Artificial Inoculation Research Articles

Comparison of different screening methods for the selection of Ascochyta blight disease on chickpea (Cicer arietinum L.) genotypes.

Chickpea (Cicer arietinum L.) is the second most important edible food grain legume, widely grown all over the world. However, the cultivation and production of chickpea are mainly affected by the Ascochyta blight (AB) disease, which causes losses of up to 100% in areas with high humidity and warm temperature conditions. Various screening methods are used in the selection of chickpea genotypes for resistance to AB disease. These methods are natural field condition (NFC), artificial epidemic field condition (AEC), marker-assisted selection (MAS), and real-time PCR (RT-PCR). The study was conducted with 88 chickpea test genotypes between the 2014 and 2016 growing seasons. The results of the screening were used to sort the genotypes into three categories: susceptible (S), moderately resistant (MR), and resistant (R). Using MAS screening, 13, 21, and 54 chickpea genotypes were identified as S, MR, and R, respectively. For RT-PCR screening, 39 genotypes were S, 31 genotypes were MR, and 18 genotypes were R. In the AEC method for NFC screening, 7, 17, and 64 genotypes were S, MR, and R, while 74 and 6 genotypes were S and MR, and 8 genotypes were R-AB disease. As a result of screening chickpea genotypes for AB disease, it was determined that the most effective method was artificial inoculation (AEC) under field conditions. In the study, Azkan, ICC3996, Tüb-19, and Tüb-82 were determined as resistant within all methods for Pathotype 1.

First report of Apple bitter rot caused by Colletotrichum godetiae in Ontario.

Bitter rot is an emerging disease of apple (Malus domestica) fruit in Ontario in part due to changing weather conditions. The disease was mostly documented in warm and humid regions such as the southern USA, and Central and South America. Thirteen Ontario orchards in the fall of 2019 and 15 in 2020 were scouted for bitter rot based on their previous history of the disease. 100 fruit were collected from ten asymptomatic trees per cultivar and two susceptible cultivars, 'Empire' and 'Ambrosia' were scouted per orchard. If an orchard did not have either one of these cultivars, 'Honeycrisp' or 'Gala' were used. The fruit was stored at 4-5 oC for five months and then left at 22 oC for two weeks and assessed thereafter for bitter rot symptoms. Monoconidial cultures of Colletrotrichum spp. were established from the symptomatic fruit using potato dextrose agar media with antibiotics at 22 oC 14-hour light cycles. The fungal isolates were divided into two groups based on colony morphology observations seven days after culturing. The first group showed light grey, cottony, aerial mycelium on top and a pink to dark red color on the reverse of the plate. The second group showed light to dark grey, cottony mycelium on top and dark green colonies on the reverse of the plate. It is difficult to identify Colletrotricuhum species solely based on morphology, therefore the representative isolates from each group were used for multilocus gene sequencing and species identification. Genomic DNA was extracted using the Qiagen DNeasy Plant Mini Kit according to the manufacturer's protocols. The ITS region was amplified and sequenced using the primers ITS-1F (Grades & Bruns 1993) and ITS-4 (White et al. 1990). Primers T1 and T2 (O'Donnell & Cigelnik 1997) were used to amplify and sequence the 750 bp region of the TUB gene. Primers GDF1 and GDR1 (Guerber et. al. 2003) were used to amplify a 280 bp region of the GADPH gene. Following an NCBI nucleotide blast search, the isolates from group 1 were identified as C. fioriniae.The ITS sequences of group 2 isolates were matched 100% to the Colletotrichum godetiae type strain CBS133.44 and they were 99% matched to the closest species C. Johnstonii CBS128532. The TUB sequences matched 100% identity to 20 sequences belonging to C. godetiae, 99.59 % identity to C. godetiae type strain CBS133.44, and 97.75% to C. Johnstonii CBS128532. The GADPH sequences matched with 100% identity to C. godetiae ON241087.1 or MT816329.1 and 99-99.5% identity to the type strain CBS133.44 and 98.61-99% identity to CBS128532. Based on the blast results the group 2 isolates were identified as C. godetiae and their sequences were submitted to GenBank with ID OP702962 for ITS and OP972240 and OP972241 for GADPH and OP972242 for the TUB gene. Out of 50 isolates collected in this work, 94% belonged to group 1 and 6% belonged to group 2. Koch's postulates were performed on selected isolates by artificial inoculation of 5 healthy detached fruits of the cultivar, 'Empire.' Fruit surfaces were wiped with 70% ethanol, dried, wounded with a sterile needle, and then inoculated with a 10 µl of spore suspension containing 1x10^6 spores /ml. Inoculated fruits were incubated in a humid chamber at 22°C in dark. Symptoms started to appear at 5 days post-inoculation and looked like small brown circular lesions which developed orange spore masses as they grew into larger lesions. The non-inoculated control fruit did not develop lesions. Fungal colonies were established from the spores collected from the inoculated fruit and found to have identical morphological characteristics to the original isolates. C. godetiae has previously been reported to cause bitter rot in apples from various countries in Europe (Baroncelli et al. 2014; Munda, 2014; Wenneker et al. 2016). C. fioriniae has previously been reported as the dominant species causing bitter rot in apples although other species including C. chrysophilum and C. noveboracense have also been reported as causal agents from the Eastern USA (Khodadadi et al. 2020). To the best of our knowledge, this is the first report of Colletotrichum godetiae causing the bitter rot of apples in Ontario, Canada.

