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1.
Phytophthora cinnamomi is an aggressive pathogen on Lupinus luteus (yellow lupin), causing root rot, wilting and death of this crop, common in oak-rangeland ecosystems ('dehesas') in south-western Spain. The oomycete, the main cause of Quercus decline in the region, was isolated from roots of wilted lupins in the field. Artificial inoculations on four cultivars of L. luteus reproduced the symptoms of the disease, both in pre- and post-emergence stages, recovering the pathogen from necrotic roots. These results suggest the potential of yellow lupin as inoculum reservoir for the infection of Quercus roots. This is the first report of P. cinnamomi as root pathogen of L. luteus.  相似文献   

2.
The dynamics of early root growth and dry matter partitioning were compared in spring wheat (Triticum aestivum L.) and wild oat (Avena fatua L.) grown in solution culture. Total root length was greater in wheat than wild oat throughout the experiment; a result of a greater number of seminal axes and greater production of lateral root length per axis. The final number of adventitious roots was greater in wheat than in wild oat, but their length was similar. Relative growth rates were also similar as was shoot:root dry weight ratio and rate of root respiration. However, wheat used the dry matter partitioned to its roots more efficiently, producing a greater specific root length (SRL, length per unit weight). Caution must be exercised when relating these results to plants growing and compet-ing in the field, but three general points are raised. First, the initial number of seminal axes can have a profound effect on the rate of early root development; second, the adventitious root system of wild oat is not inherently more vigorous than that of wheat; and third, future studies should compare SRL of wheat and wild oat in the field. If differences similar to those in the present study are found they may contribute to the greater competitive ability of wheat.  相似文献   

3.
Roots of wheat and oat seedlings were treated with diclofop-methyl (methyl 2-[4-(2′,4′-dichlorophenoxy)phenoxy]propanoate) in a specially designed Plexiglas treatment apparatus. Diclofopmethyl severely inhibited the root growth of susceptible oat seedlings but roots of resistant wheat seedlings were unaffected. Diclofop-methyl at 0.3 μM reduced the growth of oat roots to 50% of the control. Direct contact between diclofop-methyl and the inhibited root zone was necessary for growth inhibition since other parts of the seedling (roots and shoots) isolated from contact with diclofop-methyl solution by a physical barrier were unaffected. Diclofop (2-[4-(2′,4′-dichlorophenoxy)phenoxy]propionic acid), the free acid metabolite of diclofop-methyl, was somewhat more phytotoxic than the parent compound. The herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), which engenders auxin responses, slightly enhanced the inhibition of oat root growth by diclofop-methyl. The primary wheat metabolite, ring-hydroxylated diclofop, was nonphytotoxic to oat root growth, whereas the acetylated derivative of the primary water-soluble oat metabolite (neutral glucose ester of diclofop) inhibited oat root growth to the same extent as diclofop-methyl. These results support the hypothesis that the basis for selectivity between resistant wheat and susceptible oat is the metabolism of diclofop-methyl by aryl hydroxylation and conjugation but not glucose ester conjugation. Translocation is also not an important factor in the phytotoxic activity of diclofop-methyl.  相似文献   

4.
The evergreen holm oaks (Quercus ilex subsp. ilex and Q. ilex subsp. ballota) are the most representative tree species in the Iberian peninsula and the main tree species in oak‐rangeland ecosystems (dehesas). Oak decline in western, central and southern parts of Spain has been associated with root rot caused by Phytophthora cinnamomi for decades. However, Phytophthora species such as P.  quercina and P. psychrophila have recently been found associated with Quercus decline in eastern Spain where calcareous soils are predominant. Soil and root samples from two Quercus forests presenting decline symptoms in two different geographical areas in eastern Spain (Carrascar de la Font Roja and Vallivana) were analysed by amplicon pyrosequencing. Metabarcoding analysis showed Phytophthora species diversity, and revealed that an uncultured Phytophthora taxon, named provisionally Phytophthora taxon ballota, was the predominant species in both areas. In addition, a real‐time PCR assay, based on the pyrosequencing results, was developed for the detection of this uncultured Phytophthora taxon, and also for the detection of P. quercina. TaqMan assays were tested on soil and root samples, and on Phytophthora pure cultures. The new assays showed high specificity and were consistent with metabarcoding results. A new real‐time PCR protocol is proposed to evaluate the implication of different Phytophthora spp. in oak decline in eastern Spain.  相似文献   

