Tenualexin,Other Phytoalexins and Indole Glucosinolates from Wild Cruciferous Species

In general, the chemodiversity of phytoalexins, elicited metabolites involved in plant defense mechanisms against microbial pathogens, correlates with the biodiversity of their sources. In this work, the phytoalexins produced by four wild cruciferous species (Brassica tournefortii, Crambe abyssinica (crambe), Diplotaxis tenuifolia (sand rocket), and Diplotaxis tenuisiliqua (wall rocket)) were identified and quantified by HPLC with photodioarray and electrospray mass detectors. In addition, the production of indole glucosinolates, biosynthetic precursors of cruciferous phytoalexins, was evaluated. Tenualexin, (=2‐(1,4‐dimethoxy‐1H‐indol‐3‐yl)acetonitrile), the first cruciferous phytoalexin containing two MeO substituents in the indole ring, was isolated from D. tenuisiliqua, synthesized, and evaluated for antifungal activity. The phytoalexins cyclobrassinin and spirobrassinin were detected in B. tournefortii and C. abyssinica, whereas rutalexin and 4‐methoxybrassinin were only found in B. tournefortii. D. tenuifolia, and D. tenuisiliqua produced 2‐(1H‐indol‐3‐yl)acetonitriles as phytoalexins. Because tenualexin appears to be one of the broad‐range antifungals occurring in crucifers, it is suggested that D. tenuisiliqua may have disease resistance traits important to be incorporated in commercial breeding programs.     

Analysis of Vegetative Compatibility Groups of Fusarium oxysporum from Eruca vesicaria and Diplotaxis tenuifolia

From 2002 to 2004, wilted plants of different species of rocket (Eruca vesicaria and Diplotaxis spp.) were found for the first time in Europe, in greenhouse cultivations in Piedmont and Lombardy, northern Italy. The causal agent of the disease was found to be Fusarium oxysporum. Vegetative compatibility analysis was carried out on 46 isolates of the fungus, 41 of them obtained from wilted rocket (E. vesicaria and D. tenuifolia) and five reference strains, in order to increase the knowledge on the causal agent of recent epidemics of Fusarium wilt on rocket in Italy. The analysis showed the presence of two vegetative compatibility groups (VCGs) (VCG 0101 and VCG 0220) pathogenic on both kinds of rocket. The two VCG populations, which were classified as formae specialesconglutinans and raphani, respectively, are spread in the area of epidemics but are not related to the host species from which they were isolated (D. tenuifolia or E. vesicaria). This finding shows the heterogeneity of the causal agent of Fusarium wilt on rocket in Italy.     

Bacterial Communities Associated with Surfaces of Leafy Greens: Shift in Composition and Decrease in Richness over Time

The phyllosphere is colonized by a wide variety of bacteria and fungi; it harbors epiphytes, as well as plant-pathogenic bacteria and even human pathogens. However, little is known about how the bacterial community composition on leafy greens develops over time. The bacterial community of the leafy-green phyllosphere obtained from two plantings of rocket salad (Diplotaxis tenuifolia) and three plantings of lettuce (Lactuca sativa) at two farms in Norway were profiled by an Illumina MiSeq-based approach. We found that the bacterial richness of the L. sativa samples was significantly greater shortly (3 weeks) after planting than at harvest (5 to 7 weeks after planting) for plantings 1 and 3 at both farms. For the second planting, the bacterial diversity remained consistent at the two sites. This suggests that the effect on bacterial colonization of leaves, at least in part must, be seasonally driven rather than driven solely by leaf maturity. The distribution of phyllosphere communities varied between D. tenuifolia and L. sativa at harvest. The variability between these species at the same location suggests that the leaf-dwelling bacteria are not only passive inhabitants but interact with the host, which shapes niches favoring the growth of particular taxa. This work contributes to our understanding of host plant-specific microbial community structures and shows how these communities change throughout plant development.     

