Fusarium wilt in cotton (
A survey of Fov races in the U.S. was conducted from 2012 to 2013, and races 1, 2, 3, 4, and 8 were detected (Cianchetta et al., 2015). In the survey, of the 24 isolates collected in Texas (collected primarily in the Southern High Plains), 18 isolates were identified as race 1, 5 isolates as race 2, and 1 isolate as race 3. Since that survey, race 4 has been found in Texas in the far west counties of El Paso and Hudspeth (Halpern et al., 2018). Fov races 1 and 2, when combined with Mi, are associated with the destructive interaction on cotton (Cianchetta and Davis, 2015), resulting in plant mortality, stunting, chlorotic leaf symptoms, vascular and root necrosis, and substantial yield loss.
Management of the Fov/Mi complex has been more challenging from the fungal side, and hence most successful options involve reduction of Mi density through nematicides or host resistance to Mi. A high level of resistance to Mi was found by crossing “Coker Clevewilt 6” to “Mexico Wild” (PI563649) resulting in “Auburn 623RNR” (Shepherd, 1974). An important tool in the development of commercial cultivars with Mi resistance occurred when SSR markers were identified that were associated with the two Mi-resistant genes in Auburn 623RNR (Gutierrez et al., 2010). Marker assisted selection using CIR 316-201 on chromosome 11 and BNL 3661-185 on chromosome 14 was verified by recreating the original crosses between “Coker Clevewilt 6” and “Mexico Wild”, and rapidly selecting even more resistant lines (Jenkins et al., 2012). Commercial cultivars with high levels of resistance to Mi and good yielding ability (average of 17% yield increase compared to susceptible cultivars) can reduce nematode densities by >90% compared with susceptible cultivars (Wheeler et al., 2020). Other methods to reduce the density of Mi can include crop rotation to non-hosts such as peanuts or the use of nematicides. The nematicide aldicarb can reduce galling caused by Mi, reduce the incidence of Fusarium wilt, and increase yield in Fov/Mi infested fields (Colyer et al., 1997; Wheeler and Gannaway, 2005). The use of fumigants at high rates in a Fov/Mi cotton field increased yield by 200% to 400%, and decreased wilt related mortality, frequency of infection, vascular discoloration, and root-knot nematode galling (Jorgenson et al., 1978). Fumigation only increased cotton yields for cultivars that were susceptible to the Fov/Mi complex or only partially resistant, while Auburn 623RNR had similar yield both with and without fumigation (Shepherd, 1982).
Crop rotation has not been successful in reducing Fov to a level where it is no longer a threat to cotton (Davis et al., 2006). The fungus can persist for long periods in the soil in the form of chlamydospores, and even if the fungal populations are reduced, they can build up again rapidly once a susceptible crop is planted (Smith, 2007). The fungus can also be recovered from senescing plant tissue due to its saprophytic abilities (Davis et al., 2006).
The earliest selections for Fov resistance were identified from
In the Southern High Plains of Texas, Fov/Mi complex is present in many cotton fields, though it is not as common as the 500,000 ha to 700,000 ha that are infested with Mi (Starr et al., 1993; Wheeler et al., 2000). In 2003, there were some cotton fields with severe Fusarium wilt in this region, where >50% mortality occurred (T. Wheeler, personal observations). There was a consistent theme in these fields, that the newly introduced conventional FiberMax® cultivars had been planted for 2 to 3 consecutive years. After 2014, severe Fusarium wilt occurred with producers planting some new cultivars with excellent resistance to Mi. In both situations, small plot variety trials were performed to determine if certain company’s cultivars were more susceptible to the Fov/Mi complex. In 2003, the question was asked whether the conventional FiberMax cultivars were more susceptible than other Mi-susceptible cultivars, and cultivars with partial resistance to
Small plot replicated tests with commercial cotton cultivars were planted in a producer field at one location in Dawson County (Table 1) in 2004 and 2005, where severe Fusarium wilt had developed in 2003. Small plot replicated tests were also planted in three producer sites (Table 1) in 2019 (Gaines, Hall, and Lynn Counties); two sites in 2020 located in Cochran and Hall Counties; and one site (Hall County) in 2021. Each test had between 24 and 48 entries, with four replications per entry, arranged in a randomized complete block design. Plots were two rows wide (1 m centers) and 10.67 m long. A list of Mi-resistant entries in the tests can be found in Table 2. Plots were irrigated with a center pivot system at all locations, though irrigation capacities and yields differed greatly between sites. All sites were naturally infested with Mi and Fov race(s) 1 and/or 2 in the 2019 to 2021 tests. No race determination was made with the Dawson County test site. Fertilizer, irrigation, and other practices were dictated by the producer’s normal management.
