Histopatologia da interação Alternaria solani e tomateiros resistente e suscetível

Abstract

Para esclarecer a natureza da resistência à pinta-preta (Alternaria solani) em tomateiro resistente (Lycopersicon hirsutum var. glabratum) cv. CNPH 417 e suscetível (L. esculentum) cv. Miller, avaliou-se o processo de infecção, através da histopatologia. Às 6, 12, 24, 36, 48 e 72 h após as inoculações (h.a.i.) de suspensões de conídios, coletaram-se amostras de tecidos foliares que foram submetidas ao clareamento, à inclusão em resina para confecção de cortes semifinos e ao processamento para microscopia eletrônica de varredura (MEV). Pela análise das amostras clareadas, observou-se que a germinação de conídios completou-se em 24 h.a.i. O crescimento de tubos germinativos foi similar na superfície de ambos os genótipos. Entretanto, os números de apressórios formados, de penetrações nos tecidos e de lesões foram inferiores no genótipo resistente. Com relação aos eventos pós-penetração, o desenvolvimento inicial de hifas primárias e secundárias, processos posteriores de colonização e desenvolvimento de lesões, bem como a ocorrência de formação de papilas sob apressórios e de reações de hipersensibilidade foram similares em ambos os genótipos. Para a maioria dos aspectos da patogênese de A. solani, portanto, o genótipo resistente CNPH 417 comportou-se de modo similar ao suscetível, cv. Miller, exceto quanto aos números de apressórios, de penetrações e de lesões. Assim, ficou evidenciado que a resistência de L. hirsutum var. glabratum (CNPH 417) a A. solani é expressa na fase de pré-penetração, principalmente pelo baixo número de apressórios formados.Palavras-chave adicionais: Lycopersicon spp., microscopia eletrônica de varredura, resistência, formação de apressório. ABSTRACT Histopathology of the interaction between Alternaria solani and resistant and susceptible tomato plantsLight and scanning electron microscopy (SEM) were used to follow the infection process of Alternaria solani on leaves of resistant tomato (Lycopersicon hirsutum var. glabratum) cv. CNPH 417 and susceptible tomato (L. esculentum) cv. Miller. Conidial germination was completed 24 h after inoculation (h.a.i) and growth of germ tubes was similar on the leaf surfaces of both genotypes. However, on the resistant genotype the quantity of appressoria, tissue penetration and lesions were significantly less. The events after penetration were similar in both genotypes and included the initial development of primary and secondary hyphae, colonization processes and lesion development, frequency of formation of papilla and hypersensitive reactions. Although papilla production and hypersensitive reaction are considered as resistant reactions, they seem to have not contributed to the resistance of L. hirsutum var. glabratum to A. solani in this study. The resistant tomato genotype was similar to the susceptible one according to the aspects of pathogenesis studied, except regarding the number of appressoria, penetrations and lesions. Therefore, it was concluded that the resistance of L. hirsutum var. glabratum (CNPH 417) to A. solani is expressed during the p...

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

“…The absence of apparent orientation of the germ tubes on the leaf surfaces found in our work, was also reported by Araújo and Matsuoka (2004) Aveling and Venter (2003) in A. cassiae -Vigna unguiculata. 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.…”

“…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.…”

“…germinate on the leaves of the resistant cultivars and nonhost plants as well as host plants (ROTEM, 1994). Araújo and Matsuoka (2004) reported the same conidial germination of A. solani on leaves of S. lycopersicon and S. habrochaites. Spores of A. brassicae, A. brassicicola, A. raphani and A. solani germinated almost at the same rate on foliages of both host and nonhost plants, including oilseed rape, poppy, tomato and wheat (McROBERTS; LENNARD, 1996).…”

“…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.…”

Infection of Curvularia gladioli on different gladiolus genotypes

“…Albuq. ); tomato (Alternaria solani Sorauer); and soybean (P. pachyrhizi) (Bentes & Matsuoka, 2002;Araujo & Matsuoka, 2004;Magnani et al, 2007). The results of this study indicate that different genotypes of gladiolus grown FIGURE 2 -Percentages of appressorium formation of Curvularia gladioli inoculated on the lower surface of leaves of Gladiolus calliantus and Gladiolus grandiflorus vars.…”