Novel loci associated with resistance to downy and powdery mildew in grapevine.

Among the main challenges in current viticulture, there is the increasing demand for sustainability in the protection from fungal diseases, such as downy mildew (DM) and powdery mildew (PM). Breeding disease-resistant grapevine varieties is a key strategy for better managing fungicide inputs. This study explores the diversity of grapevine germplasm (cultivated and wild) from Caucasus and neighboring areas to identify genotypes resistant to DM and PM, based on 13 Simple Sequence Repeat (SSR) loci and phenotypical (artificial pathogen inoculation) analysis, and to identify loci associated with DM and PM resistance, via Genome-Wide Association Analysis (GWAS) on Single Nucleotide Polymorphism (SNP) profiles. SSR analysis revealed resistant alleles for 16 out of 88 genotypes. Phenotypic data identified seven DM and 31 PM resistant genotypes. GWAS identified two new loci associated with DM resistance, located on chromosome 15 and 16 (designated as Rpv36 and Rpv37), and two with PM resistance, located on chromosome 6 and 17 (designated as Ren14 and Ren15). The four novel loci identified genomic regions rich in genes related to biotic stress response, such as genes involved in pathogen recognition, signal transduction and resistance response. This study highlights potential candidate genes associated with resistance to DM and PM, providing valuable insights for breeding programs for resistant varieties. To optimize their utilization, further functional characterization studies are recommended.

Introgression of OsAP47 by marker-assisted selection enhanced resistance against southern rice black-streaked dwarf virus disease

Southern rice black-streaked dwarf virus disease (SRBSDVD) is the most destructive viral disease in rice. In order to breeding resistant cultivars, Insertion-Deletion (InDel) markers were developed linked to OsAP47, the first isolated major resistance gene against SRBSDVD. Marker-assisted selection (MAS) was conducted to introduce this gene into the commercial variety. A rice line carrying homozygous resistance allele of OsAP47 was selected and named Kanghei No. 201 (KH201). Evaluated by artificial inoculation, KH201 showed significantly higher resistance than the recurrent parent Suxiu No.867 (SX867). And no significant differences were detected for KH201 in the yield-related components, including spikelets per panicle (SPP), ripened grains per panicle (RGPP), 1000-grain weight (TGW) and panicles per square meter (PPSM), leading to stable theoretical yield. The results indicated that introgression of OsAP47 improved rice resistance and can avoid yield losses produced by SRBSDVD. KH201 was demonstrated as a resistance material that could be used in rice breeding.

Investigation of Using Hyperspectral Vegetation Indices to Assess Brassica Downy Mildew.