List of test locations, dates of planting, and other field specific information.
Datesz for field activities | ||||||||
---|---|---|---|---|---|---|---|---|
Latitude/ | Soil | Initial | Final | Nematode | ||||
Year | County | Longitude | Series | Planting | Harvest | Stand | Stand | Sampling |
2020 | Cochran | 33.65256 −102.6565 | Amarillo fine sandy loam | 5/19 | 11/10 | 6/11 | 11/10 | 8/10 |
2004 | Dawson | 32.78918 | Patricia loamy | 5/6 | 12/3 | 6/3 | 8/28 | 8/30 |
2005 | Dawson | −102.0631 | fine sand | 5/14 | 11/11 | 6/7 | 7/20 | … |
2019 | Gaines | 32.73526 | Patricia | 5/17 | 11/15 | 6/12 | 11/15 | 10/7 |
−102.8783 | fine sand | |||||||
2019 | Hall | 34.36166 | Miles loamy fine | 5/29 | 11/4 | 6/11 | 11/4 | 9/3 |
2020 | Hall | −100.9165 | sand | 5/15 | 11/16 | 6/4 | 11/16 | 8/17 |
2021 | Hall | 5/10 | 11/9 | 5/24 | 11/9 | 8/18 | ||
2019 | Lynn | 32.91140 | Amarillo fine | 5/15 | 11/14 | 6/6 | 11/14 | 8/20 |
−102.0075 | sandy loam |
zDates are formatted with month/day.
List of cotton cultivars used in the trials with tolerance or resistance to Mi.
Plant Variety | |||
---|---|---|---|
Company | Cultivar | Certificatez | Company description of Resistance |
BASF | FM 1621GL | 201900404 | 4 on 1-5 scale, 5 = resistant, Mi tolerant |
BASF | FM 1730GLTP | Mi/Fusarium wilt tolerance: very good (Anonymous, 2021) | |
BASF | FM 1911GLT | 201600407 | 4 on 1-5 scale, 5 = resistant, Mi tolerant |
Stoneville | LA 887 | 009100065 | Mi Resistant |
BCS | ST 5599BR | 200300279 | Mi Moderately resistant |
BASF | ST 4946GLB2 | 201300350 | 4 on 1-5 scale, 5 = resistant, Mi tolerant |
BASF | ST 5600B2XF | Mi resistance (Anonymous, 2021) | |
BCS | DP 1747NR B2XF | 201700046 | 4 on a 1-4 scale, 4 = Mi resistant |
BCS | DP 1823NR B2XF | Mi resistant; Albers and Gholston (2018) | |
BCS | DP 2141NR B3XF | Mi resistant; Albers et al. (2021) | |
BCS | DP 2143NR B3XF | Mi resistant; Albers et al. (2021) | |
Corteva | PHY 320 W3FE | 2-gene resistance to Mi (Anonymous, 2021) | |
Corteva | PHY 332 W3FE | 202000220 | Resistance to Mi |
Corteva | PHY 350 W3FE | Highly Mi resistant (Anonymous, 2021) | |
Corteva | PHY 394 W3FE | Resistance to Mi (Anonymous, 2021) | |
Corteva | PHY 400 W3FE | Resistance to Mi (Anonymous, 2021) | |
Corteva | PHY 411 W3FE | Resistance to Mi (Anonymous, 2021) | |
Corteva | PHY 443 W3FE | 202000221 | Resistance to Mi |
Corteva | PHY 480 W3FE | Resistance to Mi (Anonymous, 2021) | |
Corteva | PHY 500 W3FE | Resistance to Mi (Anonymous, 2021) | |
Corteva | PHY 545 W3FE | Resistance to Mi (Anonymous, 2021) | |
Corteva | PHY 580 W3FE | Resistance to Mi (Anonymous, 2021) |
zDescription of Mi resistance is based on the plant variety protection certificate.