Occurrence of Alternaria japonica on Seeds of Wild and Cultivated Rocket

In vitro evaluation was carried out on seed samples of wild and cultivated rocket cultivars, most frequently grown in Italy, and obtained from farms affected by the leaf spot caused by Alternaria japonica in Piedmont and Lombardy during the fall of 2010. Twelve seed samples were collected and assayed for the presence of A. japonica. The pathogen was isolated only from not disinfected seeds. Among the two seed samples of cultivated rocket (Eruca vesicaria), only one was infected by A. japonica at a level of one infected seed out of 800. Four out of ten samples of wild (Diplotaxis tenuifolia) rocket seeds were contaminated by A. japonica with the highest level of infection detected in a single sample of 3 out of 800. All tested isolates of A. japonica obtained from seeds were pathogenic on both wild and cultivated rocket.     

Abundances of thrips on plants in vegetative and flowering stages are related to plant volatiles

Western flower thrips (WFTs), Frankliniella occidentalis Pergrande, and onion thrips (OTs), Thrips tabaci Lindeman, are two cosmopolitan insect pests of agricultural and horticultural plants. Understanding the occurrence and development of thrips on plants is crucial for identifying suitable plants that can be used for developing a “push-pull” strategy against thrips. In this study, the dynamics of WFTs and OTs on plants (Allium fistulosum L., Medicago sativa L., Luffa cylindrica (L.) Roem., Ocimum basilicum L., and Schizonepeta tenuifolia (Benth.) Briq.) were investigated for two consecutive years (2018–2019). Throughout the survey, the abundances of both thrips species were strongly associated with plant species and plant phenology; both thrips species were present at relatively high densities on M. sativa but very low densities on O. basilicum and S. tenuifolia. Populations of both thrips species greatly increased during plant flowering. A Y-tube olfactory test was used to study the effects of plant volatiles in mediating thrips behaviour and showed that volatiles of M. sativa were attractive to both thrips species whether emitted by the plant in the vegetative or flowering stage, while volatiles of O. basilicum and S. tenuifolia were repellent to thrips. Additionally, because of the presence of a high number of floral chemicals, both thrips species exhibited a greater preference for volatiles emitted by plants in the flowering period over those emitted by plants in the vegetative period. Our observations indicate that plant species and flowering status play an important role in the abundance dynamics of thrips and that the volatiles of flowering plants attract thrips more strongly than volatiles emitted by vegetative plants. These findings can facilitate the screening of attractive/unattractive plants for developing push-pull strategies to control thrips.     

In vitro allelopathic properties of wild rocket (Diplotaxis tenuifolia DC) extract and of its potential allelochemical S-glucopyranosyl thiohydroximate

Abstract

An aqueous extract of wild rocket (Diplotaxis tenuifolia DC) was tested for its allelopathic activity in vitro on radish germination and seedling growth in light and darkness. The extract caused a delay in the onset and a significant decrease in the rate of germination (40%) in the light. The photo-inhibition was accompanied by an inhibition of water uptake into the seed, and a decrease of protein content as well as an increase of peroxidase activity into the seedlings. Microscopic observations suggest that the extract markedly changes radish radicle development inducing a decreased imbibition and distension of seed cells. Consistent results were obtained with some species such as purslane, lambsquarter and tree of heaven present in the cultivated wild rocket field and with cultivated lettuce and barley. Finally, a potential allelochemical, biologically active, was isolated from the extract: S-glucopyranosyl thiohydroximate at concentration of 6.3×10^?4 M.     

Genetic relationships among species of the genus Diplotaxis (Brassicaceae) using inter-simple sequence repeat markers

