Quantifying Potential Tolerance of Selected Cotton Cultivars to Belonolaimus longicaudatus.

Glyphosate-tolerant cotton cultivars were evaluated for tolerance to Belonolaimus longicaudatus in field experiments conducted from 2004 to 2005. Field trials were arranged in a split-plot design that included treatment with four levels of 1, 3-dichloropropene (0.0, 13.9, 27.8, and 41.7 1 a.i./ha) to establish a range of population densities of B. longicaudatus. Six cotton cultivars (early-to-mid maturity: DP444BG/RR SG501BR, ST5242BR; mid-to late maturity: DP451B/RR, ST5599BR, DP655BRR) were planted as whole plots. Fumigation was effective in suppressing B. longicaudatus population densities at mid-season, but not at cotton harvest, and increased cotton lint yield. The cultivar x fumigation interaction for cotton lint yield was not significant for the six cultivars evaluated, indicating that tolerance did not occur in this nematode-host combination. Early-to-mid maturity cultivars yielded significantly more than mid-to-late maturity cultivars in both years. Small but significant differences in nematode final population density were observed between cultivars that may be related to relative maturity.

Cotton Tolerance to Hoplolaimus columbus and Impact on Population Densities.

Glyphosate-tolerant transgenic-cotton cultivars were evaluated for tolerance to Hoplolaimus columbus in field experiments conducted from 2001 to 2003. The studies were arranged in a split-plot design that included treatment with 1,3-dichloropropene at 42 liter/ha to establish fumigated versus nonfumigated subplots with cultivars as whole plots. Cotton cultivars were divided by relative maturity into two separate but adjacent experiments in order to facilitate cotton defoliation, with 10 early-maturity and 5 late-maturity cultivars. Fumigation was effective in suppressing H. columbus population densities and increased cotton lint yield. The cultivar-fumigation interaction was significant for early-season cotton cultivars but not for late-season cultivars. A tolerance index ([yield of nontreated/yield of treated] × 100) was used to compare cultivar differences. Both groups of cultivars expressed significant levels of tolerance to H. columbus, but late-season cultivars tended to yield more than early-season cultivars in infested fields.

Effects of Rate and Time of Application of Poultry Litter on Hoplolaimus columbus on Cotton.

Field experiments were conducted to evaluate the effect of soil-incorporated poultry litter on the population dynamics of Hoplolaimus columbus and cotton lint yield. Rates of poultry litter applied varied from 0.0 to 27.0 t/ha and were applied in December, February, or March. Time of application did not influence population densities of this nematode or cotton yield. The rate of poultry litter applied was negatively related to the population density of H. columbus at midseason, but not at other sampling dates. The lower midseason levels of this nematode corresponded with increases in cotton lint yield in all experiments. Cotton yield increases generally were linear with respect to the rate of litter applied, although the highest rates of litter applied did not always result in the greatest cotton yield. Poultry litter can be used effectively to supply nutrients to the crop and suppress damaging levels of H. columbus. Optimal rates of litter application were from 6.0 to 13.4 t/ha. Application of poultry litter at these rates, however, may exceed nutrient levels required for best management practices.

Resistance as a Tactic for Management of Meloidogyne incognita on Cotton in North Carolina.

Selected cotton cultivars were evaluated for resistance to the southern root-knot nematode, Meloidogyne incognita, in greenhouse and field experiments. Cotton cultivars LA 887, Auburn 634, and NemX cotton were highly resistant to three North Carolina populations of root-knot nematode in greenhouse experiments compared to susceptible cultivars. The relative susceptibility of cultivars tested in the greenhouse from most to least susceptible were Deltapine 16 > Deltapine 50 > LA 887 or NemX > Auburn 634. The yields of resistant and susceptible cotton cultivars were increased by fumigation in fields infested with root-knot nematode. Reproduction of M. incognita in field plots on NemX, Paymaster H 1560, and Stoneville LA 887 was less than on susceptible cultivars. Diminished reproduction of the nematode on resistant cultivars may reduce the need for nematode control tactics in subsequent years.

Testing shelled corn for aflatoxin, Part I: estimation of variance components.

The variability associated with testing lots of shelled corn for aflatoxin was investigated. Eighteen lots of shelled corn were tested for aflatoxin contamination. The total variance associated with testing shelled corn was estimated and partitioned into sampling, sample preparation, and analytical variances. All variances increased as aflatoxin concentration increased. With the use of regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific aflatoxin concentration. Test results on a lot with 20 parts per billion aflatoxin using a 1.13 kg sample, a Romer mill, 50 g subsamples, and liquid chromatographic analysis showed that the total, sampling, sample preparation, and analytical variances were 274.9 (CV = 82.9%), 214.0 (CV = 73.1 %), 56.3 (CV = 37.5%), and 4.6 (CV = 10.7%), respectively. The percentage of the total variance for sampling, sample preparation, and analytical was 77.8, 20.5, and 1.7, respectively.

Tolerance of Selected Cotton Lines to Rotylenchulus reniformis.

The reproductive and damage potential of the reniform nematode, Rotylenchulus reniformis, on five cotton breeding lines reported as tolerant to this nematode in Texas were compared with two standard cotton cultivars, Deltapine 50 and Stoneville LA 887, in a North Carolina field naturally infested with R. reniformis. Numbers of R. reniformis in soil were suppressed at mid-season, and cotton-lint yield was increased by preplant fumigation with 1,3-dichloropropene. Population densities of R. reniformis at cotton harvest were unaffected by fumigation in 1998, but were affected in 1999. Some of the putatively tolerant breeding lines supported lower levels of R. reniformis and had higher tolerance indices to reniform nematode than the standard cultivars, but the yields of the breeding lines were significantly lower than the standard cultivars. Fumigation resulted in a 100- to 200-kg/ha increase in cotton lint yield for cultivars LA 887 and Deltapine 50.

Variability associated with testing shelled corn for fumonisin.

Variances associated with sampling, sample preparation, and analytical steps of a test procedure that measures fumonisin in shelled corn were estimated. The variance associated with each step of the test procedure increases with fumonisin concentration. Functional relationships between variance and fumonisin concentration were estimated by regression analysis. For each variance component, functional relationships were independent of fumonisin type (total, B1, B2, and B3 fumonisins). At 2 ppm, coefficients of variation associated with sampling (1.1 kg sample), sample preparation (Romer mill and 25 g subsample), and analysis are 16.6, 9.1, and 9.7%, respectively. The coefficient of variation associated with the total fumonisin test procedure was 45% and is about the same order of magnitude as that for measuring aflatoxin in shelled corn with a similar test procedure.