Development Of Leaf Spot Disease Research Articles

Effect of doses fertilizer and harvest interval on the intensity of leaf spot diseases, production and quality of citronella grass (Cymbopogon nardus L.) essential oils in ultisols soil

Until now, Indonesia is still a world exporter of essential oils, including citronella oil. So that the role of farming communities in the development of Indonesia's essential oil industry is very helpful. For this reason, a study was carried out on response of fertilization and harvest interval on the intensity of leaf spot diseases of citronella grass, and productivity in ultisols soil which was carried out from October 2020 to September 2022. The experiment was arranged in a randomized block design in factorial with 9 treatments, as the first factor is 3 levels of an organic fertilizer (NPK); P1 = 25 g clumps −1, P2 = 37.5 g clumps −1 and P3 = 50 g clumps −1. The second factor is the harvest interval with three levels which is 4 = harvest interval once every 4 months, 3 = harvest interval every 3 months and 2 = harvest interval once every 2 months, repeated three times. Each treatment plot consisted of 24 clumps with a plant spacing of 1 × 1 × 1 m. Varieties used is Serai wangi 1. Parameters observed were intensity of leaf spot diseases, vegetative growth, livestock production, oil production, quality analysis and R/C ratio. The results showed that there was an effect of fertilizer doses and harvest intervals on the development of leaf spot disease. It was seen that at the application of fertilizer doses of 37.5 g clumps −1 with harvest intervals once every three months showed the lowest disease attacks, namely on Cuvularia sp and Pestalotia sp (5.98%, 5.42% and 7.98 %, 7.44 %). In addition, the development of vegetative growth is also influenced by the application of fertilizer doses and harvest intervals on the parameters of canopy width, plant height, leaf length, leaf width and number of tillers. The best fertilizer dose is 37.50 g clump −1 successively (175.40 cm, 172.29 cm, 113.62 cm, 2.36 cm and 119.59 stems), with harvest intervals every 3 months (179.40 cm, 187.29 cm, 119.44 cm, 2.45 cm and 120.00 stems), as well as fresh leaves production tons/ha/year and oil production kg/ha/year the best is the application of fertilizer doses of 37.50 g clumps−1 with harvest intervals once every 3 months (67.81 tons−ha-year and 578.61 kg−ha- year,with, 67.40 tons–ha-th and 517.60 kg–ha-th). For oil quality, numerically, the application of fertilizer at a dose of 37.50 g of clump −1 with harvest intervals every 3 months is still high. The proper R/C ratio for farming occurs in the 2 nd year by administering a fertilizer dose of 37.50 g clump−1 and harvesting intervals once every 3 months with an increase of 116.67%. So, the citronella grass variety Serai wangi 1 can be developed on ultisol soil types by applying an organic fertilizer (NPK).

Leaf Spot Disease Development and Its Effect on Yield of Essential Oil-Producing Hemp Cultivars in Kentucky.

Leaf spot diseases are common on field hemp, causing defoliation and blighting. The most prevalent leaf spot diseases of hemp in Kentucky are Bipolaris leaf spot (Bipolaris gigantea), Cercospora leaf spot (Cercospora flagellaris), and Septoria leaf spot (Septoria cannabis). In this study, disease progression, cultivar susceptibility, and yield loss were examined using cultivars from four relatedness groups at two locations and in two growing seasons. Septoria leaf spot was the first leaf spot disease to be observed in the field, followed by Bipolaris leaf spot. Both diseases reduced canopy density. Cercospora leaf spot developed in the late reproductive stages as harvest approached. A wide range of susceptibility was documented, suggesting genetic variability across cultivars. Trump group cultivars were the most susceptible, while Otto II group cultivars were the least susceptible. Most importantly, leaf spot diseases had minimal influence on floral biomass and no effect on CBD yield, suggesting that, regardless of disease severity, leaf spot diseases may seldom warrant management. While the importance of foliar disease and corresponding yield loss can shift over time, variation in disease progress among leafspot diseases and susceptibility of hemp cultivars documented in this study suggest potential disease management through cultural practices such as cultivar and planting date selections.