Downy mildew caused by Hyaloperonospora brassicae is a severe disease in Brassica oleracea that significantly reduces crop yield and marketability. This study aims to evaluate different vegetation indices to assess different downy mildew infection levels in the Brassica variety Mildis using hyperspectral data. Artificial inoculation using H. brassicae sporangia suspension was conducted to induce different levels of downy mildew disease. Spectral measurements, spanning 350 nm to 1050 nm, were conducted on the leaves using an environmentally controlled setup, and the reflectance data were acquired and processed. The Successive Projections Algorithm (SPA) and signal sensitivity calculation were used to extract the most informative wavelengths that could be used to develop downy mildew indices (DMI). A total of 37 existing vegetation indices and three proposed DMIs were evaluated to indicate downy mildew (DM) infection levels. The results showed that the classification using a support vector machine achieved accuracies of 71.3%, 80.7%, and 85.3% for distinguishing healthy leaves from DM1 (early infection), DM2 (progressed infection), and DM3 (severe infection) leaves using the proposed downy mildew index. The proposed new downy mildew index potentially enables the development of an automated DM monitoring system and resistance profiling in Brassica breeding lines.

Evaluating Pomegranate Cultivars for Resistance to Anthracnose Fruit Rot, a Severe Fungal Disease in Florida and Southeast United States

Pomegranate (Punica granatum L.) has primarily been cultivated at home in Florida and other southeastern states. Over the past 15 years, growers, nurseries, researchers, and Extension agents have explored the potential of pomegranate as an alternative fruit crop. Early field trials revealed that pomegranates are highly susceptible to Colletotrichum gloeosporioides, causing severe anthracnose fruit rot and premature fruit drop. The development and use of disease-resistant cultivars are considered some of the best methods to manage this disease. This publication presents our findings from evaluating 35 pomegranate cultivars under natural disease pressure in central Florida and by artificial inoculation. The susceptibility of such pomegranate cultivars varied widely, with six exhibiting resistance to anthracnose fruit rot. More comprehensive research is warranted to further develop anthracnose-resistant cultivars and to enhance our understanding of disease resistance in this crop.

Biochemical changes in some banana cultivars infected by Banana bunchy top virus

Bunchy top is one of the major diseases on bananas that caused economic losses. This study aimed to determine changes in protein content, the concentration of phenolic compounds, the amount of chlorophyll, and sugar content in several Banana bunchy top virus (BBTV)-infected banana cultivars. The research involved the artificial inoculation, extraction, and biochemical analysis of banana seedlings from the cultivars Mas, Cavendish, Kepok, and Raja. Inoculation was performed using the vector Pentalonia sp.. A factorial complete randomized design (CRD) was used as the experimental design. Each experimental unit consisted of 5 repetitions. Protein, phenol, chlorophyll, and sugar content measurements were performed using a UV-Vis spectrophotometer. Test samples were in the form of fresh leaves from BBTV-infected and non-BBTV-infected plants. Regression analysis and tests for significance were performed to determine the biochemical changes that occurred after testing. The results showed that the average levels of phenols, chlorophyll, protein, and total sugars in BBTV-infected plants were significantly altered. The chlorophyll content decreased from 82–87% in Mas, Cavendish, and Raja cultivars. Total plant phenol in all BBTV-infected cultivars increased by 69.2 to 348.3 ppm. Specificity was evident in the change in protein concentration, which increased by 95 ppm and 84.5 ppm in the Mas and Cavendish cultivars, respectively. This contrasts with the Kepok and Raja cultivars, which decreased by 660.5 ppm and 113.6 ppm, respectively. Sugar levels increased from 3133.9 to 3298.6 ppm in all BBTV-infected breeds. According to the data, BBTV infection has been shown to cause physiological and biochemical changes in Mas, Cavendish, Kepok, and Raja.

Automatic Scoring of Rhizoctonia Crown and Root Rot Affected Sugar Beet Fields from Orthorectified UAV Images Using Machine Learning.

