Leaf Scars Research Articles

Factors Affecting Apple Leaf Scar Infection by Nectria galligena Conidia

Factors Affecting Apple Leaf Scar Infection by Nectria galligena Conidia

Microflora of apple leaf scars in relation to infection by Nectria galligena

The fungi present within the senescent tissue of Bramley's Seedling apple leaf scars were isolated and identified. Within a few weeks of leaf fall most scars were colonized by fungi. The most frequent species were host-specific organisms, such as Phoma limitata, Fusarium lateritium and Phomopsis mali and common saprophytes, notably Aureobasidium pullulans and Epicoccum purpurascens. Host-specific organisms were predominant in a neglected orchard, and common saprophytes in nursery stock. Only one fungus isolated, Aspergillus niger, exhibited antagonism to N. galligena in vitro. Bacterial colonies were more frequently isolated from leaf scars sampled in December than earlier or later, and among the species present Bacillus subtilis was found to be highly antagonistic to N. galligena in vitro. Artificial inoculation of leaf scars with B. subtilis immediately after leaf fall reduced the frequency of isolation of all fungal species and reduced the incidence of canker when shoots were inoculated with N. galligena either 24 h after B. subtilis or the following April, but had little effect on their infection with N. galligena in May, when the primary protective layer was found to be shed. More cankers resulted from inoculation in May than in April. The numbers of bacterial colonies recovered from leaf scars inoculated with B. subtilis remained relatively constant from autumn until the primary protective layer was shed the following summer.

Fungi associated with the new malady of coffee in South India

Amarked decline in the coffee yields was first noticed in Mysore during the monsoon period of 1957. The leading symptom which manifests between March/May was found to be chlorosis and epinasty of penultimate or subpenultimate pair of leaves followed by their death and the extension of necrosis from the leaf scar into the internodes. Occasionally, browning of the pith and intercellular mycelium was noticed. Other symptoms attributed to the New Malady are the die-back of productive branches, crinkling of leaves, witches’ broom-like growth, shortening of internodes, etc.

Observations on the Oviposition Sites and Laboratory Development of the Fundatrix and Virginopara of the Aphid Eulachnus agilis1,2

Field observations on the site of oviposition by Eulachnus agilis (Kaltenbach) showed that the majority of eggs were deposited singly in leaf scars on branches of Scotch pine, Pinus sylvestris L. The development of the fundatrices and virginoparae under controlled laboratory conditions was investigated. The times required for the fundatrices to complete a full generation were 11.5, 19.2, and 26.7 clays at the respective temperatures of 21.1°, 15.6°, and 10.0°C and a photoperiod of 12 hours. A generation of the virginoparae was completed in 13.3, 21.6, and 45.3 days at the same respective temperatures as the fundatrices and a photoperiod of 14 hours. The mean number of nymphs produced by the fundatrices was 23.5, 17.8, and 16.7 at the respective temperatures of 21.1°, 15.6°, and 10.0°C. At the same temperatures, the virginoparae produced 8.3, 13.5, and 6.2 nymphs. At each temperature, the fundatrices produced a significantly greater number of progeny than the virginoparae.

Pathogenicity of Pseudomonas morsprunorum in Relation to Host Specificity

SUMMARY: Differences in phage type between plum and cherry strains of Pseudomonas morsprunorum were stable during passage through the homologous and heterologous hosts. In experiments controlled by phage typing reisolates from lesions, both strains were specific for the homologous plant when inoculated into leaves at low concentrations (< 105/ml.) but not at high concentrations (> 106/ml.). No specificity was observed in wound inoculations of branches made during the winter. Autumn inoculation of cherry leaf scars with cherry strains resulted in severe disease, with a dose response type of relationship between inoculum concentration and infection. Plum strains were ineffective through cherry leaf scars and inhibited infection by cherry strains when present in the same inoculum. The inhibitory effect was not observed with plum strains killed by heat or streptomycin, or with plum strains inoculated live in the presence of bacteriostatic levels of streptomycin.

