing peanut, which were much higher for wide-narrow row planting pattern than row spacing of 25 cm or 30 cm. The wide-narrow row planting pattern increased the pod yield and kernel yield by 6.3%, 13.3% and 7.7%, 16.5% for Shanhua108 and 780-15 than those of row spacing of 30 cm, respectively. Wide-narrow row planting could enlarge photosynthetic area, improve the net photosynthetic rate, and increase total dry matter accumulation. Meanwhile, it could alleviate the contradictionbetween the plant individual and group, delay the senescence, and increase peanut yield.

Arbuscular mycorrhizal fungi improve photosynthetic energy use efficiency and decrease foliar construction cost under recurrent water deficit in woody evergreen species

Plants suffer recurrent cycles of water deficit in semiarid regions and have several mechanisms to tolerate low water availability. Thus, arbuscular mycorrhizal fungi (AMF) can alleviate deleterious effects of stress. In this study, Cynophalla flexuosa plants, a woody evergreen species from semiarid, when associated with AMF were exposed to two consecutive cycles of water deficit. Leaf primary metabolism, specific leaf area (SLA), leaf construction cost (CC) and photosynthetic energy use efficiency (PEUE) were measured. The maximum stress occurred on seven days (cycle 1) and ten days (cycle 2) after suspending irrigation (photosynthesis close to zero). The rehydration was performed for three days after each maximum stress. In both cycles, plants submitted to water deficit showed reduced gas exchange and leaf relative water content. However, Drought + AMF plants had significantly larger leaf relative water content in cycle 2. At cycle 1, the SLA was larger in non-inoculated plants, while CC was higher in inoculated plants. At cycle 2, Drought + AMF treatment had lower CC and large SLA compared to control, and high PEUE compared to Drought plants. These responses suggest AMFs increase tolerance of C. flexuosa to recurrent water deficit, mainly in cycle 2, reducing the CC, promoting the improvement of SLA and PEUE, leading to higher photosynthetic area. Thus, our result emphasizes the importance of studies on recurrence of water deficit, a common condition in semiarid environments.

Heart-shaped cladodes in commercial cactus pear plantations

Because of the diverse uses it has, and the multiple benefits it contributes to, cactus pear(Opuntia spp.) is considered one of the natural resources of greatest socioeconomicimportance in Mexico. Its intensive production in monoculture, associated with a reducedgenetic variability, has resulted in the proliferation of various physiopathies, and the prevalenceof pests and diseases, which reduce its productivity. In diverse cactus pear producing zones inMexico and other countries, a malformation called in this study cladode ‘acorazonamiento’(heart-shaped cladode), which is derived from the shape the cladode takes, has beenobserved; however, the causal agent is unknown at the time. Considering that its occurrencecould cause economic losses to cactus pear producers, this study describes the visualsymptomatology and the incidence and severity of heart-shaped cladode symptoms incommercial cactus pear plantations in the south and southeast of Zacatecas, Mexico. Thesymptomatology was more evident in tender buds of 6 to 20 days of age, and is characterizedby the presence of diverse malformations in the apical or lateral part of the cladodes, as wellas by the appearance of micro-scarring that reduces the vegetative and floral budding in theaffected zone; the damaged tissue presents rupture of the cuticle and epidermis, and thedetachment of cell walls. Three principal malformation symptoms were found, which werenamed in this study as: ‘heart’, ‘bean’ and ‘saw’, according to the cladode physical appearance,with the first one being the most frequent. All the plantations evaluated showed the presenceof malformed cladodes, with values that fluctuated between 12 and 30 %. Cladodes with heartshapesymptomatology may generate buds with similar appearance in a proportion of 2:1asymptomatic:symptomatic cladodes. Likewise, it was observed that the degree of severityranged between 1 to 38% of photosynthetic area reduction, and damaged cladodes may losebetween 50 to 80% of vegetative and floral buds. Derived from this, it is pertinent to perform
 studies directed towards characterizing its etiology in order to implement managementstrategies and reduce economical losses.