Mi,
Data collected (Table 1 for dates) included plant stand on either one or both rows once plants had emerged, but before Fusarium wilt symptoms began, and plant stand at harvest, or in the case of the 2004 to 2005 trials, once stands were stable (plants had stopped dying) in July or August. Plots were soil sampled in August or later (Table 1) to assay for root-knot nematode. Samples consisted of six cores per plot collected with a narrow-bladed (40 cm depth, 15 cm width at top, and 8 cm width at the bottom) shovel to a depth of 20 cm, close to the taproot. The top 6 cm of soil was discarded and then soil from 6 cm to 20 cm depth, including some roots, was removed. The soil was mixed in a bucket and then a subsample of 1,000 cm3 soil was removed and placed in a plastic bag. The soil samples were refrigerated for <2 weeks before being assayed for root-knot nematode second-stage juveniles (J2) and eggs. The test in 2005 was not sampled for nematodes.
A pie-pan assay with 200 cm3 soil + root fragments was used to extract J2 over 48 hr (Thistlethwayte, 1970). The circular pie-pans were made of glass and wire mesh (0.64 cm diameter) was placed in the pie-pan. Two pieces of facial tissue (2-ply) were laid on top of the mesh and then the soil sample was placed on the facial tissue. Tap water (250 ml) was gently added to the pie-pan without disturbing the soil, and then the wet facial tissues were arranged around the soil to hold it out of the water. A cover was placed over the pie-pan to eliminate evaporation. The extracted J2 were enumerated by concentrating the extracted liquid to 100 ml and then counting a 5 ml aliquot. A second assay with 500 cm3 soil was used to extract root-knot nematode eggs. The soil + root fragments were placed in a bucket with water (combined volume 3 l of water + soil) and stirred for 10 s. After allowing to settle for 15 s, the contents were poured over a sieve with a pore size of 230 μm and the root fragments caught on the sieve were washed into a beaker in 100 ml tap water and mixed on a stir plate for 5 min in NaOCl (0.525%) (Hussey and Barker, 1973). The mixture was poured through a sieve with a pore size of 230 μm, stacked over a sieve with a pore size of 25 μm. The contents from the bottom sieve were rinsed with tap water, washed into a beaker, dyed with acid fuchsin (Byrd et al., 1983), and the eggs were enumerated from a 5 ml aliquot taken out of the 150 ml total volume.
Plants outside of the test area which exhibited signs of Fusarium wilt were collected and
The plots were mechanically harvested with a cotton stripper designed to weigh the plot yield on load cells. Stripper plot yields consist of lint, seed, and plant debris. A 1,000 g sample was collected from harvested plots and two replications were ginned from each entry to determine lint percentage of the harvest weights.
Plant mortality was calculated as: ((Initial stand – final stand)/Initial stand) × 100.
The tests in 2004 and 2005 contained two variables, cultivar and aldicarb, in a factorial arrangement. All plots that received aldicarb were eliminated from the analysis. The individual cultivar means from 2004 were presented previously (Wheeler and Gannaway, 2005). The Mi density in Hall Co. in 2019 in replication 4 averaged 9 Mi/500 cm3 soil, and thus that replication was deleted from the data set. All other site-years and replications had sufficient Mi density (average >800/500 cm3 soil) to be utilized.
