Leaf Spot Of Cotton Research Articles

Survey, cultural and morphological studies of Alternaria leaf spot of cotton incited by Alternaria alternata

Survey, cultural and morphological studies of Alternaria leaf spot of cotton incited by Alternaria alternata

First Report of Stemphylium solani Associated with Leaf Spot of Cotton in New South Wales, Australia

Leaf spot of cotton caused by Alternaria species has been long considered a minor disease in Australia, especially when only highly resistant upland cotton ( Gossypium hirsutum) has been grown in commercial fields lately. However, leaf spot outbreaks were reported when crops were grown under favorable conditions for development of the disease. In this study, we, for the first time, fully characterized the association of Stemphylium solani with leaf spot of cotton in New South Wales, Australia. A total of 32 isolates were recovered from leaf-spot-diseased leaves collected in the 2021/22 growing season. Leaf spot symptoms often occur in small circular to irregular necrotic lesions, often surrounded by a purple halo, and are indistinguishable from those caused by Alternaria species. Sequences of the ITS, GAPDH, and calmodulin genes of the three representative isolates revealed 99.86 to 100% sequence identity to the type isolate of S. solani CBS 116586. In a neighbor-joining analysis of the concatenated sequences of the ITS, GAPDH, and calmodulin loci, the three cotton isolates were well clustered within the S. solani, with a bootstrap support of 100%, thus confirming the identification. On two true-leaf cotton seedlings, the three S. solani isolates were able to incite spot symptoms that were similar to those observed in the field. The same fungal pathogen was recovered from inoculated diseased leaves, thus confirming Koch's postulates.

Novel modified kernel fuzzy c-means algorithm used for cotton leaf spot detection

Image segmentation is a significant and difficult subject that is a prerequisite for both basic image analysis and sophisticated picture interpretation. In image analysis, picture segmentation is crucial. Several different applications, including those related to medicine, facial identification, Cotton disease diagnosis, and map object detection, benefit from image segmentation. In order to segment images, the clustering approach is used. The two types of clustering algorithms are Crisp and Fuzzy. Crisp clustering is superior to fuzzy clustering. Fuzzy clustering uses the well-known FCM approach to enhance the results of picture segmentation. KFCM technique for image segmentation can be utilized to overcome FCM’s shortcomings in noisy and nonlinear separable images. In the KFCM approach, the Gaussian kernel function transforms high-dimensional, nonlinearly separable data into linearly separable data before applying FCM to the data. KFCM is enhancing noisy picture segmentation results. KFCM increases the accuracy rate but ignores neighboring pixels. The Modified Kernel Fuzzy C-Means approach is employed to get over this problem. The NMKFCM approach enhances picture segmentation results by including neighboring pixel information into the objective function. This suggested technique is used to find “blackarm” spots on cotton leaves. A fungal leaf disease called “blackarm” leaf spot results in brown leaves with purple borders. The bacterium can harm cotton plants, causing angular leaf blotches that range in color from red to brown.