Rhizoctonia crown and root rot (RCRR), caused by Rhizoctonia solani, can cause severe yield and quality losses in sugar beet. The most common strategy to control the disease is the development of resistant varieties. In the breeding process, field experiments with artificial inoculation are carried out to evaluate the performance of genotypes and varieties. The phenotyping process in breeding trials requires constant monitoring and scoring by skilled experts. This work is time demanding and shows bias and heterogeneity according to the experience and capacity of each individual person. Optical sensors and artificial intelligence have demonstrated great potential to achieve higher accuracy than human raters and the possibility to standardize phenotyping applications. A workflow combining red-green-blue and multispectral imagery coupled to an unmanned aerial vehicle (UAV), as well as machine learning techniques, was applied to score diseased plants and plots affected by RCRR. Georeferenced annotation of UAV-orthorectified images was carried out. With the annotated images, five convolutional neural networks were trained to score individual plants. The training was carried out with different image analysis strategies and data augmentation. The custom convolutional neural network trained from scratch together with pretrained MobileNet showed the best precision in scoring RCRR (0.73 to 0.85). The average per plot of spectral information was used to score the plots, and the benefit of adding the information obtained from the score of individual plants was compared. For this purpose, machine learning models were trained together with data management strategies, and the best-performing model was chosen. A combined pipeline of random forest and k-nearest neighbors has shown the best weighted precision (0.67). This research provides a reliable workflow for detecting and scoring RCRR based on aerial imagery. RCRR is often distributed heterogeneously in trial plots; therefore, considering the information from individual plants of the plots showed a significant improvement in UAV-based automated monitoring routines.

Pre‐infection efficacy of resistance inducers against grapevine powdery mildew

AbstractPlant resistance inducers (PRIs) are of increasing interest for disease control in sustainable viticulture, but their efficacy in vineyards is still under investigation. We studied the effects of four commercial PRIs, of natural and microbial origin, on the development of powdery mildew (PM) on grapevine leaves over a 3‐year period. Disease and sporulation severity were evaluated following the artificial inoculation of PRI‐treated leaves with Erysiphe necator conidia at 1, 3, 7 and 12 days after treatment (DAT). Laminarin (LAM) and cos‐oga (COS) were the most effective in reducing both disease (57.1% and 49.5%, respectively) and sporulation (85.3% and 90.2%, respectively) severity; the reduction in PM severity provided by cerevisane (CER) was lower (27%), and that of Pythium oligandrum (PYT) was intermediate (44.9%). LAM was effective from 1 DAT, while COS and PYT were more effective when E. necator was inoculated at 7 to 12 DAT. These results open new perspectives on how PRIs are used as single, preventative interventions performed 1 to 3 days before E. necator infection, depending on the product used. The effect of PRIs on the sporulation of E. necator colonies also suggests a broader and longer effect on PM epidemics.

Grafting Bell Pepper onto Local Genotypes of Capsicum spp. as Rootstocks to Alleviate Bacterial Wilt and Root-Knot Nematodes under Protected Cultivation

In soil-based protected cultivation, the prevalence of certain diseases like bacterial wilt and nematodes in the bell pepper plant due to its successive cropping pose a threat for maximizing productivity. Considering the potential of grafting to alleviate various biotic and abiotic stresses, often relying on rootstock’s capability, we explored the potential of diverse local genotypes of Capsicum spp. to utilize as rootstocks. In this research, we assessed the performance of a commercial bell pepper cv. Massilia F1, grafted onto twenty-five rootstocks along with non-grafted and self-grafted Massilia plants under artificial inoculation conditions of bacterial wilt (Ralstonia solanacearum) and nematodes (Meloidogyne incognita) in a plastic greenhouse. The response of rootstock grafting was determined by assessing disease incidences and their effect on plants growth, yield, and physiology, as well as their efficiency in nutrient accumulation. The grafted plants exhibited varied responses to diseases depending on rootstock genotypes. Notably, Massilia grafted onto the CRS-8 and CRS-1 rootstocks exhibited high bacterial wilt resistance by showing lower percent disease incidence (PDI) (22.22 and 27.78 percent, respectively). Others, like CRS-11, CRS-12, CRS-13, CRS-21, and CRS-24, showed moderate resistance (PDI ranging from 33.33 to 38.89 percent, respectively). The self-grafted and non-grafted plants were highly susceptible and recorded complete mortality by the end of the experiment. All of the grafted plants exhibited promising resistance against nematode infestation compared to non-grafted and self-grafted plants with 26.17 and 8.67 percent root galls, respectively. The susceptible plants had lower shoot and root dry weights, while the resistant graft combinations had comparatively higher biomass. Importantly, grafting induced earliness in flowering and provided higher yields, especially in graft combinations involving the CRS-15, CRS-11, and CRS-8 rootstocks. These graft combinations exhibited significantly higher yields over the non-grafted and self-grafted plants. The plant yield was positively associated with plant height, number of leaves, fresh and dry weight of roots, number of fruits per plant, and average fruit weight, but negatively related to bacterial wilt and root-knot nematode incidences. The increased level of antioxidant enzymes such as polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and peroxidase (POD) and the higher total chlorophyll content in the resistant grafted plants indicates their better ability to cope with diseases at the cellular level. This study highlights the robust performance of certain rootstocks from Capsicum annuum (CRS-1, CRS-2, CRS-11, CRS-15) and Capsicum frutescens (CRS-8, CRS-13, CRS-22) species across multiple measured parameters. Grafting emerges as a sustainable solution for bell pepper production in bacterial wilt- and nematode-infested soil under plastic greenhouses.