5.
Pathogenicity of Aphanomyces spp. from Different Leguminous Crops in Sweden   总被引：1，自引：0，他引：1  
Host range and pathogenicity of a range of Aphanomyces spp. isolates obtained from pea roots but also from a range of other field-grown leguminous crops in southern Sweden was investigated. The Aphanomyces euteiches isolates originating from pea and the few obtained isolates originating from alfalfa, green bean and yellow sweet-clover were highly pathogenic only to pea. The A. euteiches isolated from common vetch differed from these isolates by being weakly pathogenic to pea and other legumes, but highly pathogenic to common vetch. Vetch isolates also formed a well-defined separate cluster based on principal component analysis of pathogenicity pattern on tested crops. Oospores of A. euteiches were observed in root tissue of pea as well as common vetch, alfalfa, green bean, broad bean, red clover and yellow sweet-clover in the greenhouse pathogenicity tests. An Aphanomyces sp. that morphologically differed from A. euteiches, was frequently isolated from several leguminous plants, but was non-pathogenic to all tested crops in the pathogenicity tests. In isozyme analysis the banding pattern of these isolates resembled the pattern of A. cladogamus. Another, different and so far unidentified Aphanomyces sp. from roots of green bean and broad bean, was also non-pathogenic to the tested legume species. Based on the isolates tested, the results obtained suggest that the population of Aphanomyces spp. infecting legume roots in Sweden consists of a pea-specific and a vetch-specific group of A. euteiches. Two other groups comprised (i) Aphanomyces sp. isolates that resembled A. cladogamus, and (ii) isolates, which resembled neither A. euteiches nor A. cladogamus. In addition, the host range of Swedish A. euteiches isolates was not as broad as reported for A. euteiches isolates from other countries.  相似文献   

6.
To test the hypothesis that resistance in Phytophthora cinnamomi to control by the fungicide phosphite (phosphonate) would arise in sites with prolonged use of phosphite, 30 P. cinnamomi isolates were collected from a range of sites with different phosphite‐use histories, including phosphite‐treated and untreated avocado orchards, and phosphite‐treated and untreated native vegetation sites. The colonizing ability of these isolates was tested by different inoculation methods against a range of host tissues, treated and untreated with phosphite, including mycelial stem inoculation on clonally propagated Leucadendron sp., mycelial root inoculation of lupin seedlings and zoospore inoculation of Eucalyptus sieberi cotyledons. Isolates from avocado orchards with a long history of phosphite use were, on average, more extensive colonizers of the phosphite‐treated Leucadendron sp., lupin seedling roots and Eucalyptus sieberi cotyledons. These isolates did not colonize untreated plant tissue (Leucadendron sp.) more extensively than isolates from sites with no history of phosphite use and no isolates were resistant to control by phosphite. Analysis of all isolates with microsatellite markers revealed the majority were from a single clonal lineage. Selection for decreased sensitivity to phosphite in planta has taken place within asexual clonal lineages of P. cinnamomi in sites with prolonged use of phosphite.  相似文献   

7.
In a host study of the ectoparasitic nematodeLongidorus cohni, involving six field crops, only oats were found to afford rapid nematode population build-up and to suffer severe damage. No increase in nematode population, plant damage or root symptoms was observed on wheat, barley, purple vetch, field pea or berseem clover.  相似文献   

8.
Over a concentration range of 5.0 × 10?6?7.5 × 10?4M, the selective herbicide difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) caused more pronounced inhibition of potassium ion (K+) absorption by excised seedling roots of susceptible wild oat (Avena fatua L.) compared to those of tolerant barley (Hordeum vulgare L. cv. Bonanza) or wheat (Triticum aestivum L. cv. Neepawa). At 2.5 × 10?5M difenzoquat, the relative inhibition of K+ (86Rb) absorption by wild oat root segments inceased from 30% with a 10-min uptake period to 75% with an uptake period of 90 min, whereas no inhibition at all was evident for wheat root segments even after a 90-min exposure to the herbicide. An ion efflux compartmental analysis procedure demonstrated that difenzoquat did not affect the passive permeability properties of the plasma membrane of wild oat root cells. The experimental findings indicated that difenzoquat interfered directly with the process of active ion transport across the plasma membrane of root cells.  相似文献   

