First Report of Root and Collar Rot caused by Phytophthora nicotianae on ⨯Graptoveria 'Silver Star' in Korea

⨯Graptoveria 'Silver Star' (a cross between Graptopetalum filiferum and Echeveria agavoides) from the Crassulaceae family, are an evergreen succulent with lotus constellation-shaped flowers, making it consumer favorite ornamental plant in Korea. In 2019, Korea's ornamental production was estimated at KRW 517.4 billion (EUR 382 million), from 4,244 ha of farming area according to the Ministry of Agriculture, Food and Rural Affairs of Korea. In July 2023, ⨯Graptoveria 'Silver Star' plants with chlorotic leaves, root and collar rot were observed in a greenhouse in Yongin (37°14'27.9"N, 127°10'39.19"E), Korea. To isolate the causal agent, small pieces (1 mm2) of symptomatic tissues were surface-sterilized using 1% NaOCl for 1 min, then put onto a water agar (WA) plate and incubated in the dark at 25℃ for five days. Two isolates (FD00202, FD00203) were obtained from diseased leaves, stem and roots by isolating single sporangium. To investigate the morphological characteristics of the isolates, the mycelium from potato dextrose agar (PDA) were transferred to V8 agar (V8A) followed by incubation at 25°C in the dark for 7 days. The isolates produced dense cottony mycelium, with slightly petaloid and light rossette pattern, with coralloid edges measuring 70 to 83 mm diameter. Sporangium were spheroid (30.0-48.0 µm long, 25.0-35.0 µm wide) with globose chlamydospores (17.0-50.0 µm long, 18.0-38.0 µm wide). Oogonia were not observed. Morphological and cultural characteristics of these isolates were phenotypically similar to that of Phytophthora nicotianae (Faedda et al. 2013; Abad et al. 2023). For molecular identification, genomic DNA was extracted from 5 days old cultures using the Maxwell® RSC PureFood GMO and Authentication Kit (Promega). Two gene regions, the rDNA-ITS, COX I were amplified and sequenced using primers ITS1/ITS4 and FM83/FM84, respectively (White et al. 1990; Martin and Tooley 2003). The resulting sequences were deposited in GenBank with accession no. LC783858 to LC783861. A BLASTn search of the DNA sequences from ITS, COX I showed 99.81 and 98.94% identity to P. nicotianae isolate IMI 398853, respectively. Maximum likelihood phylogenetic analyses were performed for the combined data set with ITS, COX I using MEGA7 under the Tamura-Nei model (Kumar et al. 2016). The isolates formed a monophyletic group with P. nicotianae isolate IMI 398853, CPHST BL162, and CPHST BL 44. Based on morphological characteristics and molecular analysis, the isolates were identified as P. nicotianae. T confirm their pathogenicity, inoculum was prepared in accordance with Ann (2000). Artificially wounded healthy plant roots were dipped in zoospore suspension (3.0 × 106 zoospore/ml) for 24 hours, with mock-treated plants (control) dipped in sterile distilled water (Ann. 2000). Thereafter, the plants were transplanted into new medium and kept under high humidity. Symptoms were observed after 10 days of incubation. The plants inoculated with P. nicotianae showed similar symptoms of chlorotic leaves with root and collar rot, while control remained symptomless. The pathogen was re-isolated from all inoculated plants and confirmed as P. nicotianae by morphological and molecular analysis. but not from controls, fulfilling Koch's postulates. Phytophthora nicotianae was previously report on Echeveria derenbergii and Kalanchoe blossfeldiana causing brown spot on stems and roots in California and Korea, respectively (French 1989; Oh and Son 2008). To best of our knowledge, this is the first report of P. nicotianae causing root and collar rot on ⨯Graptoveria 'Silver Star' plants in the Korea.

Characterization of Blast Resistance in a Diverse Rice Panel from Sub-Saharan Africa

There is a recent unparalleled increase in demand for rice in sub-Saharan Africa, yet its production is affected by blast disease. Characterization of blast resistance in adapted African rice cultivars can provide important information to guide growers and rice breeders. We used molecular markers for known blast resistance genes (Pi genes; n = 21) to group African rice genotypes (n = 240) into similarity clusters. We then used greenhouse-based assays to challenge representative rice genotypes (n = 56) with African isolates (n = 8) of Magnaporthe oryzae which varied in virulence and genetic lineage. The markers grouped rice cultivars into five blast resistance clusters (BRC) which differed in foliar disease severity. Using stepwise regression, we found that the Pi genes associated with reduced blast severity were Pi50 and Pi65, whereas Pik-p, Piz-t, and Pik were associated with increased susceptibility. All rice genotypes in the most resistant cluster, BRC 4, possessed Pi50 and Pi65, the only genes that were significantly associated with reduced foliar blast severity. Cultivar IRAT109, which contains Piz-t, was resistant against seven African M. oryzae isolates, whereas ARICA 17 was susceptible to eight isolates. The popular Basmati 217 and Basmati 370 were among the most susceptible genotypes. These findings indicate that most tested genes were not effective against African blast pathogen collections. Pyramiding genes in the Pi2/9 multifamily blast resistance cluster on chromosome 6 and Pi65 on chromosome 11 could confer broad-spectrum resistance capabilities. To gain further insights into genomic regions associated with blast resistance, gene mapping could be conducted with resident blast pathogen collections. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Foliar Diseases and the Associated Fungi in Rice Cultivated in Kenya

