Showing papers on "Leaf spot published in 1979"

Induced resistance of cucumber to anthracnose and angular leaf spot by Pseudomonas lachrymans and Colletotrichum lagenarium

Abstract: Infection of the first true leaf of cucumber with either Pseudomonas lachrymans or Colletotrichum lagenarium systemically protected susceptible cultivars against disease caused by subsequent challenge with either pathogen. Sonicated bacterial cells, heat-killed cells, formalin-killed cells and a cell-free culture filtrate did not protect. Suspensions of bacteria swabbed onto leaf one or infiltrated into the leaf consistently induced protection against the fungus. The bacterium protected the plant against fungal inoculum containing 103 to 106 conidia ml−1. Systemic invasion by either challenge pathogen was rarely observed in protected plants. An interval of 72 to 96 h after the inducing inoculation was necessary for protection to be expressed. Protection was still evident 37 days after the initial infection. Pseudomonas pisi, P. phaseolicola and P. angulata also protected plants, but this level of protection was significantly less than that elicited by P. lachrymans. Several other bacteria tested did not elicit protection. Populations of P. lachrymans in disks of the challenged second true leaf of unprotected plants were 103 cells greater, 5 days after challenge, than those in protected plants.

Diseases of winter oil-seed rape: occurrence, effects and control

Abstract: The results of observations begun in 1973 and of disease surveys carried out on winter oil-seed rape crops on ten farms in Hertfordshire and Bedfordshire between 1975 and 1978 are reported. The major diseases encountered in the surveys, namely downy mildew (Peronospora parasitica (FT.) Tull.), canker (Leptosphaeria maculans (Desm.) Ces. & de Not.), light leafspot or scorch (Pyrenopeziza brassicae Sutton & Rawlinson) and grey mould (Botrytis cinerea Fr.) are discussed in relation to diseases of rape grown elsewhere and the results of experiments on disease control reported. Symptoms of virus infection and root disease were rare.Early (before stem extension) use of two applications of benomyl (1·2 kg a.i./ha) decreased the incidence and severity of light leaf spot and canker and increased yield by up to 33%. Benomyl plus thiram seed treatment (5 and l·5ga.i./kg) was less effective than a benomyl foliar spray. In field experiments differences in severity of light leaf spot and canker explained a substantial part of variation in yield but downy mildew did notaccount for further variation.

Fungal Diseases of Betel Vine

Abstract: The diseases of betel vine are reviewed in relation to their occurrence, importance, diagnostic symptoms and control measures. Factors affecting disease development are discussed where known. Foot rot caused by Phytophthora palmivora and Corticium rolfsii, leaf rot caused by P. palmivora and leaf spot and anthracnose caused by Colletotrichum capsici are widespread and cause recurrent annual losses to crop yield and quality where rainfall and temperature are favourable for the pathogen. Eleven diseases of minor importance, which may gain epiphytotic proportions in specific locations and plantations where they appear, are also described briefly.

Pathogenesis of Drechslera sorokiniana leaf spot on progressively older leaves of Poa pratensis as influenced by photoperiod and light quality

Abstract: Drechslera sorokiniana leaf spot on Poa pratensis was investigated relative to photoperiod, light quality and sequential leaf development and senescence. Leaf spot expression was enhanced on each older leaf when subjected to blue-biased, far-red-rich light irrespective of photoperiod and when subjected to “balanced” light in combination with a short photoperiod (10 h). Leaf spot expression on progressively older leaves subjected to “balanced” light in combination with a long photoperiod (14 h) was inhibited. Leaf spot expression on progressively older leaves in response to orange-red-biased light in combination with a long photoperiod (14 h) was similar to that of “balanced” light, but orange-red-biased light uniquely promoted leaf spot expression on younger leaves in combination with a short photoperiod (10 h). The relationship between the calculated and projected phytochrome photoequilibrium (φ) and disease expression suggests that pathogenesis on progressively older leaves can be influenced by a light-phytochrome-pathogen interaction. Spectral and photoperiodic conditions associated with retardation or stimulation of leaf sensescence also seem to retard or stimulate pathogenesis, especially on progressively older leaves.

Enhanced Drechslera sorokiniana leaf spot expression on Poa pratensis in response to photoperiod and blue-biased light☆

Abstract: Research was initiated to determine the influence of photoperiod and light quality on the severity of Drechslera sorokiniana leaf spot on Poa pratensis . Subjecting inoculated plants to a 10 h photoperiod in combination with orange-red-biased light (spectrum A) or with a “balanced” spectrum (spectrum B) increased disease. Inoculated plants subjected to a 14 h photoperiodin combination with these spectral regimes reduced disease expression. The effect of photoperiod on disease expression was negated by blue-biased light (spectrum C), and disease was increased on all plants subjected to this spectral regime. Disease severity was substantially increased on inoculated plants subjected to the artificial extremes of continuous dark or continuous light. The results show that pathogenesis of leaf spot produced by D. sorokiniana on P. pratensis is mediated by photoperiod and light quality in a manner highly suggestive of phytochrome involvement.

