Foliar Disease Incidence Research Articles

Colletotrichum aeschynomenes Causing Anthracnose in Combretum indicum in Guangxi, China.

Combretum indicum（L.）Jongkind, distributed in Southeast Asia, is widely planted in southern China for its ornamental and medicinal value. In February 2023, anthracnose symptoms were observed on C. indicum leaves in Nanning Garden Expo (N22°43', E108°28'), Guangxi, China, causing severe defoliation of infected plants with a foliar disease incidence ranging from 40 to 60% (n = 100) in a 2 ha field. Disease symptoms began with small red spots (2 to 3 mm by 2 to 3 mm) on the leaves and gradually enlarged to larger irregular light grey lesions with yellowish halos (3 to 5 mm by 2 to 8 mm). In the late stage, spots merged into larger irregular lesions (5 to 15 mm by 6 to 13 mm) and the necrotic lesions abscised. Three diseased samples in total were collected from plants in three different locations. Symptomatic leaves were cut into small pieces (3×3 mm), disinfected with 75% ethanol solution for 10 s, 2% NaClO for 1 min followed by three washes in sterile distilled water. Tissue pieces were separately plated on potato dextrose agar (PDA) and incubated at 25°C for five days. One representative isolate from each sample (SJ-1, SJ2-1 and SJ3-1) were chosen for further analysis. Colonies were villiform, initially white, later turning gray in 7 days on PDA at 25℃. The average diameter for colonies were 8.1 cm, 8.0 cm and 8.1 cm for SJ1-1, SJ2-1 and SJ3-1, respectively. Conidia were aseptate, hyaline, cylindroid, and averaged 11.94 μm × 5.04 μm, 11.78 μm × 5.14 μm and 11.74 μm × 4.59 μm (n=90) for SJ1-1, SJ2-1 and SJ3-1, respectively. The characteristics were close to the descriptions of Colletotrichum spp. (Weir et al. 2012). Genomic DNA was extracted from 7-day-old aerial mycelia of these isolates. The internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), β-tubulin (TUB2), chitin synthase (CHS-1), calmodulin (CAL) and the intergenic region between apn2 and MAT1-2-1 (ApMat) were amplified using primers ITS1/ITS4 (White et al. 1990), GDF/GDR, ACT-512F/ACT-783R, T1/Bt2b, CHS-79F/CHS-354R, CL1C/CL2C (Weir et al. 2012) and AM-F/AM-R (Silva et al. 2012), respectively. Sequences were deposited in GenBank (ITS: OR540240-OR540242; GAPDH: PP328968-PP328970; ACT: PP328959-PP328961; TUB2: PP328971-PP328973; CHS-1: PP328965-PP328967; CAL: PP328962-PP328964 and ApMat: OR548253-OR548255). A phylogenetic analysis was made via Bayesian inference based on the concatenated sequences (ITS, GAPDH, ACT, TUB2, CHS-1, CAL and ApMat). According to morphology and phylogenetic analysis, SJ1-1, SJ2-1 and SJ3-1 were identified as C. aeschynomenes. Pathogenicity was confirmed on leaves with and without wounds of 24 one-year-old C. indicum plants in a greenhouse in Nanning, Guangxi Province. The wound was made with a sterilized needle. Wounded and unwounded leaves were inoculated with 20 μl of conidial suspension (106 spores/ml in 0.1% sterile Tween 20) of the three isolates and control plants were inoculated with water containing 0.1% sterile Tween 20 (6 leaves/plant, 3 plants/treatment). All plants were covered with plastic bags to maintain a high humidity environment and placed in a 28°C growth chamber with constant light. After 7 days of incubation, necrotic lesions were observed on inoculated wounded leaves, whereas unwounded leaves and control plants showed no symptoms. The fungi were re-isolated from symptomatic leaves, completing Koch's postulates. These species can cause severe diseases in a variety of plants worldwide, such as Manihot esculenta, Theobroma cacao and Myrciaria dubia (Sangpueak et al. 2018; Nascimento et al. 2019; Matos et al. 2020). To our knowledge, this is the first report of C. aeschynomenes causing C. indicum leaf anthracnose in China. The results will provide valuable information for management of anthracnose in C. indicum.

