Spore Discharge in Deightoniella torulosa (Syd.) Ellis

Violent spore discharge in the Hyphomycete Deightoniella torulosais described. On drying, a negative pressure develops in thesolution inside the swollen head of the conidiophore. This causesthe thin wall at the top of the conidiophore to cave inwardsand to be brought into a state of tension. The sudden appearanceof a gas phase in the conidiophore head releases this tension,and the wall rapidly returns to its original rounded shape.The conidium, which is attached to the top of the conidiophore,is thus catapulted away. This appears to be the first recordof a gas phase being associated with violent spore dischargein a fungus.     

Utilization of carbohydrates by Helminthosporium rostratum drechs. and Deightoniella torulosa (SYD). Ell. (SYN. Helminthosporium torulosum SYD.)

Summary Utilization of four carbohydrates, viz. D-glucose, D-fructose, sucrose and starch, byHelminthosporium rostratum andDeightoniella torulosa isolated from the leaves ofJasminum arborescens Vern. Newari and banana (Musa paradisiaca L.) fruits respectively, was exhaustively investigated by chromatographic technique. Chromatographic analysis of the culture medium revealed that both the organisms assimilated glucose earlier than fructose. The hydrolytic products of sucrose and starch (only glucose was detected) could be traced in the medium. In all cases dry weights of both the organisms continued to increase upto 15 days except inH. rostratum growing on starch where it decreased after 10th day. The pH changes of the media showed a drift towards neutrality.This research has been financed in part by a grant made by the United States Department of Agriculture, Agricultural Research Service, Under P.L. 480.     

The epidemiology of leaf smut disease of dahlia caused by Entyloma calendulae f. sp. dahliae (Syd.) Viegas

Entyloma calendulae f. sp.dahliae overwinters in the soil as teliospores or in dead leaf tissue. It was not seed — transmitted and did not survive in tubers although it occurred in soil attached to tubers. Teliospore germination decreased from the end of November to a minimum between January and March. Spores exposed to wintry conditions remained dormant longer than those in the laboratory. In spring and early summer some overwintered spores germinated in the soil to give rise to conidia resembling those normally produced on leaves. Fresh outbreaks of the disease occurred in July from spores which had overwintered in the soil. The host tissues nearest to the ground are infected first and the disease remains more severe on the lower part of the plant than on the upper leaves. New tissues were infected throughout the summer, giving a maximum in early autumn. Many more conidia were present in the air on wet windy days than on dry calm ones.

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Zusammenfassung Entyloma calendulae f. sp.dahliae überwintert in Erdboden als Teliosporen oder im Gewebe toter Blätter. Es war nicht durch Samen übertragen und überlebt nicht im Knollen, obwohl es in der an den Knollen haftenden Erde vorkommt. Teliosporenkeimung nahm vom Ende November bis zu einem Minimum zwischen Januar und März ab. Sporen, die winterlichen Bedingungen ausgesetzt waren, blieben längerer Zeit dormant, denn diejenigen im Laboratorium. Im Frühjahr und Frühsommer keimten manche überwinterte Sporen in der Erde, um Konidien zu entwickeln, die denen normalerweise an den Blättern vorkommenden ähnlich waren. Ein neuer Ausbruch der Krankheit kam im Juli vor, die durch die im Boden über-winterten Sporen verursacht wurden. Das Wirtsgewebe, nähst dem Boden, ist erst infiziert und die Krankheit verbleibt schwerer im unteren Teil der Pflanze, denn in den obersten Blättern. Das neue Gewebe wurde durch den Sommer infiziert und die Höhe wurde im Frühherbst erreicht. Vielmehr Sporen waren in der Luft an nassen, windigen Tagen vorhanden, denn in ruhigem, trockenem Wetter.

     

Teliospore Germination of Soybean Rust Fungus (Phakopsora pachyrhizi Syd.)

Teliospores of the soybean rust fungus (Phakopsora pachyrhizi Syd.) germinated after treatment with 10—12 wetting and drying cycles at room temperature. Spores swelled, vacuolated and germinated with a slightly curved basidium bearing 1—4 sterigmata with basidiospores. High germination rates were observed when telia were stored at 5 °C for 5—6 months before breaking dormancy.     

Development of Infection Structures by the Direct-Penetrating Soybean Rust Fungus (Phakopsora pachyrhizi Syd.) on Artificial Membranes

The development of infection structures by the directly infecting soybean rust fungus of different artificial membranes was followed by light and scanning electron microscopy. On water agar uredospores developed germ tubes without appressoria. On dialysis membranes more than 80% of the uredospores formed appressoria. With low frequencies (1–7%) also primary hyphae and/or penetration hyphae were present. When cellulose nitrate membrane filters with pore diameters ≤ 0.2 μm were used, uredospores germinated but showed a strongly reduced appressoria formation. Membranes with pores ≥ 0.1 μm allowed a development of infection structures similar to that on dialysis membranes. In experiments with paraffin oil incorporated into collodion membranes more than 90% of the uredospores formed appressoria, about 50% of the appressoria developed hyphae. Ungerminated spores and germ tubes always contained 2 nuclei. In fully developed appressoria 4 nuclei were present. Compared with stomata entering rust fungi appressoria formation by Phakopsora pachyrhizi occurred more frequently and seemed to be less dependent on specific stimuli. Moreover, in most cases only few of the appressoria formed penetration or primary hyphae. The induction of these structures seemed to be dependent on further unknown stimuli.     