Further observations on the bacteriology of jute retting

Bacteria capable of retting jute are present in pond water, in the soil of jute fields, and on the surface of jute plants. They probably enter stems over the whole surface through stomata, as well as through cut ends and leaf scars, after immersion for retting. Under laboratory conditions the shortest period of retting, three days, was achieved withBacillus polymyxa at a temperature of 40°. Retting in a tank was appreciably hastened by using the same water for successive batches of jute. Prolonged immersion involves the risk of over-retting, probably because of the action of cellulolytic bacteria. For natural retting, still the most appropriate process in East Pakistan, large clean ponds are thought to provide the most suitable conditions.

Factors Influencing Ingress of Xanthomonas pruni through Peach Leaf Scars and Subsequent Development of Spring Cankers

Factors Influencing Ingress of Xanthomonas pruni through Peach Leaf Scars and Subsequent Development of Spring Cankers

Bionomics of Agrilus acutus (Thnb.) (Col., Buprestidae) on mesta (Hibiscus cannabinus) in India

An account is given of the life-history of Agrilus acutus (Thnb.) (Buprestidae), a pest of ‘mesta’ (Hibiscus cannabinus) in india. The eggs are ovate and scale like, and are laid singly on the stem, usually near a leaf scar, and when kept at 31°C. and 73 per cent. relative humidity hatched on average in 12.4 days. The larva bores through the lower surface of the egg directly into the stem and feeds under the bark forming a sprial tunnel. A raised weal develops on the surface of the stem overlying the tunnel. Before each moult, the larva bores into the wood and makes a vertical chamber in which moulting occurs. There are normally three moults in the active feeding stages, but exceptionally four, and a prepupal moult. The rate of tunnelling is at first about 56 mm. per day and later eaches about 107 mm. The larval stage lests 26 days. The fully grown larva is 21 mm. long and bores into the wood to pupate, making a pupal chamber 11 mm. long into which it fits itself by adopting an asymmetrical U-shaped posture. After a prepupal stage of 2.5 days it pupates. The pupal period occupies about 11.7 days and a further seven days are spent by the adult in the pupal chamber. The adult female mates within a day of emergence from the stem. but does not oviposit until at least seven days have elapsed.

Uptake of IAA-2-14C by Cuttings of Ilex crenata Convexa1

Abstract Changes in levels of IAA in stem segments of Ilex have been detected by centrifugation extraction and subsequently identified by Rf. The radio-chemical was absorbed through intact tissue, leaf scars, wounds, or cut apical or basal ends of cuttings. It was not as readily transported to the base when it entered apical tissue through leaf scars as when it entered intact tissue of that region. When it entered basal ends of cuttings, some of it was carried to the apex within 48 hr.

A die-back disease of Lonicera fragrantissima caused by Botrytis cinerea

A hitherto unrecorded die-back of Lonicera fragrantissima caused by Botrytis cinerea Pers. ex Fr. which enters the shoots through wounds, fissures in the bark and leaf scars, is described. Infection is caused by conidia but sclerotia may play a minor part and may be important in over-wintering. Although conidia of B. cinerea from cabbage, dahlia, rose and Hebe brachysiphon were significantly different in size from those of the Lonicera strain, they were all capable of causing die-back of L. fragrantissima. B. cinerea was found to attack L.japonica, L. syringa, L. sempervirens, L. standishii and L. tatarica , producing in some instances a similar die-back, but no infection occurred on L. tomentella and L. periclymenum which have smooth stems.

