In the strawberry crop area of Tucuma´n (north-west Argentina) the three species of Colletotrichum causing anthracnose disease (C. acutatum, C. fragariae and C. gloeosporioides) were detected. Among all isolates characterized, one of them identified as C. acutatum (M11) and another as C. fragariae (F7) were selected due to their conspicuous interaction with the strawberry cultivar Pa´jaro. Whereas isolate M11 produced a strong compatible interaction in cv. Pa´jaro with clear disease symptoms (DSR = 5.0), the isolate F7 brought about a typical incompatible interaction (DSR = 1.0). When plants of cv. Pa´jaro were inoculated with F7 prior to the inoculation with M11, the former avirulent strain prevented the growth of the latter virulent pathogen. Experimental evidence indicated that the time elapsed between the first inoculation with the avirulent pathogen and the second inoculation with the virulent one was crucial to inhibit the growth of the latter. The growth of F7 on the plant without provoking damage and the fact that there was no in vitro antagonistic effect between the pathogens, suggests that the avirulent strain triggers a plant defensive response against M11. The defense response was further confirmed by the detection of an early oxidative burst occurring within 4 h after the first inoculation and by the observation of anatomical changes associated with defense mechanisms that lasted 50 days after the inoculation with F7. Results obtained support the hypothesis that the plant resistance against the virulent strain M11 is elicited by one or more diffusible(s) compound(s) produced by the avirulent strain F7.

The elicitor AsES (Acremonium strictum elicitor subtilisin) is a 34-kDa subtilisin-like protein secreted by the opportunistic fungus Acremonium strictum. AsES activates innate immunity and confers resistance against anthracnose and gray mold diseases in strawberry plants (Fragaria × ananassa Duch.) and the last disease also in Arabidopsis. In the present work, we show that, upon AsES recognition, a cascade of defense responses is activated, including: calcium influx, biphasic oxidative burst (O and HO), hypersensitive cell-death response (HR), accumulation of autofluorescent compounds, cell-wall reinforcement with callose and lignin deposition, salicylic acid accumulation, and expression of defense-related genes, such as FaPR1, FaPG1, FaMYB30, FaRBOH-D, FaRBOH-F, FaCHI23, and FaFLS. All these responses occurred following a spatial and temporal program, first induced in infiltrated leaflets (local acquired resistance), spreading out to untreated lateral leaflets, and later, to distal leaves (systemic acquired resistance). After AsES treatment, macro-HR and macro-oxidative bursts were localized in infiltrated leaflets, while micro-HRs and microbursts occurred later in untreated leaves, being confined to a single cell or a cluster of a few epidermal cells that differentiated from the surrounding ones. The differentiated cells initiated a time-dependent series of physiological and anatomical changes, evolving to idioblasts accumulating HO and autofluorescent compounds that blast, delivering its content into surrounding cells. This kind of systemic cell-death process in plants is described for the first time in response to a single elicitor. All data presented in this study suggest that AsES has the potential to activate a wide spectrum of biochemical and molecular defense responses in F. ananassa that may explain the induced protection toward pathogens of opposite lifestyle, like hemibiotrophic and necrotrophic fungi.

Sugarcane is known for its highly complex genetics and more knowledge is needed for better use and conservation of genetic materials. In order to identify genotypes and to assess genetic diversity, diverse data sets such as morphological and molecular markers are used as a general approach. To evaluate the usefulness of different markers, important sugarcane genotypes in Argentina were characterized by AFLP, SSR and morphological traits. All genotypes characterized were grouped in one main cluster in dendrograms using two independent softwares. Interestingly, local genotypes grouped together with USA varieties and no clear genetic differentiation could be found probably due to intensive germplasm exchange between these breeding programs. The molecular markers tested were useful for genetic diversity assessment as well as for genotype identification. These markers should be included in the internationally established characters for sugarcane variety protection as they give a better view on whole genome complexity. Additionally, genetic similarities obtained from molecular markers will provide more accurate information to breeders than the pedigree method, especially when considering the asymmetric genetic inheritance of sugarcane. Morphological traits are valuable tools to identify genotypes since they reflect external resemblance more than genetic relatedness. When they were combined with molecular markers the dendogram obtained revealed genetic relationships and the genetic diversity was better estimated. In summary, both methods appear to be useful, complementing each other and should be used together to assist sugarcane breeders in estimating genetic diversity, electing parents for crossings, identifying superior lines and to protect intellectual property rights.

