Royal Horticultural Society

SummaryThe genus Hypobathrum in Thailand is revised, based on the morphological characters found in herbarium specimens from Thailand and neighbouring countries including Bangladesh, Myanmar, Cambodia and Peninsular Malaysia. In this study, three species of Hypobathrum are recognised, among them, H. venulosum is a newly recorded species in this region. An identification key is provided for the species, along with descriptions, synonyms, distribution ranges and vernacular names (if available).

In December 2022 we inspected a Euphorbia amygdaloides cv. Purpurea in the RHS Wisley garden showing symptoms of dieback. Phytophthora root rot disease was confirmed using a lateral flow test. A sample of infected roots was apple baited as described by Pérez-Sierra et al. (2022). From the obtained cultures, media plugs were floated in filtered pond water to induce sporangia formation. The culture was homothallic with globose oogonia (n = 40), 24.8-36.5 μm (mean 31.49 μm) in diameter and a wall 0.5-2 μm thick, antheridia were paragynous, oospores were plerotic ranging in size (n = 40) from 21.6 to 33.3 μm (mean 26.5 μm) (Figure 1). Sporangia were ovoid, obpyriform, semi-papillate, caduceus and non-caducueus on branched sporangiophores (n = 40) 53-20.5 × 35.2- 13.3 μm (mean 37.6 × 25.2) with an L/B ratio of 1.5:1 (Figure 1). Chlamydospores were not observed. Based on these characteristics Phytophthora occultans was identified (Man in ‘t Veld et al., 2015; Hrabetova et al., 2022). Molecular identification was confirmed by sequencing the internal spacer region (ITS) using ITS primers (Scibetta et al., 2012) in a nested PCR (Burgess et al., 2017). In addition the cytochrome oxidase subunit 1 (COX1) and the translation elongated factor 1a (EF) genes were sequenced with COXF-CIT/ COXR-CIT and ELONGF1/ ELONGR1 primers (Hrabetova et al., 2022), respectively. Sequence analysis showed 99.56% identity for ITS (Accession No. MH171638.1), 100% identity for COX (MH620021.1, KU891804.1, OP313505.1, ON862131.1, HG962433.1, JX978159.1) and 99.18% identity for EF (KF650772.1) with P. occultans. These sequence data have been submitted to GenBank databases under Accession Nos. OR793153 (ITS); OR888541 (EF); OR888542 (COX1). Pathogenicity was confirmed by inoculating six Euphorbia amygdaloides plants at the collar with 3 mm plugs from a 10-day-old P. occultans culture grown on carrot agar (CA). The plants were kept under 22°C day / 20°C night and 60% RH and assessed five, seven and eleven days post inoculation (dpi). Four plants with 3 mm plugs of sterile CA media acted as controls. Wilt, dieback and necrotic lesions appeared 5 dpi on test plants and developed rapidly, with an average length of lesions 3.46, 4.84 and 7.74 cm at five, seven and eleven dpi respectively (Figure 2). The control plants did not develop symptoms (Figure 3). Phytophthora occultans was successfully re-isolated from the stems and roots by direct plating on selective media (Pérez-Sierra et al., 2022) followed by molecular identification and sequencing as described above. It is likely that the pathogen arrived in the RHS Wisley garden with the plant from overseas. Phytophthora occultans has been intercepted previously on nursery stock arriving in the UK (Animal and Plant Health Agency, April 2023, personal communication) and US nurseries (Reeser et al., 2015). Despite biosecurity precautions such as quarantine and visual inspections, these measures may not be sufficient to detect Phytophthora which can remain dormant until post planting. Phytophthora occultans is known to infect box (Buxus sempervirens) in Europe, including the UK (Man in ’t Veld et al., 2015; Hrabetova et al., 2022), and other ornamental plants in the USA (Reeser et al., 2015). To our knowledge this is the first time that the pathogen has been identified on Euphorbia sp. in the UK and worldwide. The authors would like to thank the garden team at Wisley for their help and co-operation.

