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.     

Bemisia tabaci (Gennadius) population density and pupal size are dependent on rootstock and nitrogen in hydroponic tomato crop

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Grafting influence on the weight and quality of tomato fruit under salt stress

Two commercial tomato cultivars were used to determine whether grafting could prevent decrease of fruit weight and quality under salt stress conditions. The cultivars Buran F1 and Berberana F1 were grafted onto rootstock ‘Maxifort’ and grown under three levels of elevated soil salinity (EC 3.80 dS m^?1, 6.95 dS m^?1 and 9.12 dS m^?1). Fruit weight reduction of grafted plants was lower (about 20–30%) in comparison with non‐grafted ones. Salt stress at the second salinity level (EC 6.95 dS m^?1) induced the highest alteration of examined growth and quality parameters. The total increase of phenols, flavonoids, ascorbate and lycopene content in the fruits of both grafted and non‐grafted plants for both cultivars had a similar trend and intensity, though some inter‐cultivar variation was observed. The possibility of grafting tomato plants to improve salt tolerance without fruit quality loss is discussed.     

Conferring high‐temperature tolerance to nontransgenic tomato scions using graft transmission of RNA silencing of the fatty acid desaturase gene

We investigated graft transmission of high‐temperature tolerance in tomato scions to nontransgenic scions from transgenic rootstocks, where the fatty acid desaturase gene (LeFAD7) was RNA‐silenced. Tomato was transformed with a plasmid carrying an inverted repeat of LeFAD7 by Agrobacterium. Several transgenic lines showed the lower amounts of LeFAD7 RNA and unsaturated fatty acids, while nontransgenic control did not, and siRNA was detected in the transgenic lines, but not in control. These lines grew under conditions of high temperature, while nontransgenic control did not. Further, the nontransgenic plants were grafted onto the silenced transgenic plants. The scions showed less of the target gene RNA, and siRNA was detected. Under high‐temperature conditions, these grafted plants grew, while control grafted plants did not. Thus, it was shown that high‐temperature tolerance was conferred in the nontransgenic scions after grafting onto the silenced rootstocks.     

Evaluation of Tomato Hybrids Carrying Ty‐1 and Ty‐2 Loci to Japanese Monopartite Begomovirus Species

Tobacco leaf curl Japan virus, Honeysuckle yellow vein mosaic virus and Tomato yellow leaf curl virus are three begomoviruses that infect tomato crops in Japan. Tomato infection by begomoviruses has increased in Japan after the development of a high level of resistance to certain insecticides in some populations of the vector B. tabaci biotypes ‘B and Q’. Ty‐1 and Ty‐2 homozygous tomato hybrids were evaluated for reaction to monopartite begomovirus species in Japan by Agrobacterium‐mediated inoculation. Test plants were evaluated by a disease assessment scale (DAS), varying from 1 = no symptoms to 4 = severe symptoms, and systemic infection was evaluated by polymerase chain reaction (PCR), using specific begomovirus primers for each virus. Ty‐1 hybrids showed tolerance to HYVMV and with a large number of plants being neither virus‐free nor symptom‐free. The response of Ty‐1 hybrids was also resistant to moderately resistant against TbLCJV. The response of Ty‐2 hybrids was resistant to highly resistant against the three monopartite begomoviruses, when compared with susceptible plants.     

The oxalyl‐CoA synthetase‐regulated oxalate and its distinct effects on resistance to bacterial blight and aluminium toxicity in rice

• Oxalic acid is widely distributed in biological systems and known to play functional roles in plants. The gene AAE3 was recently identified to encode an oxalyl‐CoA synthetase (OCS) in Arabidopsis that catalyses the conversion of oxalate and CoA into oxalyl‐CoA. It will be particularly important to characterise the homologous gene in rice since rice is not only a monocotyledonous model plant, but also a staple food crop.
• Various enzymatic and biological methods have been used to characterise the homologous gene.
• We first defined that AAE3 in the rice genome (OsAAE3) also encodes an OCS enzyme. Its K_m for oxalate is 1.73 ± 0.12 mm , and V_m is 6824.9 ± 410.29 U·min^?1·mg protein^?1. Chemical modification and site‐directed mutagenesis analyses identified thiols as the active site residues for rice OCS catalysis, suggesting that the enzyme might be regulated by redox state. Subcellular localisation assay showed that the enzyme is located in the cytosol and predominantly distributed in leaf epidermal cells. As expected, oxalate levels increased when OCS was suppressed in RNAi transgenic plants. More interestingly, OCS‐suppressed plants were more susceptible to bacterial blight but more resistant to Al toxicity.
• The results demonstrate that the OsAAE3‐encoded protein also acts as an OCS in rice, and may play different roles in coping with stresses. These molecular, enzymatic and functional data provide first‐hand information to further clarify the function and mechanism of OCS in rice plants.

