Target leaf spot of tomato incited by Corynespora cassiicola,an emerging disease in tomato production under Gangetic alluvial region of West Bengal,India

Abstract

Tomato (Lycopersicon esculentum Mill.) is a cosmopolitan vegetable and widely cultivated in almost all the countries of the world including India. Irreversible investment – production ratio for tomato cultivation in recent Indian agricultural systems arise the question, is there any biotic backlogs responsible for such a production loss. Our present investigation is based on this fact. Target leaf spot disease of tomato is caused by Corynespora cassiicola, a serious and emerging disease in India. Prolonged real time surveillance of this disease on tomato from 2010–11 to 2016–17, reflects some remarkable features of pathogenic progress in Gangetic alluvial region of West Bengal. This pathogen is the natural barrier for tomato production with a disease severity ranged between 35% and 58% which ultimately causes tremendous loss of tomato foliage and fruits. C. cassiicola was identified on the basis of morpho-cultural (ITCC Accession No. 7542) and molecular characterization (Genbank Accession No. KJ767193). Homology searching of internal transcribed spacer region of CcHaTom isolate was highly matched with Genbank Accession No. KP666184 (Cynodondactylon/India), AB873045 (Vitex negundo/India) and JN541214 (Malvaviscus concinnus/USA) with 95% similarity. Phylogenetic analysis established that KJ767193 and C. cassiicola retrieved sequences were conspecific from a common ancestral origin, which supports its neighbourhood with this fungal pathogen. Optimum temperature between 24 and 25?°C, coupled with 80–85% relative humidity triggered the disease progress. From the emerging scenario, C. cassiicola infecting tomato is the real threat for indigenous cultivars.     

First report of leaf spot disease caused by Phoma eupyrena Sacc. on Aloe vera from Madhya Pradesh,India

A leaf spot disease caused by Phoma eupyrena Sacc. on Aloe vera was reported from Madhya Pradesh, India. Disease symptoms were observed as irregular to elongated, sunken lesion on both leaf surfaces which later turns creamish brown with maroon margin. The fungal colonies were whitish or light pale to dark grey colour. The pycnidia were glabrous and solitary, papillate, and indistinctly uniostiolate averages 100–260 μm in diameter. Conidia were ellipsoidal, 4.5–7.5 × 2.5–3.75 μm in size, with two large guttules. To the best of our knowledge, this is the first report of P. eupyrena causing leaf spot disease on A. vera in India.     

Corynespora cassiicola leaf spot of pawpaw (Carica papaya L.) in Nigeria

Leaf spot of pawpaw is hereby reported for the first time in Nigeria. The symptom is characterized by a papery center surrounded by a yellow halo. The causal organism is Corynespora cassiicola. Ripe fruits and abaxial surfaces of the leaves were significantly more susceptible to infection than unripe fruits and adaxial surfaces of leaves. Growth and sporulation of the fungus on several media was investigated. The organism grew faster on malt-extract agar (MEA) derived media and slowest on potato-dextrose agar (PDA) supplemented with thiamine. Sporulation was highest on Czapek-dox agar (CDA) plus biotin and lowest on PDA and PDA + thiamine. Reasons for increased susceptibility of ripe fruit are discussed.This revised version was published online in October 2005 with corrections to the Cover Date.     

First report of Bipolaris bicolor causing a leaf spot disease on rubber tree

The rubber tree (Hevea brasiliensis) is the only resource for commercial natural rubber production and thus has economic importance in Southeast Asia. A spot disease on the leaves of a rubber tree was first discovered in 2017 in Hainan, China. In this study, the fungal isolate MA1 from the infected tissues was determined to be a pathogen of the spot disease by satisfying Koch's postulates. The isolate MA1 was identified as Bipolaris bicolor based on the morphological characteristics and multigene phylogenetic analysis. Among fungicides, prochloraz, iprodione and pyraclostrobin significantly inhibited hyphal growth of B. bicolor under in vitro conditions. This study constitutes the first report on the association of B. bicolor with leaf spot disease of rubber trees worldwide.     