Few-shot cotton leaf spots disease classification based on metric learning

BackgroundCotton diceases seriously affect the yield and quality of cotton. The type of pest or disease suffered by cotton can be determined by the disease spots on the cotton leaves. This paper presents a few-shot learning framework that can be used for cotton leaf disease spot classification task. This can be used in preventing and controlling cotton diseases timely. First, disease spots on cotton leaf’s disease images are segmented by different methods, compared by using support vector machine (SVM) method and threshold segmentation, and discussed the suitable one. Then, with segmented disease spot images as input, a disease spot dataset is established, and the cotton leaf disease spots were classified using a classical convolutional neural network classifier, the structure and framework of convolutional neural network had been designed. At last, the features of two different images are extracted by a parallel two-way convolutional neural network with weight sharing. Then, the network uses a loss function to learn the metric space, in which similar leaf samples are close to each other and different leaf samples are far away from each other. In summary, this work can be regarded as a significang reference and the benchmark comparison for the follow-up studies of few-shot learning tasks in the agricultural field.ResultsTo achieve the classification of cotton leaf spots by small sample learning, a metric-based learning method was developed to extract cotton leaf spot features and classify the sick leaves. The threshold segmentation and SVM were compared in the extracting of leaf spot. The results showed that both of these two method can extract the leaf spot in a good performance, SVM expented more time, but the leaf spot which extracted from SVM was much more suitable for classifying, thus SVM method can retain much more information of leaf spot, such as color, shape, textures, ect, which can help classficating the leaf spot. In the process of leaf spot classification, the two-way parallel convolutional neural network was established for building the leaf spot feature extractor, and feature classifier is constructed. After establishing the metric space, KNN was used as the spot classifier, and for the construction of convolutional neural networks, commonly used models were selected for comparison, and a spatial structure optimizer (SSO) is introduced for local optimization of the model, include Vgg, DesenNet, and ResNet. Experimentally, it is demonstrated that the classification accuracy of DenseNet is the highest, compared to the other two networks, and the classification accuracy of S-DenseNet is 7.7% higher then DenseNet on average for different number of steps.ConclusionsAs the step increasing, the accuracy of DesenNet, and ResNet are all improved, and after using SSO, each of these neural networks can achieved better performance. But The extent of increase varies, DesenNet with SSO had been improved the most obviously.

Colony, morphological and biochemical characteristics of cotton phyllosphere bacteria and its antagonistic activity against the Alternaria leaf spot of cotton

Cotton crop is known to suffer from number of fungal, bacterial and viral diseases. Among them, Alternaria leaf spot caused by Alternaria spp. is predominant in causing economic losses to the cotton crop in the country. Phyllosphere inhabitants termed as epiphytes may consists of a variety of bacteria and filamentous fungi. They also play a key role in carbon and nitrogen cycling and help in important environmental processes such as methanol degradation and nitrification. So, bacterial phyllosphere cultures (P1 to P8) were isolated from the Bt and non Bt cotton by leaf imprint method and dilution method. The colony characters of isolates of bacteria pertaining to their shape, size, elevation, margin, texture, appearance and pigmentation were recorded. Gram’s staining and endospore staining revealed that P1, P2, P3, P5, P8 were Gram positive, P1, P2, P5 were showing endospore staining and P1, P4, P6, P7 were rod shaped. Biochemical tests revealed that the eight isolates Bt and non Bt cotton were differed in each test and showed positive for the catalase and oxidase test. The isolates P1, P5 and P6 showed positive results to Voges proskauer test. Isolates P2, P4 and P6 revealed positive results of phyllosphere bacteria to Indole test. Whereas, isolates P1, P2 and P8 showed negative reaction to methyl red test. The phyllosphere bacterial isolates P3, P5 and P7 recorded negative reaction to gelatin liquefaction. Screening of phyllosphere microflora against Alternaria macrospora was conducted following dual culture technique for all the isolates. Phyllosphere bacterial isolate P5 recorded maximum growth inhibition with 57.41 per cent followed by P4 isolate with 53.52 per cent growth inhibition over the test fungus Alternaria macrospora. Whereas least per cent growth inhibition was reported in isolate P6 with 45.63 per cent.

