Blowin’ in the Wind: Wind Dispersal Ability of Phytopathogenic Fusarium in a Wind Tunnel Experiment

Dispersal processes play an essential role in cereal diseases caused by phytopathogenic Fusarium. However, most empirical studies of Fusarium spore dispersal have focused on vertical transport by rain splash, while wind dispersal has been mostly neglected. Our objective was to determine the ability of Fusarium conidiospores to disperse via wind under controlled conditions in a wind tunnel study. Ten Fusarium species with diverse spore varieties were studied by placing them in the wind stream at wind velocities of 5 and 8 m s−1 and collecting them after 6 m and a period of 1 h using a newly developed air sampling box. Although spore concentrations were high in the releasing Petri Dishes, the tested isolates were recaptured in only 18 of 78 runs. F. equiseti and F. cerealis were the most frequently recovered species. Changing abiotic conditions, wind speed, and spore shapes had no significant effect on Fusarium spore recapture rates. Another experiment showed that conidiospores were rarely released from the grown mycelium. Therefore, the importance of wind alone as a dispersal medium for Fusarium conidiospores may have been overestimated so far. Further studies should investigate the importance of carrier media or mobile linkers combined with the wind dispersal of spores.

Prediction of Land Erosion Events in the Down Stream Kreung Meureubo Watershed West Aceh District

This study aims to predict the occurrence of erosion in the downstream Krueng Meureubo watershed, West Aceh Regency. Erosion is the loss of topsoil due to rain splash which is analyzed as a factor of rain erosivity, but the occurrence of erosion is not necessarily calculated by the occurrence of rain alone, but many other factors, such as soil erodibility, slope and length of land, land cover and the presence or absence of land conservation efforts. the. The Krueng Meurebo watershed shows a large sediment transport, with an indication that the river is getting shallower caused by sediment deposition at the riverbed, this sediment comes from sediment carried through the process of soil erosion. The method used in analyzing the occurrence of soil erosion in this study is the USLE method and uses a Geographic Information System (GIS). The results obtained are the distribution of erosion rate values in 228 polygons, with the largest erosion rate value occurring in polygon 1 with an erosion rate of 8495.308 tons/ha/year. The smallest erosion rate occurs in polygons 30, 34, 35, 179, and 180, with an erosion rate of 0 meaning that there is no land erosion event, which occurs in organosol and glehumus and regosol soil types, land cover is settlements and water bodies. It is concluded that the occurrence of erosion in a land is very dependent on the type of soil and the type of land cover. It is recommended for land with large erosion events to take serious land conservation actions so that erosion events can be minimized and do not occur continuously which of course can cause the watershed to become critical. Conservation efforts can be carried out in various ways, one of which is by vegetative means using plants that can reduce the rate of soil erosion.

Synergistic dispersal of plant pathogen spores by jumping-droplet condensation and wind

Plant pathogens are responsible for the annual yield loss of crops worldwide and pose a significant threat to global food security. A necessary prelude to many plant disease epidemics is the short-range dispersal of spores, which may generate several disease foci within a field. New information is needed on the mechanisms of plant pathogen spread within and among susceptible plants. Here, we show that self-propelled jumping dew droplets, working synergistically with low wind flow, can propel spores of a fungal plant pathogen (wheat leaf rust) beyond the quiescent boundary layer and disperse them onto neighboring leaves downwind. An array of horizontal water-sensitive papers was used to mimic healthy wheat leaves and showed that up to 25 spores/h may be deposited on a single leaf downwind of the infected leaf during a single dew cycle. These findings reveal that a single dew cycle can disperse copious numbers of fungal spores to other wheat plants, even in the absence of rain splash or strong gusts of wind.

Claviceps sorghi (sorghum ergot).

C. sorghi is a pathogen of Sorghum bicolor found only in India and Southeast Asia. The more widespread Claviceps africana is predominant even in India; C. sorghi appears to be marginalized in its restricted range. A significant difference in invasiveness is the relative production of inoculum that spreads plant-to-plant. C. sorghi produces few to no secondary conidia from macroconidia on infected florets, whereas C. africana produces large numbers of these airborne propagules. The macroconidia of C. sorghi may themselves be transported in honeydew by wind, rain-splash, insects or direct contact between plants, but these are more limited means. Fungal sclerotia and/or the sphacelia state may be carried among harvested seed, but the seed lots can be cleaned or treated with fungicides (Bandyopadhyay et al., 1996). Alternative hosts are pearl millet (Pennisetum glaucum), wild and weedy relatives of S. bicolor, and wild grasses.

Claviceps fusiformis (pearl millet ergot).

C. fusiformis is widespread in Africa and India, where the host crop, pearl millet (Pennisetum glaucum), has been grown for thousands of years. The ergot disease it causes became a major yield constraint in India with the introduction of open-pollinated hybrid lines (Thukar and Rai, 2003). Conidia are spread from plant to plant by wind, rain-splash, and insects. Wild Pennisetum spp. are alternative hosts that may serve as reservoirs of inoculum. Ergot infection can have a significant impact on yields, with up to 70% loss in susceptible varieties (Natarajan et al., 1974). There are reports of the pathogen in the western hemisphere (San Martin et al., 1997; Velásquez-Valle et al., 1998). If the fungus has been introduced, then the use of clean seed and cultivation under particular climate conditions may prevent ergot from appearing as a significant problem in the Americas.

