First Report of Downy Mildew caused by Pseudoperonospora cannabina on Cannabis sativa in New York.

Hemp (Cannabis sativa <0.3% tetrahydrocannabinol) is an emerging crop used for grain, fiber, and cannabinoid production (Fike et al. 2020). In New York, hemp is grown both in controlled environment facilities, including greenhouses, and as a field crop. In August 2020, downy mildew-like symptoms were observed on leaves and inflorescence of hemp plants in a field research trial in Ithaca, NY. Several cultivars, including 'Auto CBD', were affected. Disease was severe with some plants reaching 75% disease severity at the individual plant level. In the most severely affected plots, there was no marketable yield. The disease was characterized by chlorotic and necrotic lesions producing sporangiophores under high humidity. Pigmented sporangia were produced on branched sporangiophores. On artificially inoculated leaves incubated at 18°C, 80% humidity, 12h light for 5d, sporangiophores produced 8-19 pigmented, lemon-shaped sporangia with mean ± SD dimensions of 25.2 ± 3.0 (18.9 to 30.4) x 18.2 ± 2.1 (14.6 to 23.2) µm (n=50). Each sporangium produced 2-5 zoospores after less than 45 min in water at room temperature (22°C). Sporangia were collected from sporulating lesions and DNA was extracted as outlined in Crowell et al. (2020). Fragments of the ribosomal internal transcribed spacer (ITS) region (White et al. 1990), the beta-tubulin ras-associated ypt1 gene (Moorman et al. 2002), and the mitochondrial cytochrome B oxidase subunit 2 (cox2) gene (Hudspeth et al. 2000) were amplified by PCR and sequenced bidirectionally. Sequences were deposited in GenBank under accession numbers OK086084, OM867581, and OM867580, respectively. BLAST searches using the amplified ITS and cox2 sequences resulted in 100% identity to Pseudoperonospora cannabina (HM636051.1, HM636003.1) with ypt1 aligning at 97.95% identity (382/390 bp) with P. cannabina (KJ651402.1). The molecular characterization identified the causal agent as P. cannabina. A representative isolate was deposited in the Cornell Plant Pathology Herbarium as CUP-070922. Sporangia were rinsed from detached leaves and used to confirm pathogenicity on whole plants. Ten 4-week-old 'Anka' plants were spray-inoculated until run off with a suspension of 1x104 sporangia mL-1. Ten control plants were sprayed with water. After inoculation, plants were placed in a 19˚C growth chamber with a 12-h photoperiod and misted for 30 min twice daily to maintain humidity above 80%. Sporangia and previously described symptoms were observed 7 days post-inoculation, while control plants were asymptomatic. The pathogen was reisolated onto detached leaves of 'Anka' from inoculated leaves where both sporangia and oospores were observed. The reisolated pathogen was confirmed morphologically and molecularly, through PCR amplification and bidirectional sequencing of the ITS, cox2, and ypt1 genes, as P. cannabina. To our knowledge, this is the first report of P. cannabina causing hemp downy mildew in New York. Depending on the severity and timing of infections, this disease could pose a significant threat to hemp production in the state. Other members of the genus, P. cubensis and P. humuli cause downy mildew on cucurbits and hops, respectively. As these can cause devastating diseases on their hosts, P. cannabina must be monitored with vigilance as an emerging pathogen (Purayannur et al. 2021; Savory et al. 2011). Literature Cited: Crowell, C. R., et al.2020. Plant Dis. 104:2949. DOI 10.1094/PDIS-04-20-0718-RE Fike, J. H., et al. 2020. Page 89 In: Sustainable Agriculture Reviews, vol 42. Springer, Cham, Switzerland. DOI 10.1007/978-3-030-41384-2_3 Hudspeth, D. S. S., et al. 2000. Mycologia 92:674. DOI 10.2307/3761425 Moorman, G. W., et al. 2002. Plant Dis. 86:1227. DOI 10.1094/PDIS.2002.86.11.1227 Purayannur, S., et al. 2021. Mol. Plant Pathol. 22:755. DOI 10.1111/mpp.13063 Savory, E. A., et al. 2011. Mol. Plant Pathol. 12:217. DOI 10.1111/j.1364-3703.2010.00670.x White, T. J., et al. 1990. Page 315 In: PCR Protocols. A Guide to Methods and Applications. Academic Press, San Diego, CA. DOI 10.1016/B978-0-12-372180-8.50042-1.

