Multilocus evidence of Phytophthora palmivora and P. tropicalis as causal agents of cacao black pod disease in southern Mexico

Phylogenomic analysis of Phytophthora cinnamomi collected from avocado in the United States reveals links to the two A2 panglobal clonal lineages

Phytophthora cinnamomi, the causal agent of phytophthora root rot (PRR), is one of the most destructive pathogens affecting avocados worldwide. Recent global population analyses of P. cinnamomi identified two panglobal clonal lineages named PcG1-A2 and PcG2-A2, both of A2 mating type. In California avocado orchards, P. cinnamomi populations were previously classified into two clades, A2 clade I and A2 clade II, with the latter likely introduced from Mexico. In this study, we conducted the genetic characterization of 125 isolates collected from avocado-producing regions of the United States and investigated their genetic relationships with previous populations from California and Mexico and with the two panglobal A2 clonal lineages using whole-genome resequencing. All isolates were estimated to be triploid based on nQuire. Phylogenetic reconstruction and fastSTRUCTURE analyses based on single nucleotide polymorphisms showed that the PcG1-A2 reference isolate clustered with the previously described California A2 clade I and with most U.S. isolates. In contrast, the PcG2-A2 reference isolate clustered with the California A2 clade II and with most Mexican isolates, supporting a Mexican origin for this lineage. Discriminant analysis of principal components, principal coordinate analysis, and minimum spanning networks further resolved two distinct groups of A2 isolates, reinforcing the presence of two clonal lineages in avocado orchards across the United States. Isolates were assigned to multilocus genotypes (MLGs), including one widespread MLG containing isolates from all sampled avocado-growing regions. Mexico exhibited the highest genetic diversity, although unique MLGs were detected at each location. These results clarify the genetic relationships among P. cinnamomi populations in avocado orchards across the United States and link the previously described California clades to the two panglobal lineages currently recognized. Our findings support a hypothesis of pathogen movement among avocado-producing regions and reveal localized subpopulations that may pose risks to the sustainability of the avocado industry. Continued monitoring of P. cinnamomi populations will be essential for developing effective PRR management strategies to increase avocado production and enhance the national industry’s profitability, competitivity, and marketability.

Occurrence of Phytophthora cinnamomi in the Rhizosphere of Declining Leucadendron elimense subsp. salteri in South Africa

Phytophthora cinnamomi is a destructive invasive plant pathogen reported from more than 5000 hosts and across all continents except Antarctica. In South Africa, P. cinnamomi poses a substantial threat to native flora, particularly members of the Proteaceae. This pathogen has been detected in diverse settings on hosts within this family, and, of especial concern, in natural populations of species under a high threat of extinction. In this study, P. cinnamomi was detected in a population of Leucadendron elimense subsp. salteri located in a nature reserve. This plant population has experienced a severe decline in recent years. Two plants collected for laboratory analysis exhibited severe collar lesions and had lost most their root system due to root rot, fitting with symptoms typically associated with P. cinnamomi infection in susceptible hosts. Samples were processed, and the presence of P. cinnamomi was confirmed morphologically and molecularly from the rhizosphere soil of both plants. There is an urgent need to mitigate the impacts of P. cinnamomi in South Africa, in particular by expediting the regulatory evaluation of potential treatments.

First Report of Phytopythium vexans Causing Stem and Leaf Necrosis on Rubber Tree (Hevea brasiliensis): Biological Characteristics and Fungicide Sensitivity

The findings provide a theoretical foundation for accurate disease diagnosis, epidemiological surveillance, and the development of effective chemical control strategies for rubber plantations.

Molecular Survey of Coconut Lethal Yellowing Phytoplasmas in Putative Insect Vectors in Ghana

Cape Saint Paul Wilt Disease (CSPWD), a lethal yellowing‐type disease of coconut associated with ‘ Candidatus Phytoplasma palmicola’ (16SrXXII‐B), continues to threaten coconut production in Ghana. As most phytoplasma putative vectors belong to the suborder Auchenorrhyncha, we conducted field surveys in CSPWD‐devastated, actively diseased and healthy coconut plantations. In total, 13,919 14,025 individuals representing five families were collected, with Derbidae being the most abundant. Nested PCR screening of 282 pooled samples (~1900 insects) detected CSPWD (16SrXXII‐B)‐associated phytoplasma in Diostrombus sp. 1, Diostrombus sp. 2 and Patara armata from actively diseased and devastated coconut plantations. Although these taxa also occurred in healthy plantations, they tested negative for the pathogen. While vector competence remains to be verified, these results provide essential baseline data for targeted surveillance and transmission studies aimed at identifying confirmed CSPWD vectors in Ghana.

Occurrence of Neopestalotiopsis rosae and Neopestalotiopsis zimbabwana Causing Leaf Blight in Blueberry in Mexico

In Mexico, blueberries are an economically important crop, with annual production of more than 80,000 tons, making the country the world's fifth‐largest producer of this fruit. In spring 2024, chlorotic spots were observed that turned into localized necrotic lesions which eventually coalesced in two commercial rabbiteye blueberry fields in the states of Michoacán and Puebla, Mexico. Based on morphological features, Neopestalotiopsis ‐like colonies were consistently recovered from symptomatic tissues. Multilocus phylogenetic analyses (ITS, β‐tub and tef1 ‐α) identified the isolates as Neopestalotiopsis rosae and N. zimbabwana . Pathogenicity was demonstrated by inoculating each isolate onto healthy blueberry plants, which developed the characteristic symptoms of the disease 9 days after inoculation, thereby fulfilling Koch's postulates. To our knowledge, this is the first worldwide report of N. zimbabwana and the first report of N. rosae in Mexico causing leaf blight on blueberry. Leaf blight is an emerging disease in blueberry fields of Puebla and Michoacán, Mexico. Therefore, the epidemiological potential of the disease should be determined, and effective, sustainable management strategies should be developed.

First Report and Morpho-Molecular Characterization of Boeremia Exigua Causing Leaf Spot of Mungbean (Vigna Radiata (L.) Wilczek)