Phylogenetic, metabolic and pathogenic characteristics of Alternaria alternata strains from wheat in China

AbstractAlternaria is an important toxigenic fungal genus endangering the quality of cereal grains. No data are available in the literature regarding the composition of Alternaria species in wheat from the main wheat‐cultivating regions of China. In this study, a total of 282 strains were isolated from wheat kernels collected in various provinces. Phylogenetic characterization was performed using two informative loci, ASA10 and ASA19, demonstrating that all strains belonged to A. alternata. A low molecular diversity was observed, which did not appear to be influenced by geographic origin. The secondary metabolite profile of the strains was evaluated in rice culture. Altertoxin I was synthesized at a high concentration by the majority of the strains, while the accumulation of altenuene was lower in both frequency and level than that of alternariol and its derivative. A. alternata did not cause readily observable symptoms on wheat spikes after spraying of the conidia at anthesis, but a higher quantity of altertoxin I and Alternaria DNA were detected in inoculated grains. Artificial inoculations of apple fruit showed that all examined strains were capable of causing typical rot symptoms and producing all four toxins to a certain degree. The widespread occurrence of A. alternata on wheat grains and its ability to synthesize various toxic metabolites may pose a serious hazard for both growers and consumers.

Performance of Symmetric Double Flat Fan Nozzles against Fusarium Head Blight in Durum Wheat

Four types of nozzles were tested on large-scale trials with a 40 m2 plot unit size. The Avi Twin 110-01 (80 L ha−1), 110-02 (160 L ha−1), 110-03 (240 L ha−1), and 110-04 (320 L ha−1) symmetric double fan injector nozzles were tested during the 2020/2021 and 2021/2022 growing seasons. This study aimed to evaluate the performance of spray nozzles with regard to deoxynivalenol (DON) accumulation in durum wheat grains. Artificial inoculation with Fusarium spp. was performed after durum heads were protected with fungicide. The percentage of heads covered with fungicide droplets, grain yield, yield-related traits, technological quality parameters, and concentrations of DON were determined. Compared to the control (without fungicide treatment), the Avi Twin 04 nozzle caused a reduction of 45.0% in the DON concentration on average across both growing seasons. This positively corresponded to the percentage of heads covered with fungicide droplets, which was highest when this nozzle was utilized. In both trial years, the DON reduction caused by the 110-04 twin nozzle was higher than that caused by the 110-01 nozzle. Treatment with the 110-04 nozzle more effectively improved the grain yield, 1000-kernel weight, and test weight compared to treatment with the 110-01 nozzle and the untreated control. The differences in technological quality were less pronounced when different spray nozzles were used.