Leaf senescence as a factor in the competitive and synergistic interactions of Drechslera sorokiniana and Curvularia geniculata on Poa pratensis

Abstract: The competitive and synergistic interactions of Drechslera sorokiniana and Curvularia geniculata on pathogenesis of leaf spot was evaluated on sequentially senescent leaves of Poa pratensis. Leaf age had no effect on the mean number of lesions produced from inoculations with D. sorokiniana or C. geniculata alone. The combination of D. sorokiniana and C. geniculata produced a significant increase in the mean number of lesions between the youngest and oldest leaves at 20, 25, and 30 °C. Disease severity on leaves of all ages resulting from inoculations at 20 and 25 °C was greatest in response to D. sorokiniana alone, followed by the combination of organisms, and by C. geniculata alone, in descending order. No difference in disease severity occurred on leaves of different ages in reponse to the inoculations at 20 °C, but a significant increase in disease occurred on the two oldest leaves at 25 °C in response to inoculations with D. sorokiniana and to the combination of organisms. At 30 and 35 °C, disease sev...

The role of pigmentation in survival of the leaf spot fungus Cercospora beticola

Abstract: SUMMARY Both germination and survival time of spores of a pigmented strain of Cercospora beticola were directly correlated with relative humidity. Pigmented cultures, under conditions of low water availability (15%) survived 242 days' continuous exposure to light (110 lx). The ability of various strains of the fungus to survive in soil was found to be influenced by pigmentation, rate of growth, inoculum ratio in the soil and the physiological state of the organism before exposure to the soil environment.

Tricladium leaf spot - a new disease of sorghum

Abstract: The disease caused by the new sp. T. sorghicolum, parasitic on crops at the experimental farm of Haryana Agric. Univ., is described. Previously reported T. spp. are either aquatic or live as saprophytes on dead leaves and wood

New plant disease record in New Zealand Alternaria dichondrae on Dichondra repens

Abstract: Alternaria leaf spot has been found in Dichondra lawns in New Zealand since 1969. In 1975 the fungus concerned was described from Italy as a new species: A. dichondrae. The recording in New Zealand has not previously been published.

Occurrence and significance of halo spot (Selenophoma donacis) on Barley in Western Australia

Abstract: Fig. 1. Halo blight on Atlas barley. RESEARCH NOTES Halo spot symptoms have been noted on barley leaves over the past two years. In 1978 it appeared in severe form at the Newdegate Research Station on barley variety Atlas . The fungus was read ily isolated using the culture techniques described by Brokenshire and Cooke (1) and Koch 's postu lates were successfully completed. Identity of the fungus was subsequently confirmed by the Commonwealth Mycological Institute (Herb. IMI 23q041) and Dr. B. M. Cooke of the University College, Dublin. The conidia produced on leaf as well as in culture were crescent shaped and unicellular. Their sizes (mean and range iniJ-Lm) were: in culture (V-8MCDA), 16.7 x 2.9 (13.0-19.5 x 2.63.9); from leaves, 18.3 x 4.2 (13.0-20.8 x 2.6-5.2). These measurements correspond closely with the description by Sprague and Johnson (7). Although this is the first record of this disease in Western Austra lia, it is possible that it has been in the State for some time, and that due to some similarity in symptoms it may have been mistaken for either scald (Rhynchosporium secalis (Oud.) J. J. Davis) or leaf spot (Drachslara vetticil/ata (O'Gara) Shoemaker). Shaw (8) identified S. dona cis stomaticola (Baumler) Sprague and Johnson on wheat in New South Wales but showed that isolates from wheat were not infective on any other gram inaceous species including barley. "There is one record of S. donacis on barley from South Australia (Collected by Dr. A. H. Mayf ield identified by Mr . J. Walker: J. Walker, personal communication. Specimen filed as DAR 28013)." Following identification of this disease, 46 entries of barley including 25 lines of the Australian Elite Nursery were inoculated at two leaf staqe using the technique of Brokenshire and Cooke (2), and assessments were made using the key devised by Cooke and Brokenshire (4). Varietal differences were not obv ious in seedlings at 2-4 leaf stage and range of mean leaf area covered var ied from 0-5 per cent. Varietal differences were however recorded at the heading stage amongst 348 breeding lines , including commercial cultivars as controls, at the Mt Barker Research Station. Varying levels of tolerance were shown with 0.9%, 4.9% and 5.7% lines classified as highly susceptible , susceptible and moderately susceptible respectively. In susceptible lines , all green leaves were almost entirely covered with lesions, and glumes and awns showed extensive browning. The observations agree with Jenkins at al (6) who found that this disease develops rapidly after ear emergence. As this disease is most severe at the time of gra in filling, under suitable conditions it could pose a major threat to barley yield in a susceptible genotype. Occurrence and Significance of Halo Spot (Selenophoma donacis) on Barley in Western Australia

Physiological alterations in the prehalo of the turmeric leaf spot disease

Abstract: The apparently healthy area around the yellow halo of the spots formed by infection of turmeric leaves byColletotrichum capsici as well as by the treatment of toxin secreted by the pathogen was found to behave differently in certain biochemical properties from healthy area. This area had a hyper rate of respiration, a lower photosynthetic rate and a reduction in major photosynthetic pigments. This biochemically different area can be considered as a prehalo.

Common Bacterial Blight of Bean

Abstract: Bacterial blight of bean is a typical leaf spot and leaf blight disease. At first, the lesions on leaves are small, translucent, water-soaked spots which later develop dry brown centers and narrow yellow halos. Lesions coalesce into irregularly-shaped areas which may include the whole leaflet. Lesions on stems and pods tend to be more restricted and sunken (Fig. 7-1A). Those on the pods frequently turn from red to brown with age. With continued development, the vascular system may also turn brown and surface cankers form on the stem.