|11-931 Project Manager: D. C. Jones|
ENHANCED ROOT KNOW NEMATODE EVALUATIONS
Peng W. Chee, University of Georgia
Host plant resistance is overall the most economical, practical, and environmentally sound method to provide crop protection against root-knot nematodes (RKN). Despite the widespread occurrence of RKN in most cotton production areas in the Southeast and that genetic resistance to RKN has existed since 1974 (Shepherd, 1974), private cultivar developers have exhibited minor interest in fulfilling this need.
Even though the registration of the Meymik brand of aldicarb has been approved in December, 2011 after the Temik brand of aldicarb was scheduled to be phased out by 2018, it is obvious that this important tool in nematode control in cotton is precariously placed in terms of availability. Temik has been the most widely used nematicide in US cotton production and works well in controlling RKN. Previously, RKN resistance in commercial cotton cultivars has been through direct utilization cultivars developed by public cotton breeders. These include the RKN-resistant CPCSD Acala NemX and the tolerant ST LA887 and PM H1560 that have been distributed by commercial cotton seed companies; none of which were particularly developed for cotton production in the Southeast. There are now four other cultivars that are directly touted in the websites of the three major commercial cotton breeders in the United States. Unbiased testing regarding the strength of the resistance offered to the cotton grower and the improvement of yield from this trait is needed to determine the value of RKN resistant cultivars in the Southeast. Additional testing of several newly released public cultivars is also needed to determine if any RKN resistance is available from these new public genetic resources. This will benefit United States producers by providing an evaluation of these cultivars for yield and decreased production costs.
Parallel yield tests of the four RKN tolerant commercial cultivars (PhytoGen PHY 367 WRF, Bayer CropScience ST 4288B2F and ST 5458B2RF, and Monsanto DP 174 RF) and four newly released public conventional cultivars (University of Georgia's GA 230, University of Arkansas' UA 48, and Louisiana State University's LA 17 and LA 35rs were planted with three checks (University of Georgia's GA 120R1B3, a resistant check; Acala NemX, a resistant check; and Monsanto's DP 0935 B2RF, a susceptible check) in soils with and without high populations of root-knot nematodes over a two year span of 2011 and 2012 at the Gibbs Farm of the University of Georgia-Tifton Campus. The tests used standard cotton agronomic practices. The test in the infested field had 8 replications the first year and 6 in the second year to cover expected biological variability of the RKN infestation of the cotton roots. The test without high nematode populations had 4 replications the first year and 5 replications for the second year. It used granular, gypsum-based Temik insecticide banded in at planting at 5 pounds/acre which is generally considered a nematicidal rate. The seed was treated with Baytan, Thiram, and Allegiance for fungal control as labeled. We have found no nematicidal effects reported by others using this seed treatment. Besides harvesting for yield, the lint percentage and fiber quality will be checked for any unexpected changes.
The first year data of the nematode counts indicate that the four touted commercial cultivars are definitely not extremely susceptible to RKN, but nothing is as resistant as the two resistant checks, GA 120R1B3 and NemX. In comparing the resistant checks, GA 120R1B3 is significantly better than NemX or any other cultivar. One conventional cultivar LA 17 appears to have a level of RKN resistance that is essentially equivalent with the commercial cultivars. All of the commercial cultivars along with LA 17 seem to cluster between the resistant checks and the susceptible check. The other conventional cultivars cluster with the susceptible check as would be expected if they are indeed susceptible. In 2011 the more resistant lines also tended to lower the number of RKNs as the year progressed. But in 2012, preliminary data indicates that this was not the case with the numbers of RKNs going up or down as the season progressed. Further investigation into this is warranted.
The highest seed cotton variety in the RKN infested field in 2011 was DP 174RF followed by two commercial cultivars and two public cultivars that were not significantly different (Fig. 2). The lowest ranking cultivar was the resistant cultivar NemX. The rankings of the cultivars for seed cotton yield do not match the ranking of the cultivars for the nematode counts. This was not unexpected since the background genetics for the agronomic performance of the cultivars is unlikely to be correlated with the RKN resistance trait. For example, NemX is an Acala cotton that is not adapted to the Southeast. The high RKN resistance of NemX cannot completely compensate for the fact that NemX is not adapted to the Southeast. The resistant check GA 120R1B3 yielded better than the NemX because it was developed in and for the Southeast and has two major genes of an elite RKN resistance.
In 2012 ST 5458B2RF was the best variety. The next 6 cultivars were not significantly different in seed cotton yield and included the two Louisiana State cultivars LA 17 and LA 35rs; the three other commercial cultivars ST 4288B2F, DP 174RF, and PHY 367WRF; and NemX. NemX is very resistant, and LA 35rs is susceptible. ST 4288B2F, DP 174RF, and PHY 367WRF along with LA 17 have a moderate level of resistance. UA 48 was the lowest yielder consistently across the replications. It, the check DP 0935, and GA 230 were in the last three places and are susceptible. The environmental effect between years appears to be obvious, but this experimental design cannot allow a statement of significance as it was done. The reason that this particular design was used was because the loss of this valuable RKN infested field resource was not allowable. As in 2011, the rankings of the cultivars for seed cotton yield do not match the ranking of the cultivars for the nematode counts.
The top yielders in the nematode clear field in 2011, GA120R1B3 and GA230, were the two cultivars developed in and for the Southeast. Another putative susceptible cultivar UA 48 with the susceptible check DP 0935 B2RF also did better in the control field vs. the infested field.
In 2012, the top seed cotton yielders that were not significantly different from the best yielder were LA 17, GA 120R1B3, NemX, and ST 4288B2F. Only GA120R1B3 was in the top group for both years. It is ironic that this happened in a field clear of RKNs and not in the infested field since it is the most resistant of the cultivars. The other three are also very to moderately resistant which leads to the question of verifying the reality of the field being clear of RKNs. Also, ST 4288B2F and LA 17 were in the bottom in 2012 and in the top in 2011. Like the infested field, the environmental effect in the clear field tests between years is very likely. The interactions between the yields of the infested field and the clear field are not distinct either between years or between the treatments. One also would expect that the RKN resistant cultivar that was developed for Georgia conditions GA 120R1B3 would rank high in both fields. Further research with additional resources will be needed to determine the nature of the interaction between the RKN resistance and the traits required for adapted cultivars.
|Project Year: 2012|
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