Molecular Diversity of Rice Yellow Mottle Virus in Uganda and Relationships with Other Strains from Africa.

Rice yellow mottle virus disease, caused by Rice yellow mottle virus (RYMV), is the most important disease of lowland rice in Uganda. However, little is known about its genetic diversity in Uganda and relationships with other strains elsewhere across Africa. A new degenerate primer pair that targets amplification of the entire RYMV coat protein gene (circa 738 bp) was designed to aid virus variability analysis using RT-PCR and Sanger sequencing. A total of 112 rice leaf samples from plants with RYMV mottling symptoms were collected during the year 2022 in 35 lowland rice fields within Uganda. The RYMV RT-PCR results were 100% positive, and all 112 PCR products were sequenced. BLASTn analysis revealed that all isolates were closely related (93 to 98%) to those previously studied originating from Kenya, Tanzania, and Madagascar. Despite high purifying selection pressure, diversity analysis on 81 out of 112 RYMV CP sequences revealed a very low diversity index of 3 and 1.0% at the nucleotide and amino acid levels, respectively. Except for glutamine, amino acid profile analysis revealed that all 81 Ugandan isolates shared the primary 19 amino acids based on the RYMV coat protein region examined. Except for one isolate (UG68) from eastern Uganda that clustered alone, phylogeny analysis revealed two major clades. The Ugandan RYMV isolates were phylogenetically related to those from the Democratic Republic of Congo, Madagascar, and Malawi but not to RYMV isolates in West Africa. Thus, the RYMV isolates in this study are related to serotype 4, a strain common in eastern and southern Africa. RYMV serotype 4 originated in Tanzania, where evolutionary forces of mutation have resulted in the emergence and spread of new variants. Furthermore, mutations are evident within the coat protein gene of the Ugandan isolates, which may be attributed to changing RYMV pathosystems as a result of rice production intensification in Uganda. Overall, the diversity of RYMV was limited and most noticeably in eastern Uganda.

Late blight in tomato: insights into the pathogenesis of the aggressive pathogen Phytophthora infestans and future research priorities.

MAIN CONCLUSION: This review provides insights into the molecular interactions between Phytophthora infestans and tomato and highlights research gaps that need further attention. Late blight in tomato is caused by the oomycota hemibiotroph Phytophthora infestans, and this disease represents a global threat to tomato farming. The pathogen is cumbersome to control because of its fast-evolving nature, ability to overcome host resistance and inefficient natural resistance obtained from the available tomato germplasm. To achieve successful control over this pathogen, the molecular pathogenicity of P. infestans and key points of vulnerability in the host plant immune system must be understood. This review primarily focuses on efforts to better understand the molecular interaction between host pathogens from both perspectives, as well as the resistance genes, metabolomic changes, quantitative trait loci with potential for improvement in disease resistance and host genome manipulation via transgenic approaches, and it further identifies research gaps and provides suggestions for future research priorities.