Histopathological Study of the Alternaria solani Infection Process in Potato Cultivars with Different Levels of Early Blight Resistance

Abstract

Histopathological analyses of the infection process ofAlternaria solani were accomplished in three potato cultivars with different levels of early blight resistance. Leaflets of Aracy (resistant), Delta (moderately resistant) and Bintje (susceptible) cultivars were inoculated at the beginning of the flowering stage. In order to study the effect of leaf age, leaf samples were collected separately, in the lower, middle and upper third of the plants. Conidia germination, appressoria formation, penetration and number of penetration sites exhibiting hypersensitive response (HR) were qualitatively and quantitatively assessed at 6, 12, 24, 48 and 72 h after inoculation. Penetration occurred most frequently through the junctions of the epidermal cells. Penetrations through stomata were rarely observed. There was no association between the events and the resistance levels, except for the number of penetration sites showing HR that was highest in Aracy, intermediate in Delta and lowest in Bintje. Similarly, the number of sites with HR was the only event associated with the leaf age. Regardless of cultivar resistance levels, the number of the penetration sites with HR was higher in leaves in the upper part of the plant. These results suggest that HR may be one of the mechanisms associated with age-related and genetic resistance to early blight in potato.

Dissection of Bacterial Wilt on Medicago truncatula Revealed Two Type III Secretion System Effectors Acting on Root Infection Process and Disease Development

“…They appeared to be the first step in bacterial infection, but they were not always associated with the wilting of the plant. The progression of early steps of the infection processes is not always associated with resistance, as described in other systems (Dita et al, 2007). Indeed, specific recognition leading to defense mechanisms may initiate after penetration of the pathogen into the host tissues (Freytag et al, 1994).…”

Oxidative burst and the activity of defense-related enzymes in compatible and incompatible tomato-Alternaria solani interactions

“…Based on these results, the authors concluded that although hypersensitive cell death is efficient against biotrophic pathogens, it does not protect plants against infection by the Oxidative burst and activity of defense-related enzymes in compatible and incompatible tomato-Alternativa solani... necrotrophic pathogens. On the contrary, Dita et al (2007) verified that the number of infection sites exhibiting HR was higher in potato plants resistant against A. solani than in the susceptible genotype after inoculation with that pathogen. They also found a relationship between the number of sites with HR and the leaf age, being the number of the penetration sites with HR higher in leaves in the upper part of the plant.…”

“…In spite of the apparent random pattern in the growth of the germ tubes, the majority of the appressoria were formed at the junctions between the epidermal cells. This has been observed by some authors in A. solani (ARAÚJO; MATSUOKA, 2004;DITA et al, 2007) and in other Alternaria species (AVELING; SNYMAN; RIJKENBERG, 1994;McROBERTS;LENNARD, 1996;BOEDO et al, 2008) infecting a variety of hosts. Hancock and Huisman (1981) suggested that the general features of leaf topography and fluctuations in the nutrient microclimate around the cell junctions could stimulate the formation of appresoria at these sites.…”

“…In general, the spores of The lesions were developed from penetrations that occurred after the formation of the appressorium. Penetration performed by Alternaria species is commonly done from appressorium, which proves the essentiality of this structure for the pathogenesis (AVELING; SNYMAN;RIJKENBERG, 1994;MCROBERTS;LENNARD, 1996;ARAÚJO;MATSUOKA, 2004;DITA et al, 2007). Consequently, a lower frequency of lesions was the result of a lower number of appressoria formed in resistant plants of CNPH 1287.…”

Evidence of recent increased pathogenicity within the AustralianAscochyta rabieipopulation

“…A spore was considered to be germinated when a germination tube was present, regardless of length or number of germ tubes per spore. All globular structures with a diameter larger than that of the germination tube or hyphae of origin were considered an appressoria(Dita et al 2007). Images of three conidia were randomly selected from a single leaf from each of four replicate plants and germ tube length was measured using Leica IM50 v4 software.…”