Global status and future prospects of research in cotton leaf curl disease

Abstract

Begomoviruses are economically important plant viruses with a wide host range infecting numerous vegetables, legumes and fibre crops worldwide. Pakistan cotton suffered with cotton leaf curl disease (CLCuD) epidemic in the 1990s resulting in huge crop losses. Since then CLCuD has become a continuous threat to cotton industry in Pakistan. Several monopartite begomovirus species and satellite molecules are associated with CLCuD. There is threat of disease spreading to other parts of the world which are currently free from CLCuD due to agricultural trade and spread of vector, Bemisia tabaci. Natural resistance in tetraploid cotton, Gossypium hirsutum against CLCuD is very limited and is not durable under field conditions due to emergence of new viral strains. Genetically engineered resistance towards CLCuD has had limited success due to transformation limitations in cotton and the diversity of begomoviruses. Molecular approaches and conventional breeding are underway for developing cotton with CLCuD resistance. There is need to introgress multiple resistance genes in cotton to produce durable resistance which would lost several years. The review is an update on the current status and future prospects of CLCuD.     

First report of Phoma betae on Aloe vera in India

Leaf spot disease of A. vera was observed in nurseries of Gwalior city afterthe post-rainy season. As the disease progressed, the tip of the leaf shrank, then dried and eventually broke. The causal agent was identified as Phoma betae A.B. Frank. This is the first report of leaf spot disease on Aloe vera caused by P. betae in India.     

Screening of chilli germplasm for resistance to Alternaria leaf spot disease

Chilli is one of the spices used to enhance the flavour and taste of cooked food. Fungal diseases are the main biological constraints in chilli production, and Alternaria leaf spot disease caused by Alternaria alternata is one of the most devastating diseases of chilli. One of the effective and environmentally friendly ways to control this disease is introgress resistance from wild relative/varieties to the cultivated one. The first step towards introgression of resistance genes is to screen the chill germplasm for leaf spot resistance. In the current study, we screened the chilly germplasm and identified the sources of leaf spot resistance, which can be harnessed in resistance breeding programmes.     

Pathogenesis of mulberry leaf spot in response to meteorological aspects of Kashmir,India

In this study, the influence of climatic factors on the development of leaf spot diseases of mulberry (Morus alba L.) in Kashmir, India was studied. It was found that the highest disease incidence and severity of Goshoerami variety was found in tree type (13.86% and 1.98%) followed by dwarf (7.53% and 1.67%) and bush (3.38% and 0.99%), respectively. Due to infection of pathogen, the relative water content and chlorophyll content of leaves were consistently decreased. The order of reduction in relative water content of infected leaves was found as: bush?>?dwarf?>?tree, while as the reduction in chlorophyll content: bush?>?tree?>?dwarf. It was also found that temperature of 25–30?°C and relative humidity of above 80% favoured the development of the disease. Rapid development of disease was found during the month of June, July and August when average temperature and relative humidity was about 25–30°C and 80%, respectively.     

Evaluation of elite genotypes of mungbean against Cercospora leaf spot disease (CLS) caused by Cercospora canescens

The AUDPC is the best measurement of CLS disease of mungbean, since it is based on several readings of disease intensity from the early to the mature stage. Thirty-one genotypes of the mungbean crop showed similar disease reactions at later stages both under the polyhouse and field conditions. Under field conditions, 22 genotypes were found moderately resistant, seven susceptible and two genotypes were highly susceptible, and under polyhouse conditions eight genotypes showed resistance, 19 moderate resistance and four genotypes were found susceptible.     

