Host specificity testing and examination for plant pathogens reveals that the gall‐inducing psyllid Calophya latiforceps is safe to release for biological control of Brazilian peppertree

Brazilian peppertree, Schinus terebinthifolia Raddi (Anacardiaceae), is one of the worst upland exotic weeds in Florida, USA. Foreign exploration for natural enemies led to the discovery of a pit‐galling psyllid, Calophya latiforceps Burckhardt (Hemiptera: Calophyidae), in the state of Bahia, Brazil, in 2010. Crawlers of C. latiforceps stimulate the formation of galls on the leaves of S. terebinthifolia resulting in leaf discoloration and in some cases leaf abscission. To determine whether C. latiforceps is a safe candidate for biological control of S. terebinthifolia, host specificity and the presence of selected plant pathogens were examined. Adult oviposition, gall formation, and adult survival of C. latiforceps were examined on 89 plant species under no‐choice and choice conditions. We found that C. latiforceps laid eggs on plants in seven families; however, crawlers stimulated gall formation and completed development to adult only on S. terebinthifolia. All crawlers on non‐target plants died, likely due to starvation caused either by the absence of a feeding stimulus or by a hypersensitive plant response. Under no‐choice conditions, 10% of adults lived for 19 days on the target weed, but adult survival was reduced to <3 days on non‐target plants. Choice testing revealed that females preferred to oviposit on S. terebinthifolia compared to non‐target plants. Molecular methods and indicator host inoculations did not detect the presence of ‘Candidatus Liberibacter solanacearum’, ‘Ca. L. asiaticus’, ‘Ca. L. americanus’, ‘Ca. L. africanus’, or plant viruses in adult C. latiforceps. We conclude that releasing C. latiforceps in the USA will have extremely low risk to non‐target plants, and provides another tool for the management of S. terebinthifolia.     

Spread of an introduced parasite across the Hawaiian archipelago independent of its introduced host

相似文献   

Genetically manipulated Brassica genotypes affect demography and performance of Diadegma semiclausum parasitizing Plutella xylostella

The performance of Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) on Plutella xylostella (L.) (Lepidoptera: Plutellidae) reared on canola's progenitor (Brassica rapa L.), two cultivated canola cultivars (Opera and RGS₀₀₃), one hybrid (Hyula₄₀₁), one gamma‐ray mutant‐RGS₀₀₃ and one transgenic (PF) genotype was compared using the age‐stage, two‐sex life table parameters. All experiments were carried out in a growth chamber at 25 ± 1°C, 65 ± 5% RH and a photoperiod of 16 : 8 (L : D) h. There were significant differences in duration of different life stages of D. semiclausum on its host larvae reared on different plant genotypes. The shortest (12.27 days) and longest (15.21 days) pre‐adult developmental times were observed on cultivar‐RGS₀₀₃ and hybrid‐Hyula₄₀₁, respectively. The intrinsic rate of increase (r) in D. semiclausum ranged between 0.189/day (cultivar‐Opera) and 0.141/day (transgenic‐PF). Moreover, the highest (20.078 offspring) and lowest (12.027 offspring) net reproductive rates (R₀) were observed on cultivar‐Opera and hybrid‐Hyula₄₀₁. The mean generation time (T) of D. semiclausum was the highest (18.34 days) and lowest (15.05 days) on mutant‐RGS₀₀₃ and cultivar‐RGS₀₀₃. The maximum and minimum parasitism values of this parasitoid were observed on canola's progenitor (44.28%) and hybrid‐Hyula₄₀₁ (37.09%). The heaviest pupae (3.82 mg) and females (3.22 mg) of the parasitoid were found on canola's progenitor and cultivar‐Opera, respectively. The results showed that performance of this parasitoid was better on canola's progenitor and cultivated plants known to have higher levels of glucosinolates concentration than others.     

