Trinh Xuan Hoat

Rust, caused by Puccinia arachidis, is one among the most destructive fungal diseases constraining global groundnut (Arachis hypogaea L.) production. While the development of disease-resistant varieties stands as the most effective approach to preventing substantial yield losses, the genetic mechanisms underlying resistance to rust is not yet well understood, emphasizing the necessity for further detailed research. In this study, 184 accessions from the ICRISAT groundnut mini-core collection were evaluated for rust resistance at Dharwad, India, across multiple seasons, as well as in Vietnam for one season. Whole-genome resequencing-based genome-wide association study (GWAS) identified five highly significant marker trait associations (MTAs) for rust resistance (p = 5.22 × 10-13 to 7.21 × 10-08). Among these, two robust rust-associated kompetitive allele specific PCR (KASP) markers, snpAH00607 at chromosome Ah01 and snpAH00609 at chromosome Ah17, were validated across diverse set of breeding and pre-breeding lines. These markers were linked to candidate genes encoding sterol C4-methyl oxidase 1-2, implicated in brassinosteroid-mediated salicylic acid signalling, and MYB transcription factor known to be associated with defense responses. The identified SNPs, validated markers, and candidate genes will serve as important resources for marker-assisted breeding of rust disease resistant groundnut varieties.

Several lineages within the Eriophyoidea, an ancient group of phytoparasitic acariform mites, produce large protective silk webs on plant surfaces. This study examined the diversity and phylogeny of web-spinning eriophyoids associated with the leaves of Mangifera indica (mango) in Asia, Africa, and North America and Lepisanthes rubiginosa (mertajam) in Vietnam. We report, for the first time, silk-producing structures in Aceria aegyptindicae and Aculops knorri, as well as the presence of tibial seta l’ I and a lobular unpaired prosomal gland in Cisaberoptus kenyae. Molecular and morphological data indicate female dimorphism in A. knorri and reveal cryptic diversity within Cisaberoptus and mango-associated Aceria. The web-spinning species C. kenyae and Ac. aegyptindicae form a strongly supported clade and frequently coexist in syntopy on mango leaves, likely co-producing silk web. Phylogenetic analyses of COI and 28S genes place this clade as sister to Cecidophyinae, while grouping Aberoptus and A. knorri with Anthocoptini and Aceriini. These results demonstrate convergence, cryptic speciation, and unexpected mutualism in web-spinning eriophyoids, providing a framework for future research on the evolution of silk producing organs in this economically important mite group.

The diversity of eriophyoid mites on ferns and conifers is notably lower than on angiosperms. To date, ~40 eriophyoid mite species from 20 genera have been recorded on ferns. Most species belong to the eriophyid subfamilies Phyllocoptinae (45%), Eriophyinae (34%), and Nothopodinae (18%), while only one represents the diptilomiopid subfamily Rhyncaphytoptinae. The greatest diversity occurs on the fern orders Polypodiales and Cyatheales, followed by Equisetales, Gleicheniales, and Schizaeales, whereas no eriophyoid taxa have been described from Marattiales. We describe two new Eriophyidae species from ferns: Cymoptus ptisanis n. sp., collected in South Africa from erinea on the lower surface of frond pinnae of Ptisana salicifolia (Schrad.) Senterre et Rouhan (Marattiales: Marattiaceae), and Nothopoda vietnamensis n. sp., collected in Vietnam from galls on fronds of Nephrolepis cordifolia (L.) C.Presl (Polypodiales: Nephrolepidaceae). Morphological descriptions of the new taxa are supplemented with partial Cox1 (PV698368, PV698369) and 28S (PV711118, PV711119) gene sequences, photographs of host plant symptoms, and a series of images documenting stages of gall formation on Nephrolepis. In this paper we also propose relaxing the generic concept of Cymoptus Keifer 1946 (as Aceria-like eriophyines missing tibial seta l′ I), question the synonymy of the poorly differentiated nothopodine genera Floracarus Keifer 1953 and Nothopoda Keifer 1951, and advocate for future comparative studies on gallogenesis induced by eriophyoids on ferns and angiosperms.

