Allelopathy of rice (Oryza sativa L.) root exudates and its relations with Orobanche cumana Wallr. and Orobanche minor Sm. germination

Allelopathy has been considered not only as an environmentally friendly approach for weed control but also a potential reason causing autotoxicity in crop production. In this study, the responses of seeds of lettuce, wheat, rice, clover broomrape (CB), and sunflower broomrape (SB) to the root exudates of rice cultivars were studied. Lettuce germination was promoted by root exudates of Yliangyou 3218 and I-Kung-Pao. Wheat seedling growth was inhibited by all nine rice species. I-Kung-Pao and Ganxin 203 exerted greater autotoxicity than other cultivars. Yongyou 15 and I-Kung-Pao induced the highest germination rate of CB, while Yongyou 13, Zhongzao 22, and I-Kung-Pao induced the highest germination rate of SB. A significantly correlation was noted between germination-inducing ability on broomrape seeds and allelopathic effects on target plants. It is suggested that using broomrape seeds germination is a better receptor for the identification of rice allelopathic potential.     

Variability of interactions between barrel medic (Medicago truncatula) genotypes and Orobanche species

A number of broomrapes ( Orobanche spp.) are major threats for grain legumes in the Mediterranean area. Previous studies have shown very high levels of resistance to Orobanche crenata in Medicago truncatula with little variation among accessions hampering, therefore, its use for genetic analysis. In order to identify alternative systems for ulterior genetic and genomic analysis, we studied early stages of the interaction between M. truncatula accessions and a range of Orobanche species. We found significant differences in the induction of germination on Orobanche aegyptiaca , Orobanche foetida var. broteri , Orobanche minor , Orobanche nana and Orobanche ramosa seeds. Accessions also varied in the number of O. aegyptiaca , O. crenata , O. foetida var. broteri , O. nana and O. ramosa attachments supported. Applications of the synthetic germination stimulant GR24 increased the germination level of Orobanche cumana and O. minor . No attachments were observed for any of these species because of physical barriers typical of host resistance. On the contrary, increase of O. nana germination by GR24 led to an increase in number of attachments albeit the normal development of the nodules was stopped in a later stage. The genetic variation observed for induction of germination and subsequent attachment will be useful for isolating and characterising genes involved in early stages of Orobanche –host plant interaction and for the study of the biosynthetic pathways of production of germination stimulants.     

Effect of brassinosteroids on salinity stress induced inhibition of seed germination and seedling growth of rice (Oryza sativa L.)

The effect of 24-epibrassinolide and 28-homobrassinolide on the inhibitionof germination and seedling growth of rice (Oryza sativa) induced bysalinity stress was studied. Brassinosteroids were found to reverse theinhibitory effect on germination and seedling growth. The activation ofseedling growth by brassinosteroids under salinity stress was associatedwith enhanced levels of nucleic acids and soluble proteins.     

Stimulation of weed seed germination by 1–(3-chlorophthalirnido) cyclohexanecarboxamide (AC 94377)

The N-substituted phthalimide, AC 94377, promoted the germination of dry-stored seeds of 17 out of 24 weed species in Petri-dish tests maintained at 22°C. In a further test it was able to substitute for light and/or alternating temperatures in promoting the germination of some species. AC 94377 was more active than GA, in stimulating Solanum nigrum seed to germinate. When mixed with soil in the laboratory, AC 94377 again promoted germination of S. nigrum but the level and persistence of activity differed between soils. In the glasshouse, with soil containing a natural weed seed population, more seedlings emerged from treated than from untreated soil but this number represented fewer than half of the apparently viable seeds present. Field applications of AC 94377 promoted the germination of hand-sown seeds of certain weed species but did not increase the number of seedlings emerging from the natural weed seed bank.     