Effects of quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested maize on the attraction of the larval parasitoid Cotesia kariyai

Cotesia kariyai Watanabe (Hymenoptera: Braconidae) is a specialist larval parasitoid of Mythimna separata Walker (Lepidoptera: Noctuidae). Cotesia kariyai wasps use herbivore‐induced plant volatiles (HIPVs) to locate hosts. However, complex natural habitats are full of volatiles released by both herbivorous host‐ and non‐host‐infested plants at various levels of intensity. Therefore, the presence of non‐hosts may affect parasitoid decisions while foraging. Here, the host‐finding efficiency of naive C. kariyai from HIPVs influenced by host‐ and non‐host‐infested maize [Zea mays L. (Poaceae)] plants was investigated with a four‐arm olfactometer. Ostrinia furnacalis Guenée (Lepidoptera: Crambidae) was selected as a non‐host species. One unit (1 U) of host‐ or non‐host‐infested plant was prepared by infesting a potted plant with five host or seven non‐host larvae. In two‐choice bioassays, host‐infested plants fed upon by different numbers of larvae, and various units of host‐ and non‐host‐infested plants (infestation units; 1 U, 2 U, and 3 U) were arranged to examine the effects of differences in volatile quantity and quality on the olfactory responses of C. kariyai with the assumption that volatile quantity and quality changes with differences in numbers of insects and plants. Cotesia kariyai was found to perceive quantitative differences in volatiles from host‐infested plants, preferring larger quantities of volatiles from larger numbers of larvae or plants. Also, the parasitoids discriminated between healthy plants, host‐infested plants, and non‐host‐infested plants by recognising volatiles released from those plants. Cotesia kariyai showed a reduced preference for host‐induced volatiles, when larger numbers of non‐host‐infested plants were present. Therefore, quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested plants appear to affect the decision of C. kariyai during host‐habitat searching in multiple tritrophic systems.     

Host plant preference and offspring performance of a leaf‐mining moth,Caloptilia fraxinella,on two Fraxinus species

The preference‐performance or ‘mother‐knows‐best’ hypothesis states that female insects choose to oviposit on a host plant that increases the performance of their offspring. This positive link between host plant choice and larval performance is especially important for leaf miners with non‐motile larvae that are entirely dependent upon the oviposition choice of the female for host plant location. Preference and performance of the ash leaf coneroller, Caloptilia fraxinella (Ely) (Lepidoptera: Gracillariidae), a specialist on ash trees, Fraxinus spp. (Oleaceae), were tested in a series of laboratory and field experiments. Female C. fraxinella were exposed to two closely related hosts, black ash, Fraxinus nigra Marshall, and green ash, Fraxinus pennsylvanica Marshall var. subintegerrima (Vahl), in oviposition choice and wind tunnel flight experiments to determine which host is most attractive for oviposition. Caloptilia fraxinella females were inconsistent in host choice, yet performance of larvae was greater on green than black ash. In preference studies, C. fraxinella preferred to oviposit on black ash when leaflets were removed from the tree, but preferred intact green ash over black ash seedlings for oviposition and host location in a wind tunnel. In the field, however, more C. fraxinella visited black ash var. ‘Fallgold’ at leaf flush than green ash at the same sites. Age of the ash leaflet also influences oviposition in this leaf miner and females preferred new over old leaflets for oviposition. Performance of C. fraxinella larvae was evaluated in field and laboratory experiments and was greater on green ash than on black ash in both experiments based on larval survival and development time parameters. The stronger oviposition and host location preference in the field for black ash were not linked to enhanced performance of offspring, as green ash was the superior host, supporting higher larval survival and faster development. A stronger host location preference in the wind tunnel for green ash over black ash, however, suggests that under certain circumstances with this moth species, ‘mother (may) know best’.     

Hypersensitive response, cell death and histochemical localisation of hydrogen peroxide in host and non-host seedlings infected with the downy mildew pathogen Sclerospora graminicola