The cone of Cyclostigma kiltorkense Haughton, from the Upper Devonian of Ireland

Cyclostigma kiltorkense Haughton (Upper Devonian, Ireland) is preserved as a compression fossil in which the plant material has been replaced by chlorite. Surprisingly fine detail is observable when the material is immersed in xylene. Re -examination of old material, and specimens from a new exposure at Kiltorcan Hill shows that the leaf scar has parichnos cicatricules but no evidence of a ligule. The cone is heterosporous, with a, Lepidostrobus organization to the cone, and the sporophyll lamina has a fimbriate margin. The megaspores have an apical prominence and spines, and conform to the dispersed spore genus Lagenicula. One mega-spore appears to have germinated, to form a protruding gametophyte. Cyclostigma is closer to Carboniferous forms than to any Devonian lycopod.

A basic study for the identification of the deciduous trees in winter by the use of punch cards (report I)

The dormant period of the deciduous trees is endowed with many useful elements for transplanting, trimming, fertilization, propagation, collection etc. in the landscaping work, but the winter time that has little necessary elements for the identification of trees, for instance, flowers, leaves, fruits, is notwithstanding furnished with much difficulties for the identification of the species of them.Therefor, an trial to identify them has been made by the use of punch cards mainly based upon the winter bud. As the identification elements of trees based mainly upon the winter bud, there are buds, twigs, leaf scars, fibro-vascuiar marks, lenticels, piths etc., and these, being combinated, make up 18 identification items, taken in the punch cards. Further, the main items: A (insertion of the winter bud in the twigs), B (insertion style of the leteral bud in the twig), D (shape of the winter bud), E (scale of the winter bud), H (shape of the leaf bud, ) I (disposition of fibre-vascular in the leaf scar) are illustrated and described, and others are only described.This method of identification is practiced as follows: in the case of Platanus orientalis L., for example, being alternate and spiral in the item A, a and are kept and others are taken away, and by putting the stick into the hole from above and drawing the cards out, the required including Platanus orientalis L. are to be obtained. Out of these cards, using the characteristics of spindle shape in the item E, ring form of the leaf scar in the item H and so on, the repeated putting in of the stick will identify Platanus orientalis L. mechanically.These operations need, of course, not be started from the item A to B, C and SD on in order, but may be begun D or E etc. The operation being simple and the repetition being able to hit the mark, will give a good way for the identification of the winter deciduous trees.

Nectria galligena . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Nectria galligena . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On apple ( Malus ) and pear ( Pyrus ). It has also been recorded on a large number of other hosts including: Acer, Betula, Carpinus, Carya, Fagus, Fraxinus, Juglans, Magnolia, Populus, Prunus, Quercus, Salix and Sorbus . DISEASE: Canker, crotch canker (40: 115), crown dieback, storage rot or late storage rot of fruits. Nectria eye-rot of fruit on tree. GEOGRAPHICAL DISTRIBUTION: Distribution appears to coincide with the major apple and pear growing areas with the exception of Australia and its probable elimination from Tasmania. (CMI Map 38, Ed. 2, 1963). TRANSMISSION: Conidia spread by rain drops (42: 494; 45, 2689). A high R.H. is essential for ascospore discharge (40: 55; 42: 494), which occurs mainly in spring and autumn. Infection is chiefly by natural wounds, leaf scars (45, 2891), occasionally from the point of attachment of the fruits (42: 691) or from pruning wounds (43, 3250). Early discharge of the ascospores (in temperate regions) increases leaf scar infection and infection in northern temperate regions is most frequent between bud-burst (mid April) and shoot formation (late May) (42: 131).