In vitro evaluation of fungicides against Alternaria leaf spot of cotton

Cotton (Gossypium hirsutum L.) is the one of the most important commercial crops of the world, which belongs to the family Malvaceae. India is the largest cotton growing country in the world with an area of around 12.35 M ha followed by United States and China with production of 36.1 M bales and productivity of 524 kg lint/ha. Cotton crop is known to suffer from number of fungal, bacterial and viral diseases. Cotton is under constant threat of foliar diseases viz., grey mildew, Alternaria leaf spot, Myrothecium leaf spot, bacterial leaf blight, rust etc. Among them, Alternaria leaf spot caused by Alternaria spp. is predominant in causing economic losses to the cotton crop in the country. Evaluation of systemic, non-systemic and combined fungicides under in vitro conditions revealed that the among eight fungicides evaluated against Alternaria macrospora (N2A isolate), Propiconazole, Hexaconazole and Tebuconazole @ 500 and 1000 ppm recorded maximum inhibition with 100 per cent inhibition and no radial growth of mycelium was observed. Pyraclostrobin and Azoxystrobin @1000 ppm showed 91.0 and 87.2 per cent inhibition respectively. Carbendazim+Mancozeb (SAAF) @ 1500 ppm and 2000 ppm showed 96.1 and 96.9 per cent inhibition respectively.

First Report of Corynespora Leaf Spot of Cotton Caused by Corynespora cassiicola in Central India

First Report of Corynespora Leaf Spot of Cotton Caused by <i>Corynespora cassiicola</i> in Central India

Etiology of Alternaria Leaf Spot of Cotton in Southern New Mexico.

Alternaria leaf spot (caused by Alternaria spp.) is one of the most common foliar diseases of cotton (Gossypium spp.) and occurs in most cotton-growing regions of the world. In surveys of commercial cotton fields, Alternaria leaf spot has increased in prevalence and incidence in southern New Mexico due to favorable environmental conditions in recent years. Incidence, severity, and etiology of leaf spot of cotton in southern New Mexico were determined. Fourteen cotton fields with plants exhibiting leaf spot symptoms were evaluated in October and November 2016, when plants were at late growth stage. Disease incidence was 100% in 13 of the fields, and averaged 70% in the 14th field. Average disease severity index for all fields ranged from 21.5 to 87.0. For identification of the causal agent, 14 isolates (one from each field) were characterized based on morphological features and PCR using universal primers ITS4/ITS5 and primers targeting the plasma membrane ATPase gene. Colonies of all 14 isolates were olive green with distinct white margins and relatively small spores when compared with reference isolates of large-spored species. All 14 isolates were identified as A. alternata. The fungus grew on potato dextrose agar from 5 to 35°C, and optimum growth occurred at temperatures between 20 and 30°C. Cotton plants inoculated with selected isolates of A. alternata displayed symptoms similar to those observed under field conditions. This is the first report of A. alternata as a causal agent of Alternaria leaf spot on cotton in southern New Mexico.

Alternaria leaf spot of cotton seedlings grown in New South Wales, Australia is predominantly associated with Alternaria alternata

Alternaria leaf spot (ALS) of cotton, especially on cotyledons is generally considered a minor disease in Australia. However, severe disease outbreaks were recorded in multiple cotton crops in southern New South Wales (NSW) in the 2017/18 season. Due to ALS being considered a minor disease, causal species have not been formally characterised in Australia. In this study, putative small-spored Alternaria alternata was predominantly recovered from diseased cotyledons sampled from ALS hot spot fields in southern NSW as well as other locations across NSW. Species status of recovered isolates as A. alternata was confirmed through morphology and sequence analyses of the internal transcribed spacer (ITS) and translation elongation factor 1-alpha (TEF1) regions. Phylogenetic analyses of the two regions both individually or in combination resulted in a well-supported group of 69 isolates (83%) clustering with the ex-type specimen of A. alternata CBS 916.96, thus confirming the preliminary morphological identifications. In artificially inoculated assays on 15-day-old cotton seedlings, a subset of selected A. alternata isolates produced similar ALS symptoms at 7 days after inoculation (DAI) as seen in the field. Koch’s postulate was fulfilled by re-isolating A. alternata from infected ALS cotyledons at 21 DAI. This is the first main stream published report of A. alternata causing ALS on cotton cotyledons in NSW, Australia.

Inhibition of Amphiphilic N-Alkyl-O-carboxymethyl Chitosan Derivatives on Alternaria macrospora.