The various groups were analyzed for percentage mortality, LMi, and lint yield within each test site using mixed model analyses (PROC GLIMMIX, SAS version 9.4; SAS Institute, Cary, NC), where group was the fixed variable and replication, or year and replication were the random variables. Significant differences between categories were determined by
In the trials conducted during 2004 and 2005, the conventional FM group (FM 819, FM 832, FM 958, and FM 966) had higher mortality (69.2%) than the transgenic FM group (58.7%), or Mi-susceptible group (55.7%) (Table 3). The Mi-resistant cultivars (ST LA887 and ST 5599BR) were intermediate (60.3% mortality) and not different from any of the groups. Transformed
Lint | ||||
---|---|---|---|---|
Cultivar | % | Mi/500 | Yield | |
Groupz | Mortality | cm3 soil | LMiy | (kg/ha) |
FM-conventional | 69.2 ax | 1,905 | 2.90 a | 941 c |
FM-transgenic | 58.7 b | 1,507 | 3.16 a | 1,309 ab |
Normal | 55.7 b | 1,742 | 3.02 a | 1,252 b |
Mi resistant | 60.3 ab | 607 | 1.93 b | 1,448 a |
Prob>F | 0.001 | 0.438 | 0.011 | 0.001 |
zFM-conventional group contained FM 819, FM 832, FM 958, and FM 966; FM-transgenic group contained FM 960B2R, FM 960BR, FM 960RR, FM 966LL, FM 981LL, FM 989BR, and FM 989RR; the non-FiberMax, susceptible group contained
yLMi was LOG10(
xValues represent the LS means from tests conducted in 2004 and 2005 using a mixed model analysis. LS means with the same letter are not significantly different (
LS, least square; Mi,
(1)
With the data sets from 2019 to 2021, percentage mortality was significantly affected by group only at the Hall Co. site (Table 4). At that site, percentage mortality was higher for R-DP (22.9%) than for all other groups (8.5%–14.9%) except ST 5600B2XF (20.3%). While the other sites did not have significant group differences, the R-DP group numerically had the highest mortality at Cochran and Lynn Counties, though the susceptible group had the highest mortality at the Gaines County site. When percentage mortality was analyzed across all six data sets, R-DP group had higher mortality (28.1%) than all other groups except for ST 5600B2XF (24.8%) (Table 5). The Mi-susceptible group had 23.3% mortality, and ST 4946GLB2 numerically had the lowest mortality at 16.5%.
Effect of cultivars with resistance to Mi and Mi-susceptible cultivars on plant mortality (%) caused by
Cultivar | County location of tests | |||
---|---|---|---|---|
Groupz | Cochran | Gaines | Hall | Lynn |
Susceptible | 13.5 | 43.3 | 14.9 bcy | 20.4 |
R-FM | 13.2 | … | 14.4 bc | 7.0 |
ST 4946GLB2 | 4.7 | 37.5 | 8.5 c | 13.6 |
ST 5600B2XF | 14.3 | 35.4 | 20.3 ab | 24.0 |
R-DP | 16.7 | 42.8 | 22.9 a | 26.0 |
R-PHY | 11.9 | … | 13.3 bc | 24.1 |
Prob>F | 0.732 | 0.701 | 0.013 | 0.317 |
zAn entire list of cultivars can be found in Appendix 1. R-FM were Mi-resistant FM 1621GL, FM 1730GLTP, and FM 1911GLT; R-DP were Mi-resistant DP 1747NR B2XF, DP 1823NR B2XF, DP 2141NR B3XF, and DP 2143NR B3XF; R-PHY were Mi-resistant PHY 320 W3FE, PHY 350 W3FE, PHY 400 W3FE, PHY 480 W3FE, PHY 500 W3FE, PHY 545 W3FE, and PHY 580 W3FE.
yValues represent the LS means from tests conducted from 2019 to 2021 using a mixed model analysis. LS means with the same letter are not significantly different (
LS, least square; Mi,
Effect of Mi resistance/ tolerance by different companies and Mi-susceptible cultivars on Mi density, mortality (%) by
% | Relative | |||
---|---|---|---|---|
Categoryz | LMiy | Mortality | Yieldx | N |
Susceptible | 3.22 aw | 23.3 b | 0.491 d | 378 |
R-FM | 3.01 a | 21.0 b | 0.600 bc | 37 |
ST 4946GLB2 | 2.78 ab | 16.5 b | 0.706 a | 23 |
ST 5600B2XF | 2.33 bc | 24.8 ab | 0.578 bc | 20 |
R-DP | 2.21 c | 28.1 a | 0.530 cd | 46 |
R-PHY | 1.85 c | 21.4 b | 0.635 ab | 89 |
Prob>F | 0.0001 | 0.011 | 0.0001 |
zAn entire list of cultivars can be found in Appendix 1. R-FM were Mi-resistant FM 1621GL, FM 1730GLTP, and FM 1911GLT; R-DP were Mi-resistant DP 1747NR B2XF, DP 1823NR B2XF, DP 2141NR B3XF, and DP 2143NR B3XF; R-PHY were Mi-resistant PHY 320 W3FE, PHY 350 W3FE, PHY 400 W3FE, PHY 480 W3FE, PHY 500 W3FE, PHY 545 W3FE, and PHY 580 W3FE.