Plant Osmoregulation as an Emergent Water‐Saving Adaptation

AbstractSoil salinity affects plant transpiration and growth through two main pathways: the osmotic effect of salt in the soil (osmotic stress; analogous to water stress) and the toxic effect of salt within the plant (ionic stress; salt specific). However, the drastic and sudden reduction of transpiration exhibited by most species in response to an increase of salinity in the root zone is mainly associated with the osmotic phase, while ionic stress appears at a later time, causing the premature senescence of leaves and the reduction of the plant photosynthetic area. To better investigate the effects of salinity on plant‐water relations, we introduce a parsimonious soil‐plant‐atmosphere continuum (SPAC) model accounting for both salt exclusion at the root level and osmoregulation—i.e., the adjustment of internal water potential in response to salt stress. The model is used to interpret a paradox observed in salt‐tolerant species where transpiration is maximum at an intermediate value of salinity ( ), and is lower in more fresh ( ) and more saline ( ) conditions. Such nonmonotonic transpiration‐salt concentration ( ) patterns can be largely explained by plant osmoregulation, while the peak of transpiration at tends to disappear over longer time scales, when ionic stress appears and morphological adaptations become predominant. Osmoregulation emerges here as a water‐saving behavior similar to the strategies that xerophytes use to cope with aridity. The maximum of transpiration at is thus the result of a trade‐off between the enhancement of salt‐tolerance and optimal carbon assimilation.

Growth performance of six multipurpose tree species based on the carbon assimilation capacity: a functional approach

This study is an attempt to evaluate six tree species with potential for growth and water use efficiency under 50% moisture stress, based on the carbon assimilation capacity in order to identify species to be grown in low moisture conditions. Plants were maintained at field capacity (control) and at 50% less than the field capacity (stress) in lysimeters for 90 days by weighing them and replenishing with the water lost. Eucalyptus comaldulensis and Melia dubia recorded 259 and 204 and 243 and 151 g plant−1 of biomass under control and moisture stress conditions respectively while Simaruba glauca and Callophylum inophyllum recorded 61–53 and 37–23 g plant−1. Photosynthetic rates of these species were in the range of 25.43–22.78 and 9.10–8.03 μmol m−2s−1 under control and stress conditions respectively, which corroborated with biomass production. Both diffusive and carboxylation processes of photosynthesis were higher in species with higher biomass. Photosynthetic rates assessed using leaf model and cumulative models go with each other. Species with higher photosynthetic rates tended to sustain under stress by reducing photosynthetic surface area and maintain the growth rates suggesting that growth performance under moisture stress depends on carbon assimilation capabilities. This was also evident in species with low photosynthetic rates which recorded lower growth rates. Species with lower carbon assimilation showed higher water use efficiency, while it was the opposite in species with higher carbon assimilation. Isohydric behavior of stomata help plants to maintain longer stomatal conductance and hence the photosynthetic rates, but lower water use efficiency. Such a strategy helps plants in sustaining growth under intermittent moisture stress. Thus slow growing species with higher water use efficiency and lower moisture consumption are useful in establishing tree cover in marginal lands with low moisture.

Optimal pre-plant irrigation and fertilization can improve biomass accumulation by maintaining the root and leaf productive capacity of cotton crop

Cotton is a major cash crop grown worldwide primarily for fiber and oil seed. As the most important cultural practices for cotton production, single pre-plant irrigation and basal fertilization for cotton plant growth and yield are well documented, but their coupling effects are poorly understood in arid regions. A 2-year outdoor pot trial was conducted to unravel the effects of pre-plant irrigation and basal fertilization on leaf area, root growth, biomass accumulation, and capacity of leaf area and root in cotton plant. Two pre-plant irrigations (i.e., W80, well-watered and W0, not watered) and two basal dressing fertilizations (F10, surface application and F30, deep application) were used in the experiments. The aboveground and reproductive biomass were highest in W80F10 after 69 days after emergence. Furthermore, W80F10 increased the root length in the 0–40 cm soil layer and the leaf area and improved the loading boll capacity of the effective root length and leaf area. The effective root length and leaf area had substantial direct effects on the aboveground and root biomass, respectively. Our data suggest that basal fertilizer surface application under adequate pre-plant irrigation is an effective strategy for optimal cotton production, which improves the coordination of water-nutrient absorption and photosynthetic areas and promotes assimilated distribution to the reproductive structures.

