First Report of Meloidogyne javanica Infecting Strawberry (Fragaria × ananassa) in the United States

Abstract

Strawberry (Fragaria × ananassa) is native to temperate regions. However, it has been produced in tropical areas, as a seasonal crop including in Florida, USA during the winter months. In March 2022, root galls resembling those induced by root-knot nematodes (Meloidogyne spp.) were observed in declining strawberry plants ‘WinterstarTM FL 05-107’ growing in an organic-certified research site in Hillsborough County, Florida, USA. To our knowledge, M. hapla is the only root-knot species reported to infect strawberry in Florida. Preliminary molecular analyses, including newly synthesized DNA sequences (TW81/AB28 = OQ469833 - OQ469836; D2A/D3B= OQ473043 - OQ473047) using extracted nematode females from the strawberry roots, initially identified the RKN as M. javanica. Nematode species confirmation was further performed using the morphology of the female perineal patterns and isozyme analysis, mainly esterase (EST) and malate dehydrogenase (MDH), DNA sequencing, (NAD5-F/NAD5-R) and the SCAR primer set (Fjav/Rjav), species-specific for M. javanica. Isozyme analyses, EST= J3, which is specific for M. javanica and MDH=N1, as well as the morphology of female perineal patterns, agreed with data previously reported for M. javanica. A pathogenicity test on strawberry ‘WinterstarTM FL 05-107’ transplants was performed using 10,000 eggs of the original M. javanica population, which induced galls on strawberry plants (Gall index, GI = 4.1) with egg masses clearly visible outside of the roots, producing an average of 1,344 eggs/gram of fresh root and 9,201 ± 4,206 eggs/root system. No galls or egg masses were observed on non-inoculated plants. Tomato ‘HM 1823’ was used as a control for the viability of the inoculum and showed numerous galls and egg masses (GI=5.0;). The newly obtained DNA sequences using NAD5-F/NAD5-R (OQ474970 – OQ474972) were compared with other sequences available in the GenBank and were shown to be 100% identical to five M. javanica populations from Polk County, Florida, USA (OM418745 – OM418749) and the complete mitochondrion genome of M. javanica (NC026556). To our knowledge, this is the first report of M. javanica infecting strawberry in the United States.