First Report of Meloidogyne javanica on Globe Artichoke in Florida, U.S.A.

Abstract

Globe artichoke (Cynara cardunculus var. scolymus L.) is native to the Mediterranean region and cultivated worldwide for its edible flower buds and the medicinal value of its leaves (Pignone and Sonnante 2004). In 2019, artichokes were planted on 29 km2 predominantly in California, with a yield of over 100 million kg (USDA 2020). It has been grown as a specialty crop in Florida since 2017 (Agehara 2017a). Meloidogyne spp. (root-knot nematodes/RKNs) can lead to yield losses to artichoke (Greco et al. 2005). In June 2020, artichokes (cv. Imperial Star) with stunting, wilting, and galled-root symptoms were observed in a research field with sandy soil located at the University of Florida Gulf Coast Research and Education Center (UF/GCREC), Wimauma, Florida. The goal of this report was to identify the RKN species collected from two symptomatic artichoke roots. Morphological measurements (mean, standard deviation and range) of 15 second-stage juveniles (J2s) included body length = 409.1 ± 31.6 (360.3 - 471.3) µm, body width = 15.4 ± 1.6 (12.4 - 18.8) µm, and stylet length = 14.7 ± 0.7 (13.9 -16.1) µm. Perineal patterns of five matured females had a high dorsal arch and double lateral lines. Morphological characteristics of the RKN cultures were consistent with the description of M. javanica (Eisenback and Triantaphyllou 1991). DNA was extracted respectively from two RKN females isolated from the diseased artichoke roots. The nematode species was confirmed with primers Fjav/Rjav and resulted in ≈ 670 bp fragment (Zijlstra et al. 2000). The COXII region of mtDNA was amplified by C2F3/1108 (Powers and Harris 1993), and the sequencing results were submitted to the NCBI with GeneBank Accession No. MZ397905. The molecular sequences had 100% identity with M. javanica in COXII (MK033440 and MK033439). The pathogenicity test was conducted in the greenhouse at UF/GCREC from May to August 2021 (temperature = 26.7 ± 4.1°C, relative humidity = 83.9 ± 14.6 %). Each of the ten 6.5-in-diameter plastic pots containing 3.8-L pasteurized soil was seeded with one artichoke seed. Five pots were inoculated with 5000 eggs of the field RKN cultures 4-week after planting, and five pots served as the untreated control. Two months after inoculation, galled symptoms were only observed in inoculated plants with an average gall index (Bridge and Page 1980) of 6.2 ± 2.2; 99,240 ± 72,250 eggs were extracted from each root system, and the nematode reproduction factor was 19.9 ± 14.4. Meloidogyne spp. has been reported on artichoke in Europe, Asia, and South America (Greco et al. 2005). This is the first report of RKN on artichoke in the United States. Meloidogyne javanica caused severe root gall symptoms and visible aboveground damage in the form of chlorosis, stunting, and wilting of artichoke planted at the UF/GCREC research farm. Meloidogyne javanica is the predominant RKN species at the UF/GCREC research farm and one of the most common RKNs in Florida (Gu and Desaeger 2021). Artichoke is a new crop in Florida, and RKNs is likely to be one of the main soilborne problems for its production in the state. Its long growing season (October - May) (Agehara 2017b) allows for high nematode reproduction rates. Several new growers have already reported RKN as a problem in their fields. For artichoke to become a commodity in Florida, managing RKNs will be critical. This report provides new information on the risk that RKNs pose to artichoke, a newly established specialty crop in Florida.