No abstract

Results obtained indicate that the white-fruited character was stable. Mother progenitors exert a strong influence on the expression of the white-fruited character. The white-fruited phenotype is due to the impairment or downregulation of the ANS gene.

The Fragaria genus has become relevant due to worldwide economic importance of the octoploid hybrid F. × ananassa. Interspecific hybridizations are widely employed in breeding programmes to introduce useful characteristics from wild species to cultivated varieties, although many reproductive barriers prevent gene flow between species. Hybrid genotypes that can act as a bridge between related wild species and cultivated strawberry could be useful to overcome those barriers. The aim of this work was to obtain interspecific hybrids of Fragaria and to analyse possible reproductive barriers. In the Banco de Germoplasma de Frutilla‐UNT, crossings were carried out among wild species of Fragaria with different ploidy levels and cultivated strawberry. To confirm hybrid condition of genotypes obtained, histological techniques and microsatellite markers were used. When wild species were crossed with cultivated strawberry in both directions, there was low production of achenes, while in crosses between wild species of Fragaria genus, achene production was very high. The percentage of germination of achenes was high when crossed species had the same ploidy level, and very low or null when they presented different ploidy levels. Although pre‐zygotic incompatibility associated to the degree of domestication and postzygotic barriers related to different ploidy levels of the progenitors were detected, new hybrid genotypes of Fragaria were obtained. These new hybrids could be used as “bridge species” in breeding programmes, since preliminary results showed no incompatibility barriers when they were crossed with Duchesnea indica.

Yellow leaf disease, caused by Sugarcane yellow leaf virus (SCYLV), is widespread around the world but very little information is available on this viral disease in Argentina. Therefore, the aims of the study were to assess the presence of SCYLV, analyze its distribution in the main sugarcane production areas of Argentina, characterize the virus, and determine histological alterations caused by its presence. For this purpose, 148 sugarcane samples with and without symptoms were collected in 2011 and 2012 from the province of Tucumán. One additional sample was collected in Salta, a different geographical, agroecological, and producing region. Results showed that SCYLV is widely distributed in commercial varieties of sugarcane throughout Tucumán in both symptomatic and asymptomatic leaves. A low but statistically significant positive correlation with virus detection and disease symptoms was found. BRA-PER was the only genotype detected by reverse-transcription polymerase chain reaction and sequence analysis of the SCYLV capsid protein gene. SCYLV-positive samples showed high starch levels in bundle sheath cells, whereas the asymptomatic ones, probably in an early stage of infection, were found to contain more chloroplasts. Symptomatic noninfected samples presented crystal formation probably associated with phytoplasma infection.

The effect of cadmium on roots of four citrus rootstocks was studied to assess the relationships between oxidative stress, carbohydrates, phenolics and antioxidant responses. Swingle citrumelo (SC), Rangpur lime (RL), Troyer citrange (TC) and Volkamer lemon (VL) genotypes were exposed to 0, 5 and 10 µM Cd over 7 days, after which Cd accumulation was markedly higher in roots compared with stems and leaves. Malondialdehyde (MDA) and lipoxygenase (LOX) activity increased in Cd-treated SC and RL roots, suggesting that a lipid peroxidation is the main driver of plasma membrane damage. In contrast, in TC and VL genotypes, LOX-mediated lipid peroxidation does not appear to play a key role in Cd-induced lipid peroxidation, but H2O2 accumulation seems to be responsible of less plasma membrane damage. Catalase (CAT), superoxide dismutase (SOD) and guaiacol and syringaldazine peroxidases (G-POD and S-POD respectively) were differentially affected by Cd. Lipid profile and ATPase-dependant proton extrusion indicated higher disfunctionalities of root plasma membrane in SC and RL genotypes than in TC and VL genotypes. Differences in carbohydrates and phenolic compounds were also observed. Histochemical analysis of G-POD activity and lignin and suberin deposition revealed differences among genotypes. A model to explain the relationships among carbohydrates, soluble phenolics, lipid peroxidation and H2O2 accumulation in Cd-exposed roots was proposed.