Nanoparticles in inhibiting Pantoea ananatis and to control maize white spot

ABSTRACT: Maize white spot (MWS) caused by Pantoea ananatis is one main maize leaf diseases, and nanoparticles (NPs) are an innovative approach for bacterial disease control. This research evaluated the toxicity of pure NPs and doped NPs with different elements in inhibiting bacterial growth and to control MWS. Pure NPs and ZnO NPs doped with silver (Ag), gold (Au), copper (Cu), iron (Fe), manganese (Mn), and nickel (Ni) at different concentrations were used to determine the toxicity for P. ananatis in vitro, evaluating the bacterial growth inhibition zone. To assess the control of MWS, in the preventive application, maize plants were sprayed with NPs of ZnO:0.1Cu, ZnO:0.05Fe, ZnO:0.2Mn and ZnO:0.7Ni at 10, 5 or 2.5 mg mL-1, and after 3 days, the plants were inoculated with bacterial suspension. To assess the curative application, plants were inoculated with the bacteria, and 3 days later sprayed with the NPs. The disease severity was assessed and the area under the disease-progress curve (AUDPC) was calculated. The doped ZnO NPs with different elements, and at different concentrations inhibited bacterial growth in vitro. NPs of ZnO:0.1Cu and ZnO:0.2Mn at 5 or 2.5 mg mL-1, in both applications reduced the severity of MWS, showing potential for use in the disease management.

Epidemiological study of Colletotrichum spp. associated with Enterolobium cyclocarpum (Jacq.) Griseb. and Platymiscium pinnatum (Jacq.) Dugand in the Colombian Caribbean Region

Epidemiological analyzes of foliar diseases associated with Colletotrichum spp. in Enterolobium cyclocarpum and Platymiscium pinnatum were performed under field conditions and without any type of intervention. At the Universidad del Magdalena (Santa Marta, Colombia), four trees for each species and four equidistant monitoring sites per tree were established. The incidence and severity were recorded for 33 weeks (March to November 2016), including two follow-up periods: dry and rainy season. Disease development curves were elaborated. Moreover, the development rate (r) and the area under the disease progress curve (AUDPC) were calculated for each follow-up period. The effect of the meteorological variables was statistically analyzed by correlation and multiple regression. In E. cyclocarpum, the highest incidence and severity were recorded between September and November with 100 and 19.6%, respectively, showing a positive correlation with relative humidity and negative with average temperature, solar radiation and wind speed. In P. pinnatum, the maximum values of incidence and severity were observed between March and April with 68.9 and 1.3%, respectively. However, correlation analyzes did not support their relationship with the environmental factors. The r values during the dry months were 0.136 and 0.107 units week-1 and the AUDPCs were calculated at 51 and 4 units week-1 for E. cyclocarpum and P. pinnatum, respectively. In the rainy months, the r values were 0.187 and 0.016 units week-1 and the AUDPCs were 186 and 2 units week-1, respectively. In conclusion, the development of the disease varies according to the forest species, time of year and some meteorological variables.

Phylogenetic distribution of Ralstonia solanacearum species complex populations in potato in Kenya

Ralstonia solanacearum is a pathogen causing bacterial wilt disease of potato, resulting in 70% potato production losses in Kenya. A study was conducted to determine the diversity of Ralstonia solanacearum species complex strains within the main potato-growing regions of Kenya. Potato tubers were collected from different potato-growing regions of Kenya from visibly wilted potato plants, including tomato and irrigation water and cultured for pathogen isolation. Genomic DNA was isolated from 135 purified cultures of RSSC isolates and PCR amplified using multiplex and sequevar primers targeting the endoglucanase partial gene sequences. Pathogenicity test using R. solanacearum strain (phylotype II sequevar I) was done on Kenya Karibu, Shangi, Chulu, Wanjiku and Money Maker cultivars. Phylogenetic analysis of the partial endoglucanase gene identified two genospecies, R. pseudosolanacearum sp. nov (1.5%) and R. solanacearum (98.5%). All R. solanacearum strains clustered in sequevar I and were distributed in all the potato-growing regions surveyed. The cultivars were grown in a greenhouse for two cycles in a randomized complete block design and inoculated with R. solanacearum strain. The severity scores were assessed and the area under disease progress curve (AUDPC) was determined. All the cultivars tested for pathogenicity exhibited wilting symptoms at varying intervals after infection, with none showing complete resistance to R. solanacearum. Cultivar Shangi exhibited minimum disease severity and progression of 41.14% and AUDPC of 1041.7, respectively while Kenya Karibu was the most susceptible with a high progression rate of 68.24% and AUDPC of 1897.5, respectively. Money Maker, Chulu and Wanjiku showed no significant difference in disease severity depicting a simultaneous rate of infection among them. These findings provide valuable information to better understand the pathogen genetic diversity in Kenya and how it spreads.

