Differential response to the South American rice water weevil (Coleoptera: Curculionidae) damage of rice cultivars with contrasting levels of resistance: implications for field management.

BACKGROUND: Oryzophagus oryzae (Costa Lima) (Coleoptera: Curculionidae) is a major pest of flooded rice paddies throughout South America, and species with very similar life histories are present in many rice-producing regions of the world (collectively rice water weevils, RWWs). The damage caused by RWW larvae on rice cultivars with contrasting levels of resistance ('BRS Pampa CL'= 'Pamp': susceptible, 'BRS Atalanta' = 'Atal': resistant-antibiosis) was evaluated in two consecutive years in the field under seven infestation levels: 0, 2, 4, 6, 8, 10 and 20 adult couples per cage with plants. RESULTS: Higher densities of adults increased the number of leaf-feeding scars and larvae on roots, respectively, at the rate ≤2.14 and 2.75 in Pamp and 2.23 and 2.48 in Atal, with the total number of larvae generated being lower in Atal. Grain yield was negatively impacted with increasing larval density on the roots, mainly by decreasing root volume and the number of grains per panicle. Root injury intensity and yield loss showed a nonlinear relationship. It was found that significant yield losses occurred with 8.37 larvae per plant in Pamp and 9.80 larvae per plant in Atal CONCLUSION: The results provided the first evidence of a tolerance limit for RWW larval damage that, even though similar between cultivars of contrasting resistance, corresponds to twice the current conventional level for larval control in Brazil. We also discuss here the potential of applying tolerance limits to manage the RWW adult population in rice fields. © 2022 Society of Chemical Industry.

A new set of differentially expressed signaling genes is early expressed in coffee leaf rust race II incompatible interaction.

New races of coffee rust are overcoming resistance genes available in germplasm and cultivated cultivars and bringing recently some coffee-producing countries in severe economic challenge. The objective of this study was to identify the genes that are linked to host resistance to the major coffee rust race II. In our study, we have identified and studied a segregating population that has a single monogenic resistant gene to coffee rust. Coffee leaves of parents, resistant, and susceptible genotypes of the F2 generation plants were inoculated with pathogen spores. A differential analysis was performed by combined cDNA-AFLP and bulk segregant analysis (BSA) in pooled samples collected 48 and 72 h postinoculation, increasing the selectiveness for differential gene expression. Of 108 differential expressed genes, between 33,000 gene fragments analyzed, 108 differential expressed genes were identified in resistant plants. About 20 and 22 % of these resistant-correlated genes are related to signaling and defense genes, respectively. Between signaling genes, the major subclass corresponds to receptor and resistant homolog genes, like nucleotide-binding site leucine-rich repeat (NBS-LRR), Pto-like, RLKs, Bger, and RGH1A, all not previously described in coffee rust responses. The second major subclass included kinases, where two mitogen-activated kinases (MAPK) are identified. Further gene expression analysis was performed for 21 selected genes by real-time PCR gene expression analysis at 0, 12, 24, 48, and 72 h postinoculation. The expression of genes involved in signaling and defense was higher at 24 and 72 h after inoculation, respectively. The NBS-LRR was the more differentially expressed gene between the signaling genes (four times more expressed in the resistant genotype), and thraumatin (PR5) was the more expressed between all genes (six times more expressed). Multivariate analysis reinforces the significance of the temporal separation of identified signaling and defense genes: early expression of signaling genes support the hypothesis that higher expression of the signaling components up regulates the defense genes identified. Additionally the increased gene expression of these two gene sets is associated with a single monogenic resistance trait to to leaf coffee rust in the interaction characterized here.