Performance of turmeric genotypes for growth, yield and foliar disease incidence under Terai region of West Bengal

Performance of turmeric genotypes for growth, yield and foliar disease incidence under Terai region of West Bengal

Impact of Soil-Applied Thyme Oil on Strawberry Yield and Disease Abundance

ABSTRACT Strawberry growers across the United States are looking for sustainable alternatives to conventional pesticides for management of soil-borne or crown-rot causing pathogens, such as plant-extracts like thyme oil. The objectives of this study were to determine the impact of soil-applied thyme oil fungicides on strawberry plant health, yield, sweetness, and foliar disease, and on the assemblage of soil microbial communities in strawberry plasticulture systems. In 2021 and 2022 the interaction of three soil-applied fungicides and three foliar fungicide programs were explored. Thyme oil was not found to improve strawberry plant growth or yield when compared to strawberries in the control. However, plants treated with mefenoxam exhibited an average winter crown weight of 2.11 g, significantly lower than control and thyme oil treatments at 3.14 g and 3.16 g, respectively. This translated into a significant yield loss where mefenoxam treated plants exhibited lowered yields at 416.04 g of fruit per plant compared to 523.57 g and 521.53 g per plant in the control and thyme oil treatments, respectively. A high incidence of foliar and fruit diseases was present; however, no interaction of soil and foliar fungicide treatments were observed for yield or fruit sweetness. Minimal root protection from pathogens was observed for all treatments and Fusarium, Pythium and Phytophthora fungi were regularly observed. Mefenoxam was observed to increase the recovery of oomycetes, which may cause Pythium and Phytophthora. No benefit from thyme oil was observed at our site and its addition as a soil fungicide would likely not benefit most growers.

Foliar disease incidence in a tropical seedling community is density dependent and varies along a regional precipitation gradient

Abstract Many studies identify fungal and oomycete phytopathogens as natural enemies capable of influencing plant species composition and promoting diversity in plant communities. However, little is known about how plant‐pathogen interactions vary along regional abiotic gradients or with tree species characteristics, which limits our understanding of the causes of variation in tree species richness. We surveyed 10,756 seedlings from 272 tree species for disease symptoms along a mean annual precipitation gradient in the tropical wet forests of Central Panama for 3 months in the early wet season (June–August) and 2 months in the following dry season (March–April). Over 99% of observed disease symptoms were caused by necrotrophic foliar pathogens, while less than 1% of symptoms were attributed to soilborne pathogens. Foliar disease incidence was inversely related to mean annual precipitation, a pattern which may be due to greater disease susceptibility among dry forest species. Foliar disease incidence increased with conspecific seedling density but did not respond to the proximity of conspecific adults. Although foliar disease incidence decreased as mean annual precipitation increased, the strength of conspecific density‐ or distance‐dependence was independent of the precipitation gradient. Seedlings of common tree species and species dispersed by non‐flying mammals had a higher risk of foliar pathogen incidence. Increased disease in common species may help reduce their dominance. Synthesis. The increases in foliar pathogen incidence with conspecific seedling density, species abundance, and dispersal mechanism indicate that foliar disease incidence is non‐random and may contribute to the regulation of tropical plant communities and species coexistence. Furthermore, the relationships between foliar disease incidence, dispersal mechanism and precipitation suggest plant‐pathogen interactions could shift as a response to climate change and disruption of the disperser community.

Lettuce tolerance to verticillium wilt after inoculation with Penicillium pinophilum and Rhizophagus intraradices

The ability to mitigate verticillium wilt is an important attribute of a biocontrol agent in terms of its global market potential. This study evaluated the protective effect of an arbuscular mycorrhizal (AM) fungus and an endophytic fungus (Penicillium pinophilum) inoculation against verticillium wilt in lettuce host. The seedlings in four treatment groups (control, AM, Penicillium, AM + Penicillium) were raised for six weeks in the presence or absence of the pathogen (Verticillium dahliae) in a growth chamber. The foliar disease incidence was evaluated and recorded as 37 %, 35 %, 3 %, and 14 % for Control, AM, Penicillium, and dual inoculated treatments, respectively. V. dahliae decreased the plant growth indices, carbon, and nitrogen contents in all groups, except in Penicillium treatment. Trace elements concentrations were reduced due to disease across board, but manganese (Mn) was modulated by the endophyte. R. intraradices and its co-inoculation with P. pinophilum did not confer protection to lettuce, despite having lower quantity of pathogen DNA in their stems than Control and Penicillium inoculated plants. In mitigating the negative effect of V. dahliae, aside in vivo pathogen antibiosis, the endophyte modulated reactive oxygen species, nitrogen, manganese, and improved host growth indices, thereby, gave the most effective bio-protection. However, its co-inoculation with the R. intraradices reduced its efficacy.

Antifungal Activity of Rue Essential Oil and Commercial Chitosan on Native Corn Foliar Diseases.