Access to water for irrigating amenity landscape and public gardens is under intense pressure due to the rising competition for water between different sectors, exacerbated by increased drought risk and climate change. Rainwater harvesting (RWH) has the potential to reduce the economic impacts of restrictions on irrigation abstraction in dry years and to build resilience to future water shortages. This study investigated the hydrological viability of RWH for the landscape and public garden sector based on an analysis of five Royal Horticultural Society gardens. A RWH model was developed and combined with on-site observations, key informant interviews and GIS analyses, to estimate irrigation demands and the volumes of harvested rainfall for contrasting agroclimatic years. The results showed that gardens located in wetter regions and with low irrigation water demand to harvestable area ratio had a higher RWH potential and could almost exclusively rely on rainwater to meet irrigation demand, even in dry years. RWH potential is more limited for gardens in drier regions where they would require larger areas to harvest rainwater and for storage. Appropriately designed rainwater harvesting systems offer the potential to remove most of the risk of irrigation abstraction restrictions during dry years and associated impacts on amenity planting quality and visitor experience.

Article H.6 of the Shenzhen Code (Turland & al. in Regnum Veg. 159. 2018) provides instructions for the formation of nothogeneric names for intergeneric hybrids. Article H.6.3 and H.6.4, dealing with the formation of nothogeneric names for intergeneric hybrids involving three or more genera, provide for a name to be formed from the name of a person to which is added the termination -ara. This is a very workable procedure. However, when the personal name used already ends with -a, addition of the termination -ara produces a double a in the name, as in ×Hayataara J.M.H. Shaw, named for Bunzô Hayata (1874–1934). There are at least 48 nothogenera in Orchidaceae where the personal name used ends with -a. None is known from other families. At times, nothogeneric names based on personal names ending with -a have been formed by the addition of a modified termination -ra as, for example, ×Iwanagara Iwanaga & Wreford for Ernest T. Iwanaga, ×Kagawara Kagawa & Wreford for Hiroshi Kagawa and ×Yamadara M. Yamada & Wreford for Masao Yamada, whereas ×Perreiraara Perreira & Wreford for Robert J. Perreira conforms to the present rule. The current proposal is designed to simplify the spelling and pronunciation of nothogeneric names by avoiding the formation of the double a in the name. A precedent exists in Art. 60.8(c) where the adjectival ending -anus/ana/anum is reduced to -nus/na/num for personal names ending with -a. It would also be instructive to include in each Example provided for Art. H.6.3 and H.6.4. the personal name on which the nothogeneric name is based. “H.6.3. The nothogeneric name of an intergeneric hybrid derived from four or more genera is formed from the name of a person to which is added the termination -ara, except when the personal name already ends with -a in which case the termination -ra is added; no such name may exceed eight syllables. Such a name is equivalent to a condensed formula.” “Ex. 6. ×Beallara Moir (in Orchid Rev. 78(929): New Orch. Hybr. [1, 3]. 1970) commemorating J. Ferguson Beall (Brassia R. Br. × Cochlioda Lindl. × Miltonia Lindl. × Odontoglossum Kunth); ×Cogniauxara Garay & H. R. Sweet (see Art. H.8 Ex. 3) commemorating Célestin A. Cogniaux (Arachnis Blume × Euanthe Schltr. × Renanthera Lour. × Vanda W. Jones ex R. Br.); ×Hayatara J. M. H. Shaw (in Sander's List Orchid Hybrids Addendum 2002–2004: xxxv. 2005, ‘Hayataara’) commemorating Bunzô Hayata (Brassavola R. Br. × Cattleya Lindl. × Laelia Lindl. × Myrmecophila Rolfe × Pseudolaelia Porto & Brade).” “H.6.4. The nothogeneric name of a trigeneric hybrid is either (a) a condensed formula in which the three names adopted for the parental genera are combined into a single word not exceeding eight syllables, using the whole or first part of one, followed by the whole or any part of another, followed by the whole or last part of the third (but not the whole of all three) and, optionally, one or two connecting vowels, or (b) a name formed like that of a nothogenus derived from four or more genera, i.e. from a personal name to which is added the termination -ara, except when the personal name already ends with -a in which case the termination -ra is added.” “Ex. 7. ×Sophrolaeliocattleya Hurst (in J. Roy. Hort. Soc. 21: 468. 1898) (Cattleya Lindl. × Laelia Lindl. × Sophronitis Lindl.); ×Rodrettiopsis Moir (in Orchid Rev. 84: ix. 1976) (Comparettia Poepp. & Endl. × Ionopsis Kunth × Rodriguezia Ruiz & Pav.); ×Holttumara Holttum (see Art. H.8 Ex. 3) commemorating Richard E. Holttum (Arachnis Blume × Renanthera Lour. × Vanda W. Jones ex R. Br.); ×Kagawara Kagawa & Wreford (Orchid Rev. 76: New Orch. Hybr. [2, 4]. 1968) commemorating Hiroshi Kagawa (Ascocentrum J. J. Sm. × Renanthera Lour. × Vanda R. Br.).”