Forecasting model of bacterial leaf spot disease of mulberry caused by Xanthomonas campestris pv. mori

In order to develop weather-based forecasting model of bacterial leaf spot (BLS) disease of mulberry caused by Xanthomonas campestris pv. mori, weekly disease severity data were recorded for three years on the ruling cultivar S-1. Daily meteorological data viz. maximum temperature, minimum temperature, maximum relative humidity, minimum relative humidity, rainfall and number of rainy days were also recorded. It was observed that BLS appeared in April/May and continued up to November with maximum severity in July. The correlation coefficient between disease severity and meteorological parameters revealed that the BLS disease severity has significant positive correlation with minimum temperatures, maximum and minimum relative humidity, rainfall and number of rainy days and negative correlation with maximum temperature. Multiple regressions analysis revealed that average of maximum temperature, minimum temperature and rainfall of preceding seven days and maximum relative humidity, minimum relative humidity of previous 9–15 days was found to maximally influence BLS disease severity. The contribution of the meteorological factors was found to be highest of minimum temperature (40.65%) followed by maximum temperature (24.20%), maximum relative humidity (16.41%), minimum relative humidity (8.07%), rainfall (5.29%) and number of rainy days (5.38%).     

Induction of resistance against Cercospora leaf spot in safflower by seed treatment with plant growth-promoting rhizobacteria

Out of seven isolates of rhizobacteria, four strains including GBO-3, INR937a, INR937b and IPC-11 were selected as inducers of systemic resistance against Cercospora carthami and tested individually for biological control of different important seed-borne fungal pathogens. The level of control achieved by each rhizobacterium varied with the pathosystem studied. The isolates GBO-3, INR937a, INR937b and IPC-11 exhibited reduced disease intensity in terms of average number of leaf lesions as compared to untreated control in protection experiments against C. carthami. Micromobilised with rhizobacterium GBO-3, INR937a, INR937b and IPC-11 safflower seeds were grown under greenhouse and challenge inoculated with C. carthami were selected for estimation of lipoxygenase, polyphenylalanine ammonia-lyase, peroxidase, polyphenol oxidase and β-1,3 glucanase activities were estimated spectrophotometrically. Increase in all enzymes was detected in foliar extracts from plants at different stages after challenge inoculation.     

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

In 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.     

Host range, vector relations and serological relationships of cotton leaf curl virus from southern India

In 1989 to 1991, leaf curl disease was observed in cotton (Gossypium bar-badense cv. Local) grown in kitchen gardens in five districts in Karnataka State, India, and in 1994 it was recorded in G. hirsutum cv. Sharada in two districts. Symptoms consist of leaf curling, vein thickening, leaf enations, and stunting and distortion of plants. The disease is caused by cotton leaf curl virus (CLCuV-K), which was transmitted by the whitefly Bemisia tabaci to 24 plant species in six families. Hosts include bean (Phaseolus vulgaris), pepper, tobacco, tomato and several weeds, almost all of which developed leaf curl, with or without vein thickening. CLCuV-K was transmitted from cotton to cotton by adult B. tabaci after an acquisition access period of 1 h, could be inoculated in 5 min, had a minimum latent period of 8 h and was retained by viruliferous insects for up to 9 days. Female B. tabaci transmitted more frequently than males. CLCuV-K is a whitefly-transmitted geminivirus. It reacted with two out of 17 monoclonal antibodies (MAbs) raised to African cassava mosaic virus and five out of 10 MAbs raised to Indian cassava mosaic virus. CLCuV-K isolates from different locations in Karnataka had similar epitope profiles. As judged by these profiles, CLCuV-K is closely related to Indian tomato leaf curl virus from Karnataka, is distinguishable from several other whitefly-transmitted geminiviruses found in India and is still more distantly related to those, including cotton leaf crumple virus from the USA, found in other continents. CLCuV-K infected all cultivars tested of G. barbadense and one of six cultivars of G. hirsutum but none of G. arboreum or G. herbaceum.     