Native corn in Cherán, Michoacán, southwestern Mexico, represents a high-impact economic, social, and religious support, although its yield is low due to fungal diseases. Fungicides are mainly used for their control, but the fungi involved create resistance. The aims of this study are to determine the incidence of foliar diseases in the field, isolate the causal fungi, evaluate the in vitro effect of the essential oil of rue (Ruta graveolens) on them, and identify the secondary metabolites. The essential oil was obtained using the steam distillation technique on fresh plants. Also used was an industrial-grade chitosan, and the commercial fungicide benomyl was used as a positive control. Rue essential oil was characterized by mass spectrometry with ultra-high-performance liquid chromatography with electrospray ionization (UHPLC-ESI). The highest incidence of disease was obtained for leaf rust (35%), followed by gray leaf spot (GLS) (24%) and leaf blight (19%). Rue essential oil inhibited 100% of the mycelial growth of Coniothyrium phyllachorae and 96% of the mycelium of Exseroilum turcicum. The benomyl fungicide effectively inhibited C. phyllachorae (86 to 91%), but not E. turcicum, with the opposite effect when using chitosan by inhibiting 89 to 90% of the latter's mycelial development. The majority compound of the essential oil of R. graveolens was 2-(3-phenylprop-2-enoyl)chromen-4-one; however, fatty acids were also detected: linoleic, palmitic, and retinoic acid.

Neopestalotiopsis sp. and Colletotrichum karstii, causal agents of leaf spots on camedor palm (Chamaedorea quezalteca) in Mexico

Since 2020, camedor palm (Chamaedorea quezalteca) plantations in the Frailesca region, Chiapas, Mexico, have been affected by foliar diseases that induce leaf spot and anthracnose symptoms that reduce production, leaf quality and thus the loss of their commercial value. The objectives of this work were to identify the causal agents and to quantify the incidence and severity of foliar diseases in plantations of camedor palm. Two fungi were recurrently isolated, one from leaves with leaf spot symptoms and the other with anthracnose, both were identified morphologically and molecularly by sequencing the internal transcribed spacer (ITS5/ITS4), pathogenicity tests were performed on healthy plants where fungal conidia were inoculated, and in the field the incidence and severity of the disease were quantified with the support of a pictographic scale. The fungi identified were Neopestalotiopsis sp. in leaf spot symptoms and Colletotricum karstii in anthracnose, both pathogens reproduced the same symptoms observed in the field, by means of pathogenicity tests. Disease incidence and severity percentages were transformed to area under the disease progress curve (AUDPC), these diseases presented an annual average incidence and severity of 35.33% (AUDPC= 14180) and 39.16% (AUDPC=12885) for leaf spot, 19.5% (AUDPC= 7123) and 55.83% (AUDPC= 20380) for anthracnose, respectively.

Effect of spontaneous arbuscular mycorrhizal colonization in bread wheat varieties on the incidence of foliar diseases and grain yield

This study aimed to determine the ability of different wheat genotypes to form a symbiosis with arbuscular mycorrhizal fungi (AMF) present in the field and the effect of such a symbiosis on disease severity and grain yield. A bioassay was performed during an agricultural cycle under field conditions in a randomized block factorial design. The factors used were application of fungicide (two levels: with and without fungicide) and wheat genotypes (six levels). Arbuscular mycorrhizal colonization, green leaf area index, and severity of foliar diseases were evaluated in the tillering and early dough stages. At maturity, the number of spikes per square metre the number of grains per spike, and the thousand-kernel weight were determined to estimate grain yield. In addition, the spores of Glomeromycota present in the soil were identified by morphological techniques. Spores belonging to 12 fungal species were recovered. Genotypic variability was found for arbuscular mycorrhization, with the cultivars Klein Liebre and Opata exhibiting the highest colonization values. The results obtained show a beneficial effect of mycorrhizal symbiosis on foliar disease resistance and grain yield in the controls, but the results varied in the case of fungicide treatment. A greater understanding of the ecological role of these microorganisms in agricultural systems can lead to more sustainable agronomic practices.

Gray Blight Disease on Euonymus japonicas Caused by Pestalotiopsis disseminata in China.