Evaluation of Coriander (Coriandrum sativum L.) Genotypes for Powdery Mildew Disease (Erysiphe polygoni DC) Resistance

Coriander (Coriandrum sativum L.) is short and bushy crop of Apiaceae family with linalool as aromatic compound, this crop is used mainly as culinary spice in India. Majorly this coriander crop is associated with powdery mildew (Erysiphe polygoni DC) disease incidence, causes serious problem in many parts of India. Screening for resistant source through artificial inoculation method which was an eco-friendly approach conductedduring Rabi-2022 at Department of Biotechnology and Crop Improvement, University of Horticultural Sciences, Bagalkot. 35 coriander accessions where are collected from Karnataka, Gujarat and Andhra Pradesh. Percent Disease Index (PDI %) was calculated for four weeks after inoculation and scored based on disease rating scale. Among them only eight genotypes (Surabhi, Asian (A-5), Mrityunjaya, Kalaburagi local, Nutan, Caribe, Samarat Ashok and Pokhara) showed slower powdery mildew symptoms (PDI value of 3.9 to 5.4%) after third week of inoculation but in fourth week all the 35 genotypes falls under susceptible (PDI more then 100%) and highly susceptible category which represents the high virulence nature of powdery mildew strain.

Non-Destructive Assessment of Agarwood Resin Formation Status in Aquilaria crassna using Near-Infrared Spectroscopy

Agarwood is a unique and valuable resin synthesized within a few tree species of the tree family Thymelaeaceae primarily as a self-defence mechanism against stress causes such as fungal invasions. Instead, artificial inoculation leads to short-time harvesting practiced in intensive commercial-level cultivations. The extraction of this resin can be done only after the harvesting where accurate estimation of resin yield is crucial for avoiding immature or underdeveloped harvesting. However, the amount of resin accumulated in the trunk cannot be estimated by the outside inspection. As a result, trees are being cut down before they have reached their maximum harvest potential. Therefore, precise detection of fragrant resin formation status inside the tree has become one of the primary challenges in the agarwood production industry. Currently, the methods available are either destructive, inefficient, or inaccurate. As such, this study evaluates the possibility of the use of NIR spectroscopy as a non-destructive and quick detection method for agarwood formations status inside trees in the in-situ mode. Near-infrared (NIR) range (588–1,025 nm) spectra were acquired from resin-formed and non-formed areas from twenty tree trunks of agarwood with five different formation levels. The best agarwood formation areas of logs were assigned as class level 1 and the least was assigned as the class level 5. The spectra were acquired near the opening made for the artificial inoculation process of considered Aquilaria crassna tree trunks. The results of Soft Independent Modelling of Class Analogies showed consistent evidence of differences in the NIR spectral profiles of all levels of agarwood formations. The SIMCA discrimination between the resin developed versus not was achieved with 86% accuracy. The accuracy rates of the degree of the presence of agarwood were obtained as 80%, 100%, 85%, 90%, and 85% respectively, as assigned levels 1 to 5 in the SIMCA models. This research revealed the potential possibility of using NIR technology for the prediction of agarwood resin status inside the agarwood tree in A. crassna before harvesting the tree as a non-destructive and rapid method.
 
 Keywords: NIR spectroscopy, Agarwood, Aquilaria crassna, Non-destructive, Agarwood formation

Characterization of Seed-to-Seedling Transmission of Alternaria brassicicola in Broccoli.

