Contribution of species abundance and frequency to aboveground forest biomass along an Andean elevation gradient

Aims: To determine whether species that contribute most to a plot's biomass are the most abundant (high local abundance at plot scale) or the most frequent (occur the most across plots at landscape scale), or both. In the tropical Andes, these patterns may change with elevation. This study assesses the contribution to plot's above-ground biomass (AGB) of the plant community abundance pattern –the prevalence of within-plot dominant species– and the over-occurrence of regionally frequent species, in an elevation gradient. Methods: We considered all trees ≥2.5 cm DBH from 446 0.1 ha plots in an Amazonia-Andes 260–4350 m elevation cline in N Bolivia. Plot AGB was calculated as the sum of AGBs for all stems contained. We grouped plots into four bins segregated by elevation and ran a bootstrap analysis over subsets of 58 random plots per bin with 100 iterations. Simpson evenness index (E) for all species in each plot was used as a measure for its species abundance. Values for each plot's species frequency was calculated as the mean of all species’ in the plot mean frequencies across the bin (i.e. the fraction of plots where each species occurs). We used linear models to correlate plot AGB with (1) elevation and mean annual precipitation (MAP), and (2) E, plot species frequency and elevation. We performed all analyses at the species, genus and family levels. Results: Plot AGB was related negatively with elevation, and thus positively with MAP, and also negatively with plot E and plot species frequency, all significant. Plot species abundance therefore contributes positively to explain the relationship with AGB along elevational gradients, while plot species frequency does so negatively (i.e. less frequent species contribute more to a plot's AGB across elevation). AGB, for both generic and familial levels was also significantly and negatively correlated with E, but not related with plot species frequency biomass at these taxonomic levels. Conclusions: Plot AGB was mainly associated with elevation and floristic composition where species, genera and families tended to be abundant at the local (plot) scale. Species that were less frequent at the regional scale contributed with more AGB regionally, while frequency at generic and familial scales did little to explain AGB patterns. This association seems stronger at lower elevations for all taxonomic levels while decreases toward higher elevation. Our study reveals a relationship between plot structural features like C stocks –influenced by species local abundances– and the distribution of taxa across the landscape

Verticillium klebahnii and V. isaacii Isolates Exhibit Host-Dependent Biological Control of Verticillium Wilt Caused by V. dahliae

Verticillium dahliae, the soilborne fungal pathogen, causes vascular wilt on many economically important crops, resulting in significant yield losses. V. klebahnii (isolate PD659) and V. isaacii (isolate PD660), two related species that cause few or no symptoms in some hosts, were evaluated as potential biocontrol agents (BCAs) in eggplant, lettuce, and tomato by pre-, post-, and coinoculation with a virulent race 1 isolate of V. dahliae (VdLs16). Initial studies demonstrated that the biocontrol efficacy of both BCAs was similar to reference BCA Talaromyces flavus (NRRL15936) across all hosts (α = 0.05). Subsequent experiments with PD659 against V. dahliae isolate Sm113 from eggplant, VdLs16 and VdLs17 isolates from lettuce, and Le1811 isolate from tomato demonstrated a significant biocontrol efficacy in eggplant and tomato but not in lettuce (at 95% confidence interval), suggesting host-dependent effectiveness of V. klebahnii. Confocal microscopy using green fluorescent protein-tagged tomato V. dahliae isolate Le1811 indicated delayed xylem colonization or lack of pathogen progression into the vascular system in a host-dependent manner on BCA-treated plants. Quantitative analyses of the expression of defense-related genes PR1a, PR5, acidic extracellular β-1,3-glucanase (GlucA), basic intracellular β-1,3-glucanase (GlucB), acidic extracellular chitinase (Chi3), basic intracellular chitinase (Chi9), and cysteine proteases (cysProteases) in tomato in the presence or absence of PD659 suggested an elevated expression of defense-related genes in compatible interaction of V. dahliae–tomato cultivar Early Pak. V. klebahnii (PD659) may delay the entry of V. dahliae by competing for space or nutrients during the initial stages of root colonization.[Graphic: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license

Effect of recombination in the maize breeding population with exotic germplasm on the yield stability

A little knowledge exists about the probability that recombination in the parental maize populations will enhance the chances to select more stable genotypes. The synthetic parent maize population ((1601/5 x ZPL913)F-2 = R-0) with 25% of exotic germplasm was used to assess: (i) genotype x environment interaction and estimate stability of genotypes using nonparametric statistics; (ii) the effect of three (R-3) and five (R-5) gene recombination cycles on yield stability of genotypes; (iii) relationship among different nonparametric stability measures. The increase of mean grain yield was significant ( lt 0.01) in the R-3 and R-5 in comparison to the R-0, while it was not significant between R-3 and R-5. Analysis of variance showed significant ( lt 0.01) effects of environments, families per set, environment x set interaction, family x environment interaction per set on grain yield. The non-significant noncrossover and significant crossover ( lt 0.01) G x (E) interactions were found according to Bredenkamp procedures and van der Laan-de Kroon test, respectively. The significant ( lt 0.01) differences in stability were observed between R-0-set 3 and R-5-set 3 determined by , R-3-set 1 and R-5-set 1 determined by ( lt 0.05), and R-0-set 3 and R-5-set 3 determined by ( lt 0.05). The significant parameters were those which take into account yield and stability so the differences could be due to differences in yield rather than stability. Findings can help breeders to assume the most optimum number of supplementary gene recombination to achieve satisfactory yield mean and yield stability of maize genotypes originating from breeding populations

Genome-wide association study reveals a set of genes associated with resistance to the Mediterranean corn borer (Sesamia nonagrioides L.) in a maize diversity panel

[Background] Corn borers are the primary maize pest; their feeding on the pith results in stem damage and yield losses. In this study, we performed a genome-wide association study (GWAS) to identify SNPs associated with resistance to Mediterranean corn borer in a maize diversity panel using a set of more than 240,000 SNPs.[Results] Twenty five SNPs were significantly associated with three resistance traits: 10 were significantly associated with tunnel length, 4 with stem damage, and 11 with kernel resistance. Allelic variation at each significant SNP was associated with from 6 to 9% of the phenotypic variance. A set of genes containing or physically close to these SNPs are proposed as candidate genes for borer resistance, supported by their involvement in plant defense-related mechanisms in previously published evidence. The linkage disequilibrium decayed (r2 < 0.10) rapidly within short distance, suggesting high resolution of GWAS associations.[Conclusions] Most of the candidate genes found in this study are part of signaling pathways, others act as regulator of expression under biotic stress condition, and a few genes are encoding enzymes with antibiotic effect against insects such as the cystatin1 gene and the defensin proteins. These findings contribute to the understanding the complex relationship between plant-insect interactions.This work was supported by the National Plan for Research and Development of Spain (projects AGL2012-33415). L.F. Samayoa acknowledges a contract JAE-Predoc from the Spanish Council for Scientific Research (CSIC).Peer reviewe