Gall mites (Eriophyoidea) are cosmopolitan microscopic phytoparasites that often transmit viruses and induce gallogenesis. The tribe Calacarini is diagnosed by a set of plesiomorphic and homoplastic traits, including elimination of setae sc shared with other lineages of Eriophyoidea. We reviewed data on the generic diversity of calacarines, revised the concept of the type genus Calacarus Keifer 1940, and proposed three zones (MZ, SMZ, LZ) in the prodorsal shields of calacarines to simplify descriptions of their shield patterns. We describe three new calacarine species (Calacarus baviensisn. sp., C. burchelliaen. sp., and Viginticus searsiaen. sp.) from indigenous dicotyledonous trees from South Africa and Vietnam and report on new findings of Paracalacarus podocarpi Keifer in Brazil, Jiangsuacarus sp. in the USA, and Calacarus pusillus Pye in Latvia and Russia. The latter represents the new most northern locality of Calacarini. Reinvestigating the type species of Jaranasia Chandrapatya & Boczek 2000 revealed that absence of setae l’’ II is the only character separating it from Jiangsuacarus Xue 2009. We proposed two new combinations: Jiangsuacarus sesleriae (Skoracka 2004) n. comb. (transferred from Jaranasia) and Procalacarus mussaendae (Keifer 1977) n. comb. (transferred from Calacarus). Partial sequences of Cox1 and 28S genes were obtained for six calacarines, some of them originating from old ethanol material kept at room temperature. Molecular phylogenetics revealed a stable cluster of “true” calacarine sequences comprising Calacarus, Jaranasia, Latitudo, and Viginticus and a polyphyletic group of erroneous sequences assigned to Calacarini in GenBank. All investigated females of calacarines have a pair of genital tubules associated with the vestibulum and hypothesized to participate in fertilization. This finding may contribute to resolving the question on how the fusion of gametes happens in gall mites.

Ginger cultivation in Vietnam is hampered by the ginger blast disease (Proxipyricularia zingiberis). The primary goal of this study was to use β-tubulin and calmodulin genes to identify the causal pathogen, and to test the fungicidal activity of various fungicides against P. zingiberis isolates in vitro and their efficacy on ginger blast disease in the field conditions. It indicated that β-tubulin and calmodulin are appropriate target genes for characterisation of P. zingiberis. The optimal conditions for the growth and development of the P. zingiberis isolates TUAF-PIG-1, TUAF-PIG-2, and TUAF-PIG-3 were determined to be PDA medium, pH 5.0, and 28 °C. Amisupertop 330SC (1.00 g L⁻¹), Tilt Super® 300EC (0.03 ml L⁻¹), Amistar Top^® 325SC (0.9 ml L⁻¹), and Ridomil Gold^® 68WG (4.5 g L⁻¹) demonstrated strong fungicidal efficacy on the growth and development of P. zingibers isolates in vitro and high efficacy on ginger blast disease in the field conditions.

Cassava mosaic disease (CMD), caused by Sri Lankan cassava mosaic virus (SLCMV), was first detected in Tay Ninh province in the southeast region of Vietnam in 2017 and is an emerging threat for cassava production in Vietnam. This study was conducted to characterize the causal agent of CMD in Nghe An province in the north-central region of Vietnam, which is more than 1,200 km away from Tay Ninh province. Genetic relationships between SLCMV isolates indicated that both DNA-A and DNA-B sequences from Nghe An province were identical with the isolates from Tay Ninh province and were highly homologous (>99.7%) with isolates from Cambodia, Thailand and China. This study confirms the gradual spread of SLCMV in Vietnam as an emerging threat to cassava production. In addition, the outcome of this study could help in the timely enforcement of effective management strategies for the cassava mosaic disease in Vietnam.

In Vietnam, ginger (Zingiber officinale) is one of the most prevalent and valuable crops used for fresh spices, medicinal purposes for domestic consumption, and exportation. In recent years, however, the blast disease has emerged as the most cost-effective component in ginger production, resulting in significant yield losses. The purpose of this study was to identify and characterise the causal pathogen isolated from blast disease-like lesions on ginger. We conducted morphological characterisation, pathogenicity test, and PCR assays with different target genes and as well as phylogenetic analyses of the ITS region, and actin gene. The findings suggested that the pathogen responsible for the blast disease on ginger was Proxipyricularia zingiberis. This is the first time P. zingiberis has been linked to ginger blast disease in Vietnam.

The fall armyworm, Spodoptera frugiperda, is an important agricultural pest native to tropical and subtropical regions of the Western Hemisphere, and has invaded Africa and further spread into most countries of Asia within two years. Here, we analyzed the genetic variation of invaded populations by comparing the nucleotide sequences of two genes: the nuclear Z-chromosome linked gene triose phosphate isomerase (Tpi) and the mitochondrial gene cytochrome oxidase subunit I (COI) of 27 specimens collected in Africa (DR Congo, Tanzania, Uganda, and Zimbabwe) and Asia (Bangladesh, Korea, Nepal, and Vietnam). The results revealed that 25 specimens were from a heterogeneous hybrid (Tpi-corn strain and COI-rice strain; Tpi-C/COI-R) of the corn strain male and rice strain female, but two specimens were from a homogenous corn strain (Tpi-corn strain and COI-corn strain; Tpi-C/COI-C). The further analysis of the fourth exon and the fourth intron sequences of the Tpi gene identified at least four subgroups of the corn strain. These four genetic subgroups were identified in Africa and Asia, suggesting no significant genetic change due to the rapid migration within two years. Our study provides essential information for understanding the genetic diversity of fall armyworm in new habitats.