Abstract Nectar and pollen are floral resources that provide food for insect pollinators, so quantifying their supplies can help us to understand and mitigate pollinator declines. However, most existing datasets of floral resource measurements focus on native plants found in rural landscapes, so cannot be used effectively for estimating supplies in urban green spaces, where non‐native ornamental plants often predominate. We sampled floral nectar sugar in 225 plant taxa found in UK residential gardens and other urban green spaces, focussing on the most common species. The vast majority (94%) of our sampled taxa are non‐native, filling an important research gap and ensuring these data are also relevant outside of the United Kingdom. Our dataset includes values of daily nectar sugar production for all 225 taxa and nectar sugar concentration for around half (102) of those sampled. Nectar extraction was conducted according to published methods, ensuring our values can be combined with other datasets. We anticipate that the two main uses of these data are (1) to estimate the nectar production of habitats and landscapes and (2) to identify high‐nectar plants of conservation importance. To increase the utility of our data, we provide guidance for scaling nectar values up from single flowers to floral units, as is commonly done in field studies.

Oak powdery mildew caused by Erysiphe alphitoides (Griffon and Maubl.; U. Braun & S. Takam.) is a common disease in European forests. One of the most susceptible species is the pedunculate oak (Quercus robur L.). Presently, a few methods are available to control powdery mildew, e.g., the use of fungicides (e.g., based on citric acid), antagonistic fungi or bacteria, chemical treatments (e.g., sulphur, potassium bicarbonate) or genetic resistance. In our study, we aimed to check the effects of using chitosan derivatives and novel active substances inducing the plants’ natural resistance: benzodiathiadiazole (both in neutral and salt form). 84 pedunculate oak seedlings were subjected to the experiment in three treatment variants (plus positive and negative controls). The plants were treated with active substances and inoculated with E. alphitoides. Although the powdery mildew symptoms appeared in all variants, they were manifested mainly by the mycelium in the form of small spots. The experiment indicated that the highest limitation of powdery mildew mycelium was achieved by applying N-methyl-N-methoxyamide-7-carboxybenzo(1,2,3)thiadiazole (BTHWA). The application of BTHWA reduced disease development by 88.9% when compared to the effects of the other variants.

Culinary herbs are commercially cultivated for their wide range of volatile compounds that give characteristic aromas and tastes. Rosemary (Salvia rosmarinus Spenn.) is an excellent model for assessment of methods improvement of volatile production as cultivars offer a wide variety of aromatic profiles due to the large family of terpene synthase genes. Arbuscular mycorrhizal fungi (AMF) associations have been shown to improve essential oil production in aromatic plants and offer one approach to enhance aroma in commercial herb production. Changes in the expression of seven different terpene synthases were compared in six rosemary cultivars in response to addition of AMF to a peat substrate. Addition of AMF profoundly influenced terpene synthase expression in all cultivars and did so without impacting the optimised plant size and uniformity achieved in these conditions. In addition, two methods for AMF application, developed with the horticultural industry in mind, were tested in this study. Uniform incorporation of AMF mixed into the growing substrate prior to planting of a root plug produced the most consistent root colonisation. Overall, our findings demonstrate the potential for the use of AMF in the improvement of aroma in culinary herbs within a commercial setting but show that outcomes are likely to greatly vary depending on variety.

Armillaria mellea is an important fungal pathogen worldwide, affecting a large number of hosts in the horticulture and forestry industries. Controlling A. mellea infection is expensive, labour intensive and time-consuming, so a new, environmentally friendly management solution is required. To this effect, endophytic Trichoderma species were studied as a potential protective agent for Armillaria root rot (ARR) in strawberry and privet plants. A collection of forty endophytic Trichoderma isolates were inoculated into strawberry (Fragaria × ananassa) plants and plant growth was monitored for two months, during which time Trichoderma treatment had no apparent effect. Trichoderma-colonised strawberry plants were then inoculated with A. mellea and after three months plants were assessed for A. mellea infection. There was considerable variation in ARR disease levels between plants inoculated with different Trichoderma spp. isolates, but seven isolates reduced ARR below the level of positive controls. These isolates were further tested for protective potential in Trichoderma-colonized privet (Ligustrum vulgare) plants where five Trichoderma spp. isolates, including two highly effective Trichoderma atrobrunneum isolates, were able to significantly reduce levels of disease. This study highlights the potential of plants pre-colonised with T. atrobrunneum for effective protection against A. mellea in two hosts from different plant families.