Aqueous extracts from Acalypha gaumeri and Bonellia flammea for leaf blight control in chrysanthemum (Chrysanthemum morifolium)

The chrysanthemum is the second most important cut flower in the world, however, its quality and commercial value is affected by the leaf blight produced by <em>Alternaria </em>spp. The objective of this work was to evaluate the causal agent of leaf blight in Chrysanthemum, and its control with aqueous extracts of <em>Acalypha gaumeri </em>and <em>Bonellia flammea</em>. The fungus was collected and identified from leaves and stems of chrysanthemum plants. Subsequently, molecular identification and pathogenicity tests were performed on chrysanthemum plants. In the field, treatments were evaluated with weekly applications of: T1: <em>B. flammea </em>bark extract, T2: <em>A. gaumeri </em>root extract, T3: negative control (water) and T4: Captan® fungicide. Prior to the application of the treatments, plants were inoculated with the isolated fungus (2.5 × 106 spores mL-1) and severity was evaluated. <em>Alternaria chrysanthemi </em>was identified as the causal agent. Based on the severity percentage, the lowest averages of the area under the disease progress curve, the lowest rates of apparent infection, the lowest intensity of the disease and the greater effectiveness in controlling the disease were observed for T2 (165, 0.017, 8 and 67%, respectively) followed by T1 (186, 0.022, 13 y 50 %, respectively) and T4 (179, 0.023, 14 y 45%, respectively), observing a significantly different than negative control T3 (369, 0.025, 25 and 0%, respectively). Plant extracts have potential to be used as an alternative in the management of <em>Alternaria </em>leaf blight in chrysanthemum.

Combination of yeast antagonists and Acibenzolar-S-Methyl reduced the severity of Fusarium head blight of wheat incited by Fusarium graminearum sensu stricto

The combination of yeast antagonists and Acibenzolar-S-Methyl (ASM) was tested against Fusarium graminearum on a spring wheat cultivar PAN3471. Two strains of Papiliotrema flavescens (Strains WL3 and WL6) and a strain of Pseudozyma sp. (MGO1) were combined with full strength ASM at anthesis, half strength ASM at anthesis and quarter strength ASM at late boot stages. The yeast and ASM treatments were applied prior to F. graminearum inoculation and disease progress was assessed over time. The combination of yeast and ASM treatments effectively reduced Fusarium Head Blight (FHB) severity and deoxynivalenol (DON) concentration compared to when the treatments were used alone. A positive correlation was observed between the Area Under Disease Progress Curve (AUDPC) and Percentage Seed Infection (PSI) (r = 0.44) whereas a negative correlation was observed between AUDPC and Hundred Seed Weight (HSW) (r = -0.77) and PSI and HSW (r = -0.44). The best combination treatment providing the highest reduction in final disease severity (41.83%), high HSW and moderate PSI was 0.075 g/l ASM at anthesis plus P. flavescens strain WL3. The highest DON reduction (19.35%) was by the treatment 0.075 g/l ASM at anthesis plus P. flavescens strain WL6. The best treatment was P. flavescens combined with 0.075 g/l ASM at anthesis. Although Pseudozyma sp. strain MGO1 did not provide the best FHB and DON reduction, its combination with ASM application improved disease control efficacy. To the best of our knowledge, this study presents the first report of the combination of P. flavescens and ASM in the management of FHB caused by F. graminearum in wheat plants.

Genome-wide association analysis of anthracnose resistance in sorghum [Sorghum bicolor (L.) Moench]

In warm-humid ago-ecologies of the world, sorghum [Sorghum bicolor (L.) Moench] production is severely affected by anthracnose disease caused by Colletotrichum sublineolum Henn. New sources of anthracnose resistance should be identified to introgress novel genes into susceptible varieties in resistance breeding programs. The objective of this study was to determine genome-wide association of Diversity Arrays Technology Sequencing (DArTseq) based single nucleotide polymorphisms (SNP) markers and anthracnose resistance genes in diverse sorghum populations for resistance breeding. Three hundred sixty-six sorghum populations were assessed for anthracnose resistance in three seasons in western Ethiopia using artificial inoculation. Data on anthracnose severity and the relative area under the disease progress curve were computed. Furthermore, the test populations were genotyped using SNP markers with DArTseq protocol. Population structure analysis and genome-wide association mapping were undertaken based on 11,643 SNPs with <10% missing data. The evaluated population was grouped into eight distinct genetic clusters. A total of eight significant (P < 0.001) marker-trait associations (MTAs) were detected, explaining 4.86–15.9% of the phenotypic variation for anthracnose resistance. Out of which the four markers were above the cutoff point. The significant MTAs in the assessed sorghum population are useful for marker-assisted selection (MAS) in anthracnose resistance breeding programs and for gene and quantitative trait loci (QTL) mapping.

