Arbuscular Mycorrhizas, Microbial Communities, Nutrient Availability, and Soil Aggregates in Organic Tomato Production

Effects of arbuscular mycorrhzal (AM) fungi on plant growth and nutrition are well-known, but their effects on the wider soil biota are less clear. This is in part due to difficulties with establishing appropriate non-mycorrhizal controls in the field. Here we present results of a field experiment using a new approach to overcome this problem. A previously well-characterized mycorrhizal defective tomato mutant (rmc) and its mycorrhizal wildtype progenitor (76R MYC+) were grown at an organic fresh market tomato farm (Yolo County, CA). At the time of planting, root in-growth cores amended with different levels of N and P, were installed between experimental plants to study localized effects of mycorrhizal and non-mycorrhizal tomato roots on soil ecology. Whilst fruit yield and vegetative production of the two genotypes were very similar at harvest, there were large positive effects of colonization of roots by AM fungi on plant nutrient contents, especially P and Zn. The presence of roots colonized by AM fungi also resulted in improved aggregate stability by increasing the fraction of small macroaggregates, but only when N was added. Effects on the wider soil community including nematodes, fungal biomass as indicated by ergosterol, microbial biomass C, and phospholipid fatty acid (PLFA) profiles were less pronounced. Taken together, these data show that AM fungi provide important ecosystem functions in terms of plant nutrition and aggregate stability, but that a change in this one functional group had only a small effect on the wider soil biota. This indicates a high degree of stability in soil communities of this organic farm.     

Grafting under water stress in tomato cherry: improving the fruit yield and quality

As the concentrations of essential vitamins and minerals and a number of other health‐promoting compounds are often low in stable crops, research is under way to understand and increase synthesis of phytochemicals in order to improve crop nutritional quality. The question addressed in this study is whether shoot genotypes or root genotypes with tolerant drought character are able to increase the fruit quality and production under moderate water stress. Zarina (drought tolerant) and Josefina (drought sensitive) were grafted self and reciprocally. The results showed that the use of cv. Zarina (drought tolerant) as rootstock (Zar × Jos) results in a greater number of fruits under water‐stress conditions, a moderate increase in some antioxidant compounds, such as ascorbic acid, phenols and flavonoids and lycopene and β‐carotene, and Zar × Jos showed high levels of sugars and organic acids, sweetness index and sugars : acids ratio, as well as important minerals, such as K and Mg, which could increase its nutritional quality under stress conditions. Overall, the use of drought‐tolerant rootstock could provide a useful tool to improve fruit yield and quality of cherry tomato fruit under moderate water stress, which in turn could mean lower costs in the use of irrigation water.     

激光处理对番茄幼苗抗盐性的影响

为明确激光对番茄耐盐性的影响,用番茄（Lycoperslcon esculentum Mill）种子为实验材料,以不同剂量的He-Ne激光辐照刚萌动的种子,用0.3%的NaCI溶液模拟盐胁迫,观察出苗时间、出苗率,测定相关的生理生化指标.结果表明：激光处理后,番茄种子的发芽率（Gr）和发芽指数（Gi）有不同程度的降低;番茄幼苗游离脯氨酸积累量、根系活力、超氧化物歧化酶（SOD）活性都有不同程度的升高;丙二醛（MDA）含量降低.分析不同处理的各项指标可知,辐照量为23.04 J/cm2是较合适的处理.说明利用一定程度的激光处理可以提高番茄的抗盐性.     

Influence of Temperature and Light Conditions on Germination,Growth and Conidiation of Oidium neolycopersici

The effect of temperature and light conditions (spectral quality, intensity and photoperiod) on germination, development and conidiation of tomato powdery mildew (Oidium neolycopersici) on the highly susceptible tomato cv. Amateur were studied. Conidia germinated across the whole range of tested temperatures (10–35°C); however, at the end‐point temperatures, germination was strongly limited. At temperatures slightly lower than optimum (20–25°C), mycelial development and time of appearance of the first conidiophores was delayed. Conidiation occurred within the range of 15–25°C, however was most intense between 20–25°C. Pathogen development was also markedly influenced by the light conditions. Conidiation and mycelium development was greatest at light intensities of approximately 60 μmol/m² per second. At lower intensities, pathogen development was delayed, and in the dark, conidiation was completely inhibited. A dark period of 24 h after inoculation had no stimulatory effect on later mycelium development. However, 12 h of light after inoculation, followed by continuous dark, resulted in delayed mycelium development and total restriction of pathogen conidiation (evaluated 8 days postinoculation). When a longer dark period (4 days) was followed by normal photoperiod (12 h/12 h light/dark), mycelium development accelerated and the pathogen sporulated normally. When only inoculated leaf was covered with aluminium foil while whole plant was placed in photoperiod 12 h/12 h, the intensive mycelium development and slight subsequent sporulation on covered leaf was recorded.     

