Monitoring Pyricularia sp. airborne inoculum in Passo Fundo, Rio Grande do Sul, Brazil

Abstract

The fungus Pyricularia sp., the causal agent of wheat blast, produces light, dry and hyaline conidia that can be removed from sporulating lesions by the wind and transported over long distances. Experiments were performed with the aim of (a) determining the relationship between the climate variables and the quantity of conidia of Pyricularia sp., and (b) obtaining technical data that can be used in the elaboration of blast forecasting models. From February 2nd, 2013 to June 7th, 2014, the number of Pyricularia sp. conidia in the air was monitored by using a spore trap and glass slides smeared with vaseline. Several climate variables were hourly recorded during the spore capturing period. The data were explored based on classification trees and relationships between the weather-based predictors and the number of trapped conidia day-1. The strongest predictors were mean relative humidity, daily mean temperature, precipitation lower than 5 mm day-1, and number of hours when temperature was between 15 and 35 °C and relative humidity > 93%.

Tracing seed to seedling transmission of the wheat blast pathogenMagnaporthe oryzaepathotypeTriticum

“…Kohli et al (2011) reported an increase in disease severity (>85%) at 25 °C with 40 hr of wetting. In addition, Danelli et al (2019) established that the increase in MoT spores is due to the mean relative humidity, the mean daily temperature, and precipitation of less than 5 mm/day, managing to predict that the highest number of spores occurred in hours in which the temperature was between 15 and 35 °C and relative humidity >93%. Moreover, Kovaleski et al (2020) established equations which identified that the highest production of conidia occurred between temperatures of 24 and 27 °C in experiments carried out in pots.…”

Towards an early warning system for wheat blast: epidemiological basis and model development

“…Highhumidity conditions may be accountable for turgor pressure buildup inside the stalk-cell, which explains the high availability of conidia under moistened conditions (Ingold, 1964;Meredith, 1962). The conidia release of P. oryzae can be triggered by either increasing levels (from 24% to 100%) or decreasing levels (from 100% to 24%) of relative humidity; maximum conidia release has been found when relative humidity levels increase from 76% to 100% (Danelli et al, 2019;Leach, 1980). Short rains (less than 5 mm) also seem to favor spore release, but intense rainfall events may also reduce P. oryzae conidia residence in sporulating lesions (Kim, 1994;Danelli et al, 2019).…”

“…The conidia release of P. oryzae can be triggered by either increasing levels (from 24% to 100%) or decreasing levels (from 100% to 24%) of relative humidity; maximum conidia release has been found when relative humidity levels increase from 76% to 100% (Danelli et al, 2019;Leach, 1980). Short rains (less than 5 mm) also seem to favor spore release, but intense rainfall events may also reduce P. oryzae conidia residence in sporulating lesions (Kim, 1994;Danelli et al, 2019). It is also plausible that under heavy rain, large raindrops vigorously damage conidiophores, releasing and washing off conidia, thereby reducing the amount of inoculum available for transport from plant to plant, field to field, and across regions.…”

“…However, this is valid only when the inoculum can be assumed as not limiting. This seems not be the case for wheat blast where grasses in the landscape serve as large reservoirs for the inoculum, but its production and amount available to infect commercial wheat is dependent on the seasonal weather (Danelli et al, 2019;Fernandes et al, 2017). Therefore, our group has employed efforts to develop weather-driven wheat blast models that take both inoculum production and infection risk into account.…”

Sensitivity to fungicides in Pyricularia populations from wheat and signal grass in Minas Gerais

“…The amount of spores in the air depends on the environmental conditions. For temperatures between 25°C and 28°C, relative humidity of 76% to 100%, and light rain (< 5 mm) the amount of spore in the air is increased (Leach, 1980;Danelli et al, 2019), and after a period of heavy rains the number of spores decreases (Silva & Prabhu, 2005;Danelli et al, 2019). As to long distance dispersal, infected seeds or grains are the most likely source of inoculum for disease establishment (Tanaka et al, 2009;Gomes et al, 2018).…”