9.
The influence of time of emergence of wild oat (Avena fatua L.) on its competition with wheat (Triticum aestivum L.) was studied, using boxes that allowed separation of root and shoot competition. The relative yield total for mixtures of wild oat and wheat, grown under different forms of competition and with different wild oat sowing times, was very close to unity, indicating that the two species competed fully for limiting resources. Wild oat was more competitive than wheat when the two species were sown simultaneously, due largely to its greater root competitive ability; the two species had similar shoot competitive abilities. When wild oat was sown 3 or 6 weeks later than wheat, wheat was more competitive than wild oat and the production of wild oat panicles was prevented. This was mainly the result of greater root competitive ability of the wheat, although shoot competitive ability was also greater. The effects of root and shoot competition were additive. It is concluded that in order to prevent the return of wild oat seeds to the soil, and hence obtain long-term benefit, it is necessary to control the wild oat seedlings emerging within the first 3 weeks after drilling a wheat crop.  相似文献   

10.
Species in the genus Phytophthora cause significant economic losses in crops and damage to forests and natural ecosystems worldwide. Currently, phosphite is the most effective chemical for disease management, but excessive phosphite concentrations can result in phytotoxicity in plants and the development of tolerance by the pathogen. Two newly developed metal chelates and phosphite (alone and in combination) were tested for their in vitro and in planta efficacy against Phytophthora cinnamomi. In glasshouse trials, 0.25% and 0.5% of each chemical treatment (phosphite, Ca chelate, Zn chelate) and Ca chelate + phosphite were used as a foliar application on 3-month-old seedlings of Banksia grandis (experiment not repeated) and Eucalyptus marginata, prior to inoculation with P. cinnamomi. All noninoculated control plants remained healthy, while significant root damage and reduction of dry root weights were observed for inoculated untreated plants. Individually, phosphite and Ca chelate significantly reduced root lesion development of P. cinnamomi compared to the control, with Ca chelate attaining superior results to phosphite at the same concentration. In combination, Ca chelate + phosphite had the largest reduction in root lesion development in both plant species; however, this result has not yet been replicated but did reflect previous in vitro results. The Zn chelate applications were not effective. Ca chelate has the potential to be developed as a fungicide to control Phytophthora species.  相似文献   

11.
Host plant preference of the Russian wheat aphid Diuraphis noxia (Kurdj.) was studied on 11 cultivars of 9 plant species: winter barley, spring barley, winter wheat, spring wheat, rye, oat, Triticale, canary grass, red millet yellow millet and maize. Seeds of the host plants were sown in a circle near the edge of pots. The host plant choice was evaluated 24 hours after releasing 55 Diuraphis noxia female adults in the middle of each pot. The suitability of different hosts for aphid development was evaluated 2, 7 and 14 days after infestation based on the mean number of Russian wheat aphid individuals per plant. Red millet, yellow millet and maize were chosen by significantly fewer aphids than grain crops. Winter and spring barley were chosen as hosts most frequently, and the progeny production was also the highest on these plants. The growth rate of D. noxia was significantly affected by the host plants and the date of assessment and their interaction.  相似文献   

12.
Methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]propanoate (dichlofop-methyl) is a selective herbicide for wild oat (Avena fatua L.) control in wheat (Triticum aestivum L.). Dichlofop-methyl inhibited IAA-stimulated elongation of oat and wheat coleoptile segments by 51 and 13%, respectively, at 10 μM concentrations. Dichlofop-methyl alone had no auxin activity at concentrations of 0.1, 1.0, and 10 μM. The inhibitory effect of dichlofop-methyl was overcome partially by increasing the IAA concentration or by application of 3,6-dichloro-o-anisic acid (dicamba), a herbicide with weak auxin activity. The de-esterified free acid metabolite, 2-[4-(2,4-dichlorophenoxy)phenoxy]-propionic acid (dichlofop), at 10 μM inhibited auxin-stimulated oat coleoptile elongation by 23%, but it did not affect wheat coleoptile elongation at the same concentration. Both dichlofop-methyl and dichlofop inhibited root growth in excised shoots and seedlings of wild oat but had no effect on wheat. Dichlofop was a more effective inhibitor of root growth than dichlofop-methyl. The results suggest that dichlofop-methyl functions as a strong auxin antagonist, while the metabolite, dichlofop, inhibits root growth and development by another mechanism. The herbicidal effect of dichlofop-methyl may be the net effect of two biologically active forms of the compound each with a different mode of action acting at different sites within a susceptible plant.  相似文献   