Correlations among morphological and biochemical traits in high-cannabidiol hemp (Cannabis sativa L.).

Cannabis sativa is cultivated for multiple uses including the production of cannabinoids. In developing improved production systems for high-cannabinoid cultivars, scientists and cultivators must consider the optimization of complex and interacting sets of morphological, phenological, and biochemical traits, which have historically been shaped by natural and anthropogenic selection. Determining factors that modulate cannabinoid variation within and among genotypes is fundamental to developing efficient production systems and understanding the ecological significance of cannabinoids. Thirty-two high-cannabinoid hemp cultivars were characterized for traits including flowering date and shoot-tip cannabinoid concentration. Additionally, a set of plant architecture traits, as well as wet, dry, and stripped inflorescence biomass were measured at harvest. One plant per plot was partitioned post-harvest to quantify intra-plant variation in inflorescence biomass production and cannabinoid concentration. Some cultivars showed intra-plant variation in cannabinoid concentration, while many had a consistent concentration regardless of canopy position. There was both intra- and inter-cultivar variation in architecture that correlated with intra-plant distribution of inflorescence biomass, and concentration of cannabinoids sampled from various positions within a plant. These relationships among morphological and biochemical traits will inform future decisions by cultivators, regulators, and plant breeders.

Cannabinoids function in defense against chewing herbivores in Cannabis sativa L.

In the decades since the first cannabinoids were identified by scientists, research has focused almost exclusively on the function and capacity of cannabinoids as medicines and intoxicants for humans and other vertebrates. Very little is known about the adaptive value of cannabinoid production, though several hypotheses have been proposed including protection from ultraviolet radiation, pathogens, and herbivores. To test the prediction that genotypes with greater concentrations of cannabinoids will have reduced herbivory, a segregating F2 population of Cannabis sativa was leveraged to conduct lab- and field-based bioassays investigating the function of cannabinoids in mediating interactions with chewing herbivores. In the field, foliar cannabinoid concentration was inversely correlated with chewing herbivore damage. On detached leaves, Trichoplusia ni larvae consumed less leaf area and grew less when feeding on leaves with greater concentrations of cannabinoids. Scanning electron and light microscopy were used to characterize variation in glandular trichome morphology. Cannabinoid-free genotypes had trichomes that appeared collapsed. To isolate cannabinoids from confounding factors, artificial insect diet was amended with cannabinoids in a range of physiologically relevant concentrations. Larvae grew less and had lower rates of survival as cannabinoid concentration increased. These results support the hypothesis that cannabinoids function in defense against chewing herbivores.

Genomic Prediction of Biomass Yield in Two Selection Cycles of a Tetraploid Alfalfa Breeding Population.

Alfalfa (Medicago sativa L.) is a widely planted perennial forage legume grown throughout temperate and dry subtropical regions in the world. Long breeding cycles limit genetic improvement of alfalfa, particularly for complex traits such as biomass yield. Genomic selection (GS), based on predicted breeding values obtained using genome-wide molecular markers, could enhance breeding efficiency in terms of gain per unit time and cost. In this study, we genotyped tetraploid alfalfa plants that had previously been evaluated for yield during two cycles of phenotypic selection using genotyping-by-sequencing (GBS). We then developed prediction equations using yield data from three locations. Approximately 10,000 single nucleotide polymorphism (SNP) markers were used for GS modeling. The genomic prediction accuracy of total biomass yield ranged from 0.34 to 0.51 for the Cycle 0 population and from 0.21 to 0.66 for the Cycle 1 population, depending on the location. The GS model developed using Cycle 0 as the training population in predicting total biomass yield in Cycle 1 resulted in accuracies up to 0.40. Both genotype × environment interaction and the number of harvests and years used to generate yield phenotypes had effects on prediction accuracy across generations and locations, Based on our results, the selection efficiency per unit time for GS is higher than phenotypic selection, although accuracies will likely decline across multiple selection cycles. This study provided evidence that GS can accelerate genetic gain in alfalfa for biomass yield.