The AtNHX1 exchanger mediates potassium compartmentation in vacuoles of transgenic tomato

NHX‐type antiporters in the tonoplast have been reported to increase the salt tolerance of various plants species, and are thought to mediate the compartmentation of Na⁺ in vacuoles. However, all isoforms characterized so far catalyze both Na⁺/H⁺ and K⁺/H⁺ exchange. Here, we show that AtNHX1 has a critical involvement in the subcellular partitioning of K⁺, which in turn affects plant K⁺ nutrition and Na⁺ tolerance. Transgenic tomato plants overexpressing AtNHX1 had larger K⁺ vacuolar pools in all growth conditions tested, but no consistent enhancement of Na⁺ accumulation was observed under salt stress. Plants overexpressing AtNHX1 have a greater capacity to retain intracellular K⁺ and to withstand salt‐shock. Under K⁺‐limiting conditions, greater K⁺ compartmentation in the vacuole occurred at the expense of the cytosolic K⁺ pool, which was lower in transgenic plants. This caused the early activation of the high‐affinity K⁺ uptake system, enhanced K⁺ uptake by roots, and increased the K⁺ content in plant tissues and the xylem sap of transformed plants. Our results strongly suggest that NHX proteins are likely candidates for the H⁺‐linked K⁺ transport that is thought to facilitate active K⁺ uptake at the tonoplast, and the partitioning of K⁺ between vacuole and cytosol.     

Methyl salicylate production in tomato affects biotic interactions

The role of methyl salicylate (MeSA) production was studied in indirect and direct defence responses of tomato (Solanum lycopersicum) to the spider mite Tetranychus urticae and the root‐invading fungus Fusarium oxysporum f. sp. lycopersici, respectively. To this end, we silenced the tomato gene encoding salicylic acid methyl transferase (SAMT). Silencing of SAMT led to a major reduction in SAMT expression and MeSA emission upon herbivory by spider mites, without affecting the induced emission of other volatiles (terpenoids). The predatory mite Phytoseiulus persimilis, which preys on T. urticae, could not discriminate between infested and non‐infested SAMT‐silenced lines, as it could for wild‐type tomato plants. Moreover, when given the choice between infested SAMT‐silenced and infested wild‐type plants, they preferred the latter. These findings are supportive of a major role for MeSA in this indirect defence response of tomato. SAMT‐silenced tomato plants were less susceptible to a virulent strain of F. oxysporum f. sp. lycopersici, indicating that the direct defense responses in the roots are also affected in these plants. Our studies show that the conversion of SA to MeSA can affect both direct and indirect plant defence responses.     

Cytokinin response induces immunity and fungal pathogen resistance,and modulates trafficking of the PRR LeEIX2 in tomato

Plant immunity is often defined by the immunity hormones: salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). These hormones are well known for differentially regulating defence responses against pathogens. In recent years, the involvement of other plant growth hormones such as auxin, gibberellic acid, abscisic acid, and cytokinins (CKs) in biotic stresses has been recognized. Previous reports have indicated that endogenous and exogenous CK treatment can result in pathogen resistance. We show here that CK induces systemic immunity in tomato (Solanum lycopersicum), modulating cellular trafficking of the pattern recognition receptor (PRR) LeEIX2, which mediates immune responses to Xyn11 family xylanases, and promoting resistance to Botrytis cinerea and Oidium neolycopersici in an SA- and ET-dependent mechanism. CK perception within the host underlies its protective effect. Our results support the notion that CK promotes pathogen resistance by inducing immunity in the host.     

Quantitative trait loci analysis of seed‐specialized metabolites reveals seed‐specific flavonols and differential regulation of glycoalkaloid content in tomato

Given the potential health benefits (and adverse effects), of polyphenolic and steroidal glycoalkaloids in the diet there is a growing interest in fully elucidating the genetic control of their levels in foodstuffs. Here we carried out profiling of the specialized metabolites in the seeds of the Solanum pennellii introgression lines identifying 338 putative metabolite quantitative trait loci (mQTL) for flavonoids, steroidal glycoalkaloids and further specialized metabolites. Two putative mQTL for flavonols and one for steroidal glycoalkaloids were cross‐validated by evaluation of the metabolite content of recombinants harboring smaller introgression in the corresponding QTL interval or by analysis of lines from an independently derived backcross inbred line population. The steroidal glycoalkaloid mQTL was localized to a chromosomal region spanning 14 genes, including a previously defined steroidal glycoalkaloid gene cluster. The flavonoid mQTL was further validated via the use of transient and stable overexpression of the Solyc12g098600 and Solyc12g096870 genes, which encode seed‐specific uridine 5′‐diphosphate‐glycosyltransferases. The results are discussed in the context of our understanding of the accumulation of polyphenols and steroidal glycoalkaloids, and how this knowledge may be incorporated into breeding strategies aimed at improving nutritional aspects of plants as well as in fortifying them against abiotic stress.