13.
The effect of benzoylprop-ethyl on plant weight, root uptake, transport and metabolism of 32P in wild oat and wheat plants was examined 4 h, 1,3 and 9 days after treatment. The fresh weight of wild oat plants was significantly reduced, due to herbicide action only, by day 9 after treatment. By day 3, shoot weight was decreased while root weight was significantly increased by 47%. No significant changes in plant weight were caused by benzoylprop-ethyl in wheat plants. Uptake of 32P by treated wild oat plants decreased by 39% compared with the control, by day 9, after an initial increase; uptake of 32P was not significantly influenced in wheat plants. By day 1 transport of 32P to the shoots was significantly reduced in wild oat plants by 34%, whereas in wheat plants it was significantly increased by 35%. Metabolism of 32P was already hampered in wild oat plants 4 h after treatment. The content of 32P was reduced on the first two sampling dates in both the roots and shoots of treated plants in all fractions except in DNA in the shoots. On day 3, this decrease was apparent especially in organic, lipidic and nucleic acid fractions in the shoots; incorporation of 32P into lipidic and RNA fractions was significantly inhibited on day 9 in both the roots and shoots of treated wild oat plants. Wheat plants responded most strongly to benzyoylprop-ethyl on day 1 after treatment, when 32P incorporation into all fractions except DNA was hampered. Differences between treated and control wheat plants gradually levelled off on days 3 and 9 after treatment.  相似文献   

14.
Pleiochaeta root rot (PRR) caused by Pleiochaeta setosa is a serious, widespread fungal disease in lupin crops, especially in Lupinus albus (broad-leaf lupin, or white lupin). PRR resistance is common in the gene pool of L. albus with various landraces from the Mediterranean region being the most resistant, and suitable for use in breeding new cultivars. Heritability of resistance is sufficient to make good gains from selection but only when controlled-environment (CE) screening is used. Field disease nurseries on loamy soil gave much lower heritability of resistance. Field disease nurseries had spatially variable spore counts despite continuous lupin cropping, and this was partly responsible (along with climatic conditions) for their reduced precision compared to tests conducted in a CE. Giving infected L. albus roots a single, most-severe-lesion score on a 0–9 scale was adequate for CE screening but not as precise or discriminating as the more time-consuming method of six scores per root. Replication in CE experiments was reduced to two pots of 16 seedlings each without sacrificing genotype discrimination.  相似文献   

15.
Phlomis purpurea (Lamiaceae), found in Quercus suber and Quercus ilex ssp. rotundifolia forest habitats in southern Portugal, is a non-host for the oomycete Phytophthora cinnamomi, the main biotic factor involved in cork oak and holm oak decline in the Iberian Peninsula. The effect of P. purpurea crude ethanol root extract was evaluated in vitro on P. cinnamomi mycelial growth, sporangial production, zoospore release and germination as well as on chlamydospore production and viability. The protection of cork oak against infection by the pathogen was also evaluated in planta. At 10 mg ml?1, in vitro inhibition of the pathogen structures was 85–100 %. In addition, P. purpurea plants were shown to protect Q. suber and Q. ilex from P. cinnamomi infection and to reduce the inoculum potential in glasshouse trials, indicating the ability to reduce root infection by the pathogen. The results suggest that P. purpurea has the potential to reduce disease spread and that their root extracts could provide candidate substances for control of the important pathogen, P. cinnamomi.  相似文献   

16.
To reduce Fusarium Basal Rot caused by Fusarium oxysporum f.sp. cepae (Foc) through crop rotation, plant species should be selected based on Foc multiplication in their roots. Foc multiplication rates in 13 plant species were tested in a greenhouse. All plant species enabled Foc multiplication. The lowest Foc levels (cfu g?1 dry root) were found for wheat, sunflower, cowpea and millet, the highest for black bean. The highest Foc levels per plant were calculated for sudan grass. These data were used to calibrate the model Pf?=?Pi/(α?+?βPi) relating final (Pf) and initial (Pi) Foc levels in the soil. The rate of population increase at low Pi (1/α) was highest for onion and black oat and smallest for sunflower. The pathogen carrying capacity (1/β) was highest for black oat and black bean, and lowest for wheat, cowpea and foxtail millet. Foc soil population dynamics was simulated for crop sequences by concatenating Pi-Pf values, considering instantaneous or gradual pathogen release after harvest. Different soil Foc populations were attained after reaching steady states. Foc populations in the sequence onion –foxtail millet - wheat – cowpea were 67 % lower than in the sequence onion – sudan grass - black oat - black beans. In this work, by combining detailed greenhouse experiments with modelling, we were able to screen crops for their ability to increase Foc population and to explore potential crop sequences that may limit pathogen build-up.  相似文献   

