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Sustainable soil management to optimize water use and enhance nutrient uptake is a promising approach for decreasing the incidence of coffee leaf rust. This work analysed soil coverings, fertilizers and soil conditioners to optimize water usage and nutrients in coffee rust management. The experiment was set up in the field in January 2016, with seedlings of Coffea arabica ‘Mundo Novo IAC – 379‐19’, susceptible to rust. The experimental design was in randomized blocks with three replications and arranged in a 3 × 2 × 5 factorial scheme. We assessed the combination of three soil coverings (plastic film, Urochloa decumbens and bare soil), two fertilizer types (conventional and controlled release) and five soil conditioners (organic compound, coffee husk, agricultural gypsum, water‐retaining polymer and control without soil conditioner). The rust incidence and foliage progress curve were integrated into the area under the rust incidence or foliage progress curve. Additionally, we assessed the leaf area index and coffee yield. The association of U. decumbens with controlled‐release fertilizers and organic compound or coffee husk increased coffee foliage and yield despite higher disease incidence. [ABSTRACT FROM AUTHOR]

Coffee leaf rust (CLR), caused by Hemileia vastatrix, poses a significant threat to global coffee production, resulting in substantial economic losses. This study explores the effectiveness of triazole derivatives synthesized from glycerol in controlling CLR in conilon coffee (Coffea canephora). In vitro assays evaluated the inhibitory effect of triazole derivatives (4a–4q) at concentrations of 10, 25, 50, 75 and 100 ppm on H. vastatrix urediniospore germination, followed by greenhouse experiments to assess their preventive and curative potential. Preventive and curative sprayings of the four most efficient triazoles were conducted on seedlings inoculated with H. vastatrix at concentrations ranging from 0 to 400 ppm, evaluating severity, sporulation, incubation and latent periods. Triazole derivatives 4b, 4d, 4f and 4o effectively suppressed H. vastatrix urediniospore germination, achieving reductions between 9.9% and 78.8%. In greenhouse trials, these compounds demonstrated preventive efficacy by prolonging incubation and latent periods, reducing sporulation and mitigating rust severity, with triazole 4f exhibiting the highest efficiency. Furthermore, the derivatives showed effectiveness in curative treatments, particularly triazole 4f. Physiological analyses indicated no significant alterations in coffee plant metabolism, suggesting the safety of these compounds for agricultural use. Molecular docking studies elucidated their mechanism of action, suggesting their potential as antifungal agents by interacting with the HvCYP51 enzyme involved in ergosterol biosynthesis. Overall, the study underscores the promising efficacy of glycerol‐derived triazole derivatives in managing CLR, providing sustainable solutions for disease control in agriculture. [ABSTRACT FROM AUTHOR]

Coffee leaf rust (CLR) is caused by the biotrophic pathogenic fungus Hemileia vastatrix. Despite being the most researched coffee disease, mysteries still exist relating to its epidemiology and biology. The objective of this work is to highlight past and present events concerning this prominent coffee disease. We start with an historical overview of the homeland of Coffea arabica, the Afromontane forest of south‐west Ethiopia, and then follow its journey across the globe linked to colonial trade and power struggles. We report the relevance of CLR to coffee production today, with a focus on the Americas and summarize unproven hypotheses in relation to the cause of recent epidemics. We present an original hypothesis concerning the first major outbreak occurring in 1869 in Ceylon (Sri Lanka), based on geopolitical connections to global trade. We review old and new options for management of the disease. The likelihood of a yet undetected alternate host of H. vastatrix is also considered as an additional piece of the epidemiological puzzle. Finally, we reflect on the interactions between H. vastatrix and a changing climate. By better understanding past events, linked to CLR, we may be better prepared for future outbreaks. [ABSTRACT FROM AUTHOR]

Coffee leaf rust is the most limiting disease for coffee cultivation in Brazil. Despite its importance, relatively little is known about the genetic diversity of Hemileia vastatrix, the rust causal agent. In this work, the DNA from 112 monopustule isolates from different geographic locations and coffee genotypes were analysed by amplified fragment length polymorphisms ( AFLP). The objectives were to assess the influence of the host and geographic origin on the diversity and population differentiation in H. vastatrix. The fungal population showed a low level of genotypic diversity. Gene diversity ( h) was 0·027 and the hypothesis of random mating in the total population was rejected, but evidence for recombination was found for two subpopulations (São Paulo and Paraná). The analysis of molecular variance revealed that 90% of the genetic distribution of the pathogen occurs among isolates within the subpopulation (states or host of origin). There was no correlation between geographic and genetic distance ( r = −0·024, P = 0·74), which together with the high number of migrants and the low degree of differentiation in populations of H. vastatrix, is consistent with the fact that the inoculum is probably easily dispersed by wind over long distances, allowing dispersal of the pathogen among coffee growing areas in Brazil. Therefore, it is difficult to predict the durability of resistant sources to coffee rust. The recommendation for the breeding programmes is thus to incorporate multigenic resistance as a control strategy. [ABSTRACT FROM AUTHOR]

The genome size of most rust species is unknown due, in part, to technical constraints, especially the difficulty in accessing spores to extract the nuclei for cytometry. Using the urediniospores of coffee rust, Hemileia vastatrix, an improved methodology involving flow cytometry was developed for accurate measurement of the nuclear genome size. The results revealed that the genome of this primitive rust fungus is unusually large - measuring 1C-value = 0·75 pg (733·5 Mb) - significantly bigger than other species quantified thus far in the more advanced rust lineages. The evolutionary consequences and the potential ecological constraints of this large genome size are discussed in relation to the epidemiology of coffee rust. [ABSTRACT FROM AUTHOR]