Euonymus japonicas is widely planted as an important landscape species throughout China. In June 2021, a serious gray blight disease was detected on E. japonicas in Henan Province (32°30'58" N, 112°19'44" E), causing severe defoliation of infected trees with a foliar disease incidence of 52 to 70% (n = 100). Gray spots initially appeared on leaves, gradually expanded into irregular white blotches with dark brown borders, eventually leading to wilting and death of the leaves. The junctions between the lesion and healthy tissue of infected leaves were cut into 3 × 3-mm pieces, surface sterilized with 1% NaClO solution for 1 min, rinsed in sterile water, and placed on PDA plates with 50 μg/ml of streptomycin. Three isolates (HY94, HY95, and HY98) were selected for subsequent experiments. The colonies reached 80-85 mm diam after 7 days at 25°C, with undulated margins, white to pale in color, with moderate aerial mycelium on the surface. Conidiomata were globose, solitary, and dark black. Conidia were ellipsoid, straight to slightly curved, 4-septate, 19 to 26.4 × 5 to 7.5 μm (n=100). The apical cell was cylindrical and hyaline, with 2 to 3 tubular apical appendages, unbranched, filiform, 2.5 to 3.5 μm in length. The basal appendage was single, unbranched, centric, 1.5 to 3 μm long. The characteristics were close to those of Pestalotiopsis spp. (Maharachchikumbura et al. 2013). The genomic DNA was extracted, and the rDNA internal transcribed spacer (ITS), the β-tubulin gene (TUB), and the translation elongation factor 1-alpha gene (TEF1) were amplified by primers ITS1/ITS4, Bt2a/Bt2b, and EF1-728F/EF1-986R, respectively (Carbone and Kohn, 1999). Sequences were submitted to GenBank with accession numbers OL840327-OL840329(ITS), OL961454-OL961456(TUB), and OL961448-OL961450 (TEF1). BLASTn analyses of ITS, TUB, and TEF1 sequences exhibited 99.46, 99.05, and 96.53% similarity to the sequences of Pestalotiopsis disseminata strain MEAN1166 (ITS, 548/551 bp; MT374688) (Silva et al. 2020), PSH2000I-066 (TUB, 418/422 bp; DQ333575), and TAP29O082 (TEF1, 250/259 bp; AB453850), respectively in GenBank. The three isolates formed a clade with the type strains, MEAN 1166 and MAFF238347 of P. disseminata in phylogenetic trees, being clearly seperated from other Pestalotiopsis spp. Based on morphological and molecular evidence, the pathogen was identified as P. disseminata (Maharachchikumbura et al. 2011). To fulfill Koch's postulates, pathogenicity was tested with three isolates. Ten healthy leaves of 5-year-old intact plants were used per isolate and inoculated with mycelial plugs on both nonwounded and wounded leaves. Control leaves were inoculated with agar plugs. The inoculated plants were placed at 28°C in a greenhouse (90% relative humidity). Distinct lesions were observed after 10 days. The pathogen reisolated was identical to that of the original cultures according to phenotype and ITS sequences. The control leaves showed no obvious symptoms. P. disseminata is known to cause disease on several important plants in China, such as Camellia japonica (Zhang et al. 2012), Pinus armandii (Hu et al. 2007), and Tripterygium wilfordii (Kumar et al. 2004). This is the first report of gray blight disease caused by P. disseminata on E. japonicas in China and worldwide. The fungal pathogen identification will provide valuable information for prevention and management of gray blight disease associated with E. japonicas.

First Report of Colletotrichum fructicola Causing Anthracnose on Rosa chinensis in China.