Switchgrass (Panicum virgatum L.) has ability to induce germination of Orobanche cumana

Orobanche cumana Wallr. (sunflower broomrape) is a devastating root parasitic weed, causing enormous crop losses worldwide. The question was whether or not switchgrass has the potential to be a ‘trap crop’ for O. cumana control. To answer this question, the field experiments, pot experiments, and laboratory experiments were conducted in this study. The ability of nine switchgrass (Panicum virgatum L.) cultivars to induce O. cumana seeds germination was tested. Results indicated that root extracts shoot extracts, rhizosphere soil, and root exudates from switchgrass induced O. cumana germination. Ability to induce germination varied significantly among growing stages, with the earlier part of growing season (grown for 2 weeks) generally inducing the highest O. cumana germination rates. The methanol was a more suitable solvent than distilled water for extracting germination stimulants from switchgrass plants. Ten-fold dilutions of the extracts generally induced higher germination rates than either undiluted or 100-fold dilutions. The germination rates of O. cumana seeds in shoot extracts treatments were positively correlated with those in the root extracts (R² = 0.6397; p < 0.01) and negatively correlated with those in the rhizosphere soil treatments ( R² = 0.4433; p < 0.05). In conclusion, it is believed that switchgrass is a potential trap crop for the control of root parasitic weed O. cumana.     

Comparative studies on Orobanche cernua L. and O. cumana Wallr. (Orobanchaceae) in the Iberian Peninsula

The systematic treatment of Orobanche cumana Wallr. and O. cernua L. is controversial. Whereas some authors consider O. cumana as an infraspecific taxon of O. cernua , others treat it as a separate species. Furthermore, the nomenclature of the sunflower broomrape is unclear, and both names arc found without qualification in the literature. The objective of the present study has been to evaluate the distribution, morphology, and ecology of O. cernua and O. cumana in the Iberian Peninsula, as well as their seed oil fatty acid profile, which is a trait of great chemotaxonomic value. O. cernua was found parasitizing wild Compositac, mainly Artemisia spp., whereas O. cumana was exclusively found on cultivated sunflower. Both species clearly differ in morphological traits, especially plant height and build, length and structure of the inflorescence, corolla length and colour. Both species are characterized by contrasting seed oil fatty acid profiles, with high oleic acid concentration in O. cernua and high linoleic acid concentration in O. cumana. The evaluation of both taxa in the Iberian Peninsula gives additional support to those authors that treat them as separate species.     

油菜素内酯浸种对盐胁迫番茄种子萌发的影响及其生理机制

为揭示油菜素甾醇类化合物提高作物耐盐的效应和机理,研究了10^-11、10^-10、10^-9、10^-8、10^-7、10^-6、10^-5 mol/L 2,4-表油菜素内酯（EBL）浸种处理对0、50、100、150、175 mmol/L NaCl胁迫7 d的番茄种子萌发、生长、溶质积累、抗氧化代谢的影响。结果显示：NaCl浓度越高的盐胁迫下,10^-9 mol/L EBL浸种可体现出越显著的促进番茄种子萌发的效应;在所有处理下,EBL浸种浓度过高,即10^-6、10^-5 mol/L EBL,均表现出对种子萌发的抑制效应。盐胁迫下种子萌发后,一定浓度的EBL浸种可表现出明显的增加种子胚根和下胚轴长,提高萌发种子鲜重和种子活力指数,其中10^-9 mol/L EBL浸种处理促进效果最适;EBL浸种浓度过高,则表现出抑制效应。150 mmol/L NaCl胁迫或非盐胁迫下,10^-9 mol/L EBL浸种均可降低萌发种子体内的O₂^·-、H₂O₂、丙二醛（MDA）和脯氨酸（Pro）含量;盐胁迫下,10^-9 mol/L EBL浸种可显著提高萌发种子可溶性糖（SS）和可溶性蛋白（SP）的含量。150 mmol/L NaCl胁迫或非盐胁迫下,10^-9 mol/L EBL处理可不同程度促进番茄种苗超氧化物歧化酶（SOD）和过氧化物酶（POD）活性的上升。综上所述,盐胁迫下,一定浓度范围内的EBL浸种可明显促进番茄种子萌发或成苗,其中以10^-9 mol/L EBL浸种的效果最好,主要是因为EBL施用可积极促进番茄种子萌发中物质转化,SS和SP等溶质积累增多,增强其渗透调节能力;同时SOD和POD酶活增强,缓解盐胁迫导致番茄种子萌发中的次生氧化胁迫。     

