Abstract
The interaction between Fusarium oxysporum f. sp. vasinfectum (Fov) and Meloidogyne incognita (root-knot nematode) resulting in Fusarium wilt (FW) of cotton is well-known. Although Belonolaimus longicaudatus (sting nematode) can also interact with Fov and cause FW, it has long been believed that virtually all of the FW in Georgia is caused by the interaction of Fov with M. incognita. In recent years, FW has been reported more frequently in Georgia, which suggests that something affecting the disease complex may have changed. In 2015 and 2016, a survey of 27 Georgia cotton fields in 10 counties was conducted. At least 10 soil and stem samples per field were collected from individual plants showing symptoms of FW to quantify plant-parasitic nematode levels and identify Fov races. Fov race 1 was identified in all samples in 2015, but one sample also had the LA110 genotype and another sample also had the LA108 genotype. In 2016, all Fov races and genotypes found in 2015 were present, however, MDS–12 and LA127/140 also were found. Meloidogyne incognita was present in 18% of fields in 2015 and 40% in 2016, whereas B. longicaudatus was present in all fields in 2015 and 75% of fields in 2016. Regardless of whether they occurred separately or together, M. incognita and B. longicaudatus were present, respectively, in 18% and 55% of individual samples in 2015 and 40% and 51% in 2016. However, M. incognita without B. longicaudatus was found in 7% of samples in 2015 and 34% in 2016, whereas B. longicaudatus without M. incognita was found in 45% of samples in 2015 and 44% in 2016. We conclude that Fov race 1 continues to be the dominant race in Georgia and many instances of FW in Georgia may be due to Fov interacting with B. longicaudatus and not M. incognita as previously believed.
Highlights
Isolate is a label originally used by Holmes et al (2009) and such isolates have been shown to be in different vegetative compatibility group (VCG) within race 1 (Bell et al, 2017)
Fov races 2 and 8 were found in Lowndes County; race 8 and genotypes LA127/140, LA110, and LA108 were found in Tift County; genotypes LA108 and LA110 were found in Cook County; genotypes LA108, LA110 and MDS–12 were found in Colquitt County; race 2 and genotype LA110 were found in Coffee County; genotype LA108 was found in Ware County; and genotype LA110 was found in Worth and Tattnall Counties (Table 2 and Figure 1)
For the fields included in our survey in 2015, the pre dominant cotton cultivar planted was DP 1252 B2RF, which is susceptible to M. incognita
Summary
Isolate is a label originally used by Holmes et al (2009) and such isolates have been shown to be in different VCGs within race 1 (Bell et al, 2017). Fov race 4 and Australian biotypes are unique because they can cause severe FW without interacting with nematodes (Kim et al, 2005), but those genotypes of Fov have not been found in the USA outside of California and Texas where Fov race 4 has been reported (Halpern et al, 2018). The movement of soil, water, equipment, plant material or seed could spread Fov race 4 or the Australian genotypes to other cotton-producing areas of the country. We conducted a survey of individual plants in cotton fields in southern Georgia showing symptoms of FW to determine which races of Fov were causing FW and which plant-parasitic nematode species were associated with the diseased plants
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