Tropical Plant Pathology最新文献

Peanut smut (Thecaphora frezzii) is one of the most important peanut diseases in Argentinian peanut production. This monocyclic soil-borne pathogen transforms kernels into spore masses. Spore liberation from broken infected pods during the harvest process is supposed to be the main mechanism of inoculum spread, with the subsequent spread among fields increasing the soil inoculum for future peanut cropping seasons. However, we are unaware of any published study on the role of wind (in terms of speed and direction) in how far smut spores spread. Therefore, we conducted an observational study where passive spore traps were distributed at harvest around six fields placed at 100, 200, 300, and 400 m away from each field’s centroid in four cardinal directions. Three time slices were sampled: from the beginning of harvest to 90-, 180-, and 270-minutes continuously during harvest. Wind speed and direction were recorded at each trap. A generalized additive model was fitted to describe the spore spread. Modeling the dispersal shows that the spread is influenced by wind speed and the smut severely damaged pods incidence present at the harvested field. Additionally, spore size and proportion of different smut spore types were assessed (from a single unit spore to a 5-multinuclear propagule). No statistical differences were observed in the proportion of the spore types trapped. However, fewer spores were trapped at distances farther from the harvested area. This work led us to understand a fundamental component of the peanut smut cycle and epidemiology, which is to design management strategies. For example, avoiding harvest on windy days (typically >10 km h^-1) to prevent the distant spread of inoculum for subsequent seasons or predicting the risk surrounding an infected field.

Abstract

Coffee leaf rust (CLR) caused by Hemileia vastatrix is a devastating worldwide disease. Early monitoring is crucial for controlling CLR quickly and efficiently. However, accurately identifying CLR in its early stages via the naked eye is challenging. Moreover, detecting H. vastatrix using PCR-based methods is time-consuming, labour-intensive, and occasionally exhibits low sensitivity. Loop-Mediated Isothermal Amplification (LAMP) technology is known for its speed, specificity, and sensitivity to identifying many pathogens accurately. Therefore, in this study, we conducted a comparative analysis of ITS sequences from H. vastatrix and other H. vastatrix and Uredinales strains available in the National Center for Biotechnology Information (NCBI) database using the BLASTn tool. Based on this analysis, we designed specific primers that target the unique region and its flanking regions within the ITS sequences of H. vastatrix. Using SYBR Green I dye, we established a LAMP technique for rapid and sensitive detection of H. vastatrix. Moreover, we optimised the LAMP protocol to enhance sensitivity and specificity for H. vastatrix detection. Under the optimised conditions, the established LAMP protocol detected as little as 1pg/μL of H. vastatrix DNA within 60min at 63°C. This sensitivity is approximately 100 times higher than that achieved using conventional PCR. Our method proved effective in detecting H. vastatrix at the early stages of CLR symptom development on the coffee leaves in field conditions.

Bacterial blight caused by Pseudomonas savastanoi pv. glycinea (Psg) is a prevalent disease in soybean crops worldwide, and crop rotation is a potential management strategy. However, the importance of alternative crops and soil as hosts of Psg is not well understood. This study aimed to assess the survival of Psg in four soil types, the phyllosphere, and rhizosphere of 12 crops rotated with soybean, and endophytic colonization of crops by Psg. The pathogenic strain Soj. 1462 of Psg, resistant to rifampicin, was used in all experiments, and culturing followed by PCR confirmed bacterial survival. Psg survived for a maximum of two days in all soil types. In both survival niches, phyllosphere and rhizosphere, sunn hemp, common bean, and turnip proved to be the crops with a shorter Psg survival period, lasting less than 28 days, while the remaining evaluated crops exhibited longer survival periods. In endophytic colonization, Psg survived for less than 35 days in these crops when inoculated in artificially wounded plants. When inoculated by spray in the same crops, the highest Psg survival was recorded up to 28 days. To reduce Psg inoculum, it is advisable to cultivate sunn hemp, common bean, and turnip in succession with soybean, given their comparatively lower recorded survival periods.

The long-tailed mealybug, Pseudococcus longispinus, is an important insect pest in grapevine growing areas in several countries, including Brazil. Metagenomic analysis of nucleic acids extracted from insect vectors makes it possible to study the diversity of insect viruses in addition to plant pathogenic viruses. In this study, insects (Ps. longispinus) were collected, and pooled throughout a plot of virus disease symptomatic vines, cultivated in growing beds, and analyzed by high throughput sequencing (HTS). The complete genome of grapevine leafroll-associated virus 2 and 3 (GLRaV-2 and -3) and a partial sequence of grapevine virus A (GVA) with two complete ORFs (coat protein and RNA-binding protein) were assembled from mealybug extracts and exhibited high nucleotide identities, up to 99%, with previously characterized homologous Brazilian isolates from grapevines. This information was validated by the detection of these viruses in the original symptomatic vines (N=76), from where mealybugs were collected, equivalent to an incidence of 34.2%, 89.5% and 36.8% for GLRaV-2, GLRaV-3 and GVA, respectively. Although one of these viruses is not transmitted by mealybugs (GLRaV-2), prospection of plant viruses infecting grapevine plants by analyzing the metagenome of insects could represent a relevant alternative to improve monitoring of viral diseases aiming at the management and control of viral diseases in vineyards or cultivation fields. This work is the first analysis of the Ps. longispinus virome in Brazil focusing on grapevine viruses.