Hypersensitive response, cell death and release of hydrogen peroxide as measures of host and non‐host defense mechanisms upon inoculation with the downy mildew pathogen Sclerospora graminicola were studied histochemically at the light microscopy level. The materials consisted of coleoptile tissues of the highly susceptible (cv. HB3), highly resistant (cv. IP18293) and induced resistant pearl millet host seedlings and non‐host sorghum (cv. SGMN10/8) and cotyledon of french bean (cv. S9). Resistance up to 80% protection against the downy mildew pathogen was induced in the highly susceptible HB3 cultivar of pearl millet by treating the seeds with 2% aqueous leaf extract of Datura metel for 3 h. Time course study with the pathogen inoculated highly resistant pearl millet cultivar revealed the appearance of hypersensitive response in 20% of seedlings as necrotic spots as early as 2 h after inoculation. In contrast, a similar reaction was observed in the highly susceptible pearl millet cultivar only 8 h after inoculation with the pathogen. In induced resistant seedlings, appearance of hypersensitive response was recorded 4 h after inoculation. Delayed hypersensitive response was observed in both the non‐host species at 10 h after inoculation. Hypersensitive response in the seedlings of the highly resistant pearl millet cultivar 24 h after inoculation showed 100% hypersensitive response, which was not observed in susceptible and non‐host species, although the induced resistant seedlings showed 90% hypersensitive response after that period of time. Cell death in the tissues of the test seedlings was also observed to change with time. Statistical analysis revealed that the tissues of highly resistant pearl millet seedlings required 2.9 h to attain 50% cell death. Tissues of induced resistant and highly susceptible pearl millet seedlings required 4.65 and 6.50 h respectively. In non‐hosts, 50% cell death was not recorded. Quantification of hydrogen peroxide in the tissue periplasmic spaces of the test seedlings revealed 2.94 h as the time required for 50% hydrogen peroxide accumulation in the tissues of highly resistant pearl millet seedlings. Tissues of induced resistant and highly susceptible pearl millet seedlings needed 3.76 and 5.5 h respectively. Fifty percent hydrogen peroxide localisation in non‐hosts could not be recorded. These results suggested the involvement of hydrogen peroxide, cell death and hypersensitive response in pearl millet host defense against S. graminicola.     

Logistic growth of the host‐specific obligate insect pathogenic fungus Entomophthora muscae in house flies (Musca domestica)

Insect pathogenic fungi (IPF) need to overcome the host immune system in order to sporulate and ensure transmission to new hosts. Some IPF produce immunosuppressive toxins, whereas others rely on rapid fungal proliferation to kill the host by sheer fungal mass, resulting in a trade‐off between allocating resources to toxin production and fungal proliferation. The obligate entomopathogenic fungus, Entomophthora muscae sensu stricto, is host specific to the common house fly, Musca domestica. E. muscae grows as protoplast cells without cell walls and is not known to produce toxins. Here, we assessed the growth of E. muscae, in vivo, using real‐time PCR to measure the amount of a single‐copy actin gene. We find that E. muscae exhibits S‐shaped logistic growth between time post‐exposure and the number of fungal nuclei. The results show that E. muscae initially grows exponentially inside the host until depletion of available nutrient sources signifies the ‘limiting capacity’ where after the host is killed. This growth pattern differs markedly from toxin‐producing IPF species of Metarhizium and Beauveria in which maximal (plateau) growth and sporulation do not occur until well after the death of the host.     

Winter hardiness of Miscanthus (II): Genetic mapping for overwintering ability and adaptation traits in three interconnected Miscanthus populations

Miscanthus × giganteus (M×g) is the primary species of Miscanthus for bioenergy feedstock production. The current leading biomass cultivar, M×g ‘1993‐1780’, is insufficiently adapted in temperate regions with cold winters such as USDA hardiness zone 5 (average annual minimum temperature of ?28.9 to ?23.3°C) or lower. Three interconnected Miscanthus F₁ populations that shared a common parent were planted in a replicated field trial at Urbana, IL (hardiness zone 5b; average annual minimum temperature of ?26.1 to ?23.3°C) in spring 2011. The winter of 2013–2014 was especially cold in Urbana, with a minimum soil temperature at 10 cm of ?6.2°C and a minimum air temperature of ?25.3°C, giving us an opportunity to evaluate hardiness on established year‐3 plants. The parent in common to all three populations, M. sinensis ssp. condensatus ‘Cosmopolitan’, is native to maritime southern Japan, and in Urbana, it is winter‐damaged most years. In contrast, the three other parents, M. sacchariflorus ‘Robustus’ (MapA), M. sinensis ‘Silberturm’ (MapB), and M. sinensis ‘November Sunset’ (MapC), are typically winter hardy in Urbana. Nearly all MapA progeny plants survived and grew vigorously in spring 2014, whereas in MapB and MapC, many progeny plants did not survive the winter, and most of the survivors were severely damaged, with poor vigor. Negative correlations between overwintering ability and spring regrowth date and autumn dormancy date suggested that the genotypes most likely to survive winters were those that emerged early in spring and/or went dormant early in autumn. Using joint‐population analysis, we identified 53 quantitative trait loci (QTLs) for nine adaptation traits, including nine QTLs for overwintering ability and 11 for spring hardiness scores. Many biologically intuitive candidate genes were observed within or near the QTLs detected in this study, suggesting their validity and potential for further study.     