We conducted a survey to assess the occurrence and severity of rice blast and brown spot diseases on popular cultivars grown in the Busia, Kirinyaga, and Kisumu counties of Kenya in 2019. Working with agricultural extension workers within rice production areas, we interviewed farmers (n = 89) regarding their preferred cultivars and their awareness of blast disease, as this was the major focus of our research. We scored the symptoms of blast and brown spot and assessed the lodging, plant height, and maturity of the crops (days after planting). Furthermore, we collected leaf and neck tissues for the assessment of the prevailing fungal populations. We used specific DNA primers to screen for the prevalence of the causal pathogens of blast, Magnaporthe oryzae, and brown spot, Cochliobolus miyabeanus, on asymptomatic and symptomatic leaf samples. We also conducted fungal isolations and PCR-sequencing to identify the fungal species in these tissues. Busia and Kisumu had a higher diversity of cultivars compared to Kirinyaga. The aromatic Pishori (NIBAM 11) was preferred and widely grown for commercial purposes in Kirinyaga, where 86% of Kenyan rice is produced. NIBAM108 (IR2793-80-1) and BW196 (NIBAM 109) were moderately resistant to blast, while NIBAM110 (ITA310) and Vietnam were susceptible. All the cultivars were susceptible to brown spot except for KEH10005 (Arize Tej Gold), a commercial hybrid cultivar. We also identified diverse pathogenic and non-pathogenic fungi, with a high incidence of Nigrospora oryzae, in the rice fields of Kirinyaga. There was a marginal correlation between disease severity/incidence and the occurrence of causal pathogens. This study provides evidence of the need to strengthen pathogen surveillance through retraining agricultural extension agents and to breed for blast and brown spot resistance in popular rice cultivars in Kenya.

Integrated Strategies for Durable Rice Blast Resistance in Sub-Saharan Africa

Rice is a key food security crop in Africa. The importance of rice has led to increasing country-specific, regional, and multinational efforts to develop germplasm and policy initiatives to boost production for a more food-secure continent. Currently, this critically important cereal crop is predominantly cultivated by small-scale farmers under suboptimal conditions in most parts of sub-Saharan Africa (SSA). Rice blast disease, caused by the fungus Magnaporthe oryzae, represents one of the major biotic constraints to rice production under small-scale farming systems of Africa, and developing durable disease resistance is therefore of critical importance. In this review, we provide an overview of the major advances by a multinational collaborative research effort to enhance sustainable rice production across SSA and how it is affected by advances in regional policy. As part of the multinational effort, we highlight the importance of joint international partnerships in tackling multiple crop production constraints through integrated research and outreach programs. More specifically, we highlight recent progress in establishing international networks for rice blast disease surveillance, farmer engagement, monitoring pathogen virulence spectra, and the establishment of regionally based blast resistance breeding programs. To develop blast-resistant, high yielding rice varieties for Africa, we have established a breeding pipeline that utilizes real-time data of pathogen diversity and virulence spectra, to identify major and minor blast resistance genes for introgression into locally adapted rice cultivars. In addition, the project has developed a package to support sustainable rice production through regular stakeholder engagement, training of agricultural extension officers, and establishment of plant clinics.

The potential of neglected and underutilized species for improving diets and nutrition

Nutrient-rich neglected and underutilized plant species could help transform food systems, provided science and policy are better connected, and greater coordination exists among the diverse stakeholders working with these species. Why have our food systems come to rely on such a narrow range of plant species of limited nutritional value? Today three staple crops (rice, maize and wheat) account for more than 50% of calories consumed while we continue to disregard the huge diversity of nutrient-rich plant species utilized by humanity throughout our history. The reasons for this situation are complex and challenging. Creative approaches are required to ensure greater integration of these plant species in agriculture and food systems, and ultimately greater food diversity on our plates and in our diets. This paper presents an overview of the nutritional value of select neglected and underutilized species (NUS) before describing in detail the work undertaken in four mega-diverse countries-Brazil, Kenya, Sri Lanka and Turkey-to increase the knowledge, appreciation, awareness and utilization of this nutrient-rich biodiversity encompassing both orphan crops and wild edible plant species. The paper highlights the novel and ingenious approaches these countries have used to prioritize a rich diversity of NUS for healthier diets and improved nutrition, and how this knowledge has been used to mainstream these plant species into production and consumption systems, including linking NUS to school meals and public food procurement, dietary guidelines and sustainable gastronomy. The paper concludes with some perspectives on the way forward for NUS and the community working on them (including researchers, universities and government agencies, national ministries, municipalities, producers, and civil society) in meeting the challenges of malnutrition and environmental sustainability in the 2030 sustainable development context.

Assessment of the Virulence Spectrum and Its Association with Genetic Diversity in Magnaporthe oryzae Populations from Sub-Saharan Africa

A collection of 122 isolates of Magnaporthe oryzae, from nine sub-Saharan African countries, was assessed for virulence diversity and genetic relatedness. The virulence spectrum was assessed by pathotype analysis with a panel of 43 rice genotypes consisting of differential lines carrying 24 blast resistance genes (R-genes), contemporary African rice cultivars, and susceptible checks. The virulence spectrum among isolates ranged from 5 to 80%. Five isolates were avirulent to the entire rice panel, while two isolates were virulent to ∼75% of the panel. Overall, cultivar 75-1-127, the Pi9 R-gene donor, was resistant to all isolates (100%), followed by four African rice cultivars (AR105, NERICA 15, 96%; NERICA 4, 91%; and F6-36, 90%). Genetic relatedness of isolates was assessed by single nucleotide polymorphisms derived from genotyping-by-sequencing and by vegetative compatibility tests. Phylogenetic analysis of SNPs of a subset of isolates (n = 78) revealed seven distinct clades that differed in virulence. Principal component analysis showed isolates from East Africa were genetically distinct from those from West Africa. Vegetative compatibility tests of a subset of isolates (n = 65) showed no common groups among countries. This study shows that blast disease could be controlled by pyramiding of Pi9 together with other promising R-genes into rice cultivars that are adapted to East and West African regions.