Cotton leaf spot (Alternaria macrospora) is a widespread disease that occurs in the main cotton-producing area of China. In managing this disease, a novel chitosan-based biopesticide, an amphiphilic N-alkyl-O-carboxymethyl chitosan derivative, was prepared. The product was selected from variations of chitosan with different molecular structures, which were obtained via a two-step reaction. First, carboxymethyl chitosans with varying molecular sizes were obtained by etherification with chloroacetic acid; then the carboxymethyl chitosan was alkylated with C4–C12 fatty aldehyde through a Schiff-base reaction. This procedure resulted in derivatives of amphiphilic N-alkyl-O-carboxymethyl chitosan, which showed strong antifungal activities against A. macrospora, and the efficacy was determined by its molecular structure.

Effect of Some Environmental Factors on Incidence and Severity of Angular Leaf Spot of Cotton in Yola and Mubi, Adamawa State, Nigeria

Environmental factors such as relative humidity and rainfall generally have been found to increase the incidence, rate of spread and severity of diseases thereby reducing yield of crops. Study was conducted on five cotton varieties, which were artificially inoculated with bacterial blight pathogen to determine the effects of rainfall and relative humidity on incidence and severity of angular leaf spot (ALS) and yield of seed cotton in Yola and Mubi. Results showed that the severity of ALS was higher in Yola (58.65%) at 13 WAS assumed to be due to higher relative humidity range of 76% - 87% and low rainfall of 2 - 40.6 mm. This is assumed to have favoured disease development as against that of Mubi location which recorded lower severity (51.11%) due to lower relative humidity (42% - 55%) and rainfall (37 - 73 mm). Results further revealed that at 13 WAS, SAMCOT-8 had low incidence (66%) and severity (39%) in Yola. This was against the much higher corresponding incidence and severity of 82% and 42% respectively that was observed in Mubi during the same period. SAMCOT-10 and SAMCOT-9 varieties were found to be highly susceptible to the disease at the same period. SAMCOT-8 recorded the highest yield of 390.00 kg?ha?1 in Yola and 868.09 kg?ha?1 in Mubi while the lowest yields of 227.17 kg?ha?1 was observed on SAMCOT-10 in Yola while 461.61 kg?ha?1 was obtained on SAMCOT-9 in Mubi. The variation in yield among these varieties might be due to the differences in their reactions to the disease. There is a need to conduct further trials in these locations to confirm the level of resistance or other aspects of these varieties to the disease.

First Report of Nigrospora oryzae Causing Leaf Spot of Cotton in China.

Cotton (Gossypium hirsutum L.) is widely cultivated for the important economic value of the fiber. In the summer of 2011, a leaf spot of cotton plants cv. Wanza40 was observed in 11 fields (total of about 4 ha) in Qianshan County in southwest Anhui Province, China. Approximately 30% of the plants in each field were symptomatic. Affected plants exhibited brown to reddish, irregular foliar lesions, each with a brown border near the vein of the leaves. A sign of fungal infection was a dark leaf mold observed on lesions on the abaxial surface of leaves. Sections of symptomatic leaf tissues were surface-sterilized (in 75% ethanol for 30 s, then 1% NaOCl for 1 min), rinsed three times in sterile distilled water, and plated onto potato dextrose agar (PDA). A fungus consistently recovered from symptomatic leaf samples produced colonies that were initially white and then became grayish brown with the onset of sporulation. Black, spherical to subspherical, single-celled conidia (10 to 12 × 14 to 16 μm) were borne on a hyaline vesicle at the tip of each conidiophore. Morphological characteristics of the fungus were similar to that of Nigrospora oryzae (2). The internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) from a representative strain of the fungus, AHC-1, was amplified using the primers ITS1/ITS4 (4) and sequenced (GenBank Accession No. JQ864579). The ITS sequence had 99% identity with >553 bp of the ITS sequence of an N. oryzae isolate (GenBank Accession No. EU918714.1). On the basis of morphological data and ITS rDNA sequence, the isolate was determined to be N. oryzae. A pathogenicity test was performed on detached, young leaves of 4-month-old healthy cotton plants of cv. Wanza40. Six leaves were inoculated by placing a colonized agar piece (5 mm in diameter) from 7-day-old cultures of the fungus on pushpin-wounded leaves. Another six leaves treated with sterile PDA plugs served as a negative control treatment. Leaves were incubated in petri dishes and maintained at 25°C in a growth chamber programmed for 12 hours of fluorescent white light/day. After 5 days, brown to black lesions were observed on all inoculated leaves, whereas no symptoms developed on control leaves. N. oryzae was consistently reisolated from symptomatic leaves but not from the control leaves. N. oryzae is a weak pathogen on a wide range of plants, and has been described as the causal agent of lint rot on cotton (1,3), but to our knowledge this is the first report of N. oryzae causing a leaf spot of cotton in China.