Inter-simple sequence repeat (ISSR) amplification was evaluated for its applicability as a genetic marker system to establish relationships among ten Diplotaxis species. ISSR amplification generated multiple banding profiles with the 12 primers from all DNA samples, with an average of 41.2 fragments per primer. This average was clearly higher for the 5′ triple-anchored primers than for other primers. The banding profiles were highly repeatable across separate PCR runs. DNA mixing procedures were found to be appropriate strategies to generate banding patterns representative of each species studied. Similarity values were calculated considering 494 ISSR bands, and a dendrogram was constructed based on the similarity matrix. The ten Diplotaxis species were clustered into two major groups. The first group consists of five species, Diplotaxis tenuifolia and Diplotaxis cretacea, and Diplotaxis muralis with their putative parents (D. tenuifolia and Diplotaxis viminea). In the second group three species are clustered that are closely related (Diplotaxis virgata, Diplotaxis catholica and Diplotaxis siettiana), in addition to Diplotaxis harra, and Diplotaxis erucoides, which has lowest similarity values with the rest of the species studied. The two groups defined in the present work may be concordant with the idea suggested by several authors of a biphyletic origin for Diplotaxis. The genetic relationships among the ten Diplotaxis species estimated by the polymorphism of ISSR markers are in agreement with those previously inferred by other morphological, biochemical and molecular data, indicating the reliability of the ISSR approach for this purpose. Received: 3 January 2000 / Accepted: 31 March 2000     

The attractiveness of flowering herbaceous plants to bees (Hymenoptera: Apoidea) and hoverflies (Diptera: Syrphidae) in agro‐ecosystems of Central Spain

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Il sospensore embrionale nelle Cruciferae. I. Morfologia e struttura

Abstract

Embryo suspensor in Cruciferae. I. Morphology and structure. — Embryo suspensors in seven species of Cruciferae (Alyssum argenteum All., Brassica nigra (L.) Koch, Capsella bursa-pastoris (L.) Medicus, Diplotaxis erucoides (L.) DC., Eruca sativa Miller, Lepidium graminifolium L., Matthiola tricuspidata (L.) R. Br.) were morphologically investigated. These species have significant differences in their seeds, so that probable differences could be found in the structure of their ovules and therefore of their suspensors. Results indicate that it is impossible to generalize on the suspensor morphology and structure even in the same family. In Eruca sativa and Brassica nigra polyploidy and polyteny were found, suggesting a probably important metabolic function of their suspensors. In the other species polyteny was not present; a various degree of polyploidy could probably be assumed, suggesting a less active function of suspensors, maybe absorption and transport of nutritive material from the integuments to the developing embryo. The development of the endosperm is almost the same in all species, so that seems to be improbable a negative correlation with the suspensor and endosperm function in the early embryogenesis.     

Intergeneric hybridization between Diplotaxis siettiana and crop brassicas for the production of alloplasmic lines

Summary Intergeneric hybrids were produced between Diplotaxis siettiana and Brassica campestris through embryo rescue. The hybrids were completely pollen sterile and backcrosses with pollen of B. campestris did not yield any seeds. Induction of colchiploidy restored pollen fertility and backcross pollinations yielded viable seeds. Cytological details of the hybrid, amphidiploid and backcross progenies were studied. Both pollen-sterile and pollen-fertile plants have been obtained in backcross 2 progeny. This hybrid (D. siettiana x B. campestris) was used as a bridge cross to transfer the cytoplasm of D. Siettiana to two other incompatible cultivars of Brassica — B. juncea and B. napus. Pollinations of the amphidiploid (D. siettiana x B. campestris, 2n = 36) with pollen of B. juncea/B. napus readily produced seeds without embryo rescue. These hybrids were grown to flowering and their cytological details were studied. Seeds have been produced from backcross pollinations of both these hybrids with the pollen of the respective cultivars. The results clearly show the feasibility of producing alloplasmic lines in all the three oilseed brassicas.     

Morphological and molecular screening of French bean (Phaseolus vulgaris L.) germplasm using SCAR markers for Colletotrichum lindemuthianum (Sacc. and Magn.) Scrib. causing anthracnose resistance

This study was carried out to screen Phaseolus vulgaris L. germplasm accessions for anthracnose resistance genes to the fungus Colletotrichum lindemuthianum. (Sacc. and Magn.) Scrib. This fungus is made up of many pathogenic races which poses a challenge in developing resistant plant varieties; however, screening for and selection of resistant plant sources plays an important role in developing resistant plant lines. This screening work involved examining 69 accessions consisting of two resistant lines (D-line, L-line) and two susceptible varieties (Kanchana and Jwala). Fourteen SCAR primers specific to anthracnose disease resistance in the French bean were used. Of these 14 SCAR primers, 5 of them, SAS13, SF10, SC08, SZ04 and SBB14, produced amplification with good monomorphic bands.     