Prediction of cotton leaf curl virus disease and its management through resistant germplasm and bio-products

Cotton leaf curl virus disease reduces the cotton yield significantly every year and is transmitted by Bemisia tabaci. The study was designed to evaluate 15 varieties/lines against the disease. Multiple regression analysis was performed based on a-biotic environmental variables (maximum air temperature, minimum air temperature, relative humidity and rainfall) to predict disease incidence and its vector (Bemisia tabaci). Two bio-products were evaluated against the whitefly population to control the disease. Out of 15 cotton varieties/lines, no one was found highly resistant against the disease. Five varieties/lines (BT BT-980, BT-457, KIRAN, BT-666 and SLH-BT-6) exhibited moderately resistant response. Maximum air temperature (34–35.5 °C), minimum temperature (25.75–26.25 °C), relative humidity (64.14–66%), rainfall (1–2 mm) and wind speed (5.50–5.75 Kmh^?1) favoured the disease development. Maximum whitefly population was favoured by maximum air temperature from 34–35.5 °C, 25.8–26.2 °C minimum air temperature, 64.14–66% relative humidity, 1–2 mm from rainfall and 5.50–5.75 Kmh^?1 wind speed. Datura stramonium was found more effective as compared to Aviara (Homoeopathic) but not from the positive control (Acetamiprid).     

Genetic basis of resistance to zonate leaf spot disease in forage sorghum

Summary Generation mean analysis was carried out for ten crosses between two resistant and two susceptible parents to find the genetic basic of resistance to zonate leaf spot disease in forage sorghum. In all crosses except one, at least one type of non-allelic interaction was present. Both additive and dominance gene effects were significant for most crosses. Duplicate type epistasis was present for the inheritance of this disease. Resistance to this disease revealed overdominance. Appropriate breeding plans were suggested to exploit the disease resistance.     

Efficacy of some plant extracts in the management of cercospora leaf spot of groundnut in the Sudan savanna of Nigeria

Field trials were conducted to evaluate the efficacy of neem seed, garlic clove, onion bulb, ginger rhizome and pawpaw leaf extracts applied as foliar spray in controlling cercospora leaf spot of groundnut in the Sudan savanna of Nigeria during the 2002 and 2003 cropping seasons. Ridomil was used as a positive check while the control was left untreated. Three spray regimes (once, twice and thrice) were evaluated. A strip plot design with three replications was used in setting up the experiments. Ex-Dakar, a cercospora leaf spot susceptible Spanish Valencia groundnut variety, was used as planting material. All the plant extracts reduced the incidence and severity of cercospora leaf spot in both seasons compared to the untreated crops. However, neem seed and garlic clove extracts significantly reduced the incidence and severity of the disease compared to the other plant extracts. Ridomil was more effective in controlling the disease than the plant extracts. Three sprays with the plant extracts gave better control of the disease than one or two sprays in the season. The highest seed yield of 3115 kg/ha and 3311 kg/ha in 2002 and 2003, respectively, were obtained with neem seed extract treatment while the lowest seed yield of 2134 kg/ha and 2334 kg/ha in 2002 and 2003, respectively, were recorded from the untreated crops. Also the highest seed yield of 3124 kg/ha and 3418 kg/ha in 2002 and 2003, respectively were obtained following three sprays compared to 2523 kg/ha and 2641 kg/ha for one spray in 2002 and 2003, respectively and 2840 kg/ha and 3085 kg/ha for two sprays in 2002 and 2003, respectively. The highest haulm yield of 4121 kg/ha and 4089 kg/ha in 2002 and 2003, respectively were also obtained following treatment with neem seed extract. The lowest haulm yield of 2951 kg/ha and 3045 kg/ha in 2002 and 2003 respectively, were recorded from the control. Three sprays gave higher haulm yield (4265 kg/ha and 4279 kg/ha in 2002 and 2003, respectively) than one and two sprays in the season. Neem seed extract could therefore be used to control cercospora leaf spot and to improve groundnut production in the Sudan savanna of Nigeria.     

First report of Alternaria leaf spot caused by Alternaria alternata (Fries.) Kiessler on Sonchus oleraceus L. and Convolvulus arvensis L. in Algeria

Alternaria leaf spot caused by Alternaria alternata (Fries.) Kiessler was found on sow thistle (Sonchus oleraceus L.) and field bindweed (Convolvulus arvensis L.) in the experimental station of ENSA (Ecole Nationale Supérieure d'Agronomie) in Algiers, Algeria, during the winter of 2016. Necrotic spots in the form of concentric circles were observed on the leaves of both weeds with disease incidence of approximately 70% and disease severity ranging from 50% to 70%. Fungi were isolated from the infected leaves and identified as A. alternata, based on morphological and molecular analyses (using genetic marker internal transcribed spacer, ITS of rDNA). Pathogenicity tests confirmed that A. alternata is the causing agent of leaf spot disease of sow thistle and field bindweed in accordance with the original symptoms. To the best of our knowledge, this is the first report of sow thistle and field bindweed naturally infected by A. alternata in Algeria.     