Yield and Disease Responses of Improved Groundnut Genotypes Under Natural Disease Infection in Northern Uganda: Implication for Groundnut Disease Management

Groundnut production in Uganda is constrained by groundnut rosette disease (GRD), the main cause of yield loss experienced by farmers. We conducted the current study to assess the responses of improved groundnuts to diseases (rosette and late leaf spot) and yield under local conditions. Four released groundnut genotypes (Serenut 5R, Serenut 8R, Serenut 9T and Serenut 14R) were evaluated in four locations in northern Uganda for two seasons in 2019. We established the experiment following randomised complete block design with three replications. GRD severity (harvest) and late leaf spot (LLS) severity (harvest) on the four genotypes were not significantly (P &gt; 0.05) different but positively correlated with the Area Under Disease Progress Curve (AUDPC). Genotype-by-location interaction for LLS AUDPC, GRD AUDPC and dry pod yield were significant (P &lt; .001). Season-by-genotype interaction was not significant (P = 0.367). Days to 50% flowering were also not significant (P &gt; 0.05). Highest and lowest yields were recorded for Serenut 9T in the Omoro district (1,291 kg/acre) and the Amuru district (609 kg/acre), respectively. Dry pod yield was significantly (P &lt; 0.001) negatively correlated with GRD severity and GRD AUDPC. Yield performance of the four genotypes was not significantly (P &lt; 0.05) different in the districts, except for Kitgum, where yields of Serenut 9T and Serenut 8R were significantly (P &lt; 0.05) higher. These genotypes could be used to manage GRD by smallholder farmers in Northern Uganda. Special consideration should therefore be given to these four groundnut genotypes for GRD management in the Acholi sub-region.

The efficacy of acibenzolar-S-methyl (ASM) in inducing resistance against Fusarium graminearum sensu stricto in wheat (Triticum aestivum L.)

Four ASM (acibenzolar-S-methyl) concentrations were applied on wheat plants at different growth stages prior to inoculation with 1x105 conidia/ml of Fusarium graminearum. Thereafter, disease severity was monitored and recorded over time. All ASM concentrations reduced disease severity compared to the control. The best treatment, providing the lowest Area Under the Disease Progress Curve (AUDPC) units, high average Hundred Seed Weight (HSW) and reduced average Percentage Seed Infection (PSI), was 0.075 g/L ASM applied at anthesis. A weak but significant positive correlation was observed between AUDPC and PSI (r = 0.33; p = 0.0001). However, a moderate and weak negative correlation was observed between AUDPC and HSW (r = - 0.41; p < 0.0001) and HSW and PSI (r = - 0.18; p = 0.04) respectively. Higher ASM concentrations were more effective when applied at anthesis and lower concentrations at late boot. Moreover, repeated applications (applied at both late boot and anthesis) did not improve disease reduction. A disease reduction and deoxynivalenol (DON) reduction of up to 28.97% (0.075 g/L ASM applied at anthesis) and 18.79% (0.0375 g/L ASM applied at anthesis) was observed. However, DON and zearalenone (ZEA) reduction did not always correspond with disease severity reduction of tested treatments. This accentuates the importance of the development of integrated control strategies for the improved and effective management of Fusarium head blight (FHB) in wheat.

Selection of Diploid and Tetraploid Banana Hybrids Resistant to Pseudocercospora fijiensis

Black Sigatoka, a disease caused by the fungus Pseudocercospora fijiensis, can lead to the complete loss of banana and plantain production in the absence of chemical control. The development of resistant cultivars is the focus of many banana breeding programs and is an alternative to the use of fungicides. In order to define a refined method of selection in genetic breeding programs, this study evaluated 23 improved diploids, seven tetraploids, and two commercial cultivars in the presence of P. fijiensis. Four selection criteria were considered: means of the disease severity index (ID) and area under the disease progress curve (AUDPC) estimated over the total period of the experiment, only in summer, only in winter, and the emission and harvesting of bunches. The selection of genotypes was more effective in the winter, and the evaluation of four leaves no. 3 emitted after six months of growth was efficient at differentiating the resistant and susceptible genotypes. For the improved diploids and tetraploid hybrids, DI varied from 0.0 to 48.8 and from 15.1 to 63.5, respectively, and the AACPD for the improved hybrids and tetraploid hybrids varied from 0.0 to 2439.5 and 1000.2 to 3717.7, respectively. The tetraploid hybrid of the Prata-type CNPMF0906 and the commercial cultivar, which is a hybrid of the BRS Princesa Silk type, showed quantitative resistance and can be used by banana producers. Results suggest that the guidelines adopted for the selection of genotypes resistant to black Sigatoka may include methodologies that reduce the evaluation time. In addition, new sources of resistance to the disease and the influence of its genetic inheritance in future crosses were found.