Project description:Embryogenic cultures derived from a zygotic embryo of the avocado cv. Anaheim, were selected for resistance to the culture filtrate (CF) of Rosellinia necatrix, the causal agent of avocado white root rot. Cultures were obtained through recurrent selections in progressively increasing concentrations of fungal CF (from 20% up to 80%).
Project description:To understand the molecular foundation of the SE induction and development in avocado, we compared by proteomics approach, the embryogenic (EC) and non-embryogenic (NEC) cultures of two avocado varieties. Although Criollo and Hass EC exhibits particularities in the proteome and metabolome profile, in general, we observed a more active phenylpropanoid pathway in EC than NEC. Our proteomic pipeline consisted of a peptide labeled with TMT6plex and synchronous precursor selection (SPS) MS3
Project description:Grafting is typically utilized to merge adapted seedling rootstocks with highly productive clonal scions. This process implies the interaction of multiple genomes to produce a unique tree phenotype. However, the interconnection of both genotypes obscures individual contributions to phenotypic variation (rootstock-mediated heritability), hampering tree breeding. Therefore, our goal was to quantify the inheritance of seedling rootstock effects on scion traits using avocado (Persea americana Mill.) cv. Hass as a model fruit tree. We characterized 240 diverse rootstocks from 8 avocado cv. Hass orchards with similar management in three regions of the province of Antioquia, northwest Andes of Colombia, using 13 microsatellite markers simple sequence repeats (SSRs). Parallel to this, we recorded 20 phenotypic traits (including morphological, biomass/reproductive, and fruit yield and quality traits) in the scions for 3 years (2015–2017). Relatedness among rootstocks was inferred through the genetic markers and inputted in a “genetic prediction” model to calculate narrow-sense heritabilities (h2) on scion traits. We used three different randomization tests to highlight traits with consistently significant heritability estimates. This strategy allowed us to capture five traits with significant heritability values that ranged from 0.33 to 0.45 and model fits (r) that oscillated between 0.58 and 0.73 across orchards. The results showed significance in the rootstock effects for four complex harvest and quality traits (i.e., total number of fruits, number of fruits with exportation quality, and number of fruits discarded because of low weight or thrips damage), whereas the only morphological trait that had a significant heritability value was overall trunk height (an emergent property of the rootstock–scion interaction). These findings suggest the inheritance of rootstock effects, beyond root phenotype, on a surprisingly wide spectrum of scion traits in “Hass” avocado. They also reinforce the utility of polymorphic SSRs for relatedness reconstruction and genetic prediction of complex traits. This research is, up to date, the most cohesive evidence of narrow-sense inheritance of rootstock effects in a tropical fruit tree crop. Ultimately, our work highlights the importance of considering the rootstock–scion interaction to broaden the genetic basis of fruit tree breeding programs while enhancing our understanding of the consequences of grafting.
Project description:White root rot disease caused by Rosellinia necatrix is one of the most important pathogens affecting avocado productivity in temperate, tropical and subtropical climates. Control of this disease is complex and nowadays, lies in the use of physical and chemical methods, although none have proven to be fully effective. Detailed understanding of the molecular mechanisms underlying white root rot disease has the potential of aiding future developments in disease resistance and management. In this regard, this study used RNAseq technology to compare the transcriptomic profiles of R. necatrix during infection of susceptible avocado `Dusa´ roots with that obtained from the fungus cultured in rich medium. The transcriptomes from three biological replicates of R. necatrix colonizing avocado roots (RC) and R. necatrix growing on potato dextrose agar media (PDA) were obtained using Illumina sequencing. A total of 12,104 transcripts were obtained, among which 1937 were differentially expressed genes (DEG), 137 exclusively expressed in RC and 160 and PDA. Interestingly genes involved in the production of fungal toxins, detoxification of toxic compounds, hormone biosynthesis, gene silencing and plant cell wall degradation were overexpressed during the infection process. In addition, 23 out of the 137 contigs, only expressed during R. necatrix growth on avocado roots, were predicted as candidate effector proteins (CEP) by the CSIRO tool with a probability above 60%. The PHI (Pathogen Host Interaction) database revealed that 11 R. necatrix CEP were previously annotated as effectors genes proven experimentally via pathogen-host interaction.
Project description:The aim of this study was to evaluate the physiological response and the expression analysis of `Dusa´ avocado rootstocks subjected to two different levels of water stress, and their subsequent recovery. At the beginning of the experiment, avocado plants were divided in Control plants (watered to field capacity (Fc) throughout the experiment) and stressed plants that were subjected to controlled substrate drying-up until they reached 50% of Fc (mild-WS) and 25% of Fc (severe-WS), respectively. Afterwards, plants were fully irrigated to assess drought recovery response. A set of physiological measurement were taken at leaf and whole-plant levels to assess avocado response to each level of water stress and rewatering. Root samples were collected in mild-WS and severe-WS and gene expression analysis was carried out using a targeted cDNA avocado stress microarray containing transcripts from de novo sequencing of 'Dusa' in response to biotic and abiotic stress. Avocado gene expression profiles under different levels of water stress are discussed in order to shed light on the molecular mechanisms associated with water deprivation in Dusa avocado rootstocks.
Project description:Pollination is limiting for avocado production. We examined whether adding bumblebees (BBs; ca. 10 hives/ha) to conventional honeybees (HB; 5 hives/ha) would improve 'Hass' avocado pollination and yields. A preliminary trial (2017/18) in an avocado orchard with four consecutive rows of 'Hass' followed by one row of 'Ettinger' serving as a pollenizer (20% 'Ettinger') showed a considerable increase in 'Hass' yield in rows adjacent to (up to 80 m from) the BB hives vs. distant rows (=controls). In 2018/19, the trials were extended to three additional orchards. A significant yield increase was obtained in the BB hive-adjacent trees compared to BB hive-distant ones. Similar results were obtained in 2019/20, in experiments conducted throughout the country. The SNP analysis, to determine the parents of 'Hass' fruit at varying distances from the BB hives, showed no differences in the cross-pollination rate ('Hass' × 'Ettinger'). However, pollination rates and the number of germinating pollen grains per stigma decreased with distance from the hives, and correlated to the negative gradient in yield. Taken together, our data suggest that adding BB hives to 'Hass' avocado orchards, at ca. 10 hives/ha resulting in 0.5-1.0 BB visits/tree per min, increases pollination and, accordingly, total yield.