yLMi = LOG10(Mi/500 cm3 soil + 1).
xRelative yield = (plot yield – minimum plot yield in the test)/(maximum plot yield in the test – minimum plot yield in the test).
wValues represent the LS means from tests conducted in 2019 to 2021 using a mixed model analysis. LS means with the same letter are not significantly different (
LS, least square; Mi,
LMi was significantly affected by cultivar group for all locations (Table 6). The R-PHY group had significantly lower LMi than all other groups in Lynn County, and numerically the lowest density in Hall County. This group was not planted at the Gaines County site, due to a request from the producer to limit non-dicamba tolerant cultivars to one entry (ST 4946GLB2). R-DP had the lowest LMi at Cochran County and significantly lower LMi than the S group at Gaines and Hall Counties. When analyzed across all six trials, LMi was higher for the susceptible group (LMi = 3.22) and R-FM (3.01) than for R-PHY (1.85), R-DP (2.21), and ST 5600B2XF (2.33) (Table 5). ST 4946GLB2 had higher LMi (2.78) than R-DP and R-PHY.
Effect of cultivars with resistance to Mi and Mi-susceptible cultivars on Mi density.
County location of tests | ||||||||
---|---|---|---|---|---|---|---|---|
Cultivar | Cochran | Gaines | Hall | Lynn | ||||
Groupz | Mi | LMix | Mi | LMi | Mi | LMi | Mi | LMi |
Susceptible | 9,070 | 3.61 ay | 3,789 | 3.11 a | 4,444 | 2.93 a | 5,406 | 3.35 a |
R-FM | 3,952 | 3.35 ab | … | … | 2,785 | 2.68 ab | 4,510 | 3.56 a |
ST 4946GLB2 | 2,640 | 3.02 ab | 1,145 | 2.96 ab | 1,127 | 2.42 ab | 1,390 | 2.95 ab |
ST 5600B2XF | 1,050 | 2.90 b | 370 | 1.96 b | 740 | 2.13 abc | 1,110 | 2.33 b |
R-DP | 763 | 1.85 c | 693 | 2.13 b | 1,421 | 1.95 bc | 785 | 2.76 ab |
R-PHY | 2,999 | 3.26 ab | … | … | 466 | 1.51 c | 165 | 1.26 c |
Prob>F | 0.001 | 0.001 | 0.096 | 0.003 | 0.001 | 0.001 | 0.321 | 0.001 |
zThe entire list of cultivars can be found in Appendix 1. R-FM were Mi-resistant FM 1621GL, FM 1730GLTP, and FM 1911GLT; R-DP were Mi-resistant DP 1747NR B2XF, DP 1823NR B2XF, DP 2141NR B3XF, and DP 2143NR B3XF; R-PHY were Mi-resistant PHY 320 W3FE, PHY 350 W3FE, PHY 400 W3FE, PHY 480 W3FE, PHY 500 W3FE, PHY 545 W3FE, and PHY 580 W3FE.