China rose (Rosa chinensis Jacq.) is a popular ornamental plant grown widely in China. In September 2021, a serious leaf spot disease was observed on R. chinensis in Rose plantation of Nanyang Academy of Agricultural Sciences in Nanyang (112°25'41″N, 32°54'28″E), Henan Province, causing severe defoliation of infected plants with a foliar disease incidence of 50 to 70% (n = 100). The early symptoms were irregular brown specks on the leaves, mostly at the tip and margin of the leaves. Then the specks gradually expanded into round amorphous and became dark brown, eventually leading to large irregular or circular lesions. Twenty symptomatic samples were collected from several individual plants, and the junction areas between infected and healthy tissues were cut into 3×3 mm pieces. These tissues were sterilized in 75% ethanol for 30 seconds and 1% HgCl solution for 3 min, rinsed thrice in sterile water, and placed on potato dextrose agar (PDA) plates, incubated at 25°C for 3 days. The edges of the colony were cut and transferred to new PDA plates for purification. These isolates were isolated from the original diseased leaves and showed similar phenotypes in morphological characters. Three representative purified strains (YJY20, YJY21, and YJY30) were used for further study. Colonies were villiform, initially white, later turning gray and greyish-green. Conidia were unitunicate, clavate, and averaged 17.36 (11.61 to 22.12) - 5.29 (3.92 to 7.04) µm in diameter (n=100). The characteristics were close to those of Colletotrichum spp. (Weir et al. 2012). The genomic DNA was extracted, and the rDNA internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GADPH), calmodulin genes (CAL), actin genes (ACT), chitin synthase 1 genes (CHS-1), manganesesuperoxide dismutase (SOD2), and β-tubulin 2 genes (TUB2) were amplified from genomic DNA by primers ITS1/ITS4, GDF/GDR, CL1C/CL2C, ACT-512F/ACT-783R, CHS-79F/CHS-345R, SODglo2-F/SODglo2-R, and Bt2a/Bt2b, respectively (Weir et al. 2012). Sequences were submitted to GenBank with accession numbers OP535983, OP535993, OP535994(ITS), OP554748, OP546349, OP546350(GAPDH), OP546351-OP546353(CAL), OP546354-OP546356(ACT), OP554742-OP554744(CHS-1), OP554745-OP554747(SOD2), and OP554749-OP554751(TUB2). BLASTn analyses of ITS, GAPDH, CAL, ACT, CHS-1, SDO2 and TUB2 sequences exhibited 99.62%, 98.40%, 99.72%-99.86%, 96.85%-96.86%, 99.26%-100%, 100% and 99.33% similarity to the sequences of Colletotrichum fructicola strain ICMP 18581, respectively in GenBank. These morphological features and molecular identification indicated that the pathogen possessed identical characteristics as C. fructicola (Weir et al. 2012). Pathogenicity was tested through in vivo experiments. Six 1-year-old intact plants were used per isolate. The test leaves of plants were gently scratched with a sterilized needle. Conidial suspension of the pathogen strains were inoculated on the wounded leaves at a concentration of 107 conidial/mL. The control leaves were inoculated with distilled water. The inoculated plants were placed in greenhouse at 28℃ and 90% humidity. After 3-6 days，anthracnose-like symptoms were observed on inoculated leaves of five plants while the control plants remained healthy. The strains of C. fructicola were reisolated from the symptomatic inoculated leaves, confirming Koch's postulates. To our knowledge, this is the first report of C. fructicola causing anthracnose on Rosa chinensis in China. C. fructicola has been reported to affect numerous plants worldwide, including grape, citrus, apple, cassava, mango （Qili Li et al. 2019）, and tea-oil tree (X. G. Chen et al. 2022), among others (Oliveira et al. 2018). This identification research will facilitate subsequent assistance with disease control and field management of plants.

Avaliação de cultivares de cenoura de verão em sistemas de semeadura em canteiro e leira

ABSTRACT In Brazil, carrots are usually grown in beds 30 cm heigh and 1 to 1.8 width. Although widely used, these beds present problems regarding cultural practices and disease management, especially in spring/summer seeding. The aim of this study was to compare the agronomic performance of carrot cultivars in summer cultivation in bed and ridge. Ten carrot cultivars were evaluated in two experiments in strips (bed and ridge), in a randomized complete block design with three replications. Seeds were sown on November 23, 2021, in Brasília-DF. At 90 days, evaluation of foliar diseases was performed, and at 100 days, evaluation of characteristics related to root yield was carried out. Total production was higher in bed, but there was no difference for commercial production in the two cultivation methods. The ridge favored root development, providing a greater mean root mass. Cultivation in ridge did not reduce the incidence of foliar diseases in carrots, but proved to be an alternative for commercial production of summer carrots.

Evaluation of Different Chemicals for Controlling Powdery Mildew of Black Gram

One of the major constraints of black gram production is Powdery mildew (Erysiphe polygoni) disease. This study was an attempt of assess the efficacy of different chemicals against powdery mildew disease. The Experimental design was RCBD with three replication and Binamash-1 variety was planted under natural field conditions. Four chemicals viz. salicylic acid (1g/L), copper shulphate (0.5g/L), chitosan (0.1g/L) and thiovit (2g/L) was evaluated against powdery mildew disease. Those chemicals were applied 3 times with 7days interval after the disease initiation. Disease incidence and percent leaf area infection data was recorded three time after the application of treatments and other agronomic data was recorded after harvest. All the treatments were performed better than control in reducing the incidence of powdery mildew disease and percent leaf area infection. During the experimental period (Khrif -2, 2020), there was no incidence of other fungal foliar disease. Results represent that thiovit @ 2g/L performed best in controlling powdery mildew disease incidence (41%), percent leaf are infection (33%) and highest seed yield (520.57 kg/ha) among the treatments. We can conclude this study that, Thiovit (80% sulphur fungicide @ 2g/L) was best for controlling powdery mildew of black gram among the treatments and it (applied 3 times with 7days interval after the disease initiation) can be used for controlling this disease.