First Report of Target Spot Caused by Corynespora cassiicola on Cotton in Georgia

In 2005, crop consultants in southwestern Georgia reported an unusual occurrence of leaf spot in cotton (Gossypium hirsutum L.). Initial symptoms first developed as brick red dots that led to the formation of irregular to circular lesions with tan-to-light brown centers. Lesions further enlarged and often demonstrated a targetlike appearance formed from concentric rings within the spot. Observations included estimates of premature defoliation up to 70%, abundant characteristic spots on the leaves and bracts, and losses of several hundred kg of lint/ha. When symptomatic leaves were submitted to the University of Georgia Tifton Plant Disease Clinic in Tifton, GA, for identification in 2008, the causal agent was tentatively diagnosed as Corynespora cassiicola (Berk. & M.A. Curtis) C.T. Wei on the basis of similar symptoms and signs previously reported on cotton (3). In September 2011, symptomatic leaves were obtained from diseased cotton within a field (var. DP 1048B2RF) near Attapulgus, GA. Symptomatic tissue from diseased leaves was surface disinfested in 0.5% sodium hypochlorite for 1 min and plated on potato dextrose agar (PDA). Ten isolates were incubated at 21.1°C for 2 weeks with a 12/12 h light/dark cycle using fluorescent light located approximately 70 cm above the cultures. After 1 week, two isolates were transferred to quarter strength PDA for enhanced sporulation and were grown under the same conditions. Conidiophores from the isolated fungus were simple, erect, intermittently branching and septate, and gave rise to single, subhyaline conidia. Conidia had 4 to 17 pseudosepta and were 50 to 197 μm long and 7 to 16 μm wide, straight to curved, and obclavate to cylindrical. Pathogenicity tests were conducted by spraying 10 cotton seedlings (DP 555BR and DP 1048B2RF, two to four true leaf stage) until runoff with a blended suspension from a 2-week-old pure culture of the fungus diluted with 100 mL of sterile water. Five plants were sprayed with sterile water as noninoculated controls. Cotton seedlings were then incubated in a moist chamber at 21.1°C for 48 h. Within 1 week, all inoculated plants showed symptoms similar to those of diseased field plants. Symptoms were not observed on noninoculated control plants. The fungus was reisolated five times from symptomatic leaves and grown in pure culture. Conidia and conidiophores were identical to the morphology of the original isolates, and were similar to descriptions of C. cassiicola (2). To confirm the identity of the pathogen, DNA was extracted from a week-old culture and amplified with specific primers for loci "ga4" and "rDNA ITS" (1). DNA sequences obtained with the Applied Biosystems 3730xl 96-capillary DNA Analyzer showed 99% identity to C. cassiicola from BLAST analysis in GenBank. The resulting sequence was deposited into GenBank (Accession No. JQ717069). To our knowledge, this is the first report of this pathogen in Georgia. Given the increasing prevalence of this disease in southwestern Georgia, its confirmation is a significant step toward management recommendations for growers. Because foliar diseases caused by C. cassiicola are commonly referred to as "target spot" in other crops (e.g., soybeans), it is proposed that Corynespora leaf spot of cotton be known as "target spot of cotton."

