Sequence Tag Site and Host Range Assays Demonstrate that Radapholus similis and R. citraphilus are not Reproductively Isolated

Males of citrus-parasitic Radopholus citrophilus (FL1) were mated with non-citrus-parasitic R. similis (FL5) females. Progeny inherited a 2.4-kb sequence tag site (DK#1) and the ability to reproduce in citrus from the paternal parent (FLl); both traits were absent in the maternal line (FL5). The hybrid progeny produced offspring in roots of citrus seedlings over an 8-month period and therefore were considered reproductively viable. Genomic DNA hybridization studies indicated that one or more copies of DK#1 were present in R. citrophilus FL1. It is not likely that DK#1 represents a citrus parasitism gene because it was amplified from some burrowing nematode isolates that did not parasitize citrus and because DK#1 contains no open reading frames. Inability to reliably test individual nematodes for their ability to parasitize citrus was a constraint to obtaining F2 data required for definitive genetic characterization of citrus parasitism in burrowing nematodes, and alternate approaches will be required. Although the physical relationship of DK#1 and the citrus parasitism locus remains undefined, results of controlled mating studies using these parameters as genetic markers enabled us to identify hybrid F₁ progeny. Therefore, R. similis and R. citrophilus are not sibling species since gene flow between the two does not appear to be restricted via geographic isolation (sympatric in Florida) or by genetics.     

THE CYTOSKELETON OF THE NAKED GREEN FLAGELLATE SPERMATOZOPSIS SIMILIS (CHLOROPHYTA):FLAGELLAR AND BASAL BODY DEVELOPMENTAL CYCLE1

Flagellar and basal body development during cell division was studied in the biflagellate green alga Spermatozopsis similis Preisig et Melkonian by light microscopy of immobilized living cells, statistical analysis of flagellar lengths during the cell cycle, and electron microscopy of cells and isolated cytoskeletons. Interphase cells display two flagella of unequal/subequal length. An eyespot located in an anterior lobe of the chloroplast is connected to the basal body bearing the shorter flagellum by means of a five-stranded microtubular root. Until cell division, the two parental flagella attain the same length. During cell division, each cell forms two new flagella that grow to a length of 1.5 μm before they are distributed in a semiconservative fashion together with the parental flagella to the two progeny cells at cytokinesis. During the following interphase, the flagella newly formed during the preceding cell division grow to attain the same length as the parental flagella until the subsequent cell division. The shorter of the two flagella of a cell thus represents the developmentally younger flagellum, which transforms to the mature state during two consecutive cell cycles. Interphase cells display only two flagella-bearing basal bodies; two nascent basal bodies are formed during cell division and are connected to the microtubular d-roots of respective parental basal bodies with which the newly formed basal bodies are later distributed to the progeny cells. During segregation, basal body pairs shaft into the 11/5 o'clock direction, thus conserving the 1/7 o'clock configuration of basal body pairs of interphase cells. Prior to chloroplast and cell division, an eyespot is newly formed near the cell posterior in close association with a 1s microtubular root, while the parental eyespot is retained. During basal body segregation, eyespot-root connections for both the old and newly formed eyespots are presumably lost, and new associations of the eyespots with the 2s roots of the newly formed basal bodies are established during cytokinesis. The significance of this “eyespot-flagellar root developmental cycle” for the absolute orientation of the progeny cells is discussed.     

一株特殊生境荒漠药用植物沙蓬内生真菌Rhinocladiella similis中苯甲酸大环内酯化合物

从一株特殊生境荒漠药用植物沙蓬的内生真菌Rhinocladiella similis中分离得到4个苯甲酸大环内酯化合物,包括2个新化合物rhinoclactones E（2）和F（1）、2个已知化合物8,9-dihyrogreensporone D（3）和8,9-dihydrogreensporone A（4）。基于高分辨质谱与核磁共振谱数据以及相关文献比对,确定了新化合物与已知化合物的结构。化合物1和2是一对立体异构体,在大环内酯环中并有一个呋喃环,这种环系统在自然界比较稀少。化合物1-4对3株肿瘤细胞株和植物病原真菌没有抑制活性。本结果进一步丰富了该真菌的化学成分研究,暗示特殊生境荒漠植物内生真菌具有产生结构新颖的次级代谢产物的潜力,是发现新活性天然产物的一个新的重要宝库;此外,根据化合物的结构特征与生物活性结果,本文还探讨了这些化合物潜在的生态学功能。     

Evaluation of legume intercrops on the population dynamics and damage level of burrowing nematode (Radopholus similis) in banana (Musa spp.)