Morphophysiological mechanism of rice yield increase in response to optimized nitrogen management

The yield-increasing mechanism of an optimized nitrogen fertilizer application (OFA) in rice was reported in this work through a three-year test. Results showed that the number of branches and spikelets increased, panicle length, the diameter and vascular bundle number of panicle-neck internode improved with OFA. Under the condition of OFA, high effective leaf areas, especially for the flag and the second upper leaf areas, increased, the net photosynthetic rate of the upper three leaves promoted, so the photosynthetic productivity went up by a large margin; moreover, the content of soluble protein and chlorophyll of leaf also increased, and the content of soluble sugar and malondialdehyde (MDA) decreased, as a result in slowing down the senescence speed in leaves, and increasing the photosynthetic time. Gene expression level, including MOC1, LAX1, SP1, GS1;1, were up-regulated obviously in different panicle initiation stage under OFA condition, which conduced to the increase in the secondary branches and spikelets. So we concluded that the changes in organ formation and panicle structure, together with the responses in physiological and molecular made the photosynthetic area, rate and time all increased with OFA, which provided the matter basis for the big panicle development, consequently, got a higher yield.

Understanding Yield Loss and Pathogen Biology to Improve Disease Management: Septoria Nodorum Blotch - A Case Study in Wheat.

The estimated potential yield losses caused by plant pathogens is up to 16% globally and most research in plant pathology aims to reduce yield loss in our crops directly or indirectly. Yield losses caused by a certain disease depend not only on disease severity, but also on the weather factors, the pathogen's aggressiveness, and the ability of the crop to compensate for reduced photosynthetic area. The yield loss-disease relationship in a certain host-pathogen system might therefore change from year to year, making predictions for yield loss very difficult at the regional or even at the farmer's level. However, estimating yield losses is essential to determine disease management thresholds at which acute control measures such as fungicide applications, or strategic measures such as crop rotation or use of resistant cultivars are economically and environmentally sensible. Legislation in many countries enforces implementation of integrated pest management (IPM), based on economic thresholds at which the costs due to a disease justify the costs for its management. Without a better understanding of the relationship between disease epidemiology and yield loss, we remain insufficiently equipped to design adequate IPM strategies that will be widely adapted in agriculture. Crop loss studies are resource demanding and difficult to interpret for one particular disease, as crops are usually not invaded by only one pest or pathogen at a time. Combining our knowledge on disease epidemiology, crop physiology, yield development, damage mechanisms involved, and the effect of management practices can help us to increase our understanding of the disease-crop loss relationship. The main aim of this paper is to review and analyze the literature on a representative host-pathogen relationship in an important staple food crop to identify knowledge gaps and research areas to better assess yield loss and design management strategies based on economic thresholds.

Glasshouse studies of inherent root growth of seedling avocado rootstock cultivars

In order to mimic loss of root function caused by Phytophthora cinnamomi, differences in inherent root growth of avocado seedlings of ten different rootstock cultivars across the three ecological races were investigated. A 2-pot root harvesting system was used and roots were harvested at three different intervals to assess tolerance to root removal. Seedling 'Velvick' produced the largest amount of harvested roots. However, when results were standardised by the total area of mature leaves, there were no significant differences found between rootstock cultivars in cumulative, root growth. Relative to total photosynthetic area, cultivars 'Kidd' and 'Fuerte' (produced the most roots in the absence of root trimming. Overall, increased trimming decreased cumulative root output (P<0.001). For root growth of harvested roots, significant interactions were observed between cultivars and trimming treatment, with the cultivar 'A10' best able to withstand regular mechanical root removal. Significant interactions were also observed between cultivars and trimming treatment for the parameter of root diameter. Most cultivars generally produced thicker roots over time, except for varieties 'Reed' and 'Velvick', for which the average thickest roots were the youngest. Regressing dry weight of harvested roots with projected area in root images, 'Velvick' seedlings had the steepest relationship while 'Edranol' roots had the flattest.