Alternaria brassicicola is part of a complex of Alternaria species that causes leaf blight and head rot in brassica crops such as broccoli, kale, cabbage, cauliflower, and collards. Seed can serve as a potential source of inoculum for the transmission of A. brassicicola in broccoli as demonstrated earlier; however, seed-to-seedling transmission of pathogen was never characterized empirically. So, the objectives of this study were to (i) re-evaluate the effect of artificial seed infestation on seed germination and seed-to-seedling transmission of A. brassicicola in broccoli; (ii) determine the effect of A. brassicicola-seed inoculum levels on seed-to-seedling transmission; (iii) evaluate if variations in A. brassicicola aggressiveness affect A. brassicicola seed-to-seedling transmission; and (iv) evaluate seed treatments that can reduce seed-to-seedling transmission of A. brassicicola in broccoli. Artificially infested seedlots were generated by inoculating broccoli seeds with a spore suspension of 1 × 105 conidia/ml of A. brassicicola using the vacuum infiltration method. Inoculated (n = 10 seedlots; 300 seeds/seedlot) or control seedlots in three replicates were planted on two layers of sterile blotter paper saturated with sterile water in transparent plastic boxes and incubated at 20°C and >90% relative humidity (RH) under continuous fluorescent light. Percent seed germination and percent seed-to-seedling transmission were recorded every other day for 21 days. Percent seed germination was significantly affected with artificial pathogen inoculation. One hundred percent of the seedlots transmitted the pathogen to broccoli seedlings, and seed-to-seedling percentages of the seedlots varied considerably. A strong linear and significant relationship between A. brassicicola inoculum level and seed-to-seedling transmission (%) within each seedlot was observed. Interestingly, variations in aggressiveness of A. brassicicola isolates did not affect seed-to-seedling transmission, as 100% of the seedlots were able to transmit the pathogen. Seed treatment with Miravis (a.i. pydiflumetofen 18.3%) significantly increased seed germination and reduced seed-to-seedling transmission percentages in A. brassicicola-inoculated seedlots. These results indicate that artificial seed inoculation with A. brassicicola can result in consistent seed-to-seedling transmission with significant impact on seed germination. Seed inoculum density of ≥104 conidia/ml is necessary for reliable transmission of A. brassicicola. Further seed-to-seedling transmission is not dependent on aggressiveness of A. brassicicola isolates and seed treatment with Miravis can significantly reduce pathogen transmission in broccoli seedings. Overall, this study provides detailed characterization of seed-to-seedling transmission of A. brassicicola in broccoli that can be further used to determine inoculum threshold, which has potential applications in seed-health testing and sample size determination. Furthermore, we also provide options for effective seed treatments that can significantly reduce A. brassicicola seed-to-seedling transmission and may potentially aid in managing seedborne fungal infection.

Biological Control and Cross Infections of the Neofusicoccum spp. Causing Mango Postharvest Rots in Spain

Mango is one of the main subtropical crops growing in southern Spain. Spanish mango fruit production can be efficiently transported to the rest of Europe, and these mangoes are very appreciated for their quality and flavour. However, postharvest rots have been detected in stored mango fruits, making their commercialization difficult. The causal agents associated with such rot symptoms have been isolated and identified. Because the mango crops used to share the same growing area with avocado crops, fungal presence on surrounding asymptomatic avocado fruits was also analysed to detect potential cross infections. Artificial inoculation with Neofusicoccum parvum and N. mediterraneum was able to reproduce rot symptoms in mango but was also able to induce rots in avocado fruits. To approach a biological control strategy against these rot-producing fungi, two very well-known antagonistic biocontrol bacteria, Pseudomonas chlororaphis PCL1606, and Bacillus velezensis UMAF6639, were tested. The obtained results revealed that both bacteria can control the fungal rots on stored mango and avocado fruits under controlled conditions. Additionally, the strain B. velezensis UMAF6639 showed the ability to persist on the fruit surface of adult commercial trees in experiments under open field conditions, helping to prevent the appearance of these postharvest diseases.

In‐field climatic factors driving Sclerotinia head rot progression across different sunflower planting dates

AbstractSclerotinia head rot, caused by Sclerotinia sclerotiorum, is a major disease limiting sunflower production in tropical and subtropical agroecological zones. Sporadic outbreaks across South Africa have resulted in major losses, yet little is known about the in‐field climatic factors driving this infection. Short‐interval, staggered plantings have been proposed as a control method for Sclerotinia head rot, which help to limit the number of plants in a susceptible developmental stage during conducive environmental conditions. However, this complicates field management practices, especially if working at the fringes of a planting window due to delayed rains. This study aimed to investigate the effect of planting date on Sclerotinia head rot progression in monthly plantings across the summer period. Artificial mycelial plug inoculations were performed at the R5.9 flowering stage in an open field. Disease establishment, progression and severity were monitored at 3‐day intervals for 30 days. We show that disease establishment was delayed by low relative humidity or extreme low temperatures in the January and March planting dates where the first lesions were only observed 6 days post‐inoculation. Consistently high temperatures above 27°C also suppressed disease progression and produced low area under the disease progress curve (AUDPC) scores of 75.15 and 29.4 for the October and November planting dates, respectively. These findings suggest that regardless of season or location, selecting a planting date that ensures the sunflower bloom period aligns with the hottest, driest part of the season will probably suppress Sclerotinia head rot in regions with average summer highs above 27°C.