Pepper pathogenesis‐related protein 4c is a plasma membrane‐localized cysteine protease inhibitor that is required for plant cell death and defense signaling

Xanthomonas campestris pv. vesicatoria (Xcv) type III effector AvrBsT triggers programmed cell death (PCD) and activates the hypersensitive response (HR) in plants. Here, we isolated and identified the plasma membrane localized pathogenesis‐related (PR) protein 4c gene (CaPR4c) from pepper (Capsicum annuum) leaves undergoing AvrBsT‐triggered HR cell death. CaPR4c encodes a protein with a signal peptide and a Barwin domain. Recombinant CaPR4c protein expressed in Escherichia coli exhibited cysteine protease‐inhibitor activity and ribonuclease (RNase) activity. Subcellular localization analyses revealed that CaPR4c localized to the plasma membrane in plant cells. CaPR4c expression was rapidly and specifically induced by avirulent Xcv (avrBsT) infection. Transient expression of CaPR4c caused HR cell death in pepper leaves, which was accompanied by enhanced accumulation of H₂O₂ and significant induction of some defense‐response genes. Deletion of the signal peptide from CaPR4c abolished the induction of HR cell death, indicating a requirement for plasma membrane localization of CaPR4c for HR cell death. CaPR4c silencing in pepper disrupted both basal and AvrBsT‐triggered resistance responses, and enabled Xcv proliferation in infected leaves. H₂O₂ accumulation, cell‐death induction, and defense‐response gene expression were distinctly reduced in CaPR4c‐silenced pepper. CaPR4c overexpression in transgenic Arabidopsis plants conferred greater resistance against infection by Pseudomonas syringae pv. tomato and Hyaloperonospora arabidopsidis. These results collectively suggest that CaPR4c plays an important role in plant cell death and defense signaling.     

Engineering fire blight resistance into the apple cultivar ‘Gala’ using the FB_MR5 CC‐NBS‐LRR resistance gene of Malus × robusta 5

The fire blight susceptible apple cultivar Malus × domestica Borkh. cv. ‘Gala’ was transformed with the candidate fire blight resistance gene FB_MR5 originating from the crab apple accession Malus × robusta 5 (Mr5). A total of five different transgenic lines were obtained. All transgenic lines were shown to be stably transformed and originate from different transgenic events. The transgenic lines express the FB_MR5 either driven by the constitutive CaMV 35S promoter and the ocs terminator or by its native promoter and terminator sequences. Phenotyping experiments were performed with Mr5‐virulent and Mr5‐avirulent strains of Erwinia amylovora, the causal agent of fire blight. Significantly less disease symptoms were detected on transgenic lines after inoculation with two different Mr5‐avirulent E. amylovora strains, while significantly more shoot necrosis was observed after inoculation with the Mr5‐virulent mutant strain ZYRKD3_1. The results of these experiments demonstrated the ability of a single gene isolated from the native gene pool of apple to protect a susceptible cultivar from fire blight. Furthermore, this gene is confirmed to be the resistance determinant of Mr5 as the transformed lines undergo the same gene‐for‐gene interaction in the host–pathogen relationship Mr5–E. amylovora.     

The high‐quality genome of Brassica napus cultivar ‘ZS11’ reveals the introgression history in semi‐winter morphotype

Allotetraploid oilseed rape (Brassica napus L.) is an agriculturally important crop. Cultivation and breeding of B. napus by humans has resulted in numerous genetically diverse morphotypes with optimized agronomic traits and ecophysiological adaptation. To further understand the genetic basis of diversification and adaptation, we report a draft genome of an Asian semi‐winter oilseed rape cultivar ‘ZS11’ and its comprehensive genomic comparison with the genomes of the winter‐type cultivar ‘Darmor‐bzh’ as well as two progenitors. The integrated BAC‐to‐BAC and whole‐genome shotgun sequencing strategies were effective in the assembly of repetitive regions (especially young long terminal repeats) and resulted in a high‐quality genome assembly of B. napus ‘ZS11’. Within a short evolutionary period (~6700 years ago), semi‐winter‐type ‘ZS11’ and the winter‐type ‘Darmor‐bzh’ maintained highly genomic collinearity. Even so, certain genetic differences were also detected in two morphotypes. Relative to ‘Darmor‐bzh’, both two subgenomes of ‘ZS11’ are closely related to its progenitors, and the ‘ZS11’ genome harbored several specific segmental homoeologous exchanges (HEs). Furthermore, the semi‐winter‐type ‘ZS11’ underwent potential genomic introgressions with B. rapa (A_r). Some of these genetic differences were associated with key agronomic traits. A key gene of A03.FLC3 regulating vernalization‐responsive flowering time in ‘ZS11’ was first experienced HE, and then underwent genomic introgression event with A_r, which potentially has led to genetic differences in controlling vernalization in the semi‐winter types. Our observations improved our understanding of the genetic diversity of different B. napus morphotypes and the cultivation history of semi‐winter oilseed rape in Asia.     

