Biology subjects

Laranjeira, F. F.

Publications and source records attributed to Laranjeira, F. F..

4 recordsLinked to original sources

bioRxiv2019

Spatiotemporal dynamics and modelling support the case for area-wide management of citrus greasy spot in a Brazilian smallholder farming region

Citrus greasy spot (CGS), caused by Zasmidium citri, induces premature defoliation and yield loss in Citrus spp. CGS epidemiology is well understood in areas of high humidity such as Florida (USA), but remains unaddressed in Brazil, despite differing climatic conditions and disease management practices. We characterize the spatiotemporal dynamics of CGS in the Reconcavo of Bahia, Brazil, focusing on four hierarchical levels (quadrant, plant, grove and region). A survey conducted in 19 municipalities showed that disease is found throughout the entire region with a prevalence (i.e. proportion of affected sampling units) of 100% in groves and plants, and never lower than 70% on leaves. Index of dispersion (D) values suggest the spatial pattern of symptomatic units lies somewhere between random and regular. This was confirmed by the parameters of the binary power law for plants and their quadrants (log(A)<0 and b<1). Variability in disease severity at different plant heights (0.7 m, 1.3 m and 2.0 m) was tested, but no consistent differences were observed. We introduce a simple compartmental model synthesising the epidemiology of the disease, in order to motivate and guide further research. The data we have collected allow such a model to be parameterised, albeit with some ambiguity over the proportion of new infections that result from inoculum produced within the grove vs. external sources of infection. By extending our model to include two populations of growers - those who control and those who do not - coupled by the spread of airborne inoculum, we investigate likely performance of the type of cultural controls that would be accessible to citrus growers in Northeastern Brazil. Our model shows that control via removal of the key source of inoculum - i.e. fallen leaves - can be very effective. However, successful control is likely to require area-wide strategies, in which a large proportion of growers actively manage disease.

ecology↗

bioRxiv2019

Illuminance affects epidemiological parameters of banana Yellow Sigatoka in Brazil

The Sigatoka leaf spots are among the most important banana diseases. Although less damaging than black sigatoka, yellow sigatoka (Pseudocercospora musae) still prevails in some regions. This study aimed at testing the hypothesis of light interference in monocyclic parameters of yellow sigatoka epidemics. Grande Naine plantlets kept under contrasting shading conditions had their leaves 1 and 2 inoculated. Evaluations were performed for 60 days. For each inoculated leaf, the time until symptom onset (incubation), presence of infectious lesions (latency), and disease severity (extensive leaf necrosis) according to Stovers scale modify per Gauhl (1994), called here only Stovers scale, were registered. Logistic regression was used to assess the relative occurrence risk and survival analysis was used to check the effects of variables on relevant epidemiological parameters. The risks of sporulation and of reaching high severities were lower for plants kept under shading regardless of the acclimation conditions and no effect of leaf age was detected. The logistic regression showed symptoms appearing in both conditions (p=0,85), but have significance difference in occurrence of latent lesions (p=0,013) and necrosis (p<0,0001). The necrosis risk in non-shaded environment arrived 66%. The survival analysis showed significance difference in the time to appear the symptom evaluated in all tested variables (p<0,0001) in function of the cropping system. Lower illuminance negatively affected the incubation, latency and infectious periods, and severity. A shaded system could be tested to produce organic bananas in areas of high risk of occurrence of Yellow sigatoka disease.\n\nSignificance and Impact of the StudyYellow Sigatoka (Pseudocercospora musae) is a banana disease that can cause severe damage if left uncontrolled. Its control is based mostly on fungicides.Our results show that shading downregulates the epidemiological parameters of that disease such as incubation, latent and infectious periods, and symptoms severity. These results can be the basis for testing alternative cropping systems and producing organic bananas.

microbiology↗

bioRxiv2019

Modelling in vitro mycelial growth, sporulation and spore germination of Pseudocercospora musae under different illuminance levels

Banana is one of the most produced fruits in the world. Many diseases infect the culture and yellow sigatoka is one of the most important. Light may interfere in the pre-penetration parameters of the fungus. The aim of this study was to evaluate the action of light on aspects of the life cycle of the causal agent. The action of light was tested in vitro on the mycelial growth, sporulation and germination of the fungus. For the mycelial growth 10 colonies were transferred to each Petri plate, by evaluating the green weight of a plate at each moment, in mg, at zero, 15, 21, 28, 35 and 42 days of cultivation according to different illuminance levels. Under the same conditions, the sporulation was also quantified at 5, 7, 11, 13 and 14 days. For germination, equal volumes of a spore suspension were placed in small glass containers, which then were set in mini-shades (different illuminances). Every 1h, lacto-phenol was added to a glass from each environment paralyzing the growth, at the same time, illuminance measurements were made with a light meter. The data obtained from sporulation (linear relation) and germination (positive exponential behavior) were significant for the illuminance levels tested.\n\nSignificance and Impact of the StudyYellow Sigatoka disease, caused by Pseudocercospora musae, is still one of the most importante banana diseases in Brazil. Its control demands the use of fungicides. New environmental-friendly control methods should be developed. Therefore, the behaviour of both fungus and plant-fungus interaction should be known. We modelled the in vitro behaviour of P. musae in function of light intensity. Our results can help to develop shading strategies to control yellow Sigatoka.

microbiology↗

bioRxiv2019

Modelling the in vitro pre-infection dynamics of Colletotrichum spp. isolated from yellow passion fruit in function of environmental variables

Brazil is the largest world producer of yellow passion fruit, but the mean yield (14.3t.ha-1) is less than half the potential of the crop. Part of this difference can be explained by plant health problems, including anthracnose caused by Colletotrichum spp. In regions with favorable climatic conditions, anthracnose can be a factor of significant yield reduction, but these regions have not yet been zoned. The objective of this study was to model the pre-infection dynamics of the fungus. The influence of temperature and photoperiod was studied on mycelia growth, sporulation and conidia germination. Mathematical models were fitted to the results and the optima for the environmental variables were estimated. The maximum mycelia growth was estimated to occur at 26.5{degrees}C. Between 24.5{degrees}C and 28.5{degrees}C the fungus grew from 95% to 100% of the estimated maximum. Temperatures below 13{degrees}C or above 34{degrees}C were harmful to mycelia growth. Temperatures over 26{degrees}C were the most favorable to sporulation while below 13{degrees}C sporulation was only 5% of the maximum. Optimum germination occurred between 25{degrees}C and 29{degrees}C with the ideal wetness period between 11h and 13h. These results can be used as a basis for zoning the risk of anthracnose occurrence in passion fruit producing regions.\n\nSignificance and Impact of the StudyMany diseases affect the yellow passion fruit crop, limiting its yield; among them anthracnose, caused by Colletotrichum spp. The disease occurs in both field (leaf and stem symptoms) and post-harvest (fruits) conditions. Understanding the role environmental conditions play in the biological cycle of such diseases is essential for developing management strategies. By modelling mycelial growth, spore production and spore germination of Colletotrichum spp. as affected by temperature, photoperiod and wetness period, it was possible to characterize the pathogens pre-infectional dynamics. The results should be used as a first approximation to estimate the risk of anthracnose occurrence in pre- or post-harvest.

microbiology↗