Analisis Perbandingan Perkembangan Penyakit Bercah Daun (Cercospora capsici) pada Tanaman Cabai Merah (Capsicum annuum L) di Dataran Tinggi dan Dataran Rendah selama Musim Hujan Studi Kasus di Kabupaten Karo dan Deli Serdang

This study aims to analyze the comparison of the development of leaf spot disease (Cercospora capsici) in red chili plants (Capsicum annuum L.) in highland and lowland areas during the rainy season. Leaf spot disease is a serious problem that hinders proper growth in chili plants. The research was conducted in December 2022 using a descriptive survey method, focusing on the issue of leaf spot disease in chili plants in farmers' fields. The results showed that the average percentage of symptomatic chili plants affected by leaf spot disease in the highland area was 50.89%, while in the lowland area, it was 29.77%. The average level of leaf spot disease incidence in the highland was 26.79%, whereas in the lowland, it was 24.61%. From these findings, it can be concluded that leaf spot disease (Cercospora capsici) has a higher incidence rate in red chili plants in the highland compared to the lowland during the rainy season. Knowledge of this difference can assist farmers in taking appropriate preventive or intervention measures to address disease outbreaks in red chili plants in both regions.

First report of Diaporthe eres causing leaf spot on Platanus acerifolia in China.

Platanus acerifolia Willd. is one of the world famous urban greening trees, known as "the king of street trees" (Loretta et al. 2020). In August 2021, severe leaf spot disease was observed on P. acerifolia with 15% incidence on a street of Haidian district (116°29'E, 39°95'N), Beijing municipality, China. Typical symptoms were small and irregular brown spots with or without yellow haloes, which gradually expanded, coalesced and became necrotic lesions. For pathogen isolation, the leaf lesions were cut into small tissue pieces, disinfected by 0.3% sodium hypochlorite for 2 min and 70% ethanol for 40 s, rinsed in sterile distilled water, and then incubated on potato dextrose agar (PDA) plates. After incubation at 28°C for 4 days, three fungal isolates (FTDX2, FTDX3, and FTDX6) with similar colony characteristics were obtained after single spore isolation. Colonies were white with fluffy aerial mycelia, abundant pycnidia with black stomata appeared and cream-white liquid oozed after 20 days. Alpha conidia were 7.9 ± 0.6 × 2.5 ± 0.3 μm (n= 30), aseptate, hyaline, fusiform to ellipsoidal, and often biguttulate, while beta conidia were 22.7 ± 1.3 × 1.1 ± 0.1 μm (n= 30), aseptate, hyaline, linear, curved or hamate. The morphological characteristics were consistent with those of Diaporthe sp. (Udayanga et al. 2014). For further identification, total DNA was extracted from the three isolates. The internal transcribed spacer (ITS) region, translation elongation factor 1-α (EF1-α), beta-tubulin (TUB), calmodulin (CAL) and histone (HIS) genes were amplified and sequenced with primers ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Carbone and Kohn 1999), BT2a/BT2b (Glass and Donaldson 1995), CL1/CL2A (O'Donnell et al. 2000) and CYLH3F/H3-1b (Crous et al. 2014), respectively. The sequences were all deposited in GenBank (accession nos. OL870615 - OL870617 for ITS, OL870618 - OL870620 for EF1-α, OL870621 - OL870623 for TUB, OL870624 - OL870626 for CAL, and OL870627 - OL870629 for HIS) and aligned using BLASTn, obtaining 99-100% homology with the corresponding sequences of known Diaportheeresstrains in NCBI. Phylogenetic analysis of the combined sequences attributed the three isolates to the Diaportheeres clade. Pathogenicity tests were performed on three healthy one-year-old P. acerifolia plants using the randomly selected isolate FTDX2. The leaves were inoculated with 20 µl of spore suspension (106conidia/ml), with or without wound pretreatment, sterilized water inoculation under the same condition was used as control. All the treated plants were incubated in the greenhouse at 25°Cand 90% RH with a 12-h photoperiod. After 8 days,the inoculated plants showed spot symptoms on leaves similar to those previously observed, whereas the control leaves remained symptomless. Lesions on the wounded leaves were much larger in size compared with those unwounded. The same pathogen was re-isolated and identified based on morphological characteristics and gene sequencing data, fulfilling Koch's postulates. Diaporthe ereshas been reported to cause leaf spot on many horticultural plants, such as Photinia fraseri (Song et al. 2019) andPodocarpus macrophyllus (Zheng et al. 2020). To our knowledge, this is the first report ofD. erescausing leaf spot onPlatanus acerifoliain China. This finding is a valuable contribution to the knowledge on leaf spot disease development in horticultural plants.