Specificity of Interactions Between Wild Lactuca spp. and Bremia lactucae Isolates from Lactuca serriola

Specificity of interactions between eight Lactuca species and 8 Bremia lactucae isolates was studied in seedlings and adult plants of 36 Lactuca accessions plus one L. serriola × L. sativa hybrid. Pathogenicity of the isolates and/or plant susceptibility was expressed by sporulation intensity. A highly compatible relationship was observed in all of L. serriola accession/isolate interactions tested. A differential reaction was found in numerous cases testifying to physiological specialization of the pathogen in a wild pathosystem. Nonspecific nondifferential compatibility (quantitative resistance) can be expected in L. serriola PI 281876. Age dependent resistance (seedlings versus adult plants, and vice versa) and heterogeneity of reactions were also recorded. The comparisonof B. lactucae isolates from L. sativa and L. serriola has shown a significant shift of pathogenicity in favour of L. serriola accessions. A high level of resistance was found in the L. serriola × L. sativa hybrid. The existence of basic incompatibility can be expected in L. saligna and L. virosa as well as in such taxonomically remote species as L. viminea, L. squarrosa and L. biennis. Other taxonomically remote species, i.e. L. dentata and L. alpina, exhibited a compatible reaction, although the reaction of the former was differential. A high level of sporulation was recorded in all accession/isolate interactions of L. alpina.     

Notes on the taxonomy of Diplotaxis DC. (Brassiceae)

Taxonomic changes in three species of Diplotaxis are proposed. Diplotaxis erucoides (L.) DC. subsp. cossoniana (Boiss.) Martinez-Laborde, comb, et stat. nov. is proposed for the Algerian subspecies of D. erucoides. Two North African varieties are raised to subspecific rank: D. tenuisiliqua Del. subsp. rupestris (Ball) Martinez-Laborde, stat. nov. and D. muralis (L.) DC. subsp. ceratophylla (Batt.) Martinez-Laborde, stat. nov.     

Some Physiological Aspects of Bacterial Wilt of Forage Grasses Caused by Xanthomonas campestris pv. graminis

The effect of host-plant age, environmental humidity and temperature on the development of the wilting disease of Lolium perenne L., caused by Xanthomonas campestris pv. graminis, was examined. Very young plants were more resistant than older ones. Dry and warm conditions favoured the development and expression of the disease symptoms. Losses in yield were observed under several environmental conditions.     

Water relations and adaptations to increasing water deficit in three perennial legumes, Medicago sativa, Dorycnium hirsutum and Dorycnium rectum

Dorycnium hirsutum (L.) Ser. and Dorycnium rectum (L.) Ser. are Mediterranean perennial legumes that may have potential as alternative forage plants to Medicago sativa (lucerne, alfalfa) for low rainfall dryland agriculture. Strategies for surviving periods of water deficit are vital for perennial plants in water-limited environments. This experiment compared leaf physiological and morphological adaptations to increasing water deficit among D. hirsutum, D. rectum and M. sativa. Plants were grown in the glasshouse in large pots (7.8 L, 1 m deep, 10 cm diameter) containing a sandy clay loam (14% available water content) to limit differences between root foraging among the species. Watering was withheld for 21 days and predawn and midday leaf water and osmotic potential were determined. Mid-morning rates of gas exchange were measured at five times as soil water was depleted. After 35 days of withholding water, plant recovery was measured. D. hirsutum and M. sativa reduced stomatal conductance at leaf water potentials below −1.8 MPa and water-stressed D. hirsutum osmotically adjusted by up to 0.68 MPa. D. rectum differed from the other species; leaf water potential was maintained at high levels until soil water content had reached low levels, and reductions in stomatal conductance and photosynthesis were not associated with leaf water potential. D. hirsutum and M. sativa displayed leaf morphological adaptations that may contribute to greater resistance of water deficit. Only one of five D. rectum plants survived the water-stress treatment compared to five of five for D. hirsutum and four of five for M. sativa. The water relations and physiology of D. hirsutum observed in this study suggest that it possesses adaptations suitable for arid environments. On the other hand, the poor survival and water relations of D. rectum indicate that it is poorly adapted to situations where water deficit is common.     