Molecular mechanism underlying pseudopeloria in Habenaria radiata (Orchidaceae)

Habenaria radiata (Orchidaceae) has two whorls of perianth, comprising three greenish sepals, two white petals and one lip (labellum). By contrast, the pseudopeloric (with a decreased degree of zygomorphy) mutant cultivar of H. radiata , ‘Hishou’, has changes in the identities of the dorsal sepal to a petaloid organ and the two ventral sepals to lip‐like organs. Here, we isolated four DEFICIENS ‐ like and two AGL 6 ‐like genes from H. radiata , and characterized their expression. Most of these genes revealed similar expression patterns in the wild type and in the ‘Hishou’ cultivar, except Hr DEF ‐C3. The Hr DEF ‐C3 gene was expressed in petals and lip in the wild type but was ectopically expressed in sepal, petals, lip, leaf, root and bulb in ‘Hishou’. Sequence analysis of the Hr DEF ‐C3 loci revealed that the ‘Hishou’ genome harbored two types of Hr DEF ‐C3 genes: one identical to wild‐type Hr DEF ‐C3 and the other carrying a retrotransposon insertion in its promoter. Genetic linkage analysis of the progeny derived from an intraspecific cross between ‘Hishou’ and the wild type demonstrated that the mutant pseudopeloric trait was dominantly inherited and was linked to the Hr DEF ‐C3 gene carrying the retrotransposon. These results indicate that the pseudopeloric phenotype is caused by retrotransposon insertion in the Hr DEF ‐C3 promoter, resulting in the ectopic expression of Hr DEF ‐C3 . As the expression of Hr AGL 6‐C2 was limited to lateral sepals and lip, the overlapping expression of Hr DEF ‐C3 and Hr AGL 6‐C2 is likely to be responsible for the sepal to lip‐like identity in the lateral sepals of the ‘Hishou’ cultivar.     

Selection, biological properties and fitness of resistance-breaking strains of Tomato spotted wilt virus in pepper

In glasshouse tests, infective sap from plants infected with 17 different isolates of Tomato spotted wilt virus (TSWV) from four Australian states was inoculated to three Capsicum chinense accessions (PI 152225, PI 159236 and C00943) carrying single genes that confer hypersensitive resistance to TSWV. The normal response to inoculation was development of necrotic (hypersensitive) local lesions in inoculated leaves without systemic invasion, but 3/1386 infected plants also developed systemic susceptible reactions in addition to hypersensitive ones. Similarly when two isolates were inoculated to C. chinense backcross progeny plants, 1/72 developed systemic susceptible reactions in addition to localised hypersensitive ones. Using cultures from the four plants with susceptible reactions and following three to five further cycles of serial subculture in TSWV‐resistant C. chinense plants, four isolates were obtained that gave systemic susceptible type reactions in the three TSWV‐resistant accessions, and in TSWV‐resistant cultivated pepper (C. annuum). When three of these isolates were inoculated to tomato (Lycopersicon esculentum) breeding lines with single gene resistance to TSWV, resistance was not overcome. Similarly, none of the four isolates overcame partial resistance to TSWV in Lactuca virosa. When TSWV isolates were inoculated to tomato breeding lines carrying partial resistance from L. chilense, systemic infection developed which was sometimes followed by ‘recovery’. After four successive cycles of serial passage in susceptible cultivated pepper of a mixed culture of a resistance‐breaking isolate with the non resistance‐breaking isolate from which it came, the resistance‐breaking isolate remained competitive as both were still found. However, when the same resistance‐ breaking isolate was cultured alone, evidence of partial reversion to wild‐type behaviour was eventually obtained after five but not four cycles of long term serial subculture in susceptible pepper, as by then the culture had become a mixture of both types of strain. This work suggests that resistance‐breaking strains of TSWV that overcome single gene hypersensitive resistance in pepper are relatively stable. The findings have important implications for situations where resistant pepper cultivars are deployed widely in the field without taking other control measures as part of an integrated TSWV management strategy.     