Impact of leaf spot disease on beetroot production in Jaffna peninsula, Sri Lanka

The present study focuses on the aetiology of leaf spot disease and its impact on beetroot production in the Jaffna peninsula. A survey and field study was carried out to understand present status of the disease. The fungus associated with the leaf spot lesions was isolated and identified based on morphological features and sequence analysis. The survey has shown drawbacks in the cultivation practices, such as selection of cultivation season, selection of variety and inadequate weed management practices. The initial symptoms were noted in seedling stage, and the disease incidence and severity progressed with time. The disease incidence and severity index were 85% and 2.71 at 48 days. The field experiment has revealed the negative correlation between leaf spot disease development and yield. The fungal isolates produced obclavate shape, hyaline, multiseptated conidia on dark coloured unbranched sparingly septate conidiophores. The isolates showed 99.25% sequence identity with Cercospora beticola.

The effects of aqueous eucalyptus (Eucalyptus globulus Labill.). leaf extract in the control of early development of leaf spot disease (Cercosporiosis) of groundnuts (Arachis hypogaea L.)

The effects of aqueous eucalyptus (Eucalyptus globulus Labill.). leaf extract in the control of early development of leaf spot disease (Cercosporiosis) of groundnuts (Arachis hypogaea L.)

Temperature Drives Contrasting Alternaria Leaf Spot Epidemic Development in Canola and Mustard Rape from Alternaria japonica and A. brassicae.

Recent surveys of canola (Brassica napus) crops across southern Australia highlighted that Alternaria leaf spot on canola is not solely caused by Alternaria brassicae but that other Alternaria spp. are also involved, including A. japonica. Studies were undertaken into the effects of different temperatures (14 and 10°C [day and night] or 22 and 17°C [day and night]) on development of Alternaria leaf spot caused by A. japonica as compared with A. brassicae in cotyledons (embryonic leaves) and true leaves (first leaves) of canola (B. napus 'Thunder TT') and mustard rape (B. juncea 'Dune'). Both pathogens expressed less disease at lower temperatures of 14 and 10°C with percent disease index (%DI) of 19.1 for A. japonica and 41.8 for A. brassicae, but expressed significantly more disease at higher temperatures of 22 and 17°C with %DI of 80.8 and 88.2 for the same pathogens, respectively. At 14 and 10°C, mustard rape cotyledons showed less disease (percent cotyledons disease index [%CDI] = 18.1) from A. japonica but showed more disease (%CDI = 75.0) from A. brassicae. However, at 22 and 17°C, cotyledons and true leaves of both canola and mustard rape showed significantly more disease and varied in expressing the disease severity to the two pathogens; true leaves of mustard rape showed less disease (percent true leaf disease index [%TDI] = 48.4) from A. japonica but showed more disease (%TDI = 92.0) from A. brassicae. At 22 and 17°C, cotyledons of canola expressed more disease from A. japonica (%CDI = 99.1) than from A. brassicae (%CDI = 70.7). At the lower temperature, both host species showed the least disease, with mean %DI of 27.3 and 33.5 for canola and mustard rape, respectively, as compared with the higher temperatures, where there was a greater DI, with %DI values of 87.9 and 81.2 for these same host species, respectively. We believe that these are the first studies to highlight the critical role played by temperature for A. japonica as compared with A. brassicae in Alternaria leaf spot disease development and severity. These findings explain how temperature affects Alternaria leaf spot severity caused by A. japonica as compared with A. brassicae on different foliage components of canola and mustard rape.

