Project Summaries

12-211  Project Manager: D. C. Jones


Ted P. Wallace, Mississippi State University

Mississippi cotton production losses attributed to reniform (82,286) and root-knot (13,714) nematodes totaled 96,000 bales in 2011 (Blasingame et al., 2012). Although some commercial varieties are advertised as having a level of resistance to root-knot nematodes, all commercial varieties of cotton are susceptible to reniform nematodes. Although the use of nematicides such as 1,3 dichlorpropene (Telone II) and aldicarb (Temik) have been shown to reduce losses, results from such use have been inconsistent (Overstreet, et al., 2001; Baird, et al., 2000; Davis, 2000).  Currently, crop rotation with corn or soybean cultivars offers one of the most effective means to reduce RN nematode numbers for profitable cotton yields (Davis, et al., 2000). However, crop rotation is not always a viable alternative. Development of resistant or highly tolerant cotton genotypes is sorely needed, not only for Mississippi, but for most major cotton growing regions of the US. This project continues a breeding program designed to identify and develop nematode resistant breeding lines adapted to Mississippi.  The successful transfer of reniform resistant from G. longicalyx into G. hirsutum (Upland), and the development of associated molecular markers to aid in selection has provided breeders a new source of resistance for nematode breeding (Dighe, et al. 2005, Robinson and Bell, 2006). A more recent source of reniform resistance was developed by transferring resistance from G. barbadense into G. hirsutum (Bell et al., 2013). This project has attempted to exploit these two sources of resistance using Mississippi adapted germplasm.

Plots for MAS to test for reniform and root-knot nematode resistance were planted on May 17 in field 9 at Stoneville, MS. The tests were planted with minimal moisture, but after planting, rain amounts of 3.68" in April, 2.03" and May were received followed by a flooding rain in June of 6.39". Because of the rains crop maturity was delayed several weeks. Hand harvesting of individual plant selections and boll samples was completed November 5, and replicated yield plots were harvested on November 30.

Crosses were made to provide new segregating populations for marker assisted selection. Prior to crossing, resistance was confirmed by marker analysis of 20 plants per plot. Resistant plants within plots were tagged for use as parental plants. At least 5 set bolls were completed for each cross. Following harvest, crosses were ginned, delinted, and shipped to the Tecoman, Mexico winter nursery for seed increase and advancement to F2. Seed (F2) from the increase will be subject to marker assisted selection during the 2013 growing season. The most advanced lonren lines (31), evaluated in replicated yield trials were planted to single row plots in a 1 x 1 skip row configuration. Initial plans were to evaluate 15-20 plants per entry to confirm homogeneity for resistance. However, due to the large number of samples tested in segregating populations, plans were amended to skip homogeneity testing in the field and do root-tip testing of only the best performing lines as determined by replicated yield testing. Populations from MAS in 2011 of F2, F2F3, and F2F4 homozygous for resistance were tested with markers for homogeneity (reniform & root-knot resistance). Leaf samples were collected from 5 plants per population (195 entries + 7 checks) and the 1,010 samples tested with the following markers for reniform and root-knot resistance. Based upon marker results 26 individual plant selections (IP's) were made within populations found to be segregating, and 71 homogenous populations were selected by bulking the 5 plants. The IP's will be tested for homogeneity in 2013 and the populations will be evaluated for yield and fiber in progeny row testing.

Segregating F2, F2F3, and F3F4 populations (107) were planted to two row plots. Leaf samples were collected from 20 plants per plot (2140 samples) and evaluated with markers to identify plants homozygous and heterozygous for resistance reniform and/or root-knot nematodes. Selected lines were ginned, delinted, and shipped to the Tecoman winter nursery for seed increase. In 2013 selected IP's will be planted to progeny rows for homogeneity testing and ratings for agronomic performance. Homogeneity testing (root-tip tissue marker testing) of the most advanced Lonren derived breeding lines in the spring of 2012 was used to identify 31 lines for evaluation in replicated yield trials. Lines were evaluated in trials at three locations (Stoneville and Starkville, MS, and at the Tennessee Valley Research and Extension Center-TVREC, Belle Mina, AL) on nematode infested soils with populations ranging from low (treatment threshold level) to extremely high. Preliminary results of this trial were presented at the 2013 Beltwide Cotton Conferences. Most all lonren derived lines suffered significant stunting and reduced yields compared to Barbren and commercial check varieties. When grown in soils with high reniform nematode populations of reniform (TVREC), most all lonren derived breeding lines were severely stunted with reduced yields. Theories regarding lonren germplasm suggest that either the mode of high resistance does not allow for tolerance, resistance is linked to deleterious genes, or a combination of the two. Two lonren lines performed similarly to commercial checks and may represent recombinants that are more tolerant to high reniform populations. These two lines will be evaluated more extensively to determine if the genotypes represent favorable recombinants.


Project Year: 2012

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