Homogenous Segmentation based Edge Detection Techniques for Proficient Identification of the Cotton Leaf Spot Diseases

In this work we express technological strategies using mobile captured symptoms of cotton leaf spot images and classify the diseases using neural network. The system has been trained to achieve intelligent farming for rural area farmers, including early recognition of diseases in grows, selective fungicide application,etc..This research work proposes an automatic image preprocessing techniques. At first, the captured images are processed for improvement. Other edge detectors presented in earlier works can detect edges on different size objects. In this Research work, a homogeneity operator can take the difference of the center pixel and a pixel that is two or three pixels away. The major objective of this Research work is to use Homogeneity-based edge detector segmentation, which takes the result of any edge detector and divides it by the average value of the area. This work has been implemented in the real time software and produces best results.

Alkaloids isolated from leaves of Prosopis juliflora against Xanthomonas pathovars

Aqueous extract, different solvent extracts and isolated constituents of leaves of Prosopis juliflora (Sw.) DC. (Fabaceae) were assayed for antibacterial activity by cup diffusion method against three phytopathogenic Xanthomonas pathovars viz., Xanthomonas axonopodis pv. malvacearum, X. a. pv. phaseoli and X. campestris pv. vesicatoria associated with angular leaf spot of cotton, common blight of bean and bacterial spot of tomato respectively and 14 human pathogenic bacteria. Aqueous, methanol and ethanol extracts showed significant antibacterial activity against all pathovars of Xanthomonas and the activity varied among 14 human pathogenic bacteria. Methanol extract was subsequently fractioned and monitored by bioassay leading to the isolation of active fraction and confirmed as alkaloids by further phytochemical analysis. The active fraction recorded highly significant antibacterial activity in vitro (MIC 6, 5 and 4 µg/ml for Xanthomonas pathovars and 3 and 5 µg/ml against Staph. aureus and Strep. faecalis) compared with synthetic antibiotics such as Bact-805 and K-cycline tested at the recommended dosage for phytopathogenic bacteria and Gentamycin and Streptomycin discs for human pathogenic bacteria.

Mecanismo genético de resistência em três cultivares de algodoeiro a Xanthomonas axonopodis pv. malvacearum

A mancha angular do algodoeiro (Gossypium hirsutum) causada por Xanthomonas axonopodis pv. malvacearum (Xam) é uma doença de importância econômica para o Brasil, e sua severidade depende de fatores climáticos e da cultivar. A doença não é controlada por produtos químicos sendo que seu controle depende da utilização de sementes sadias, e resistência varietal. DeltaOPAL, EPAMIG Liça, e Fibermax 986 são importantes fontes de resistência a Xam, pois além de resistência, apresentam boas características agronômicas. O objetivo do presente trabalho foi estudar o mecanismo de resistência à mancha angular envolvendo cruzamentos entre as três cultivares resistentes e a suscetível BRS Ita 90, em casa de vegetação. Populações parentais, F1 e F2 foram avaliadas após inoculação com um isolado agressivo de Xam. As três cultivares apresentaram mecanismos diferentes de resistência. Nas cultivares DeltaOPAL e EPAMIG Liça a resistência é conferida por um gene dominante, enquanto que em Fibermax 986, a resistência é dada por dois genes dominantes, independentes e complementares.