Response of Ugandan common bean varieties to Pseudocercospora griseola and Angular leaf spot disease development in varietal mixtures

ABSTRACTAngular leaf spot (ALS) is one of the most economically important bean diseases in Africa. One promising control option for the disease is the use of mixtures of resistant and susceptible varieties. This research evaluated (1) the reaction of farmer preferred bean varieties to ALS in the screenhouse and on-station and (2) the effect of different spatial arrangements of resistant and susceptible bean varieties on ALS disease development. For the latter, five mixture combinations and two controls were laid out in a Randomized Complete Block Design having three replicates. Analysis of variance and least significant differences (LSDs) were used to compare disease levels in both studies above. Varietal screening showed significant differences in varietal reaction to ALS. Screenhouse disease scores ranged between 0 and 5, compared to 0.7–3.9 in the field. For the varietal mixture trial, the lowest disease levels and the highest mixture efficiencies were observed for the combination of equal proportions of the susceptible and resistant varieties randomly mixed (even mixture) prior to planting. We conclude that even mixtures reduce the amount of ALS disease that develops in the season.

Floricultural Quality Traits and Probing Mechanisms of Silicon Mediated Disease Resistance of Dendrobium

Dendrobium sp. (Orchidaceae) is the most ‘in demand’ cut flower in the export and local market due to its vivid and variable flower coloration. However, the production of quality flowers is a major obstacle and is the main factor contributing to the export potential of the cut flower industry in Sri Lanka. This research was focused on improving floricultural quality, growth and enhancing disease resistance of Dendrobium by preharvest application of soluble silicon. The experiments were conducted in a mesh house at 50% shade and were designed as a Completely Randomized Design (CRD). Each treatment or control plant consisted of 12 replicates and the experiment was repeated twice. The orchid plants were potted in clay pots and provided with 100 mg/L of sodium silicate at weekly intervals, showed significantly higher shoot length, leaf length and number of leaves compared to silicon provided bi-weekly or in the controls. Plants grown in a newly designed aeroponic system and treated with 100 mg/L silicon weekly showed significantly improved floricultural quality traits: a higher number of flowers per spike and higher spike length, higher spike thickness and higher flower length and diameter compared to the plants treated at 50 mg/L or untreated plants. Natural disease development of leaf spot disease was significantly lower in plants treated with silicon as compared to the control. The average leaf thickness, cuticle thickness and total soluble phenol content were significantly higher in plants treated with silicon. These results indicate that mechanical barriers in the form of cuticle thickness and leaf thickness contribute towards the reduction of disease development. Increased levels of total soluble phenols in leaves of silicon treated plants may be also contributing biochemically towards warding off disease.

Salicylic acid and cysteine contribute to arbutin-induced alleviation of angular leaf spot disease development in cucumber

Arbutin induced suppression of angular leaf spot disease in cucumber resulting from lower populations of Pseudomonas syringae pv lachrymans in the infected tissues. This study provides insight into mechanisms that may potentially account for this effect. In the absence of the pathogen, exogenous arbutin-induced expression of PR1, the marker of salicylic acid signaling, increased the content of salicylic acid and modulated the cysteine pool. This suggested that arbutin promoted cucumber plants to a “primed” state. When challenged with the pathogen, the arbutin-treated plants showed strongly reduced infection symptoms 7 days after inoculation. At this time point, they were characterized by higher contents of free and protein-bound cysteine due to higher cysteine biosynthetic capacity related to increased activities of serine acetyltransferase and cysteine synthase when compared with plants infected without arbutin treatment. Moreover, in the arbutin-treated and infected plants the contents of free salicylic acid and its conjugates were also increased, partly owing to its biosynthesis via the phenylpropanoid pathway. We suggest that arbutin-induced abrogation of angular leaf spot disease in cucumber could be mediated by salicylic acid and cysteine-based signaling.

KEMAMPUAN BAKTERI ENDOFIT TANAMAN SEMANGKA DALAM MENEKAN PERKEMBANGAN PENYAKIT BERCAK DAUN YANG DISEBABKAN OLEH JAMUR COLLETOTRICHUM SP.