Recent advances in the biocontrol of Orobanche (broomrape) species

Parasitic broomrapes (Orobanche spp.) are majoruncontrolled weeds in the Mediterranean regions of Europe and the NearEast causing major losses to vegetable, grain legume, and sunflowercrops. Selective herbicides alone cannot provide persistent, season-longcontrol of these parasites, and much methyl bromide is used for theircontrol, where affordable. Thus they are excellent targets forbiocontrol. The recent progress by the COST 816 Orobancheworking group in this area is reviewed herein. Natural infestation bythe fly Phytomyza orobanchia of seed capsules of Orobanchecrenata parasitising faba bean halved Orobanche seedproduction while inundative releases of adults reduced it to 5%of viable seeds. The fungi Fusarium arthrosporioides E4a andF. oxysporum E1d, as well as strains of bacteria were isolatedfrom diseased, juvenile, Orobanche flower stalks. They arepathogenic to O. aegyptiaca, O. crenata and O. ramosaon most vegetable crops. A F. oxysporum f. sp.orthoceras was specifically pathogenic to O. cumana onsunflowers. All were used in various experiments with a modicum ofsuccess. Methods were developed to formulate isolated mycelia, whichcould eventually allow the use of transgenic hypervirulent pathogens inasporogenic (deletion) mutants (as a failsafe against spread).Mycotoxins were also isolated from different Fusarium and otherfungal species that kill Orobanche, and are being consideredfor direct use, or to augment other strategies. All threeFusarium spp. used have been transformed with gusand/or gfp genes allowing tracing their movement in theenvironment, and opening the way to future transformations tohypervirulence.     

果翅对梭梭属(Haloxylon)种子萌发行为的调控

种子萌发行为的受控机制是生殖生态学的重要研究内容。通过果翅存留实验研究了在不同贮藏时期果翅对梭梭和白梭梭种子萌发的影响。结果表明：①新成熟的梭梭种子具有高的萌发率（〉90％）。梭梭果翅对秋天新成熟的种子萌发有显著的抑制作用（萌发率〈50％）,使种子处于强迫休眠状态;果翅对种子萌发的抑制作用随着贮藏时间的推移逐渐降低,到翌年春天（4月）这种抑制作用已完全解除,果翅对梭梭种子的抑制主要是化学抑制。果翅对梭梭种子萌发行为的调控作用确保了种子在合适的时间萌发与种群的成功定居,也正是梭梭在荒漠地区广泛分布的主要原因。②新成熟的自梭梭种子萌发率为59．5％,贮藏1个月后达到80％。表明种子存在短时期的生理后熟现象。白梭梭果翅在每一贮藏时期对其种子的萌发都具有显著的抑制作用,翅＋种子（将果翅与种子剥离。一起放人培养皿中）也部分地抑制种子的萌发,因此,果翅对白梭梭种子萌发的抑制既有化学抑制也存在机械抑制。果翅对种子萌发的抑制,限制了白梭梭的分布。     

度胁迫对罂粟种子萌发影响及其活力变化规律的研究

为妥善保存罂粟种质资源及防止种子老化,研究了温度对罂粟种子萌发及种子活力的影响。结果表明:罂粟为高温敏感低温萌发型种子,发芽的适宜温度为10～20℃,最适温度为18℃左右,低于5℃和高于20℃的温度,种子萌发受到抑制;在对其进行丸化包衣时,加热温度应控制在60℃以内,时间应控制在60min以内;在常温库存条件下,罂粟种子活力随贮藏年限的增加而下降,贮藏时间超过五年后,发芽率低于50%,不宜作种用,在作为种质资源保存时,须每隔五年繁殖一次。     

Comparison of Sex Pheromonal Activity on the American Cockroach between Acetates and Propionates of Verbenyl Type Alcohols