Screening of cauliflower (Brassica oleracea var. botrytis L.) genotypes for resistance to the root-knot nematode (Meloidogyne incognita)

The root-knot nematode (RKN) Meloidogyne spp. incurs substantial economic losses in vegetable crops. The present investigation involved glass-house-based screening performed by artificial inoculation of a set of 62 cauliflower accessions against RKN infestation. The PAUCE-292 genotype exhibited a resistant reaction to RKN infestation while genotypes PAUCE-15, PAUCE-16, PAUCE-19C and PAUCM-PI exhibited a moderately resistant reaction. Nematode inoculation reduced various growth parameters including plant height, plant weight and root length as compared to control but a higher percent reduction was recorded for the susceptible and highly susceptible genotypes. The root galling intensity was recorded to be high in susceptible and highly susceptible genotypes. The root-morphoanatomy studies on selected genotypes revealed no specific association of the studied traits with RKN reaction. But, optical microscopy revealed elaborate lignification and gall formation on RKN inoculation in susceptible PAUCM-SD3 and highly susceptible PAUCM-STAR accessions. The total phenol and flavonoid contents were maintained at significantly high levels in resistant genotype(s) in the initial 2.5-week post-inoculation of nematode juveniles. Therefore, this study provides biochemical cues on the mechanism of RKN resistance in cauliflower accessions.

Fusarium clavum causes sugar beet seedling root rot in Wyoming, USA

Seedling rot in sugar beet was observed at Snyder Farms, Wyoming, USA, in April 2022. The diseased seedlings exhibited water-soaked brown to blackish lesions in hypocotyls with poor root systems. Four fungal isolates were retrieved from the diseased samples, and their morphological features were found to be identical to those of previously reported Fusarium species. Artificial inoculation with isolates developed similar symptoms to those observed in the field samples. Based on morphological characteristics, pathogenicity assays, sequence homologies of the internal transcribed spacer, translation elongation factor (tef1α), largest subunit of RNA polymerase II (rpb2), β-tubulin (β-tub), and multilocus phylogenic analyses with tef1α and rpb2, the causal agent was identified as Fusarium clavum (F. incarnatum-equiseti species complex 5). This is the first worldwide report of sugar beet seedling rot caused by F. clavum, detected in Wyoming, USA. This finding will help to formulate effective management practices to manage the pathogen and prevent its widespread occurrence.

Evaluation of Sweet Potato (Ipomoea batatas) for Early Blast Disease (Alternaria solani)

Aims: Early blight disease (Alternaria solani) is one of the main biotic factors limiting sweet potato production in the tropics. A multi-locational research was carried out to screen and identified sweet potato accessions that are resistant to the disease.
 Methodology: 21 sweet potato accessions were collected from different agro-ecological zones of Nigeria and screen against Alternaria solani by artificial inoculation of the pathogen in three diverse agro-ecological conditions. The accessions were named against their place of condition. The research were laid out in a Randomized Complete Block Design (RCBD) with three replications. Data were collected on days to 50% flowering, fresh root weight per plant, number of root per plant, number of main branches per plant, and above ground fresh biomass yield per plant at 15 weeks after planting (WAP). Disease scoring was done using rating scale 0f 0-9 and analyzed with IRRI STAR software.
 Results: The result revealed that there are variations in the 21 accessions studied. Offa performed best across the three environments followed by Umudike while Ado-Ekiti had the least performance in term of root yield. The screening shows that none of the 21 accessions is highly resistant. Four of the accessions were resistant, six accessions were moderately resistant, four accessions were susceptible, and three accessions were moderately susceptible while 4 accessions were highly susceptible to the pathogen.
 Conclusion: The findings concluded that the resistant accessions that gave high number roots could be used as a gene pool for Alternaria solani resistance breeding for cultivar improvement. The use of the identified resistant accessions with high root yield by farmers is encouraged pending the time commercial Alternaria solani resistant cultivars will be readily available and accessible.