Ability of watermelon endophytic bacteria to suppress development of leaf spot disease caused by Colletotrichum sp. A studi on assay of endophytic bacteria to control Colletotrichum sp., causal agent of leaf spot disease on watermelon, was conducted. Colletotrichum sp. was isolated from infected leaf of leaf spot disease, while endophytic bacteria were isolated from stem, leaf, and root of watermelon healthy plant. Antagonistic assay was conducted by dual culture method. Hyphal abnormalities as a result of antagonistic assay was observed using light microscope. To determine the ability of endophytic bacterial isolates to control leaf spot disease, watermelon seeds were treated by dipping the seed in endophytic bacterial suspension. Seven endophytic bacterial isolates showed to inhibit Colletotrichum sp. to some extent. Two isolates DS 01 and BS 01 showed relatively high inhibition zone compared to others, therefore were choosen for further study. Abnormal hyphae such as broken, lysis, twisted, curled, and swollen hyphae were recorded as the result of antagonistic assay. Watermelon seed treatment revealed that dipping the seed in endophytic bacterial suspension of DS 01 and BS 01 reduced leaf spot disease to 12 and 24%, but inhibited seed growth by 12% and 44%, respectively. It seemed that all treatments showed to reduce seedling performance i.e seedling height, leaf number, and dry weight, compared to that of (-) control. DS 01 however seemed to increase dry weight of watermelon plants.

Bahasa Indonesia

Leaf spot disease of oil palm caused by Curvularia sp. is the major disease in nursery. Implementation of best nursery practices is the key to prevent it. Generally, fungicides are used only if epidemic of leaf spot diseases occur in the field. The objectives of this research were to determine causal agent of leaf spot disease of oil palm and the potential alternative weed host around the nursery, to select suitable fungicides, and to study the effect of fungicides rotation to disease incidence. The results showed that the causal agent of leaf spot disease of oil palm was Curvularia lunata. The fungus was also found on grasses, Cyperus rotundus and Imperata cylindrica. Difeconazol, copper oxide, and propineb suppressed leaf spot disease in nursery. Application of fungicide by rotation between difeconazol and copper oxide with frequency every 10 days suppressed the development of leaf spot disease of oil palm in the nursery.

Weather based forewarning model for Alternaria leaf spot of safflower (Carthamus tinctorius L.) in scarcity zone of Maharashtra

An experiment was carried out in post rainy (rabi) seasons of 2006-07 to 2010-11 for studying the effect of environmental factors and crop phenology on Alternaria leaf spot disease development in safflower under three different sowing conditions viz., early, normal and late at Zonal Agricultural Research Station, Solapur in Maharashtra, India. The studies revealed that subnormal temperature coupled with above normal humidity and rainfall contributed significantly for the disease incidence and its spread under different sowing situations. Safflower plants were susceptible to Alternaria carthami at all growing stages, but susceptibility increased as the plants matured. Further, the percent disease index (PDI) has progressed at linear rate throughout the plant growth and it was negatively correlated with maximum temperature under late sown condition, while it was positively correlated with rainfall, minimum temperature, relative humidity (morning and evening) in addition to age of crop. By employing step down linear regression models, the incidence of Alternaria leaf spot on safflower can be predicted to an extent of 97.6%, 95.3% and 92.2% accuracy under early, normal and late sowing conditions, respectively while with non-linear models the prediction rate for the leaf spot under above sowing situations was improved to 99.8%, 99.6% and 99.4%, respectively.

Factors affecting incidence and severity of leaf spot disease on lettuce caused by Septoriabirgitae