Organic Fertilizer Application Mediates Tomato Defense Against Pseudomonas syringae pv. Tomato, Possibly by Reshaping the Soil Microbiome.

Bacterial speck caused by Pseudomonas syringae pv. tomato is a serious foliar disease on tomato. However, it is still unknown how organic fertilizers application mediates plant defense against foliar pathogens by altering the composition of the soil microbial community. We conducted a 2-cycle pot experiment involving chemical and organic fertilizers and tracked tomato foliar pathogen incidence. Using microbiome sequencing, we then compared the differences in bulk and rhizosphere microbial communities. The results showed that, compared with soils amended with chemical fertilizer, soils amended with organic fertilizer gradually and significantly presented a reduction in tomato foliar disease, and the bacterial richness and diversity significantly increased. Moreover, the bacterial and fungal compositions of the bulk soil and rhizosphere soil of the organic fertilizer and chemical fertilizer treatments were different from each other. More importantly, the abundance of some potentially beneficial bacteria, such as Luteolibacter, Glycomyces, Flavobacterium, and Flavihumibacter, increased in the organic fertilizer-amended soil, and these genera were significantly negatively correlated with the incidence of tomato foliar disease. These results suggest that organic fertilizers can alter the taxonomy of the soil microbiome and that some specific beneficial microbial communities may play an important role in reducing the infection of foliar pathogens by inducing plant resistance.

No evidence of foliar disease impact on crop root functional strategies and soil microbial communities: what does this mean for organic coffee?

Global climate change is increasing pest and pathogen pressures on plant communities, deteriorating optimal plant functioning. In plant communities, root functional trait expression and microbial communities are important indicators of plant functioning belowground, and, when confronted with pathogens aboveground, can simultaneously reflect plant defence strategies. Yet, while research is continuing to emerge on the response of root functional traits and microbial processes to pathogens aboveground, little work has investigated these interactions in tree‐crops, or the role organic amendments play in moderating these relationships. The main objective of this study is to disentangle the dynamic effects of pathogens and amendments on root functional traits (i.e. specific root length and area, root diameter, root length density, root nitrogen and root carbon to nitrogen ratio) and root endophytic fungal communities. As a model, we use Coffea arabica (coffee) variety Caturra along a gradient of coffee leaf rust – a foliar disease prominent in coffee systems – under contrasting but widespread amendment regimes in biodiverse agroforestry systems. We found that root trait expression varies along established conservation and collaboration gradients, where fungal endophyte community composition varies significantly as a function of root traits. Belowground resource acquisition strategies do not change with foliar disease incidence, suggesting they may be decoupled. Rather, amendment regimes differentially shape root trait expression and microbial communities, where coffee plants under organic amendments, regardless of foliar disease incidence, expressed greater acquisitive traits and enhanced collaboration with symbiotic fungi. This is an important first step in disentangling the dynamic inter‐relationships between plant traits, endophytes and pathogens, generating new questions on the role of amendments in sustainable pathogen management in biodiverse agroecosystems.

Microclimate Modification through Groundnut-Pigeon Pea Intercropping System and its Effect on Physiological Responses, Disease Incidence and Productivity

Background: Groundnut (Arachis hypogaea) is the predominant leguminous oilseed crop of India which has turned out to be a sensitive victim to climate change episodes like rising CO2 levels, erratic rainfall pattern, high temperature and moisture stress leaving deleterious imprints in physiology, disease resistance, fertility and productivity. Globally climate change is anticipated to pull down groundnut productivity by 11-25%. Agronomic manipulations like altered time of sowing, intercropping and irrigation management helps in microclimate modification towards reaping higher productivity and economic returns in groundnut. Methods: Field experiments were conducted during 2019-2021 on sandy clay loam soil (Fluventic Ustropept) in a Randomized Block Design with three factors viz., differential cropping systems (sole groundnut, groundnut + red gram intercropping), rainfed and irrigation systems and differential sowing windows (Second fortnight of June, first and second fortnights of July). Growth parameters, physiological traits viz., photosynthetic rate, transpiration rate, stomatal conductance, canopy temperature and light interception, incidence of foliar diseases viz., leaf spot and rust; soil borne disease viz., stem rot, root rot and productivity of groundnut were recorded at critical crop growth stages. Result: Canopy temperature was higher in sole groundnut system while light interception was higher in groundnut - redgram intercropping system, however system productivity did not register statistical superiority between the cropping systems. Irrigated system exerted its influence over rainfed system in terms of pod and kernel yield of groundnut. Sowing of groundnut during second fortnight of June was beneficial than July sowing in pod and kernel yield of groundnut due to uniform distribution of rainfall during the growth and reproductive phases of crop. Although differential cropping systems did not register their impact on disease incidence of groundnut, irrigated system and first sowing windows recorded minimum incidence of root rot, stem rot, early leaf spot, late leaf spot and rust diseases compared to rainfed system and July sowing.

