Identification of resistant or tolerant commercial cotton cultivars to the Fusarium wilt root-knot nematode disease complex and the identification of Fusarium oxysporum f. sp. vasinfectum races in Alabama

Abstract

Fusarium oxysporum Schltd.:Fr. f. sp. vasinfectum (Atk.) W.C. Snyd. and H. N. Hans (FOV) is the causal agent of Fusarium wilt in cotton. This causal agent is a soil-dwelling fungus that can remain dormant for many years in soil and has proven difficult to manage. There is an association between this disease-causing fungi and the Southern root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood (RKN). The nature of this association is not understood, but the fungal spores gain entry to the plant via wounds in the root systems caused by nematodes’ stylets. Symptoms of Fusarium wilt in cotton include plant wilting throughout the season, interveinal chlorosis and necrosis, leaf abscission, yield reduction, and death. Commercial cotton cultivar trials were conducted in 2013 and 2014 to screen commercially available cotton lines for resistance or tolerance to the Fusarium wilt root-knot nematode disease complex. One trial in 2013 and two trials in 2014 were set up as single row, completely randomized block designs and analyzed for Fusarium wilt disease incidence, M. incognita population density, and yield. In 2013, FiberMax 1944 GLB2 had the highest yield, lowest Fusarium wilt incidence, and the lowest nematode density of all cultivars tested. Phytogen 339 WRF and Phytogen 499 WRF yielded significantly higher than the resistant check and had low wilt incidence; Phytogen 499 WRF had low nematode egg density and Phytogen 339 WRF had high nematode egg density. Stoneville 4747 GLB2, first included in this study in 2014, was the highest yielding cultivar with low wilt incidence and low nematode egg density. Stoneville 4946 GLB2, Phytogen 499 WRF, and Phytogen 427 WRF were also significantly higher yielding than the resistant check. Deltapine 1454NR B2RF, a new cultivar marketed as M. incognita-resistant, had the lowest nematode population density, but higher Fusarium wilt incidence. Cultivars with exceptional performance in 2013 also performed well in 2014. Isolates of the fungus were taken from symptomatic plants throughout the seasons and were extracted for DNA. Sequences were amplified by PCR for race identification. A total of 123 samples were identified to race. Races detected in 2013 were 1, 8, LA 108, LA 110, and LA 127/140. In 2014, the same races were detected with the exception of LA 110, which was not found. Races 3, 4, and LA 112 were not detected in either year. Race 1 was the predominate race isolated in both years.