Sex pheromonal activity was evaluated for propionates of 4 alcohols having a 6,6-dimethyl-bicyclo[3.1.1]heptane skeleton by behavioral assay with the male American cockroach. Their activities were compared with the corresponding acetates. The propionates were active at 20 μg or 500 μg, demonstrating stronger activities than the corresponding acetates. The male to female response ratio (M/F ratio) in EAG was also evaluated for the acetates and propionates, as well as for germacrene-D and camphor. The order of the behavioral activity was represented by that of the ratio. Sex pheromonal activity of (+)-verbanyl propionate (7) and germacrene-D were compared. Stronger activity was consequently observed in 7 at 5 μg dose, supporting the M/F ratio result.     

Isolation and preliminary characterization of ferritin from clover seeds

Ferritin from clover (Trifolium subterraneum) seeds was isolated and characterized. It was shown to contain polypeptide units of 28–26.5 kDa. The apparent molecular mass of the native protein was 560 kDa. The average iron cores were 4 nm in diameter and contained 1300 iron atoms, with Fe:P = 4:1. Purified clover apoferritin was shown to be functional by means of iron uptake experiments. Plots of initial velocities of iron uptake (at pH 6.7) into clover and horse spleen apoferritins were found to have similar profiles.     

三药槟榔种子休眠与萌发的研究

对三药槟榔种子休眠和萌发的基本特性进行研究,结果表明种子的休眠属于综合休眠;种壳对种子 萌发的抑制作用不是由于其对水分透过的限制,而是种皮的机械束缚和透气性差;种子还需要一段低温的生 理后熟过程才能解除休眠。种子经0．2％的高锰酸钾溶液浸泡15 min,0．3％亚硝酸钠和0．2％的硝酸钾溶液 浸种24℃后,发芽速度均显著加快,以0．3％亚硝酸钠处理效果为最佳。种子在15、4℃和室温(昼24～32 ℃／夜18～24℃)三种不同温度下贮藏60 d后,在4℃贮藏的种子发芽情况最好。种子不耐脱水,采用硅胶脱 水,含水量降低至22％以下,种子活力显著降低。     

Recognition of root exudates by seeds of broomrape (Orobanche and Phelipanche) species

Background and Aims

The long co-existence of broomrapes and their hosts within the same environment has culminated in a strong adaptation and effective parasitism. As a first step of specialization in the parasitic process, seed receptors of parasitic plant species vary in their ability to recognize compounds released by their hosts. This work aims to investigate potential patterns for the reception requirements needed to activate germination within Orobanche and Phelipanche species.

Methods

Induction of the germination of seeds of nine Orobanche and Pheliphanche species by root exudates of 41 plant species was studied and subjected to biplot multivariate analysis.

Key Results

A high level of specialization in root exudate recognition was found in Orobanche densiflora, O. gracilis and O. hederae, which germinated almost exclusively in contact with root exudates from the plants they infect in nature. At the opposite extreme, Phelipanche aegyptiaca, P. ramosa and O. minor were highly generalist, germinating when in contact with the root exudates of most plant species. Orobanche crenata, O. cumana and O. foetida showed intermediate behaviour.

Conclusions

A universal germination stimulant for all broomrape species has not being identified to date. The synthetic stimulant GR24 is active against most of the weedy broomrape species, but fails with the non-weedy species tested in this study and with the very recent weedy species O. foetida. In addition, germination behaviour of broomrape species depends on the crop plant tested. Weedy broomrapes with a broad host spectrum respond better to the different exudates released by a wide range of crops and wild species than do non-weedy broomrapes, which have a narrow host spectrum and are more restricted to their host range. Root exudates of many plant species were active in stimulating germination of seeds of Orobanche and Phelipanche species for which they are not described as hosts, representing interesting examples of potential trap crops.Key words: Xenognosis, broomrape, root exudate, germination, Orobanche, Phelipanche     

Effect of different primate species on germination of Ficus (Urostigma) seeds

We examined the germination of Ficus seeds (subgenus Urostigma) after defecation by six primate species (New World monkeys, Old World monkeys, and apes). Seeds from figs (control) and primate feces were placed in a thermostatically controlled chamber for 30 days. Seeds defecated by Alouatta palliata, A. pigra, and Cercopithecus aethiops showed significantly higher germination rates than control seeds. In addition, seeds from A. palliata feces germinated significantly faster than control seeds and seeds from C. aethiops and Pan troglodytes. These differences may be due to the different digestive characteristics of the six primate species. Zoo Biol 23:273–278, 2004. © 2004 Wiley‐Liss, Inc.     