Eucalyptus leaf diseases associated with Neofusicoccum spp. in North Africa

This study represents the first survey reporting the occurrence of Neofusicoccum species associated with Eucalyptus foliar diseases in semi-arid areas in North African countries. Based on morphological features and phylogenetic analyses of internal transcribed spacer (ITS) of nuclear ribosomal DNA (rDNA), translation elongation factor 1-alpha (TEF1) and β-tubulin (TUB2) genes, two species were identified: Neofusicoccum mediterraneum recovered from leaf spots on E. gillii in Tunisia and Neofusicoccum cryptoaustrale reported from leaf blight of E. torquata and E. odorata in Libya. Artificial inoculation trials on leaves confirmed the pathogenicity of the isolates to E. torquata, E. odorata and E. gillii. This report points out the threat posed by pathogens to non-native Eucalyptus in North Africa and suggests a likely movement of various pathogenic fungi from other hosts to Eucalyptus mainly E. ododrata trees that are totally infested by N. cryptoaustrale. Thus, it is recommended that E. odorata should not be planted in semi-arid areas. Further prospections of Eucalyptus arboretums are required to assess the incidence of foliar diseases on Eucalyptus plantations and to take appropriate and prompt measures against disease spread.

First report of Cucurbit chlorotic yellows virus infecting cantaloupe (Cucumis melo L.) in Texas.

Texas is a major producer of cucurbits such as cantaloupe (Cucumis melo L.), but outbreaks of virus-like diseases often adversely affect yields. Little is known about the identity of the causal or associated viruses. During studies conducted in fall 2020 to explore the virome of cucurbit fields in Texas, a commercial cantaloupe field (~4.1 ha) in Cameron County was observed with virus-like symptoms of interveinal chlorotic mottle and foliar chlorosis and disease incidence was estimated at 100%. Virus-like symptoms including mosaic and leaf curl were also observed in six additional fields across five south and central Texas counties of Atascosa, Hidalgo, Fort Bend, Frio, and Wharton. Forty-six plants, which included 32 symptomatic and 14 non-symptomatic, were sampled from these fields for virus diagnosis and each sample was subjected to total nucleic acid extraction according to Dellaporta et. al. (1983). Initially, equal amounts of nucleic acids from 14 symptomatic plants (two/field) were pooled into one composite sample for preliminary diagnosis by high throughput sequencing (HTS). The cDNA library obtained from the composite sample with a TruSeq Stranded Total RNA with Ribo-Zero Plant Kit (Illumina) was sequenced on the Illumina NextSeq 500 platform, generating ~26.3 M single-end HTS reads (75 nucleotides [nt] each). Analyses of the reads according to Al Rwahnih et al. (2018) revealed several virus-like contigs; among them 23 contigs (206 to 741 nt) shared 98 to 100% nt identities to isolates of cucurbit chlorotic yellows virus (CCYV), genus Crinivirus, family Closteroviridae. Three pairs of CCYV-specific primers were designed from the HTS contigs with primers CCYV-v1330: 5'-AGTCCCTTACCCTGAGATGAA/CCYV-c2369: 5'-CGGAGCATTCGACAACTGAATA targeting ~1 kb fragment of the ORF1a (RNA1), primers CCYV-v4881: 5'-ATAAGGCGGCGACCTAATC/CCYV-c5736: 5'-GATCACTTGACCATCTCCTTCT targeting a ~0.9 kb fragment encompassing the coat protein (CP) cistron of CCYV (RNA2), and primers CCYV-v6362: 5'-CACCTCTTCCAGAACCAGTTAAA/CCYV-c7423: 5'-TGGGAACAACTTATTTCTCCTAGC targeting ~1 kb spanning partial minor coat protein (CPm) and p26 sequences (RNA2). Total nucleic acid extracts of each of the 46 samples from the seven fields were tested by two-step reverse transcription polymerase chain reaction using all three CCYV-specific primer pairs and they yielded amplicons of expected sizes from all five symptomatic cantaloupe samples from the Cameron County field and one additional symptomatic butternut squash sample from a field in Hidalgo County. The DNA bands from three randomly chosen cantaloupe samples were cloned and sequenced as previously described (Oke et al. 2020). In pairwise comparisons, the obtained 1,040 nt ORF1a (MW584332-334), 753 nt complete CP (MW584335-337), and 1,062 nt CPm/p26 (MW584338-340) gene specific sequences from the three samples shared 100% nt identity with each other, and 99-100% nt identities with corresponding RNA1 (AB523788) and RNA2 (AB523788) sequences of the exemplar isolate of CCYV. This is the first report of CCYV in Texas, thus expanding the current geographical range of the virus in the U.S. that includes California (Wintermantel et al. 2019) and Georgia (Kavalappara et al. 2021). The abundance of whiteflies of the Bemisia tabaci species complex in south Texas and other major U.S. cucurbit production areas presents additional challenges to virus disease management.