Fusicladium effusum (pecan scab).

F. effusum is a fungal pathogen that causes pecan scab, which can result in severe economic losses on susceptible cultivars and resulting harm to the pecan industry in areas with high rainfall where pecan is grown. The disease develops on leaves, fruits and shoots and results in loss of photosynthetic area and reduced fruit size and quality. Pecan scab can also lead to reduced fruit set in the following year due to plant stress. Fungicides used to control pecan scab are costly. It is introduced to new areas through movement of infected host material. Despite quarantine restrictions, it is likely that human-mediated transfer has occurred between the native habitats in south-eastern USA and Mexico, and locations where pecan is grown as an exotic in South America, South Africa and New Zealand. F. effusum overwinters as stroma and conidia in lesions on shoots and fruit shucks, and the conidia are dispersed in wind and rain splash. The pathogen is a threat to all pecan-growing regions with a humid, wet environment.

Didymella fabae (leaf and pod spot).

Ascochyta blight is the most severe disease of cool-season pulses (Davidson and Kimber, 2007). D. fabae (anamorph: Ascochyta fabae) attacks Vicia faba and can survive and reproduce in and spread from crop debris or be transported in infected seed. Introduction on infected seed occurred in Australia and Canada in the 1970s, and was probably the means for the pathogen's original spread to countries outside southwestern Asia. Ascospores are disseminated by wind from the debris as primary inoculum and secondary cycles are initiated by conidia spread by rain splash from plant lesions. The fungus is host-specific in causing disease, but may be able to survive in non-host plants and reproduce on their debris. It is not treated as a phytosanitary risk or listed as an invasive pathogen by major organizations. Seed certification is the primary means of preventing its spread to new areas and the importation of new genotypes of the fungus to areas already infested.

Phyllachora maydis (black spot of maize).

P. maydis, a perithecial ascomycete, causes a tar spot disease of maize that is usually a minor problem. More significant damage to leaves and yield is caused by the fungus Monographella maydis whose infection follows that of the tar-spot fungus, at least where studied in Mexico (Hock et al., 1992; 1995). The source of initial inoculum for both fungi is not determined. The disease they cause occurs in the cooler and higher elevations of Mexico, and Central and South America, and the West Indies, so their ability to spread over land through other climatic zones may be limited. Not known to be seedborne or to infect other species, P. maydis could be transported on fresh or dry maize leaves or husks, or products made from them, from which ascospores would have to be produced and carried by wind or rain splash to maize [Zea mays].

Estimating the Effect of Rain Splash on Soil Particle Transport by Using a Modified Model: Study on Short Hillslopes in Northern China

Splash erosion is an important soil erosion process in sloping lands. This study aims to improve the model of rain splash transport based on the results of previous studies and field experiments involving rainfall simulation. A field study was conducted to examine the effects of rainfall properties, herbaceous cover and surface flow on splash processes on hillslopes in northern China. On the basis of the experimental results, a comprehensive model of rain splash was established through the quantitative analysis of the interactive effects of rainfall kinetic energy, vegetation coverage and overland runoff depth on splash erosion rate and the probability density of splashed particles and maximum splash distance. The results showed that the estimated and observed values of splash transport exhibit high consistency and adaptability. However, several discrepancies were observed between the estimated and observed values for events with high vegetation coverage. These differences can be ascribed to the variation in overland runoff connectivity and the differences in soil surface cohesion at various wetness degrees. The proposed model provides insights into splash erosion characteristics and suggestions for erosion control practices on hillslopes.

Seasonal Precipitation Variability and Gully Erosion in Southeastern USA

This study examines the relationship between gully erosion in channels, sidewalls, and interfluves, and precipitation parameters (duration, total accumulation, average intensity, and maximum intensity) annually and seasonally to determine seasonal drivers for precipitation-related erosion. Ordinary Least Square regression models of erosion using precipitation and antecedent precipitation at weekly lags of up to twelve weeks were developed for three erosion variables for each of three geomorphic areas: channels, interfluves, and sidewalls (nine models in total). Erosion was most pronounced in winter months, followed by spring, indicating the influence of high-intensity precipitation from frontal systems and repeated freeze-thaw cycles in winter; erosion in summer was driven by high-intensity precipitation from convectional storms. Annually, duration was the most important driver for erosion, however, during winter and summer months, precipitation intensity was dominant. Seasonal models retained average and maximum precipitation as drivers for erosion in winter months (dominated by frontal systems), and retained maximum precipitation intensity as a driver for erosion in summer months (dominated by convectional storms). In channels, precipitation duration was the dominant driver for erosion due to runoff-related erosion, while in sidewalls and interfluves intensity parameters were equally important as duration, likely related to rain splash erosion. These results show that the character of precipitation, which varies seasonally, is an important driver for gully erosion and that studies of precipitation-driven erosion should consider partitioning data by season to identify these drivers.