Diadegma insulare development is altered by Plutella xylostella reared on water‐stressed host plants

Natural enemies of herbivores function in a multitrophic context, and their performance is directly or indirectly influenced by herbivores and their host plants. Very little is known about tritrophic interactions between host plants, pests and their parasitoids, particularly when the host plants are under any stress. Herbivores and their natural enemies’ response to plants under stress are diverse and variable. Therefore, in this study we investigated how diamondback moth, Plutella xylostella (L.), reared on water‐stressed host plants (Brassica napus L. and Sinapis alba L.) influenced the development of its larval parasitoid, Diadegma insulare (Cresson). No significant differences were observed in development of P. xylostella when reared on water‐stressed host plants. However, all results indicated that water stress had a strong effect on developmental parameters of D. insulare. Development of D. insulare was delayed when the parasitoid fed on P. xylostella, reared on stressed host plants. Egg to adult development of D. insulare was faster on non‐stressed B. napus than non‐stressed S. alba followed by stressed B. napus and S. alba. Female parasitoids were heavier on non‐stressed host plants than stressed counterparts. Furthermore, the parasitoid lived significantly longer on stressed B. napus. However, body size was not affected by water treatment. Most host plant parameters measured were significantly lower for water‐stressed than non‐stressed treatments. Results suggest that development of this important and effective P. xylostella parasitoid was influenced by both water stress and host plant species.     

Influence of cabbage resistance and colour upon the diamondback moth and its parasitoid Oomyzus sokolowskii

Host plant resistance and biological control are vital integrated pest management tools against the diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), but to date no study has investigated this system including the DBM parasitoid Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae). We examined oviposition and development of P. xylostella exposed to two commercial cabbage cultivars (green ‘Chato de quintal’ and red ‘Roxo’) and possible effects upon O. sokolowskii. Under free‐choice tests, DBM females laid significantly more eggs on plants of the green cabbage, even though several population growth parameters showed that DBM developed better on the red cabbage. Furthermore, a laboratory free‐choice test with artificially green‐ and red‐painted kale leaf discs demonstrated a similar oviposition preference pattern, with green colour being preferred over red colour. The preference was apparently visually mediated; olfactometer tests showed similar attraction of moths to both green and red cultivars in choice and non‐choice tests. Host plant cultivar had no statistically significant effect on female parasitoid behaviour towards DBM larvae, nor on parasitoid numbers or longevity. Moreover, wasps parasitizing DBM larvae reared on the green cultivar developed more quickly and in larger numbers per parasitized larva. Thus, feeding on green cabbage rather than red does not hinder, and potentially even enhances, control of DBM by O. sokolowskii. On a practical level, these results suggest that intercalating green cabbage cultivars as a trap crop might help protect more profitable red cultivars in growing fields.     

Influence of salt stress on C4 photosynthesis in Miscanthus sinensis Anderss.

• Miscanthus sinensis Anderss. is a good candidate for C₄ bioenergy crop development for marginal lands. As one of the characteristics of marginal lands, salinization is a major limitation to agricultural production. The present work aimed to investigate the possible factors involved in the tolerance of M. sinensis C₄ photosynthesis to salinity stress.
• Seedlings of two accessions (salt‐tolerant ‘JM0119’ and salt‐sensitive ‘JM0099’) were subjected to 0 mm NaCl (control) or 250 mm NaCl (salt stress treatment) for 2 weeks. The chlorophyll content, parameters of photosynthesis and chlorophyll a fluorescence, activity of C₄ enzymes and expression of C₄ genes were measured.
• The results showed that photosynthesis rate, transpiration rate, chlorophyll content, PSII operating efficiency, coefficient of photochemical quenching, activity of phosphoenolpyruvate carboxylase (PEPC) and pyruvate, orthophosphate dikinase (PPDK) and gene expression of PEPC and PPDK under salinity were higher after long‐term salinity exposure in ‘JM0119’ than in ‘JM0099’, while activity of NADP‐malate dehydrogenase (NADP‐MDH) and NADP‐malic enzyme (NADP‐ME), together with expression of NADP‐MDH and NADP‐ME, were much higher in ‘JM0099’ than in ‘JM0119’.
• In conclusion, the increased photosynthetic capacity under long‐term salt stress in the salt‐tolerant relative to the salt‐sensitive M. sinensis accession was mainly associated with non‐stomatal factors, such as reduced chlorophyll loss, higher PSII operating efficiency, enhanced activity of PEPC and PPDK and relatively lower activity of NADP‐ME.