AbstractIn the 1990s during wet seasons a new disease causing brown leaf spots on lettuce (Lactuca sativa) was found for the first time in many lettuce‐growing areas of Austria and Germany. The causal agent, a new pathogenic species called Septoria birgitae, may be responsible for total crop loss. To study how temperature, inoculum density and leaf wetness period influence disease incidence and severity of leaf spot on lettuce caused by S. birgitae, we carried out in vivo experiments in growth chambers and in the field. Additionally, we evaluated the relevance of infected plant debris acting as a primary inoculum source in soil for subsequent crops. S. birgitae produces spores over a wide temperature range between 5°C and 30°C, and can infect plants at temperatures between 10°C and 30°C, with an optimum between 20°C and 30°C. Spores of S. birgitae at a density of at least 103 conidia mL–1 are essential for disease outbreak on lettuce. Because leaf wetness is crucial for releasing conidia from pycnidia, we studied the impact of leaf wetness duration on disease development under various temperature conditions. For relevant leaf spot disease development on lettuce in vivo, a leaf wetness duration of at least 24 h and temperatures higher than 10°C were necessary. Leaf spot disease development in the field required several leaf wetness periods longer than 20 h at approximately 15°C at the beginning of crop cultivation. Incorporating S. birgitae infected plant debris in soil as a primary inoculum was not relevant for leaf spot disease outbreak in the next year. However, in cases of continuous cropping of lettuce on the same field and in the same season, Septoria‐infected lettuce debris may become more relevant.

Effect of Various Factors on the Development of Leaf Spot Disease in Mulberry

Effect of various factors such as temperature, relative humidity, balanced fertilizer and plant spacing on the development of leaf spot disease in mulberry caused by Cercospora moricola was studied. High disease development was recorded in the month of August and September when outdoor temperature and relative humidity were 25-30 ºC and above 80%, respectively. Application of balanced fertilizer and plant spacing on this disease development was also studied and showed a distinct effect on severity of this disease. A balanced dose application of NPK fertilizer decreased disease severity to 6-8%. Balanced fertilizer application in the soil resulted lower infection by leaf pathogen in comparison with imbalanced fertilizer application in the soil. Disease development was also found to be high at close plant spacing (60 × 60) cm than distance spacing (90 × 90) cm. DOI: http://dx.doi.org/10.3329/jesnr.v5i1.11583 J. Environ. Sci. & Natural Resources, 5(1): 205 - 209, 2012

Chilling stress--the key predisposing factor for causing Alternaria alternata infection and leading to cotton (Gossypium hirsutum L.) leaf senescence.

Leaf senescence plays a vital role in nutrient recycling and overall capacity to assimilate carbon dioxide. Cotton premature leaf senescence, often accompanied with unexpected short-term low temperature, has been occurring with an increasing frequency in many cotton-growing areas and causes serious reduction in yield and quality of cotton. The key factors for causing and promoting cotton premature leaf senescence are still unclear. In this case, the relationship between the pre-chilling stress and Alternaria alternata infection for causing cotton leaf senescence was investigated under precisely controlled laboratory conditions with four to five leaves stage cotton plants. The results showed short-term chilling stress could cause a certain degree of physiological impairment to cotton leaves, which could be recovered to normal levels in 2–4 days when the chilling stresses were removed. When these chilling stress injured leaves were further inoculated with A. alternata, the pronounced appearance and development of leaf spot disease, and eventually the pronounced symptoms of leaf senescence, occurred on these cotton leaves. The onset of cotton leaf senescence at this condition was also reflected in various physiological indexes such as irreversible increase in malondialdehyde (MDA) content and electrolyte leakage, irreversible decrease in soluble protein content and chlorophyll content, and irreversible damage in leaves' photosynthesis ability. The presented results demonstrated that chilling stress acted as the key predisposing factor for causing A. alternata infection and leading to cotton leaf senescence. It could be expected that the understanding of the key factors causing and promoting cotton leaf senescence would be helpful for taking appropriate management steps to prevent cotton premature leaf senescence.

Influence of nutrition on the development of leafspot disease of fluted Pumpkin (telfairia occidentalis Hook F) caused by Phoma Sorghina

Influence of nutrition on the development of leafspot disease of fluted Pumpkin (telfairia occidentalis Hook F) caused by Phoma Sorghina