17.
Experiments were performed to elucidate the biochemical nature of the differential response of resistantVicia atropurpureacv. Popany and susceptibleVicia sativacv. Yovel to the parasitic weedOrobanche aegyptiaca. Plant root material was obtained by growing vetch plants in association withOrobancheseeds on glass microfibre filter sheets inserted in polyethylene bags replenished by nutrient solution. Higher concentrations of bound phenolics, free phenolics and lignin, and higher activity of peroxidase were observed in cv. Popany roots as a result ofO. aegyptiacainfection than were found in cv. Yovel vetch. No differences in hydroxyproline-rich glycoproteins levels were detected between infected and non-infected roots of either vetch cultivar. These results suggest that the resistant vetch defense mechanism involves elevated induction of the phenylproponoid pathway uponOrobancheinfection, conferring mechanical and chemical barriers confronting the invading parasite.  相似文献   

18.
The decline of cork oak (Quercus suber) stands in Iberian Peninsula is associated with infection by Phytophthora cinnamomi. Most Phytophthora species secrete elicitins, which can enhance defence reactions against some pathogens. Here cytological and physiological effects of the elicitins cryptogein and capsicein on cork oak root infection by P. cinnamomi were evaluated. The progression of the pathogen in root tissue and its effects on total fatty acid (TFA) composition of roots and leaves were analysed in seedlings. Net photosynthesis (P n ), stomatal conductance (g s ), chlorophyll a fluorescence measurements (quantum yield of linear electron transport ? e , photochemical quenching q P, non-photochemical quenching NPQ) and carotenoid determinations were carried out in well established (4?months) plants. In elicitin-treated roots, 2?days after inoculation, the pathogen which presented loss of viability and membrane degradation was mainly restricted to the intercellular spaces of the cortical parenchyma, and did not reach the vascular cylinder. Electron dense materials accumulated in the intercellular spaces of the cortex next to disorganized hyphae, suggested to be related with defence reactions. Cryptogein (or its interaction with P. cinnamomi) induced enhanced lipid synthesis in leaves, which may contribute to preserve membrane stability. P. cinnamomi decreased P n , g s , ? e , and q P, whereas elicitin-treated plants displayed values similar to controls. Overall, the results indicated a resistance response of cork oak against this oomycete, induced by the elicitins.  相似文献   

19.
The interference of allelopathic weeds with crop plants might be mediated by volatile allelochemicals. In this study, the essential oil constituents of two weeds, wild oat (Avena fatua) and crabgrass (Digitaria sanguinalis), were investigated in relation to their effects on the growth and allelochemical production of wheat (Triticum aestivum). Subsequently, by means of gas chromatography and gas chromatography‐mass spectrometry, 52 compounds were identified from the crabgrass essential oil, particularly a signaling compound called methyl jasmonate, while 28 constituents were detected in the wild oat essential oil. Both essential oils were rich in terpenoids and inhibited the growth of wheat in air, filter paper and soil media but their inhibition varied with the growth medium and the weed species. In both the air and the filter paper media, there were not significant differences in the dry weight of wheat between the wild oat and the crabgrass essential oils. However, there was a greater reduction in the dry weight of the wheat root and plant with the wild oat essential oil than with the crabgrass essential oil in the soil medium. Furthermore, the production of the allelochemical, 2,4‐dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one, in wheat was induced by the essential oils. The results suggest that allelopathic interference with wheat by wild oat and crabgrass affects not only the biomass allocation, but also the allelochemical production, of wheat.  相似文献   

20.
The effects on plant growth of applying trifluralin or nitralin combination with simazine, atrazine, prometryne and linuron to the upper 5-cm root region of vetch (Vicia sativa L.), pea (Pisum sativum L.) and soybean (Glycine max) were investigated. Foliar injury due to herbicides of the second group was markedly reduced in each species by simultaneous treatment with trifluralin or nitralin both of which inhibited lateral root growth without affecting aerial plant growth or tap root extension growth. This inhibition of lateral root growth in roots treated with trifluralin or nitralin was associated with reduced uptake and subsequent transport to the foliage of 14C-labelled simazine in vetch and pea and 14C-labelled atrazine in soybean. This probably accounted for the reduction in simazine and atrazine phytotoxicity. In the presence of trifluralin or nitralin comparatively higher amounts of radioactivity were retained in the roots of pea and soybean and this reduced the amount of 14C available for transport to the foliage. This was not evident in vetch.  相似文献   

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