A standard area diagram (SAD) set to aid assessment of the severity of coffee leaf rust ( Hemileia vastatrix) was prepared and validated, and the characteristics of the rust lesions on Coffea arabica and C. canephora leaves were compared. The results indicated that the lesions were similar, so one scale could be used to evaluate the severity of rust on both species. The proposed SAD set contains illustrations of leaves with six disease severities (2·5, 5, 10, 20, 40 and 80%). The SAD set was validated by 10 raters with no previous experience of disease evaluation. The severity of rust was first estimated without using the SADs, and the same raters assessed the leaves again using the SADs. Regression analysis and Lin's concordance correlation ( ρ c) analysis of estimated against actual disease severity showed precision and accuracy was significantly better using the SADs, for most raters, with improvements in both the slope and intercept of the regressions, and the values of u, υ (components of accuracy and precision of the ρ c) and ρ c improved to 60, 70 and 90% of raters, respectively, when the SADs were used. The absolute error was ≤38% without the SADs, and ≤22% with them. Severity estimates were more reliable using the SADs ( R2 = 0·70-1·00 unaided, and R2 = 0·80-1·00 using the SADs). The SAD set improved rater assessments for the estimation of arabica and conilon rust severity, and can be used for assessing rust severity for many purposes, including plant breeding, fungicide screening and pathotype characterization. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess whether defence responses in coffee ( Coffea arabica) were linked to a specific developmental stage of the rust fungus Hemileia vastatrix. Histological observations in compatible and incompatible high-yielding Brazilian coffee cultivars showed that the fungus produced ‘pioneer’ haustoria in adjacent and subsidiary stomatal cells soon after entering the stomata, followed by later developed ‘secondary haustoria’ which invade mesophyll cells. In the incompatible interaction between Race II and cv. Tupi, a strong and transient H2O2 generation at infection sites was detected at 39 h post inoculation (hpi) during secondary haustoria formation. In addition, clear-cut differences in defence gene expression between compatible and incompatible interactions were only observed during the secondary haustoria formation. Transcripts of the pathogenesis-related (PR) genes CaPR1b and CaPR10 accumulated to maximal levels at 39 hpi (38- and 86-fold, respectively) in the incompatible interaction, but stayed at low levels in the compatible interaction. In contrast, the CaWRKY1 gene and the CaRLK gene were only induced in the susceptible cultivar. These results indicated that the specific resistance of cv. Tupi was expressed after differentiation of the H. vastatrix secondary haustoria. Analysis showed no evidence of specific recognition of coffee rust at the pioneer haustoria stage, suggesting that haustoria components are not recognized by, or not secreted into, the subsidiary and adjacent cells of the stomata. Additionally, the present study provides new insights into the colonization process of the coffee rust fungus. [ABSTRACT FROM AUTHOR]

The entomogenous fungus, Lecanicillium lecanii is hyperparasitic on Hemileia vastatrix, the cause of coffee leaf rust in the laboratory, and has frequently been observed attacking it in the field. The existence of a complex ecological web involving the spatially clustered mutualism of an ant ( Azteca instabilis) with a scale insect ( Coccus viridis), where the scale insect was infected by L. lecanii, prompted a search for a spatial correlation between the attack of L. lecanii on the scale insect and the incidence of rust in a commercial coffee crop. A weak but statistically significant effect of hyperparasitic control of coffee rust was observed on two distinct scales: in a 45-ha plot and on a scale of approximately 10 m. It was concluded that this effect was linked to an indirect effect of the ant–coccid mutualism, where L. lecanii was a parasite of the coccid. [ABSTRACT FROM AUTHOR]

The effects of crop management patterns on coffee rust epidemics, caused byHemileia vastatrix, are not well documented despite large amounts of data acquired in the field on epidemics, and much modelling work done on this disease. One main reason for this gap between epidemiological knowledge and understanding for management resides in the lack of links between many studies and actual production situations in the field. Coffee rust epidemics are based on a seemingly simple infection cycle, but develop polycyclic epidemics in a season and polyetic epidemics over successive seasons. These higher-level processes involve a very large number of environmental variables and, as in any system involving a perennial crop, the physiology of the coffee crop and how it affects crop yield. Crop management is therefore expected to have large effects on coffee rust epidemics because of its immediate effect on the infection cycle, but also because of its cumulative effect on ongoing and successive epidemics. Quantitative examples taken from a survey conducted in Honduras illustrate how crop management, different combinations of shade, coffee tree density, fertilization and pruning may strongly influence coffee rust epidemics through effects on microclimate and plant physiology which, in turn, influence the life cycle of the fungus. We suggest there is a need for novel coffee rust management systems which fully integrate crop management patterns in order to manage the disease in a sustainable way. [ABSTRACT FROM AUTHOR]

The age of a leaf at the time of inoculation affected both development of infection structures on the leaf surface and subsequent sporulation. In the case of the susceptible genotypes, cv. Caturra and line NC-169, there was a decrease in the number of appressoria formed, with an increase in age of fully expanded leaves. On the selected resistant line, NP-547, significantly fewer appressoria were formed on the fourth leaf pair than on younger or older leaf pairs. Appressoria were formed significantly more readily over stomata of leaf pairs one, two, three, four and six than over five and seven of the susceptible selections. On the youngest leaf pair a significantly large percentage of appressoria formed away from stomata compared with the percentages obtained for older leaf pairs, where a large proportion of germinated uredospores did not form appressoria. The reaction type of the susceptible genotypes was a greater value on younger than older leaf pairs, and the reverse was true of the resistant genotype. The latent period (inoculation to sporulation) was shorter on NC-169 than on cv. Caturra. No uredospores formed on NP-547. Uredosorus density decreased with an increase in leaf age on the susceptible genotypes. [ABSTRACT FROM AUTHOR]