Genetic diversity of carotenoid-rich bananas evaluated by Diversity Arrays Technology (DArT)

The aim of this work was to evaluate the carotenoid content and genetic variability of banana accessions from the Musa germplasm collection held at Embrapa Cassava and Tropical Fruits, Brazil. Forty-two samples were analyzed, including 21 diploids, 19 triploids and two tetraploids. The carotenoid content was analyzed spectrophotometrically and genetic variability was estimated using 653 DArT markers. The average carotenoid content was 4.73 μg.g (-1) , and ranged from 1.06 μg.g (-1) for the triploid Nanica (Cavendish group) to 19.24 μg.g (-1) for the triploid Saney. The diploids Modok Gier and NBA-14 and the triploid Saney had a carotenoid content that was, respectively, 7-fold, 6-fold and 9-fold greater than that of cultivars from the Cavendish group (2.19 μg.g (-1)). The mean similarity among the 42 accessions was 0.63 (range: 0.24 to 1.00). DArT analysis revealed extensive genetic variability in accessions from the Embrapa Musa germplasm bank.     

Lectin Binding Studies on the Cell Walls of Soybean Rust (Phakopsora pachyrhizi Syd.)

Walls of uredospores, infection structures, intercellular hyphae and haustoria of the soybean rust fungus (Phakopsora pachyrhizi) were studied by electron microscopy using gold-labeled wheat germ lectin (WGL) and Concanavalin A (ConA) as cytochemical probes. Receptors for WGL (probably chitin) were detected in all fungal walls included in this study. WGL-binding occurred throughout the entire walls (uredospores, appressorial cone, penetration hyphae, haustorial mother cells) or only to the inner wall layers (germ tubes, appressoria, intercellular hyphae).     

Chitosan-induced defence responses in tomato plants against early blight disease caused by Alternaria solani (Ellis and Martin) Sorauer

The in vitro antifungal properties of chitosan and its role in protection of tomato from early blight disease were evaluated. Chitosan inhibited the radial and submerged growth of Alternaria solani at 1?mg/ml and control tomato plants from blight pathogen. Chitosan was able to induce the level of chitinase activity and new isoforms of chitinase, resulting in the reduction of early blight disease severity in tomato leaves. These results suggested the role of chitosan in activation of defence responses as well as protecting tomato plants from A. solani infection.     

Chitosan-induced defence responses in tomato plants against early blight disease caused by Alternaria solani (Ellis and Martin) Sorauer

The in vitro antifungal properties of chitosan and its role in protection of tomato from early blight disease were evaluated. Chitosan inhibited the radial and submerged growth of Alternaria solani at 1 mg/ml, and controls tomato plants from blight pathogen. Chitosan induces the level of chitinase activity and new isoforms of chitinase resulting in the reduction of early blight disease severity in tomato leaves. These results suggested the role of chitosan in activation of defence responses as well as protecting tomato plants from A. solani infection.     

New microsatellite markers for bananas (Musa spp)

Thirty-four microsatellite markers (SSRs) were identified in EST and BAC clones from Musa acuminata burmannicoides var. Calcutta 4 and validated in 22 Musa genotypes from the Banana Germplasm Bank of Embrapa-CNPMF, which includes wild and improved diploids. The number of alleles per locus ranged from 2 to 14. The markers were considered highly informative based on their polymorphism information content values; more than 50% were above 0.5. These SSRs will be useful for banana breeding programs, for studies of genetic diversity, germplasm characterization and selection, development of saturated genetic linkage maps, and marker assisted selection.     

Comparison of damage levels caused by Radopholus similis and Helicotylenchus multicinctus on bananas in Uganda

Field surveys were done in 1997 and 1998 in Masaka district, Uganda, an area which is experiencing a decline in banana production, to assess level of damage caused by nematodes Radopholus similis and Helicotylenchus multicinctus at farm level. Ten farms within a radius of 2 km were selected and nematode damage assessed. The major nematodes encountered were Pratylenchus goodeyi, R. similis and H. multicinctus. P. goodeyi and H. multicinctus were more abundant than R. similis but R. similis had a stronger and significant correlation with root damage. A subsequent pot trial examined pathogenicities of R. similis and H. multicinctus in pure and mixed cultures on tissue cultured‐banana plantlets. R. similis alone and in mixed population reduced root fresh weight significantly, and the percentage of root necrosis ranged between 22.8–41.6% and 18.3–45.5% for March 1998 and March 1999 trials, respectively. The difference in damage caused by R. similis alone and in mixed population was not statistically significant, and was higher than the damage caused by H. multicinctus alone. There were no significant differences in pathogenicity among the R. similis isolates from different parts of Uganda.     

A New Jamaican species of lisianthius (Gentianaceae)

Lisianthius adamsii, from the central and western parishes of Jamaica, is described as new. It is remarkable in having coriaceous leaves and ventricose corollas.     

First report of leaf spot disease caused by Corynespora torulosa MCC-1368 on cotton plant from India

In present study, the leaf spot disease of cotton plant emerged in the North Maharashtra region of India was reported. The fungal phytopathogen associated with inducing the leaf spot disease symptoms was isolated and characterised. The isolated fungus was identified as Corynespora torulosa (Deposition accession number, MCC-1368; Genbank accession no. MF462072) based on morphological and cultural characteristics and molecular analysis of ITS region. The pathogenicity of fungal phytopathogen was verified by Koch’s postulates. To our knowledge, this is the first report of incidence of leaf spot disease caused by Corynespora torulosa on cotton plant.