Location: Crop Genetics Research2013 Annual Report
1a. Objectives (from AD-416):
Develop management practices for pest control in cotton. Evaluate and develop elite cotton germplasm for yield, quality and pest resistance. Develop improved agronomic practices for cotton production in an environment of changing technology.
1b. Approach (from AD-416):
Determine response of pests to available control practices. Evaluate response of cotton to management practices such as planting date, fertility practices and plant growth control. Measure pest response to application of control measures. Develop elite cotton germplasm and measure response in state yield tests. Transfer genes for resistance to diseases, insects and nematode into Delta-type cotton using traditional and molecular-assisted practices. Test alternative means to control pests with tolerance to normal control practices.
3. Progress Report:
Subobjective: Identifying the impact of bacterial blight on cotton lint yield: Bacterial blight (angular leaf spot) of cotton, caused by Xanthomonas citri subsp. malvacearum (Xcm), can be a devastating foliar disease. The seedborne nature of the disease is the primary reason for widespread adoption of acid-delinted seed. In general, Xcm can cause seedling blight, leaf spot, lesions on stems, petioles, and bolls. In severe cases, bacterial blight in susceptible varieties results in defoliation, a reduction in plant height, and subsequent yield loss on the order of 20-25%. Poor fiber quality and excessive yield reductions can be the result of elongated periods of environmentally conducive conditions. During 2011 and 2012, a bacterial blight epidemic was identified throughout Mississippi (MS). Many of the fields with excessive infection had not recently been in cotton production or had never produced cotton. Based on the available literature, the primary source of the bacterium is from infested seed. However, numerous methods of secondary infection can occur once a point source exists within a given field. The majority of the commercially available cotton varieties are susceptible to the bacterium. Field-level bacterial blight inoculation trials of commercially available varieties have been conducted for the past six years in Stoneville, MS. However, in an attempt to further our knowledge regarding the pathosystem, yield and cotton quality variables in addition to disease ratings were considered important. The main objective of the project was to determine the reaction of 22 commercially available cotton varieties to bacterial blight inoculation. Foliar rating observed 14 days after inoculation (in 2011) suggested approximately 5 of 22 varieties expressed some form of tolerance to Xcm. Specifically, DP 1133 B2RF, FM 1740B2F, FM 9058F, PHY 375 WRF, and ST 5288B2RF conferred tolerance. Foliar symptoms did not develop in 2012. Seed index was significantly influenced by the inoculation by variety interaction. In general averaged over varieties, seed from inoculated plants weighed 0.6 gram less in 2011 and 0.3 gram less in 2012 than seed from non-inoculated plots. Averaged across varieties, plots receiving inoculation with Xcm yielded approximately 26% less lint than non-inoculated plots, resulting in a 214 pounds/acre lint yield decrease in 2011. However, the reduction in 2012, without the development of observable bacterial blight symptoms translated into 29 pounds lint/acre reduction or a 3% decrease. Fiber micronaire was also influenced by the main effect of inoculation. Micronaire was reduced by 0.19 or 4% when comparing inoculated versus non-inoculated varieties, respectively. Subobjective: Assess the efficacy of cultural and chemical management options to minimize losses to reniform nematode in Mississippi: A series of trials in different locations were conducted comparing the efficacy of seed treatment nematicide-insecticides to manage the reniform nematode. These trials are conducted under the protocol of the cotton Hi-Lo Vigor National Seedling Disease Trial. During 2012 the trial was planted as early as possible (April 12, 2012). The early planting time was included because of reports that early planting was a method for reducing nematode populations. Reniform nematode numbers were all above the threshold (1,000 per pint of soil) in all of the trials at planting. Approximate seeding rate was 4 seeds per foot and a randomized complete block was used that included four replications. Subobjective: Disease incidence by soil potash fertilization interactions: Year one trial results were variable, with little response to potash fertilization in all trials that were harvestable. Potash deficiency was observed in one trial conducted at the Delta Research and Experiment Station during 2012. The deficiency symptom occurred in the trial evaluating soil and foliar applied potash levels across varieties. The symptoms were sporadic and could not be determined to relate to any single treatment; however they were only observed in the DP 0912 variety. Soil test values for the research site suggested that a response to potash would more than likely not be expected. Disease incident did not appear to coincide with the late season potash deficiency in this trial. For trials evaluating potash fertilization across multiple varieties, the interaction of variety x fertilization strategy was non-significant. Similar to the interaction, the main effect of potash fertilization strategy was also non-significant. Only the main effect of cotton variety influenced final cotton yield in the trial. In general, the more aggressively growing, longer season varieties tended to have the greatest lint yields. More specifically, PHY499WRF and ST5458B2F produced similar and greater cotton lint yields when compared with DP0912B2RF. Soil test extractable potassium at the experimental location was 225 milligram/kilogram which is in the range were a response to potash would be marginal to none based on older correlation data. However late season potash deficiency was observed in the trial. Reasons for the reduced yield in the variety that showed visual symptoms for potash deficiency may not be due to a classical soil deficiency, since adequate potash levels were reported for the soil and no yield increases were observed from potash application for any treatment combination. Disease incidence was also deemed to be minimal. For 2013, more frequent disease ratings will be taken to determine the yield limiting factor in the specific micro environment, when late season potash deficiency appears and leads to early cutout and misshaped bolls.