Analysis of the Phylogenetic Relationships Among Several Species of Gramineae Using ACGM Markers

To study the transferability of rice (Oryza sativa L.) genome data, we used amplified consensus genetic markers to analyze the phylogenetic relationships among several species and genera in Gramineae. Ten accessions representing five grass genera (Oryza, Zea, Setaria, Triticum, and Phyllostachys) were used. According to the genetic distances, a cluster tree was constructed. The relationships among the five genera could be simply described as ((Oryza + (Zea + Setaria)) + Triticum) + Phyllostachys. The results suggest that the genetic distance between rice and maize (Z. mays L.) or rice and millet (Setaria italica L.) is closer than that between rice and wheat (Triticum aestivum L) or rice and bamboo.     

Microsatellite fingerprinting in lettuce (Lactuca sativa L.) and wild relatives

Southern hybridisation with a single microsatellite probe, (TCT)₁₀, sufficed to discriminate between a representative set of cultivars/accessions of lettuce, Lactuca sativa L., and its wild relatives L. serriola, L. saligna and L. virosa. Variability within cultivars was tested in a relatively modern cultivar (Hector), where no variation was found, and in an older and morphologically more variable cultivar (Madrilene), where heterogeneity was observed in the TCT fingerprint. (TCT)₁₀ fingerprinting should be useful for variety identification and homogeneity testing in lettuce. Received: 25 July 1997 / Revision received: 5 August 1997 / Accepted: 30 August 1997     

Identification of a set of RFLP probes for subspecies differentiation in Oryza sativa L.

Sixty-eight indica-japonica tester-differentiating RFLP probes were tested in seven indica and seven japonica varieties of rice (Oryza sativa L.) with four enzyme digestions (EcoRI, EcoRV, HindIII and DraI). Twenty-one DNA clones were isolated as indica-japonica subspecies-differentiating probes. A set of 13 probes was established as core probes for subspecies differentiation and a pooled blotting analysis was carried out to facilitate the application of RFLP in rice genetics and breeding practice. A dendrogram of 12 wide-compatibility varieties was constructed based on RFLPs detected by 13 core probes with single enzyme digestions. It was speculated that most RFLPs of indica-japonica differentiating probes were generated by insertions/deletions, which may be of great significance for the origin and differentiation of subspecies in Oryza sativa L.     

Inheritance of isozymes in Brassica campestris L. and genetic divergence among different species of Brassiceae

Electrophoretic investigations of Brassica campestris revealed 8 polymorphic loci that had not been described earlier. The inheritance of 7 of them was determined by crosses between different accessions of B. campestris. A phylogeny of B. campestris, B. nigra, B. alboglabra, Sinapis arvensis and S. alba was estimated from the analysis of 15 isozyme loci. The phylogeny showed a close relationship between B. nigra and S. arvensis and a less close relationship between B. campestris and B. oleracea. S. alba was remotely-related to all of the other species.     

Mixoploidy in wild and cultivated species of Cruciferae capable of hybridizing with rapeseed Brassica napus

The number of chromosomes in cells of the root meristem of seedlings of wild and cultivated species of Cruciferae plants capable of hybridizing with rapeseed Brassica napus is studied. Only diploid metaphases are observed in seedlings of Brassica juncea, Diplotaxis tenuifolia, and Raphanus raphanistrum. In B. napus and B. cretica roughly 5% of the seedlings are mixoploid. Diploid cells are dominant in the mixoploids, though hypo-and hyperdiploids are also encountered. Nearly 20% of the seedlings of B. campestris and R. sativum are mixoploid, a significant fraction of which contains di-triploid chimeras. In B. nigra less than one-half of the seedlings are truly diploid, the majority of the plants being mixoploid. Seedlings containing preferentially tetraploid and triploid cells are dominant. The biological significance and possible causes of the newly discovered mixoploidy are discussed.