Pseudomonas mors-prunorum . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Pseudomonas mors-prunorum . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Prunus spp. especially plum and cherry. DISEASE: Bacterial canker, leaf spot and shoot wilt of stone wits. A definite seasonal cycle occurs in which a winter canker alternates with a summer leaf spot (Crosse, 1954). The symptoms are indistinguishable from those caused by P. syringae on stone fruits. GEOGRAPHICAL DISTRIBUTION: Mainly in Europe, where it has been reported from Denmark, Finland, France, Germany, Great Britain, Greece, Ireland, Netherlands, Switzerland, Rumania, U.S.S.R. (Ukraine), Yugoslavia and, recently, (46, 381) from Italy. Also in Australia (N.S.W.) and Canada (N.S.). (CMI Map 132, Ed. 2, 1966). TRANSMISSION: The pathogen is probably introduced into new orchards most frequently on plant material, where infected spurs may show such slight symptoms as to pass unnoticed (Crosse, 1954). The pathogen is spread locally by wind and rain. In early summer young leaves can be invaded but stems become difficult or impossible to infect at this time. As the leaves mature they lose their susceptibility and large numbers of bacteria are found on their surfaces. These bacteria are carried by rain to infect the branches, which are again susceptible in the autumn, through wounds and incompletely healed leaf scars. This autumn infection leads to the canker phase that develops slowly through the winter and in the spring causes infection of the new leaves as they expand. In summer the bacteria in the cankers die out. The cankers are not, therefore, perennial, but are readily reinfected in the autumn.

Studies onBotrytis cinerea in tomatoes influence of methods of deleafing on the occurrence of stem lesions

Deleafing is a normal procedure in tomato crops and subsequent infection of the leaf scars byBotrytis cinerea frequently gives rise to stem lesions. Where deleafing is done by breaking off the petiole close to the stem, a cambium forms and the leaf scar is sealed after about seven days. Two to three days after deleafing, only a thin surface layer of dried cells is visible but at that time the leaf scar is unlikely to become infected by conidia of the fungus. When deleafing is done by cutting the petiole about 5 cm from the stem, abscission of the stumps occurs after about three weeks. When the petiole stump is inoculated with conidia ofB. cinerea, abscission occurs after about eight days. In neither case is abscission complete. In old, but still green leaves, an abscission layer gradually develops at the petiole base, so deleafing by cutting the petioles of old leaves might be a promising method of avoiding stem infection byB. cinerea.

Bacterial canker of stone‐fruits: Infection experiments with Pseudomonas mors‐prunorum and P. syringae

SUMMARYThe effect was compared of inoculating Pseudomonas mors‐prunorum and P. syringae at high inoculum concentration through wounds in plum stems and cherry branches, and through cherry‐leaf scars. In the wound inoculations a North American cherry strain of P. syringae was considerably more virulent than any of three indigenous cherry strains of P. mors‐prunorum, but two pear strains of P. syringae were less virulent. P. mors‐prunorum showed a much greater capacity to invade through leaf scars, particularly towards the end of the leaf‐fall period, when all three P. syringae strains were largely ineffective. Evidence is discussed which suggests that the greater infectivity of the P. mors‐prunorum strains through leaf scars was related to their capacity to colonize the host tissues from small inocula. The P. syringae strains died out in cherry cankers earlier than P. mors‐prunorum strains and they were less stable during host passage. The results of the experiments indicate that virulence in these organisms is a complex phenomenon and determined by several factors.

