Location: Crop Genetics Research
2019 Annual Report
Objectives
Objective 1. Characterize new sources of reniform nematode resistance in Gossypium (G.) arboreum and G. herbaceum germplasm accessions and identify DNA markers associated with resistance.
Objective 2. Introgress reniform nematode resistance from G. arboreum and G.
herbaceum accessions into G. hirsutum and develop breeding lines with resistance.
Objective 3. Determine effectiveness of unique sources of reniform resistance fromdiploid Gossypium germplasm accessions on nematode growth, reproduction, and
infection.
Objective 4. Characterize plant growth and development and yield responses to reniform nematode in susceptible and resistant cotton lines and define the relationships between soil fertility and reniform nematode severity with respect to plant damage and yield loss.
Subobjective 4a. Characterize plant growth and development and yield responses to reniform nematode in susceptible and resistant cotton lines.
Subobjective 4b. Define the relationships between soil fertility and reniform nematode severity with respect to plant damage and yield loss in susceptible and resistant cotton lines.
Objective 5. Evaluate impacts of integrated reniform nematode management practices on cotton yield, quality and reniform nematode population densities.
Subobjective 5a. Investigate the efficacy of new commercially-available nematicides on the management of the reniform nematode, cotton yield and cotton fiber quality.
Subobjective 5b. Investigate the effect of rotation with non-host/poor-host crops on management of the reniform nematode and crop yield.
Approach
Develop populations by crossing resistant accessions with one or more Gossypium (G.) arboreum accessions classified as susceptible or highly susceptible. Ovule culture will be used for the introgression of resistance from G. arboreum and G. herbaceum accessions to G. hirsutum varieties. Gossypium accessions with high levels of resistance to reniform nematode will be evaluated in growth chamber experiments to measure the effects of the resistance on number of infections, rate of development of females after infection, and production of eggs. Classical growth and agronomic analysis will be conducted over two years under field conditions at Mississippi State University’s Delta Research and Extension Center in Stoneville, Mississippi. A nutrient response experiment will be conducted under controlled environmental conditions. The relative efficacy of new seed-applied and in-furrow nematicides against the reniform nematode will be evaluated on one susceptible and two resistant cotton lines in a field trial to be established in two naturally-infested sites in Stoneville, Mississippi. A field trial will be established in a reniform nematode infested site in Stoneville, Mississippi.
Progress Report
This research is designed to improve our understanding of the effects of reniform nematode (Rotylenchulus reniformis) on yield losses in upland cotton (Gossypium hirsutum) and to develop management strategies that will reduce those losses. In fiscal year 2019, research was conducted in Stoneville, Mississippi, by ARS researchers and university collaborators.
Resistance to reniform nematode does not exist naturally in upland cotton, so related species are the subject of studies to identify resistance to this nematode and move that resistance into upland cotton. Previous work by this research team has identified reniform nematode resistance in several accessions of the related Asiatic cotton species Gossypium arboreum, and this species was the focus of our investigations related to Objective 1 this year. Highly resistant Gossypium arboreum accession PI 529740 was crossed with susceptible Gossypium arboreum accession PI 527929 to create a population that we used to determine how the resistance trait was inherited. This information is critical to plant breeders, because it provides information on the number of plants that breeders would need to develop and screen within a single population to identify resistant individuals. Results showed that at least two recessive genes control resistance in PI 529740, which means that if this source of resistance is used, large breeding populations will be necessary to identify progeny that have both of the required genes.
Transferring resistance from Asiatic cotton to upland cotton is difficult. There are incompatibilities between the two species that do not allow them to cross-pollinate and set viable seeds, so specialized breeding approaches are needed. The transfer process requires a special technique called ovule culture for extracting the developing hybrid cotton embryos, growing them on artificial media, and regenerating plants. This process is very time consuming, as there is a long period where the plants are maintained growing on artificial media. Approximately 1,300 embryos were successfully extracted from 65 hybrid crosses between 24 resistant Asiatic cotton accessions and upland cotton during the 2018 field season, but most of the plants growing on artificial media were lost during the government shutdown. As a result, progress on Objective 2 was slowed, as many crosses will need to be done again during the 2019 field season.