Leaf Spot of Cotton Rose Caused by Corynespora cassiicola in Korea

A leaf spot of cotton rose (Hibiscus mutabilis) occurred severely in the flower beds of cotton rose around Uiryeong-gun, Gyeongnam Province in Korea. The causal fungus was identified as Corynespora cassiicola on the basis of cultural and morphological characteristics of the fungus. The fungus grew well on potato dextrose agar and the colony color was gray to brown. Conidia were solitary or catenate, obclavate to cylindrical in shape, and pale olivaceous brown or brown in color. They had 420 pseudosepta, and measured 35.2~173.6 × 8.8~19.9 μm. Conidia germinated as a bipolar type. Conidiophores were pale to mid brown in color, and measured 74.2~275.6 × 3.8~10.8 μm. Optimal temperature for mycelial growth was 30°C. The fungal isolate grown on PDA showed strong pathogenicity to cotton rose plant. This is the first report on the corynespora leaf spot of cotton rose (Hibiscus mutabilis) caused by Corynespora cassiicola in Korea.

Symptomless infections in alternaria leaf blight of cotton

A symptomless phase of Alternaria macrospora leaf blight that occurs in commercial cultivation of cotton between visible disease outbreaks was studied to determine its cause and effect. Most plants between the two outbreaks of leaf blight epidemics in the field were infected but symptomless; yet during the outbreaks the number of infected symptomless plants was minimal. Drought, high temperature, low humidity, and high salinity increased plant resistance to leaf blight by decreasing visible symptoms and causing symptomless infections. Symptomless plants provided inoculum to infect and produce a visible disease in healthy plants when favorable conditions for disease development resumed. Plant age had minimal influence on symptom-lessness, and sunlight exposure had none. Defoliation was related to the density of spots on leaves and to the virulence of the strain. Polyphenoloxidase activity and phenol accumulation were similar in both disease phases. Plants having visible symptoms produced more spores, but spores from symptomless plants were detached more easily by air currents. Symptom-lessness apparently is a common manifestation of alternaria leaf blight of cotton. It is probably influenced by agroenvironmental parameters that induce the two phases of disease expression. Key words: Alternaria macrospora, cotton leaf blight, leaf spot of cotton, symptomless infections.

Symptom expression and ethylene production in leaf blight of cotton caused by Alternaria macrospora and Alternaria alternata alone and in combination

The interaction between the cotton leaf pathogens Alternaria macrospora and Alternaria alternata was studied using dual inoculation at dosages (≈ 103 spores/(mL ∙ pathogen)) that did not produce symptoms with either pathogen alone. This dual inoculation produced the typical disease symptoms (spots and shedding) and disease severity similar to inoculation with 104 spores/mL of A. macrospora alone. Neither pathogen produced ethylene in culture; however, they induced production of ethylene concentrations by diseased tissue that were correlated to both disease severity and leaf shedding. Plants infected by both pathogens produced the highest concentration of ethylene. Leaf discs either from leaves exhibiting symptoms or from symptomless infected leaves produced similarly high concentrations of ethylene. Inoculation of any site of the leaf with A. macrospora alone or with both pathogens resulted in shedding of the leaf. Pretreating inoculated plants with several ethylene inhibitors or an auxin decreased ethylene production, disease severity, and leaf shedding. Alternaria alternata apparently triggers symptom expression by A. macrospora in leaf blight disease of Pima cotton, and disease is manifested by the production of ethylene that leads to the typical leaf shedding symptom. Key words: Alternaria macrospora, Alternaria alternata, cotton leaf blight, defoliation, ethylene, fungus – fungus interaction, leaf spot of cotton, symptomless infections, virulence.

Effects of Foliar Diseases on Gas Exchange Processes: A Comparative Study

The effects of 10 different foliar diseases on the photosynthetic and transpirational activities of five annual and three perennial crops were examined under field conditions. The following pathosystems were investigated: leaf rust, powdery mildew, and Septoria tritici blotch of wheat; rust of corn; downy mildew of cucumber; Alternaria leaf spot of cotton; powdery mildew of pepper; Pestalotia of mango; powdery mildew of peach; and powdery mildew of grapes. Visual estimates of infection do not always indicate adequately the effect of a pathogen on these physiological processes (...)