     

The effectiveness of grafting to improve salt tolerance in tomato when an ‘excluder’ genotype is used as scion

If the main effect of long-term exposure of tomato plants to salinity is the accumulation of toxic concentrations of Na⁺ and Cl⁻ in the leaves, then the selection of ‘excluder’ rootstocks should increase tolerance to salinity in grafted tomato plants, independently of the genotype used as the scion. The question addressed in this study is whether shoot genotypes with an ‘excluder’ character are able to increase their salt tolerance when grafted onto rootstocks of the same characteristics. Moneymaker (with excluder character) was grafted onto two root genotypes, Radja and Pera, selected for their very different ability to regulate the transport of saline ions to the shoot over time. Grafting onto either Pera or Radja improved fruit yield compared to the self-grafted plants of Moneymaker (M/M) when the plants were grown at 50 mM NaCl, whereas there was no effect of either rootstock or of grafting per se (M/M) on fruit yield in the absence of or at 25 mM NaCl. The relationship between the salt responses to mid- and long-term depended on the stress level; after 27 d of 150 mM NaCl treatment, both graft combinations enhanced similarly their salt tolerances as did in the long-term experiment. Moreover, the tolerance induced by rootstock was related to the low rates of saline ion accumulation in their leaves. However, the positive effect of rootstock was only observed with rootstock Pera when the grafted plants were grown at 50 mM NaCl (the same salt level used in the long-term experiment) for 35 d. According to the physiological changes induced by rootstock in the leaves, the different salt responses seem to be due to the fact that the osmotic effect predominated on the toxic effect under these last conditions. Consequently, in order to select rootstocks care must be taken in the timing of any selection process: the stress level and length of exposure to salinity must be sufficient for the true differences in salt tolerance for toxicity to be shown. Taken together, these results show the effectiveness of grafting to enhance fruit yield in tomato and provide evidence that the positive effect induced by rootstock is related to the re-establishment of ionic homeostasis.     

Potential of bioinsecticidal Bacillus thuringiensis inoculum to suppress gray mold in tomato based on induced systemic resistance

The potential of the active ingredient of a commercial bioinsecticide, XenTari^® (Bacillus thuringiensis [BT] serovar aizawai strain ABTS‐1857), to suppress gray mold in tomato plants was elucidated. First, a suspension of the active ingredient of XenTari^® and a liquid culture of the bacterial strain as BT inocula were sprayed onto detached leaves or drenched into pots of tomato seedlings, and then, propagules of the gray mold fungus, Botrytis cinerea, were inoculated onto the leaves. The gray mold disease was significantly suppressed when rhizospheres were drenched with either inoculum, but not when inocula were sprayed onto detached leaves of seedlings. Both BT inocula were verified not to directly inhibit the mycelial growth of B. cinerea based on in vitro culture plate assays. Additionally, real‐time RT‐PCR analysis verified that the active ingredient increased the expression levels of defence‐related genes, such as PR‐1(P6) and P4, in the leaves of tomato seedlings. These results suggest that the active ingredient has the potential to suppress gray mold disease in tomato, not through direct antagonistic interactions with B. cinerea, but rather through systemic activation of the plant defence system by increased expression of several defence‐related genes.     

Performance of Galia-type melons grafted on to Cucurbita rootstock in Monosporascus cannonballus-infested and non-infested soils

Galia‐type melons grafted on to the Cucurbita rootstock‘TZ 148’and non‐grafted controls were evaluated for vegetative development under greenhouse conditions. In general, the development of grafted and non‐grafted plants was similar within a cultivar. The horticultural and pathological performances of the Galia‐type melons ‘Carrera’, ‘NUN‐5554’, ‘6003’ and ‘Arava’ were evaluated in experiments conducted in non‐infested and Monosporascus‐infested soils. In non‐infested soil, grafted and non‐grafted ‘Carrera’, ‘NUN‐5554’ and ‘Arava’ had the same yields. The yield of grafted ‘6003’ was significantly higher than that of its non‐grafted control. Responses of grafted and non‐grafted Galia‐type melons to Monosporascus cannonballus were evaluated and compared in the spring and autumn growing seasons. Significant differences in disease incidence were found among cultivars, between grafted and non‐grafted plants, and between growing seasons. Disease reduction and the beneficial effect of grafting on yield were more pronounced in the spring. The results indicate that Galia‐type melons can be grafted successfully, but the cultivation of the grafted plants should be adapted to each growing area and season.     

