Pre-Infection Stages of Austropuccinia psidii in the Epidermis of Eucalyptus Hybrid Leaves with Different Resistance Levels

Abstract

Rust is a major Eucalyptus spp. disease, which is especially damaging for early-stage plants. The aim of this study was to verify the pre-infection process of Austropuccinia psidii (A. psidii) in the leaves of three phenological stages of Eucalyptus clones with different resistance levels. Plants from the hybrids of Eucalyptus urophylla × Eucalyptus grandis (E. grandis) with variable levels of resistance to this disease were used. The pathogen was inoculated in vitro on abaxial leaf discs of first, third, and fifth leaf stages and maintained under conditions suitable for disease development. Subsequently, samples from these discs were collected 24 and 120 h after inoculation and processed using scanning electron microscopy analysis. No symptoms were seen in any leaf stage of the resistant clone. Additionally, a low incidence of A. psidii germination (1.3-2%) and appressoria (0-0.5%) in three leaf stages was observed. However, the first leaf stage of the susceptible clone presented germination of large numbers of urediniospores (65%) with appressoria (55%) and degradation of the cuticle and wax. From the third stage, the percentage of germinated urediniospores (<15%) and appressoria (<2%) formation of this clone decreased. Protrusions on the leaf surface, associated with the pathogen, were observed on the first and third leaf stages of the resistant clone and on the fifth stage of the susceptible clone, suggesting a possible defensive plant reaction.

Morphology and infection process of Olivea neotectonae in teak leaves

“…It can be verified that the direct penetration by leaf stomata was the main route used by O. neotectonae, a fact not yet documented for this patossystem. In the most of Puccinia species, and others rust agents causal, the penetration occurs via stomata (SILVA et al 2017), as observed in this study. This study provides the first microscopic evidence of the infection process of Olivea neotectonae in leaves of teak plants.…”

Variability and Disturbances as Key Factors in Forest Pathology and Plant Health Studies

“…Most of the literature in this area in fact has focused on gene-for-gene resistance, but the effects of other types of resistance have been less widely studied [18]. The paper on the Eucalyptus rust Austropuccinia psidii [19] provides solid evidence of a phenological type of resistance present in older leaves, while even more complex is the report by Chieppa et al [20] suggesting that genetically inherited susceptibility to a vascular fungus results in great susceptibility to changes in water availability. While interspecific competition driven by pathogens is well known [21], the example by Chieppa et al [20] is a classic example of virtually unstudied intraspecific competition cryptically driven by a pathogen.…”

“…Such hosts, being exotic, generally can be regarded as planted off-site. This is the case for Austropuccinia psidii on Eucalyptus planted in South America [19], for Lecanosticta acicola on Pinus radiata grown in Spain [12], and likely for the many cultivated hosts of Lasiodiplodia theobromae [24].…”

Responses of resistant and susceptible hybrid clones of Eucalyptus urophylla × Eucalyptus grandis to infection by Ceratocystis fimbriata

“…In addition, for the first 12 h, the cuttings remained in the horizontal position to avoid the displacement of the inoculum deposited in the wound. Stem fragments (0.5 × 0.5 cm) were collected 12, 24, 36, 48, and 60 h after inoculation (hai) and prepared for SEM using the protocols described by Silva et al (2017). The experiment was performed using a completely randomized design with five replications per treatment (one cutting per replication) and repeated once.…”