Efficacy and economics evaluation of seed rhizome treatment combined with preplant soil fumigation on ginger soilborne disease, plant growth, and yield promotion.

Ginger (Zingiber officinale Roscoe) is widely planted around the world. Owing to continuous planting, ginger is seriously affected by soilborne fungi, bacteria, and nematodes. Although preplant soil fumigation is an effective prevention strategy of soilborne diseases, individual fumigant and technology could not provide effective control of ginger soilborne disease. In our research, different combinations of soil fumigants and seed rhizome treatments were evaluated by monitoring the soil pathogens population, ginger growth, yield, and estimation of economic benefits. Soil fumigation effectively reduced the population of soilborne pathogens, and chloropicrin had a better control effect on soilborne pathogens than dazomet did. Preplant soil fumigation and seed rhizome treatment not only provide good control of soilborne disease, but also reduced the incidence of plant foliar pest and disease. Average yield increase rate of seed rhizome treatment was 12.0%; the highest yield increase was 24.4%. The average cost of seed rhizome treatment only increased by about 2.86%, but the rate of net revenue increase for the seed rhizome treatment reached up to 19.1%. Seed rhizome treatment is a very cost-effective soilborne disease control technology. In the management of soilborne diseases, the combined application of soil fumigation and seed rhizome treatment can reduce the risk of crops infected by soilborne diseases and ensure high and stable crop yields. © 2021 Society of Chemical Industry.

Biosensor Technologies for Early Detection and Quantification of Plant Pathogens.

Plant pathogens are a major reason of reduced crop productivity and may lead to a shortage of food for both human and animal consumption. Although chemical control remains the main method to reduce foliar fungal disease incidence, frequent use can lead to loss of susceptibility in the fungal population. Furthermore, over-spraying can cause environmental contamination and poses a heavy financial burden on growers. To prevent or control disease epidemics, it is important for growers to be able to detect causal pathogen accurately, sensitively, and rapidly, so that the best practice disease management strategies can be chosen and enacted. To reach this goal, many culture-dependent, biochemical, and molecular methods have been developed for plant pathogen detection. However, these methods lack accuracy, specificity, reliability, and rapidity, and they are generally not suitable for in-situ analysis. Accordingly, there is strong interest in developing biosensing systems for early and accurate pathogen detection. There is also great scope to translate innovative nanoparticle-based biosensor approaches developed initially for human disease diagnostics for early detection of plant disease-causing pathogens. In this review, we compare conventional methods used in plant disease diagnostics with new sensing technologies in particular with deeper focus on electrochemical and optical biosensors that may be applied for plant pathogen detection and management. In addition, we discuss challenges facing biosensors and new capability the technology provides to informing disease management strategies.

Survey of Major Wheat Diseases in South Eastern Ethiopia

Wheat foliar mainly rusts, and root and foot diseases are important biological constraints to wheat production in Ethiopia especially in Arsi and West Arsi - main wheat belt areas of Ethiopia. Both fungal diseases incurred huge economic losses annually. In 2020 main growing season, assessment was carried out with the stress to ascertain the state of major foliar, root and foot diseases of wheat in Arsi and West Arsi zones of Ethiopia. The assessment result showed yellow rust, septoria leaf blotch and stem rust diseases among foliar; fusarium head blight from spike diseases; eyespot and take all from foot and root were found prevalent. The incidence of foliar diseases viz septoria leaf blotch, yellow and stem rust was 100%, 92.7% and 11.8% respectively. While take all and eyespot were observed 52.4% and 48.5% in the same order. Unlike its incidence, maximum disease severity was caused by yellow rust with higher epidemics on Kubsa and Ogolcho varieties that occupied largest volume in assessed farms. Take- all and eyespots were observed on fields where continuous monocropping is practiced with severity ranges of 0-5 and 0-3 respectively. Thus, it is advisable that much works are needed to train producers to use up-to-date released wheat varieties in order to reduce rust diseases and conduct crop rotation and residue management for the control of foot and root diseases thereby decline associated yield losses.