Plants that are considered resistant to reniform nematode will reduce the population of the nematode over time. However, not all resistant cotton varieties will achieve this reduction in the same manner. Experiments to determine what mechanisms our most resistant plants use to suppress nematode populations continued in support of Objective 3. Possible mechanisms include limiting the number of nematodes that can infect the plant roots, stopping growth and development of the nematodes after they infect the roots, or limiting reproduction by the nematodes. Experiments involving two resistant Gossypium arboreum lines (A2-190 and A2-100) were completed on schedule last year, but data analysis scheduled for completion 2019 has been delayed. When work resumed after the government shutdown, research priorities were revised to be sure that all experiments planned for 2019 would start on schedule. Experiments evaluating the effects of resistance in two additional Gossypium arboreum lines (A2-354 and A2-690) are in progress and on schedule. Data analysis for both the 2018 and 2019 experiments will be forthcoming.
To characterize plant growth and development and yield responses to reniform nematode in susceptible and resistant cotton varieties, a repeat of a field trial that was originally conducted in 2017 was successfully completed during the 2018 field season. The trial was conducted in a field that was naturally infested with reniform nematode. Results from 2018 were similar to those from the prior year. Briefly, differences between susceptible varieties (Deltapine 16 and PHY 490 W3FE) and resistant lines (08SS110-NE06 and 08SS100) were evident as soon as one month after planting with respect to physiological effects on the cotton plants, with resistant varieties having greater transpiration, photosynthesis, stomatal conductance, and carbon dioxide assimilation efficiency than the susceptible varieties. These differences in physiological functions of the plants translated to differences in the rate of plant growth and development, with resistant varieties reaching specific vegetative and reproductive stages of development more quickly and exhibiting greater vigor. Resistant varieties had higher yields than susceptible ones and resulted in less reniform nematode reproduction. Results from this work have been summarized and reported at the Crop Science Society annual meeting (2018) and the Beltwide Cotton Conferences (2019). A manuscript is currently in preparation. This work supports Objective 4 and Subobjective 4.A.
Cotton growth and development can be influenced by availability of plant nutrients, so the research under Objective 4 and Subobjective 4.B. seeks to define the relationships between soil fertility and reniform nematode severity with respect to plant damage and yield loss in susceptible and resistant cotton varieties. Three greenhouse studies evaluated the effects of nitrogen, potassium, and phosphorus on plant growth and reproduction and pathogenicity of reniform nematode on the same varieties used in the field trial described above. In the first nitrogen trial, which is complete, the four varieties grown in the presence and absence of reniform nematode were subjected to four different levels of nitrogen (150%, 100% {recommended}, 50%, and 0%) from the time of emergence until 60 days after sowing. Overall, significant increase in plant height, node number, leaf area, dry weights, taproot length, chlorophyll content, and net photosynthesis were associated with increasing nitrogen levels. When nematode absence and presence were compared, the resistant varieties showed significantly greater values for the above measured parameters when compared to susceptible varieties. Reniform nematode populations in the pots grown with resistant varieties were significantly smaller than those in pots grown with susceptible varieties. However, no effect of nitrogen was observed on the reproduction of reniform nematode population. Analyses of the data from the studies involving potassium and phosphorus are underway, and all three experiments are currently being repeated. Further research is needed to investigate the role of mineral nutrition as a management strategy for nematode management in cotton.
The fifth project objective is to determine how to best manage the use of new cotton varieties with resistance to reniform nematode in a production environment. Resistant varieties are being evaluated in conjunction with commercial seed-treatment nematicides (Subobjective 5.A.) and crop rotation (Subobjective 5.B.).