Stereological analysis of celery leaves infected by Septoria apiicola

Changes caused by Septoria apiicola during the development of leaf spot disease in celery were quantified stereologically in susceptible cvs, a partially resistant parental wild celery line, fully resistant parsley and lovage. Thick sections, cut in vertical orientation, were stained and using a camera lucida, were superimposed on a lattice grid for stereological analysis. The volume of each component within the leaf space was calculated using the Cavalieri method. In healthy tissue volume fractions of intercellular space, palisade layers and, to a lesser extent, collenchyma, vascular tissue and oil ducts were greater in the more resistant genotypes. This coincided with a reduction in the volume fraction of mesophyll tissue. Estimates of absolute volume fraction were similar. In both resistant and susceptible celery the principal response to infection was a substantial decrease in the volume fractions and absolute volumes of palisade and mesophyll tissue. Volume fractions of mesophyll and palisade tissues declined by 97% in susceptible lesions and by 98% in resistant lesions. The fungus was not observed in xylem or phloem cells. No appreciable changes were observed in either collenchyma or oil duct tissues in response to infection in resistant and susceptible genotypes. Infection had no effect on the epidermis or stomata and these remained intact until late in the infection cycle, when pycnidia erupted through the epidermis of the upper and lower leaf surfaces. No hyphae were found in leaf sections of lovage or parsley, and fungal growth was severely restricted in all resistant material bred from wild celery. In wild celery lines, S. apiicola did not produce any, or produced very few, pycnidia and the volume fraction of vegetative hyphae was lower than that in susceptible cvs, where the fungus proliferated extensively within the lesions and many pycnidia were produced. This accounted for 30–50% of the fungal material in lesions on susceptible celery plants. The amount of fungus (21%) was less in lesions on resistant celery and in this material 96% of the fungus was present as vegetative hyphae. In lesions formed on susceptible celery 26% of the fungal tissue was reproductive and of that 11% was conidia whereas in resistant celery, where pycnidia were present, these structures were morphologically abnormal and did not contain conidia. Stereological analysis demonstrated clear differences in plant and pathogen response during infection of resistant and susceptible celery by S. apiicola.

Late Leaf Spot Progression on Peanut as Affected by Components of Partial Resistance

Components of partial resistance to late leaf spot (Cercosporidium personatum) and disease progression on 14 peanut genotypes were quantified in field experiments at Marianna, Florida, during 1988 and 1989. The resistance components measured were 1) incubation period, 2) latent period, 3) maximum percentage of lesions that sporulated, 4) lesion size, 5) lesion number, 7) degree of sporulation, and 7) percent necrotic area. Lower area under the disease progress curve (AUDPC) values, reduced apparent infection rates, and lower end-of-season disease levels were observed on genotypes UF81206-1, PI 261893, US29-b3-B, and US202-b2 compared to other genotypes in the study. Both apparent infection rate and AUDPC values were highly correlated with latent period (r = −0.68 to −0.79, P ≤ 0.01) and maximum percentage of lesions that sporulated (r = 0.72-0.81, P ≤ 0.01). Latent period and maximum percentage of lesions that sporulated were the components most highly correlated with late leaf spot disease development, and these two components were highly correlated with one another (r = -0.84). Using either of these two components to evaluate peanut genotypes for resistance to late leaf spot may facilitate more rapid selection of lines with improved levels of rate-reducing resistance

Sources ofCycloconium oleaginum (Cast.) conidia for infection of olive leaves and conditions determining leaf spot disease development in the region of S�tif, Algeria

In the region of Setif, peacock leaf spot disease caused byCycloconium oleaginum was found to be most prevalent in the period from late autumn to spring and of minor significance in the period from the beginning of July until the middle of November. Severity of infection on the lower parts was greater than on the upper parts of the trees. Damage on leaves facing north was much greater than on those facing south. Production of conidia leaf spots was found to be high in spring and late autumn but very low in summer and early autumn. Temperatures from 15 to 18°C were found optimal for the growth of the fungus. Reduced growth was seen at 3, 1 and 25°C with total inhibition at 30°C. Our results suggest that fallen leaves play no role in new infections and the role of the remaining spots on the tree during summer is of little importance. Four phases for the infection of new leaves were determined. In the first, during late spring, three newly opened pairs of leaves were infected, this infection remains hidden until late autumn. The second phase occurs in early autumn after rain. The third stage in late autumn and in the beginning of winter is characterized by the occurrence of new leaf spots which are usually concentrated on the basal pair of newly grown leaves. The fourth phase of infection, at the beginning of spring, is the most important of all. The infected leaves at this stage, comprise the infection source for all the following stages.