Pseudomonas syringae . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Pseudomonas syringae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On a very wide range of host plants including representatives of the following genera: Chrysanthemum, Citrus, Cyamopsis, Hibiscus, Juglans, Malus, Pennisetum, Persica, Phaseolus, Piper, Prunus, Pyrus, Rosa, Sorghum, Synura, Trifolium, Vicia, Vigna and Zea . Several species of Pseudomonas described in the literature are likely to prove synonymous with P. syringae and the host range is probably even wider than that given by Elliott (31: 105) p. 90. Poplar canker, at one time attributed to a forma specialis of P. syringae (32: 522), is now known to be caused by an entirely distinct pathogen, Aplanobacterium populi Ride (37: 604). DISEASE: Bacterial canker of stone fruits causing gum exudation on trunks, limbs, twigs and fruit; blighting of buds and blossom; leaf spot and shoot wilt. Also on hosts other than Prunus causing blossom blight and die-back in pear, blossom blight of apple, blast or black pit of citrus, lilac blight, bacterial brown spot of string bean and lima bean, and bacterial leaf blight of sudan grass and other Gramineae . The symptoms of blossom blight on apple ant pear have often been confused with fire blight incited by Erwinia amylovora (CMI Descript. 44) and boron deficiency (41: 46; 35: 463). The symptoms on stone fruit trees are generally indistinguishable from those incited by P. morsprunorum . The reddish-brown leaf spots on bean incited by P. syringae lack an extensive yellow halo which serves to distinguish the symptoms from those of the halo blight pathogen, P. phaseolicola (CMI Descript. 45) except under dry conditions (17: 578). GEOGRAPHICAL DISTRIBUTION: World-wide in all the major fruit growing areas (CMI Map 336, 1957). On other hosts the distribution may be more restricted as in bacterial brown spot of bean which has been reported only from the Netherlands (34: 567), Tanganyika (34: 350) Queensland (33: 110), New South Wales (17: 578), and from parts of U.S.A. (43: 2453; 37: 63). TRANSMISSION: The pathogen is spread by wind-driven rain and is favoured by cold spring weather, rain and high humility. Penetration is through stomata or wounds caused by insects, pruning or hail (31: 63, 183; 12: 281). Frost injury is also a predisposing factor for citrus blast and blossom blight of pear (42: 177; 43, 2329). Spur and node infections of cherry are reported to occur through leaf scars in England (35: 198), but in Oregon they have been shown to originate more commonly at the base of the external bud scales (42: 270). Pseudomonas syringae is seed borne on bean and the pathogen has been found to survive in soil over one but not two winters in Wisconsin (37: 63).

Aplanobacterium populi, the cause of bacterial canker of poplar

From cankers ofPopulus candicans Ait. in the Netherlands a bacterium was isolated which was identical withAplanobacterium populi Ride, the causal pathogen of bacterial canker of poplars. Cuttings ofP. candicans inoculated with bacteria through freshly made leaf scars showed typical symptoms of the disease.

Observations on the biology of chrysanthemum eelworm Aphelenchoides ritzema‐bosi (Schwartz) Steiner in florists' chrysanthemum

SUMMARYIn stained sections of eelworm‐infested chrysanthemum leaves the earliest effect of the attack is the appearance of a brown substance inside the leaf cells; this browning extends and ultimately reaches the leaf epidermis. The number of chloroplasts dwindles, the cell walls break down and large spaces appear in the leaf. Finally the leaf shrinks, the epidermis disintegrates and the brown substance is found on all the cell walls. The collenchyma around the main veins, where it reaches the upper and lower epidermis, does not break down until the final stage of attack.Cuttings of thirteen chrysanthemum varieties, each artificially infested with about 110 eelworms, showed leaf blotches, stunting, blindness, browning of the stem and leaf petiole, leaf distortion, leaf scars or feeding areas and puffy, blistered and puckered leaves. Infested cuttings with severe symptoms may produce side‐shoots or breaks which seem healthy but become badly infested later in the season when the plants are wetted by rain or prolonged mists. The eelworms often failed to penetrate further than the substomatal space in the youngest leaves. All the symptoms listed above, except leaf blotches, probably result from ectoparasitic feeding by the eelworm.

DIDYMELLA STEM‐ROT OF OUTDOOR TOMATOES

Experiments were made during 1954‐7 on the control of Didymella stem‐rot of tomatoes, by applications of various fungicides. The toxicity of a wide range of compounds to the fungus and to tomato plants was determined in the laboratory and promising compounds were then tested in the field. There were two main test methods, in both of which the plants were infected artificially at varying periods before or after treatment with the fungicides. In one method the inoculum was applied to leaf scars and in the other to the stem bases, the fungicides being sprayed on to the same sites.Of the compounds tested, maneb was the most successful, showing both eradicant and protectant properties at 1 and 2%. Captan (0.25 and 0.5%) was a good protectant but was less effective as an eradicant. Attempts were made to test the compounds under conditions of natural spread of the disease but this was so slight that the results were not conclusive.