Elevated atmospheric CO2 influences the interaction between the parasitic angiosperm Orobanche minor and its host Trifolium repens

The influence of the root holoparasitic angiosperm Orobanche minor Sm. on the biomass, photosynthesis, carbohydrate and nitrogen content of Trifolium repens L. was determined for plants grown at two CO₂ concentrations (350 and 550 μmol mol⁻¹). Infected plants accumulated less biomass than their uninfected counterparts, although early in the association there was a transient stimulation of growth. Infection also influenced biomass allocation both between tissues (infected plants had lower root:shoot ratios) and within tissues:infected roots were considerably thicker before the point of parasite attachment and thinner below. Higher concentrations of starch were also found in roots above the point of attachment, particularly for plants grown in elevated CO₂. Elevated CO₂ stimulated the growth of T. repens only during the early stages of development. There was a significant interaction between infection and CO₂ on growth, with infected plants showing a greater response, such that elevated CO₂ partly alleviated the effects of the parasite on host growth. Elevated CO₂ did not affect total O. minor biomass per host, the number of individual parasites supported by each host, or their time of attachment to the host root system. Photosynthesis was stimulated by elevated CO₂ but was unaffected by O. minor . There was no evidence of down-regulation of photosynthesis in T. repens grown at elevated CO₂ in either infected or uninfected plants. The data are discussed with regard to the influence of elevated CO₂ on other parasitic angiosperm-host associations and factors which control plant responses to elevated CO₂.     

草食动物对结缕草种子散布及发芽力的影响

研究了草食动物(牛、山羊)对辽东半岛结缕草种子散布及发芽力的影响。结果表明:风干牛粪、羊粪中结缕草种子的数量分别为101.7和6.88粒.g-1;牛、羊的采食和消化对结缕草种子的生活力没有影响,但提高了其发芽率(分别为74.12%和67.77%)、发芽势(分别为24.34%和17.72%)及活力指数(分别为41.86和37.38),缩短了其发芽时间(分别为12.53和12.70d);牛粪和羊粪中结缕草种子的发芽率虽有提高但没有达到其生活力水平;牛对结缕草种子散布及发芽力的影响效果均好于山羊。     

Survival of rhizobia on arrowleaf clover seeds under stresses of seed-coat toxins,heat and desiccation

Eighteen strains of Rhizobium leguminosarum bv. trifolii that had been found to be heat- and desiccation-stress tolerant in soil were tested for their resistance to Trifolium vesiculosum, Savi (arrowleaf clover) coat toxins using an agar plate technique and for survival on seed. They were further tested for their tolerance to seed coat toxins in combination with heat and desiccation stresses. The zone of inhibition in agar ranged from no inhibition to 21 mm diameter of growth inhibition around seed. Inoculation on seed under conditions of 28 °C and 100% relative humidity for 7 days resulted in a range of survival from nearly 100% to less than 1%. The correlation between zone of growth inhibition and survival on seed was not statistically significant. Strains that were desiccation or heat tolerant in soil were not necessarily desiccation or heat tolerant on seed but strains that were heat tolerant in soil were better able to survive on glass beads at 37 °C than strains that were not heat tolerant in soil. The zone of rhizobial inhibition on an agar medium was not a valid method to screen for isolates better able to survive on seed and the ability of rhizobia to withstand heat or drought stress on seed was not related to their ability to survive in soil. This revised version was published online in August 2006 with corrections to the Cover Date.