Location: Crop Genetics Research Unit
2013 Annual Report
Efficacy trials for seed treatment nematicides were conducted in the greenhouse using the Ray Leach SC10-R container. Cotton lines susceptible and resistant to the reniform nematode were planted in nematode infested soil. These same lines were treated with different seed treatment nematicides to evaluate the effectiveness of the nematicides. The trial was attempted twice. In both cases, reniform nematodes were added to the soil prior to planting. These nematodes were from a culture obtained from the USDA-ARS. When the experiment was harvested, there were no reniform nematodes detected in the soil.
Field trials were established during 2012 to evaluate the efficacy of seed treatment nematicides on commercially available cotton lines as well as two advanced breeding lines that have some degree of nematode resistance. The commercial cultivar was DPL 0912B2RF, and the two breeding lines included resistance derived from G. barbadense and G. longicalyx. The trials were conducted in two fields with different native reniform populations, one moderate to low and the other relatively high. Nematicides and cotton lines were combined in a 3 x 4 factorial treatment arrangement in a randomized complete block design with at least four replications in each field. Measurements taken included plant population, plant height, multiple nematode sampling (pre, mid, and post-harvest), yield and fiber quality. Preliminary analysis includes each parameter analyzed individually for each location separately.
In general, seed treatments and/or inbred resistance produced equal to or lower cotton yield when compared with commercial cotton with no seed treatment nematicides. Similarly, soil nematode level was not influenced by the main effect of treatment. In one trial a significant main effect of treatment level influenced cotton yield. It appeared that longicalyx derived lines produced lesser amounts of cotton yield when compared to the other two varieties. For 2013, cotton has been planted to experimental sites in bulk to build-up the native reniform population for testing in 2014.
Differing crop rotations were established to be evaluated to determine influence on seasonal changes in soil reniform nematode populations and crop yield during 2012. A split plot design was used where whole plots consist of crop rotation, and subplots include two commercial cotton lines and two lines with known resistence to reniform nematode from breeding stock derived from G. barbadense and G. longicalyx. Reniform samples were collected before crop establishment and after harvest from each plot during 2012. In 2012, cotton served as the base for the rotational partners with all treatments being imparted except for where cotton follows corn in rotation. For 2013 all rotations have been planted and cotton occurs in two of the four preplanned rotations, preplant nematode samples have been taken and the plots are looking exceptionally well.
Results from 2012 indicated that initial plant population was not influenced by treatment. Plant height, lint yield, and 10-week nematode counts were influenced by treatment with the two advanced breeding lines being markedly different from the commercial cotton. In general, the Barbren lines were taller, while the Lonren lines were smaller in stature when compared with commercially grown cultivars. Also at 10 weeks after planting, breeding lines with resistance to reniform showed lesser soil nematodes in samples than commercially available cotton. However, when comparing lint yield the commercial cultivars produced similar lint yields to each other but drastically greater lint yields when compared to the advanced breeding lines.
A series of three trials in different locations were conducted comparing the efficacy of seed treatment nematicide-insecticides to manage the reniform nematode. Each of these trials were planted as early as possible and at the regular planting time. The early planting time was included because of reports that early planting was a method of reducing nematode populations. Reniform nematode numbers were all above the threshold (1,000 per pint of soil) in all of the trials at planting. In Trial One, reniform nematode numbers ranged from 481 to 1,829 per pint of soil at planting. At harvest, nematode numbers increased in some plots to over 11,000 per pint of soil. There were no significant differences in nematode numbers between the untreated seed and treated seed at planting, 10 weeks after planting, and at harvest. There were significant differences in the reproductive factor at 10 weeks but not at harvest. There were significant differences in percent seedling survival at four weeks between the no seed treatment, or seed treated with fungicides alone and the seed treated with fungicides and nematicides. There were significant differences in seed cotton yields between the different treatments.
In Trial Two, reniform nematode numbers ranged from 1,251 to a high of 3,946 per pint of soil at planting. At harvest, nematodes ranged from 4,716 to 19,635 per pint of soil. There were significant differences in nematode numbers between the untreated and treated seed at planting, 10 weeks after planting, and at harvest. There were significant differences in the reproductive factor at 10 weeks or at harvest. There were significant differences in percent seedling survival between the treated and untreated seed four weeks after planting. Several of the treatments had seed cotton yields which were significantly higher than the untreated seed or seed treated with fungicides alone.
In Trial Three, reniform nematode numbers ranged from 674 to a high of 3,658 per pint of soil at planting. At harvest, nematodes ranged from 5,390 to 14,534 per pint of soil. There were significant differences in nematode numbers between the untreated and treated seed at planting, 10 weeks after planting and at harvest. There were significant differences in the reproductive factor at 10 weeks and at harvest. There were significant differences in percent seedling survival and in seed cotton yields between the untreated and treated seed.
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. During 2011 and 2012, a bacterial blight epidemic was identified throughout Mississippi. 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 lint/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.