     

Mix‐planting pubescent and glabrous cassava affects abundance of Typhlodromalus aripo and its prey mite Mononychellus tanajoa

There is an increasing awareness that vegetation diversity can affect herbivore and natural enemy abundance and that plants can play a major role in directly manipulating natural enemy abundance for protection against herbivore attacks. Using data from cassava fields, we aimed at (i) testing the capacity of the predatory mite Typhlodromalus aripo to control the herbivorous mite Mononychellus tanajoa in a chemical exclusion trial; and (ii) testing, based on the differential preference by T. aripo for cassava cultivars, how combinations of two morphologically different cassava cultivars with differential suitability to the predator can improve its population densities on the non‐favourable cultivar, thereby reducing M. tanajoa densities with subsequent increases in cassava yield. The study was conducted in a cassava field in Benin, West Africa. The experiments confirmed that T. aripo effectively suppresses M. tanajoa populations on both cultivars and showed, in the no‐predator‐exclusion experiments, that cultivar combinations have significant effects on M. tanajoa and T. aripo densities. Indeed, T. aripo load on the non‐preferred cultivar was lowest in subplots where the proportion of T. aripo‐preferred cultivar was also low, while, and as expected, M. tanajoa load on the non‐preferred cultivar showed decreasing trends with increasing T. aripo densities. The possible mechanisms by which cultivar mixing could increase predator load on the non‐favourable cultivar were discussed. Our data showed that appropriate cultivar combinations effectively compensate for morphologically related differences in natural enemy abundance on a normally predator‐deficient cultivar, resulting in lower pest densities on the non‐favourable cultivar. In practical terms, this strategy could, in part, enhance adoption of cultivars that do not support sufficient levels of natural enemies for pest control.     

Control of Colletotrichum coccodes on Tomato by Grafting and Soil Amendments

Eight trials were carried out in 2011 and 2012 in Northern Italy to evaluate the efficacy of grafting, compost and biofumigation with Brassica carinata against Colletotrichum coccodes on tomato. Four trials were carried out in commercial farms, and four trials were carried out in plastic tunnels at an experimental centre. The rootstocks ‘Armstrong’, ‘Arnold’, ‘Beaufort’, ‘Big Power’, ‘Brigeor’, ‘Emperador’, ‘King Kong’, ‘Spirit’ and ‘Superpro V295’ were tested. Host plants included several tomato F1 hybrids: ‘Amantino’, ‘Arawak’, ‘CLX 37438’, ‘Cauralina’, ‘CU 8301’, ‘CU 8506’, ‘DRK 7021’, ‘E 34431’, ‘E 50070’, ‘EXP’, ‘Gotico’, ‘Ingrid’, ‘ISI 61401’, ‘ISI 61402’, ‘Profitto’, ‘Punente’, ‘Rugantino’ and ‘Tomahawk’. Tomato roots from the control plots were 34 to 87% diseased in both naturally and artificially infested soil. Among the nineteen commercial tomato hybrids tested, in the presence of a very high disease pressure in a naturally infested soil, ‘Rugantino’ was the least affected by C. coccodes, showing 32% infected roots. ‘Tomahawk’ grafted onto ‘Arnold’, ‘Armstrong’ and ‘Superpro V295’ was significantly less affected by C. coccodes, while ‘Arawak’ grafted onto ‘Armstrong’, ‘Arnold’, ‘Emperador’ and ‘Beaufort’ provided very good control of root rot in the different trials. Compost addition and biofumigation with Brassica pellets were also tested with and without grafting. Soil amendment with compost, in the case of the ‘Arawak’ and ‘Tomahawk’, resulted in a slightly improved disease control only on non‐grafted plants. When grafting and biofumigation were combined in a soil naturally infested with C. coccodes and Meloidogyne arenaria, biofumigation did not improve C. coccodes control in comparison with grafting alone. In a naturally infested soil, compost alone and combined with biofumigation improved disease control only on non‐grafted ‘Tomahawk’ plants. In general, grafting by itself provided very good results in terms of disease control, which were not significantly improved by combination with compost and/or biofumigation.