A Novel Approach to Tally Aculops cannabicola (Acari: Eriophyidae) for Field and Laboratory Studies.

The hemp russet mite, Aculops cannabicola (Farkas) is a key pest of hemp (Cannabis sativa L.). Given its microscopic size, estimating the size of its populations can be a major limitation to control this pest. Here, we describe a method to count A. cannabicola using photographs taken with a handheld digital microscope. We compared the consistency and strength of the relationship between photographic- and microscope-based counts of mites from infested plants. Among the three sections of the leaflet, the maximum consistency levels were observed in the proximal (50%) and middle photographs (50%). However, it reached from 64% to 100% when the three sections were considered. Photographic and a microscope-based counts were positively correlated (>0.7). A single photograph can be a good predictor of the total mites per leaflet, however, using two pictures (proximal and middle sections) will increase the consistency of the abundance of A. cannabicola per leaflet. A minimum of 22 leaflets per sampling event can support a strong correlation between the microscope and photographic counts. Our method requires low budget and training and takes short time (0.4 to 1.3 min per leaflet) to count mites per sample. Additionally, photographs can be stored on a smartphone, computer, or tablet, allowing users to share, store and process the photos. This method simplifies counts of A. cannabicola on hemp for research purposes and provides a practical tool for growers to assess mite populations for management decisions. In addition, it may be useful for monitoring eriophyid mites on cultivated plants.

Screening Triploid Hybrids of 'Lakeland' Limequat for Resistance to Citrus Canker.

Resistance of citrus genotypes to Xanthomonas axonopodis pv. citri, the cause of Asiatic citrus canker (ACC), was evaluated by injection infiltration of 103 and 104 CFU/ml through stomates on the abaxial surface of immature leaves. Citrus genotypes for screening comprised two autotetraploids and nine triploid hybrids of 'Lakeland' limequat (Citrus aurantifolia × Fortunella japonica) and their progenitors ('Lakeland' limequat, the autotetraploids 'Femminello' lemon (Citrus limon) and 'Giant Key' lime (C. aurantifolia), and the somatic hybrids 'Key' [also known as 'Mexican'] lime + 'Valencia' orange and 'Hamlin' orange + 'Femminello' lemon). 'Meiwa' kumquat (Fortunella crassifolia) and 'Pineapple' sweet orange (C. sinensis) were used as known resistant and susceptible standards, respectively. Lesion number per inoculation site and bacterial population per lesion were recorded 15 to 19 days after inoculation. The assay was performed four times during a spring-summer-fall period under greenhouse conditions. Canker lesions were consistently produced by stomatal inoculation with 104 but not 103 CFU/ml. Susceptible and resistant genotypes were separated based on lesion number per inoculation site and bacterial population per lesion. Spearman's rank correlation analysis for lesion numbers on 15 genotypes common to all four assays showed significant correlations among the genotype rankings. Genotype rankings were also significantly correlated between the two bacterial population assays. Lesion number per inoculation site is sufficient for assessment of resistance of citrus genotypes to ACC without the necessity of conducting bacterial population assays. 'Lakeland' limequat is a promising seed parent for breeding acid citrus fruit that is resistant to ACC.