Lethal and behavioral sublethal side effects of thiamethoxam on the predator Harmonia axyridis

Thiamethoxam (TMX) is one of the most effective neonicotinoid insecticides for the control of green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), and various side effects can be expected in its natural enemies. The multicolored Asian lady beetle or harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is an important predator against M. persicae in greenhouses and fields. In this study, we evaluated the toxicity of TMX to H. axyridis and the effect on the functional response of this predator to M. persicae through three routes of exposure. Acute toxicity bioassays indicated that LC₅₀ values of TMX on H. axyridis through direct residual contact (‘contact’), systemic application (‘systemic’), and leaf‐dip treatment (‘leaf‐dip’) were 18.99, 21.26, and 15.39 mg a.i. l^?1, respectively. The hazard quotient indicated a potential hazard of this agrochemical regardless of the exposure routes. The mortality caused by the lowest rate, 2 mg a.i. l^?1, was not significantly different compared with the control group. For the three routes of sublethal TMX exposure, the type‐II functional response was a good fit to the prey consumption of H. axyridis. Predation was most affected by leaf‐dip treatment, followed by contact and systemic treatments, which had similar effect. For all exposure routes, the predation capacity of the predator recovered quickly after transfer to untreated cabbage leaves. Thiamethoxam applied systemically was the least toxic to H. axyridis and did not affect the functional response of the predator. However, the sublethal effects of TMX through both contact and leaf‐dip application may reduce the population growth of H. axyridis and consequently impair the biological control of M. persicae by this predator. These results illustrate that the assessment of potential effects of TMX on H. axyridis is crucial to develop effective integrated pest management programs for M. persicae in China.     

Phytophthora Crown and Root Rot of Apricot Caused by Phytophthora palmivora in Turkey

Forty‐nine Phytophthora isolates were obtained from roots and crown of apricot trees with symptoms of decline grown in commercial orchards in Malatya, Elaz?? and Diyarbak?r provinces, Turkey, in 2011 and 2013. All of the recovered isolates were identified as Phytophthora palmivora on the basis of morphological characteristics. Blast analysis of ITS region sequences of rDNA of 5 isolates revealed 100% identity with a reference isolates of P. palmivora from GenBank. Isolates of P. palmivora were pathogenic on 12‐month‐old wild apricot rootstock ‘Zerdali’ plants that were wound inoculated on the roots and on the crown. This study demonstrated that P. palmivora is the cause of the crown and root rot found on apricot in Turkey. To our knowledge, this is the first report of P. palmivora on this host plant.     

Invasive submerged freshwater macrophytes are more plastic in their response to light intensity than to the availability of free CO2 in air‐equilibrated water

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Outbreak of Rhizopus Rot Caused by Rhizopus oryzae on Seedlings of Grafted Cucumber on Pumpkin Rootstock in South Korea

In 2013, an outbreak of Rhizopus rot caused by Rhizopus oryzae occurred in cucumber grafted onto pumpkin rootstock sampled from seedling farms in Changnyeong, South Korea. A water‐soaked appearance of the affected tissue was the first symptom of this soft fungal rot in the seedling stems of grafted cucumber. Lesions at the graft sites softened and rapidly, rotted, and turned brown or dark brown. Measurements and taxonomic characteristics were most similar to R. oryzae. DNA sequencing and phylogenetic analysis of the internal transcribed spacer rRNA gene region confirmed that the isolates were indeed R. oryzae. Koch's postulates were supported by pathogenicity tests conducted on healthy plants. Based on mycological characteristics, pathogenicity test, and molecular analysis, the causal fungus was identified as R. oryzae Went & Prinsen Geerligs. To our knowledge, this is the first report of Rhizopus rot caused by R. oryzae in seedlings of grafted cucumber on pumpkin rootstock in South Korea.     

Grafting tomato (Solanum lycopersicum) onto the rootstock of a high-altitude accession of Solanum habrochaites improves suboptimal-temperature tolerance

Grafting is regarded as a promising tool to broaden the temperature optimum of elite tomato cultivars. However, suitable low-temperature tolerant tomato rootstocks are not yet available and its breeding is hampered by a lack of variation in low-temperature tolerance within the cultivated tomato. In this study, therefore, the impact of grafting tomato (Solanum lycopersicum Mill. cv. Moneymaker, Sl) onto the rootstock of a cold-tolerant high-altitude accession of a related wild species (Solanum habrochaites LA 1777 Humb. & Bonpl., Sh) was examined at different combinations of optimal (25 °C) and/or suboptimal (15 °C) air/root-zone temperatures (RZT), i.e. 25/25, 25/15, 15/25 and 15/15 °C. Self-grafted tomato plants were used as controls. Both scion/rootstock combinations, Sl/Sl and Sl/Sh, were grown hydroponically and compared for biomass production and partitioning, plant morphology, carbohydrate partitioning and leaf C and N status. Grafting tomato onto Sh increased the relative growth rate of shoots with 26 and 11% at 25/15 and 15/15 °C, respectively. This increase could be attributed to stimulation of the leaf expansion rate. Graft combinations with Sh rootstocks were characterized by higher root mass ratios, particularly at 15 °C RZT. Suboptimal RZT strongly reduced the relative growth rate of Sl roots but not of Sh. This was correlated to differences in inhibition of root elongation. In contrast to tomato grafted onto Sh, leaf total C and total N concentrations increased in self-grafted tomato plants in response to 15 °C RZT. The increase in leaf total C concentration of Sl/Sl graft combinations at 15 °C RZT could be ascribed largely to starch accumulation. This study illustrates that growth of vegetative tomato plants at suboptimal temperature is for a significant part inhibited by its poor root development. Grafting tomato onto a low-temperature rootstock provides an alternative tool to reduce, in part, the grow-limiting effects of suboptimal RZ temperature on the shoot. To improve the low-temperature tolerance of existing commercial tomato rootstocks, S. habrochaites LA 1777 appeared to be a valuable germplasm pool.     