Post‐infectional dynamics of leaf spot disease in Withania somnifera

Withania somnifera is a high value medicinal plant, native to Indian sub‐continent, and is extensively used in traditional systems of medicine. It is highly prone to leaf spot disease caused by Alternaria alternata, that may affect the quality of crude herbal drugs. In the present study, the accumulation of ROS (reactive oxygen species) was detected histochemically within the infected host tissue, using H₂DCFDA (2′,7′‐difluorodihydrofluorescein diacetate) and DAB (3,3′‐diaminobenzidine) staining methods. This ROS accumulation was linked with the process of disease initiation. The microscopy studies were conducted to explore the site of pathogen invasion into the host tissue. Some changes related to tissue degeneration during the infection process have also been reported. The observed changes in the form of reducing sugar and phenolic content showed an enhancement during infestation. Carbon, nitrogen and sulphur exhibited a decreasing trend with the progression of disease. Both the net rate of photosynthesis (A) and stomatal conductance (g_S) showed a similar trend except that g_S increased at the early stage of infection when the protruding fungal hyphae obstructed the stomatal closure. Further, the disintegration of chloroplasts was also observed in the infected leaves. Overall, the present study highlights a few potential targets for enhancing the disease resistance against the leaf spot pathogen of W. somnifera.     

First report of Alternaria sp. PMK1: causative agent of leaf spot disease on parthenium weed

Congress grass, Parthenium hysterophorus L. (Asteraceae, tribe Heliantheae), is an erect and much branched annual or ephemeral herb, known as a pest for environmental, medical and agricultural reasons. Survey of fungal pathogens of P. hysterophorus was conducted in Kurukshetra and its adjoining areas, Haryana, India. A leaf spot pathogen Alternaria sp. PMK1 was isolated. Koch's postulates were performed and proved that this isolate was pathogenic to this weed. This is the first report of this pathogen causing leaf spot on parthenium weed.     

Antifungal potential of zinc against leaf spot disease in chili pepper caused by Alternaria alternata

The fungal pathogen, Alternaria alternata is responsible for causing leaf spot disease in many plants, including chili pepper. Zinc (Zn) an essential micronutrient for plant growth, also increases resistance in plants against diseases, and also acts as an antifungal agent. Here, in vitro effects of ZnSO₄ on the propagation of A. alternata were investigated, and also in vivo, the effect of foliar application of ZnSO₄ was investigated in chili pepper plants under disease stress. In vitro, ZnSO₄ inhibited fungal growth in a dose-dependent manner, with complete inhibition being observed at the concentration of 8.50 mM. Hyphae and conidial damage were observed along with abnormal activity of antioxidant enzymes, Fourier-transform infrared spectroscopy confirmed the major changes in the protein structure of the fungal biomass after Zn accumulation. In vivo, pathogen infection caused the highest leaf spot disease incidence, and cumulative disease index, which resulted in a significant reduction in the plant’s growth (length and biomass), and physiochemical traits (photosynthetic pigment, activity of catalase, peroxidase, polyphenol oxidase, and phenylalanine ammonia lyase). The heat map and principal component analysis based on disease, growth and, physico-chemical variables generated useful information regarding the best treatment useful for disease management. Foliar Zn (0.036 mM) acted as a resistance inducer in chili pepper plants that improved activities of antioxidants (CAT and POX), and defense compounds (PPO and PAL), while managing 77% of disease. The study indicated foliar ZnSO₄ as an effective and sustainable agriculture practice to manage Alternaria leaf spot disease in chili pepper plants.