Abstract

Botrytis cinerea Pers. is a polyphagous fungal pathogen that can cause significant damage in the field, warehouse, and greenhouse conditions. In Turkey, fungicides with site-specific modes containing the active ingredients boscalid and pyraclostrobin are used to control B. cinerea. In this study, it was aimed to determine the mutations associated with resistance to boscalid and pyraclostrobin active substances in B. cinerea isolates obtained from tomato, pepper, eggplant, and lettuce in Turkey. In the in vitro bioassay, a conidial germination test was performed. It was determined that 26% of the isolates used in the bioassay test were resistant. After that, mutations associated with resistance were investigated. Mutations associated with boscalid resistance were found in 18 isolates whose SdhB gene was sequenced. No mutations were detected in sensitive MH51 and Ant34 isolates. It has been determined that N230I and H272R mutations were found to be frequent in B. cinerea populations in Turkey. P225F mutation was detected only in the B4 isolate obtained from the pepper in Antalya. The mutations associated with boscalid resistance detected in this study are reported for the first time in Turkey. The G143A mutation associated with pyraclostrobin resistance was detected in all the isolates sequenced.

Abstract

Ratoon stunting disease (RSD) is a pervasive bacterial disease in the world, which seriously affects the yield and quality of sugarcane. To clarify the incidence of RSD in various ecological zones, different varieties, and crop cycles in Yunnan, 214 samples were collected from three planting regions situated in the North Tropic Humid and South Subtropical Humid zones. These samples underwent molecular detection for RSD. The results showed that the highest positive detection rate of RSD was 88.57% in Longzhang in the South Subtropical Humid zones. RSD was detected in 18 main planting or promoting varieties, the positive detection rate was 42.86%-100%. For the crop cycles, RSD occurred in different degrees from newly planted to fourth ratoon crop. The results reveal significant differences in RSD incidence dynamics among sugarcane varieties, crop cycles, and ecological areas. Notably, during the transition from newly planted to second ratoon crop, RSD incidence increased with the duration of ratoon years in different ecological sugarcane areas. Furthermore, there was a tendency for RSD incidence to increase with successive ratoon years in varieties Yuetang 93-159, Yunzhe 08-1609, Liucheng 05-136, Yunzhe 05-51, Liucheng 03-182, Chuantang 79-15 and Yunzhe 05-49.

Asian soybean rust (ASR), caused by the pathogen Phakopsora pachyrhizi, is one of the most notable soybean diseases in Paraguay because of the associated productivity losses and expenditures related to fungicide use. There is also concern regarding the environmental impact of excessive fungicide use. In addition, the decreased sensitivity of ASR pathogens to various fungicide groups has been reported in recent years. To effectively control ASR, it is necessary to combine fungicides with resistant varieties. To introduce ASR resistance genes (Rpp: Resistance to P. pachyrhizi) into Paraguayan soybean cultivars, the effectiveness of Rpp resistance genes must be determined, as a few are rendered ineffective due to virulence changes in the pathogen population. In this study, the effectiveness of 12 different soybean genotypes with different Rpp genes was evaluated using 18 P. pachyrhizi samples obtained in the 2016/17, 2017/18, 2018/19, and 2019/20 seasons and compared with the previous eight seasons from 2007 to 2015. Yearly changes in virulence were observed in a few differentials; however, these changes were not always from avirulent to virulent. Further, all differential varieties with a single resistance gene showed resistant phenotypes in less than 50 % of the samples in their least effective years. Considering these observations, the introduction of a single resistance gene poses a risk in breeding for ASR resistance. The differentials carrying a single gene, Rpp1-b or Rpp5, tended to show high frequencies, specifically 86.9–89.8 % resistance in the tested samples from 2007–2019, and that of the Rpp-pyramided line carrying Rpp2 + Rpp4 + Rpp5 was 97.0 %. Therefore, the introduction of two or more resistance genes, via combination with Rpp1-b and/or Rpp5, or the introduction of Rpp2 + Rpp4 + Rpp5 would be effective and durable for mitigating the Paraguayan ASR pathogen.