Two trials were planted in June of 2019 using the reniform nematode resistant variety M123-1337 to determine if management of the nematode could be improved by combining resistance with nematicides that were applied either in-furrow or directly on the seed. New, commercially available seed-applied products that were tested were BioST, Nemastrike, and COPeO Prime. In-furrow nematicides tested were Velum Total and Temik. Each trial was planted in a separate field, both of which have had a history of reniform nematode. Data collection is in progress.
The second year of a five-year rotational study (Subobjective 5.B.) was completed in late 2018. Reniform nematode populations at planting in 2018 ranged from 0 to 2,098 per kilogram of soil following peanut, 0 to 3,496 per kilogram of soil following corn, and 0 to 8,391 per kilogram of soil following cotton. Corn, continuous cotton, and plots of cotton cultivars susceptible or resistant to reniform nematode were the main rotational crops for the 2018 field season. Corn reduced nematode numbers by 46% during the cropping season, whereas nematode populations increased by as much as 52% on susceptible cotton. Maximum numbers of reniform nematodes per kilogram of soil at harvest averaged 4,894 on corn to 19,578 on cotton. Yield data were collected and analysis is in progress.
Plots for the third year of the rotation study were established on schedule in 2019. Rotational crops included this season are peanut, reniform nematode resistant soybean, corn, and continuous cotton. Early-season sampling for reniform nematode has been completed, and additional sampling is planned throughout the remainder of the season to monitor the impact of the rotational hosts on reniform nematode populations.
Accomplishments
1. Single nucleotide polymorphisms detect genetic variability in reniform nematode populations. The reniform nematode is a microscopic worm that lives in the southern United States and feeds on roots of two economically important crops, cotton and soybean. Scientists are working to develop cotton and soybean varieties with resistance to this pest, but progress is slow because we do not yet have a clear understanding of how much variation there is in nematode populations, and how that variability affects the utility and longevity of resistant varieties. To gain a better understanding of genetic diversity in reniform nematode populations, USDA ARS researchers in Stoneville, Mississippi, extracted DNA from 26 different reniform nematode isolates representing Louisiana, Mississippi, Arkansas, South Carolina, Georgia, Hawaii, and Alabama. We used a technique called single nucleotide polymorphisms (SNPs) that looks for one change in a very long sequence of nucleotides that make up the nematode’s genetic code, identified 162 likely places where these single nucleotide changes exist, and tested 31 of them to determine if they could distinguish within isolates from the same state as well as between isolates from different states. We successfully documented both within-state and between-state variability in the first study of its kind to report the use of SNP assays to test for genetic variability in reniform nematode. Scientists may be able to build on the information from this study to find SNPs associated with traits of interest in the nematode, such as those associated with the ability of nematode to reduce plant yield, that would be extremely useful in resistance breeding programs.
Review Publications
Erpelding, J.E., Stetina, S.R. 2019. Screening cotton genotypes for reniform nematode resistance. Journal of Visualized Experiments. 147:e58577. https://doi.org/10.3791/58577.
Khanal, C., McGawley, E.C., Overstreet, C., Stetina, S.R., Myers, G.O., Kularathna, M., McInnes, B., Godoy, F.C. 2018. Reproduction and pathogenicity of endemic populations of Rotylenchulus reniformis on cotton. Nematropica. 48:68-81.
Gillen, A.M., Mengistu, A., Arelli, P.R., Stetina, S.R., Bellaloui, N. 2018. Registration of soybean germplasm line DB0638-70 with high yield potential and diverse genetic background. Journal of Plant Registrations. 13:96-102. https://doi.org/10.3198/jpr2018.03.0016crg.
Khanal, C., Kularathna, M.T., Ray, J.D., Stetina, S.R., McGawley, E.C., Overstreet, C. 2019. Single nucleotide polymorphism analysis using KASP assay reveals genetic variability in Rotylenchulus reniformis. Plant Disease. 103:1835-1842. https://doi.org/10.1094/PDIS-11-18-1975-RE.