Water browning mediates predatory decimation of the Arctic fairy shrimp Branchinecta paludosa

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Can chilling tolerance of C4 photosynthesis in Miscanthus be transferred to sugarcane?

The goal of this study was to investigate whether chilling tolerance of C₄ photosynthesis in Miscanthus can be transferred to sugarcane by hybridization. Net leaf CO₂ uptake (A_sat) and the maximum operating efficiency of photosystem II (Ф_PSII) were measured in warm conditions (25 °C/20 °C), and then during and following a chilling treatment of 10 °C/5 °C for 11 day in controlled environment chambers. Two of three hybrids (miscanes), ‘US 84‐1058’ and ‘US 87‐1019’, did not differ significantly from the chilling tolerant M. ×giganteus ‘Illinois’ (Mxg), for A_sat, and Φ_PSII measured during chilling. For Mxg grown at 10 °C/5 °C for 11 days, A_sat was 4.4 μmol m^?2 s^?1, while for miscane ‘US 84‐1058’ and ‘US 87‐1019’, A_sat was 5.7 and 3.5 μmol m^?2 s^?1, respectively. Miscanes ‘US 84‐1058’ and ‘US 87‐1019’ and Mxg had significantly higher rates of A_sat during chilling than three tested sugarcanes. A third miscane showed lower rates than Mxg during chilling, but recovered to higher rates than sugarcane upon return to warm conditions. Chilling tolerance of ‘US 84‐1058’ was further confirmed under autumn field conditions in southern Illinois. The selected chilling tolerant miscanes have particular value for biomass feedstock and biofuel production and at the same time they can be a starting point for extending sugarcane's range to colder climates.     

The physiological and nutritional responses to an excess of boron by Verna lemon trees that were grafted on four contrasting rootstocks

Citrus species are sensitive to an excess of boron (B). Currently, this toxicity is becoming a serious problem in the soils of arid and semi-arid environments throughout the world, where high concentrations of B may occur due to the agricultural use of wastewater. Citrus rootstocks can greatly influence the tolerance of citrus trees to different abiotic stresses. However, little is known about how the rootstock influences the tolerance of these trees to an excess of B. In this study, the effects of the nutrient solution’s B concentration (0.25, 2, 4.5 or 7?mg?l^?1) on the growth and other physiological, nutritional and biochemical parameters of Verna lemon trees that were grafted on four contrasting rootstocks [Carrizo citrange (CC), Cleopatra mandarin (CL), Citrus macrophylla (CM) and sour orange (SO)] were investigated. The plants were grown in a greenhouse in pots containing a universal substrate media and were watered daily with a Hoagland nutrient solution containing different concentrations of B. The results showed that the plant growth was progressively inhibited with an increasing concentration of B in the nutrient solution. However, the shoot was more sensitive to the B toxicity than were the roots. In addition, the growth inhibition was reduced in trees that were grafted on CL and CM when compared with those that were grafted on CC and SO. The concentration of B in the leaves, stems and roots also increased with an increase in the concentration of external B in the following order: leaves?>?roots?>?stem. The rootstock also had an influence on the B concentration in the different plant tissues. In the leaves, the B concentration was lowest in the plants that were grafted on the SO rootstock followed by the plants that were grafted on either the CM or CL rootstock and highest in the plants that were grafted on the CC rootstock. The net assimilation of CO₂ ( $ A_{{{\text{CO}}_{2} }} $ ) and the stomatal conductance (g _s) leaf gas exchange parameters were reduced with an excess of B in the leaves, and this reduction was less pronounced for trees on CM and CL. The intercellular CO₂ concentration (C _i) and the chlorophyll fluorescence indicated that the reduction of $ A_{{{\text{CO}}_{2} }} $ that was found with an excess of B was mainly due to non-stomatal factors. The mineral nutrition and organic solute data are also shown in this study. All of the data indicate that the tolerance to an excess of B is not related to the concentration of B that has accumulated in the leaves, which indicates that a combination of rootstock-dependent physiological, biochemical and anatomical responses determine the tolerance to an excess of B in citrus plants.