Brazil stands out as the third largest corn producer in the world, showing self-sufficiency to supply its entire national demand. However, maize red stunt, caused by maize bushy stunt phytoplasma (MBSP), is one of the most harmful diseases to this crop, requiring fast and accurate detection methods to deal with this threat. One such method is loop-mediated isothermal amplification (LAMP), a fast, sensitive, and highly specificity tool that can be used in field analysis. From this perspective, this study aimed to develop a LAMP protocol through comparative genomics for MBSP in maize. To design the sets of primers, the MBSP genome sequence and sequences of other pathogens were used in the RUCS software (Rapid identification of PCR primers for Unique Core Sequences) to select only core unique sequences. Three sets of primers had the desired criteria and were synthetized. The most promising primer set, MBSP-LP, was used to test the LAMP assay together with the Warmstart colorimetric LAMP 2X master mix (NEB) Kit. The reaction optimization uses a 4:1 proportion of primers and a temperature of 65 °C for 60 minutes. The collection of 51 samples of corn with and without symptoms was tested with a typical nested-PCR and compared with the proposed LAMP assay. Considering the presence and absence of symptoms, there was confirmation that the symptomatic plants were positive for LAMP in a greater proportion than for nested-PCR. The proposed LAMP assay proved to be sensitive, detecting up to 0.1 fg µL^-1 of DNA. The use of plant material directly in the reaction was evaluated for the presence of any inhibitors of the reaction. It was identified that there are no inhibitors in the maize plant tissue, and this LAMP assay can be used without the DNA extraction step.

The Stem-end rot (SER) postharvest disease of mango (Mangifera indica L.) fruits is a significant economic threat to mango production. Without proper management strategies, it can lead to up to 100 % postharvest losses. Despite its importance, very little information is known about this disease in Côte d'Ivoire. This research aimed to determine the incidence and severity of SER in mango orchards, assess how preharvest climate parameters affect the disease and determine the pathogenic fungi associated with SER. Mango SER was evaluated on 1500 mango fruits collected from 15 orchards in Boundiali, Ferkéssédougou, Korhogo, Odienné, and Sinématiali departments. Mango SER incidence ranged from 10 % to 30 %, while severity ranged from 5 % to 20 %. No significant differences in these parameters were observed between the different departments (P>0.05). The study also revealed a positive low correlation between SER disease incidence and mean air temperature (r = 0.36) and minimum air temperature (r = 0.26) data, indicating that preharvest weather conditions may have a marginal impact on mango SER disease intensity in the postharvest phase. Pathogenic fungi associated with SER were isolated and identified using morphological characteristics and multilocus sequence analysis of the rDNA internal transcribed spacer (ITS) region and the translation elongation factor 1-alpha (tef1-α). Various fungal species associated with mango SER disease were also identified, with Lasiodiplodia species (74%) being the most prevalent (including Lasiodiplodia theobromae, L. euphorbicola, and L. caatinguensis), followed by Colletotrichum gloeosporioides, Curvularia pseudobrachyspora, Diaporthe endophytica and Fusarium mangiferae. However, only Lasiodiplodia species and Diaporthe endophytica induced SER symptoms. This study was the first ever evaluation of mango SER disease and associated fungal pathogens identification in Côte d'Ivoire. This result will assist researchers in developing a control method for mango SER.

Soybean Phytophthora root rot (PRR) caused by Phytophthora sojae is one of the most devastating diseases of soybean worldwide. This study was conducted to develop new effective biocontrol agents for the control of the disease and explore the action mechanism. Eleven antagonistic bacterial strains against P. sojae were isolated from the soybean field soil samples, and among the strains, BS-4 not only had the strongest inhibitory activity against P. sojae, but also had good inhibition to other four species of oomycetes in Phytophthora and eight fungal pathogens. Based on 16S rDNA sequence analysis and the physiological and biochemical properties, the strain BS-4 was identified as Bacillus altitudinis. Strain BS-4 culture filtrate had significant inhibitory effects on the pathogens, and the inhibition rates were stronger than those in the dual culture. BS-4 filtrate kept a high bioactivity to P. sojae at a high temperature, even at 121℃, and in the pH range of 5 to 12. The germination of zoospores and the formation of sexual organs were seriously affected by BS-4 filtrate. Furthermore, detached leaf assays and greenhouse experiments showed that BS-4 suspension and culture filtrate all had good disease control efficacy, and in the field experiment, BS-4 suspension reduced the disease index and increased the biomass of soybean shoots and roots, significantly (P < 0.05), with control effect of 75.29% on PRR. It is suggested that B. altitudinis strain BS-4 is a novel potential biocontrol agent to control PRR, and will have a broad application prospect in PRR biocontrol.