yValues represent the LS means from tests conducted from 2019 to 2021 using a mixed model analysis. LS means with the same letter are not significantly different (
xLMi was LOG10(
LS, least square; Mi,
Lint yield was significantly affected by group at all locations (Table 7). At the Cochran County site, R-FM, R-PHY, and ST 4946GLB2 had higher yields than the susceptible cultivars or R-DP. At the Gaines County site, ST 4946GLB2 had higher yields than ST 5600B2XF and susceptible cultivars. At the Hall County site, the susceptible cultivars had lower yields than all other groups except for R-DP. At the Lynn County site, susceptible cultivars yielded less than R-FM, ST 4946GLB2, and R-PHY. Relative yield was highest for ST 4946GLB2 (0.7058), and significantly higher than all groups except R-PHY (0.6351,
Effect of cultivars with resistance to Mi and Mi-susceptible cultivars on lint yield in fields with
Cultivar | County locations of tests | |||
---|---|---|---|---|
Groupz | Cochran | Gaines | Hall | Lynn |
Susceptible | 840 bcy | 216 b | 1,696 b | 732 b |
R-FM | 954 a | … | 1,846 a | 864 a |
ST 4946GLB2 | 1,038 a | 376 a | 2,026 a | 877 a |
ST 5600B2XF | 952 ab | 208 b | 2,006 a | 761 ab |
R-DP | 770 c | 268 ab | 1,824 ab | 837 ab |
R-PHY | 1,004 a | … | 1,970 a | 847 a |
Prob>F | 0.001 | 0.007 | 0.001 | 0.008 |
zAn entire list of cultivars can be found in Appendix 1. R-FM were Mi-resistant FM 1621GL, FM 1730GLTP, and FM 1911GLT; R-DP were Mi-resistant DP 1747NR B2XF, DP 1823NR B2XF, DP 2141NR B3XF, and DP 2143NR B3XF; R-PHY were Mi-resistant PHY 320 W3FE, PHY 350 W3FE, PHY 400 W3FE, PHY 480 W3FE, PHY 500 W3FE, PHY 545 W3FE, and PHY 580 W3FE.
yValues represent the LS means from tests conducted from 2019 to 2021 using a mixed model analysis. LS means with the same letter are not significantly different (
LS, least square; Mi,
In Cochran County, lint yield was negatively correlated with mortality (
In Cochran County, lint yield (kg/ha) was fitted to a quadratic term for percentage mortality and a linear term with LMi (Fig. 2; Eq. 2), mortality2 had a partial
2)
In Gaines County, Lint yield (kg/ha) was fitted to percentage mortality (Fig. 2; Eq. 3):
3)
Fusarium wilt was most severe in this Gaines County test, and even though the irrigation was terminated prematurely (presumably due to severe disease and subsequent low yield potential), the percentage mortality explained three to six times more of the variation in yield than for the other tests.
In Hall County, Lint yield (kg/ha) was fitted to a quadratic model with percentage mortality (Fig. 2; Eq. 4):
4)
In Lynn County, Lint yield (kg/ha) was described only by LMi (Fig. 2; Eq. 5)
5)
Two races of Fov were identified across all locations from 2019 to 2021. In 2019, the Gaines County site isolate was molecularly characterized as Fov race 2, while Lynn and Hall County sites were Fov race 1. In 2020, races 1 and 2 both occurred in the same field at the Cochran County site. For all 3 yr, only race 1 was found at Hall County.
Tolerance and/or resistance to Fusarium wilt (referring only to those races that require
The catastrophic Fusarium wilt problems observed by several producers after the introduction of some
The R-DP cultivars possessed more susceptibility to Fusarium wilt than did ST 4946GLB2, R-PHY, R-FM and Mi-susceptible cultivars, even though R-DP cultivars had excellent Mi resistance. ST 4946GLB2, which was thought to be the most Fusarium wilt tolerant cultivar at the start of the 2019 to 2021 trials, did indeed have the lowest percentage mortality and highest overall lint yields in Fusarium wilt/Mi trials, but was not statistically superior to other groups except for R-DP for Fusarium wilt mortality. With regard to Mi resistance, significant separations could be seen between groups, particularly for the R-DP and R-PHY groups compared with more Mi-susceptible groups.
The original source of resistance for Mi in many cotton breeding programs was Auburn 623RNR, which was released by Shepherd (1974). This line was the most Mi and Fov resistant line available at that time in
Mi-resistant gene(s) do not by themselves confer resistance to Fov, or there are Mi-susceptible cultivars that may have resistance to Fov (Hyer et al., 1979; Wang et al., 2009; Ulloa et al., 2011). The resistance to Fov observed in Auburn 623RNR was not simply a product of having both the chromosome 11 and chromosome 14 Mi-resistant genes, since this cultivar exhibited high resistance to both Mi and Fov (Shepherd, 1974). Marker-assisted selections have been useful for development of Mi-resistant cotton varieties. However, there is no indication within the development of U.S. cotton varieties (based on PVPs) that molecular markers are being utilized to identify Fov resistance. There have been several studies to determine the genes involved with Fov race 1 resistance in