Radopholus similis is the most destructive plant parasitic nematode in banana production systems. A glasshouse experiment was carried out to evaluate the effect of legume intercrops on R. similis population and damage level in banana. A trial was laid out in a randomised complete block design with five treatments and five replications. The treatments were banana/cowpea (Vigna unguiculata) intercrop, banana/sunn hemp (Crotalaria juncea) intercrop, sole banana, sole banana with nematicide (Fenamiphos) and sole cowpea. Sunn hemp intercrop was suppressing R. similis population densities and reduced banana root damage the most compared to tested treatments. The legume intercropped banana plants had a significantly higher fresh root mass as the sole-cropped banana with nematicide while the sole-cropped banana without nematicide had significantly lowest fresh root mass. Sunn hemp and cowpea legumes are recommended for adoption by smallholder banana farmers as alternatives to nematicide use.     

Oviposition-stimulatory activity of phenanthroindolizidine alkaloids of host-plant origin to a danaid butterfly, Ideopsis similis

Oviposition response of Ideopsis similis (L.) (Lepidoptera: Danaidae) was examined for 12 phenanthroindolizidine alkaloids present in its host plant, Tylophora tanakae (Maxim.) (Asclepiadaceae). At least five alkaloids, i.e. (+)‐isotylocrebrine (3,4,6,7‐tetramethoxyphenanthroindolizidine; l ), (+)‐3‐demethyliso‐ tylocrebrine ( 3 ), (+)‐isotylocrebrine N‐oxide ( 5 ), (+)‐6‐demethyltylocrebrine ( 8 ) and (–)‐7‐demethyltylophorine ( 10 ), were found to individually stimulate oviposition by females. Of these, compounds 1, 3 and 10 were regarded as key components most responsible for host recognition or preference. However, female egg‐laying was much higher in response to a mixture of the five alkaloids. In two‐choice bioassays, more eggs were deposited on samples comprising the five alkaloids than on samples consisting of a single alkaloid. This suggests strongly that host selection by the butterfly is mediated by the synergistic action of several phenanthroindolizidine alkaloids present in the host plant.     

Distribution of PERIOD-immunoreactive neurons and temporal change of the immunoreactivity under long-day and short-day conditions in the larval brain of the flesh fly Sarcophaga similis

The flesh fly Sarcophaga similis show a clear photoperiodic response; they develop into adults under long days, whereas they arrest their development at the pupal stage under short days. Although the involvement of a circadian clock in photoperiodic time measurement is suggested in this species, the anatomical location of the clock neurons responsible for the time measurement has been unknown. We detected two PERIOD-immunoreactive cell clusters in the larval brain; one cluster was located at the dorsoanterior region and the other at the medial region. We further investigated their temporal changes in PERIOD-immunoreactivity and compared their patterns under different photoperiods.     

The development of the metacercariae of Microphallus similis in vitro and in the mouse

The development of the progenetic metacercariae of Microphallus similis in the mouse and under a range of in vitro cultivation systems was studied and compared. The flukes began egg production after 24 h in the mouse and by Day 4 post infection large numbers of eggs were present. These eggs began to embryonate in utero and contained a ball of cells; however, subsequent incubation in sea water failed to produce recognisable miracidia. In the majority of culture systems, gametogenesis and vitellogenesis occurred. Large numbers of abnormal eggs of three basic types were produced in vitro; these defects were probably related to the premature tanning of the eggshell precursors within the vitellaria and ducts. Apparently normal eggs were also produced, but they were probably unfertilized since sperm were rarely observed in vitro and they failed to embryonate.     

Effect of Endophytic Fusarium oxysporum on Host Preference of Radopholus similis to Tissue Culture Banana Plants

The burrowing nematode Radopholus similis is one of the major constraints to banana (Musa spp.) production worldwide. Resource-poor farmers can potentially manage R. similis by using naturally occurring banana endophytes, such as nonpathogenic Fusarium oxysporum, that are inoculated into tissue culture banana plantlets. At present, it is unclear at what stage in the R. similis infection process the endophytes are most effective. In this study, the effect of three endophytic F. oxysporum isolates (V5w2, Eny1.31i and Eny7.11o) on R. similis host preference of either endophyte-treated or untreated banana plants was investigated. No differences were observed between the proportion of nematodes attracted to either root segments excised from endophyte-treated or untreated plants, or in experiments using endophyte-treated and untreated tissue culture banana plantlets. These results imply that the early processes of banana plant host recognition by R. similis are not affected by endophyte infection.