Source: UNIV OF ARKANSAS submitted to
DEVELOPMENT OF DROUGHT TOLERANT SWEET POTATO FOR HOT-HUMID SOUTHEAST ARKANSAS AND NORTH MISSISSIPPI AND TRANSFER OF TECHNOLOGY TO FARMERS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
NRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
0214390
Grant No.
2008-55100-04525
Project No.
ARX03032
Proposal No.
2008-00995
Multistate No.
(N/A)
Program Code
56.0E
Project Start Date
Sep 1, 2008
Project End Date
Aug 31, 2011
Grant Year
2008
Project Director
Onyilagha, J. C.
Recipient Organization
UNIV OF ARKANSAS
(N/A)
PINE BLUFF,AR 71601
Performing Department
AGRICULTURE
Non Technical Summary
The University of Arkansas at Pine Bluff (1890 Institution) and the Mississippi State University (1862 Institution) have teamed up to conduct research to select sweet potato varieties that will tolerate the drought summer conditions in the Mid-South, US and help to reduce production costs associated with irrigation. Sweet potato farmers in the Mid-South, including the States of Arkansas and Mississippi face similar problems of severe drought summer conditions requiring them to incur additional irrigation expenditures. Drought conditions are most detrimental on poor rural limited-resource farmers that cannot afford irrigation facilities, and most of the sweet potato farmers in the Mid South are limited-resource farmers. Therefore, high input costs such as irrigation costs limit the capacity of rural farmers in meaningful agribusiness. The major objective of the project is to select drought tolerant sweet potato lines through research in plant-water relations. The selected lines or varieties will be very useful in any future breeding program aimed at developing new sweet potato germplasm with high yield and drought tolerance characteristics. The hypothesis is that planting drought tolerant sweet potato will increase profitability to farmers in the mid-South U.S. by reducing irrigation and associated production overhead costs. Our efforts will lead to profitable sweet potato agribusiness and enhance agricultural sustainability.
Animal Health Component
(N/A)
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2011450108050%
2031450102050%
Knowledge Area
203 - Plant Biological Efficiency and Abiotic Stresses Affecting Plants; 201 - Plant Genome, Genetics, and Genetic Mechanisms;

Subject Of Investigation
1450 - Sweet potato;

Field Of Science
1080 - Genetics; 1020 - Physiology;
Goals / Objectives
The adverse effect of drought on the agricultural industry has long been recognized. Drought conditions negatively impact crop survival and yield. Drought necessitates additional irrigation periods, and this increases the overhead production costs. Research into drought tolerant plants is being intensified in order to minimize its overall impact on the agricultural enterprise. The prolonged period of drought during summer in the Mid-South of the United States reduces sweet potato yield, as well as the quality of roots, and causes huge economic losses to farmers. Since it is known that drought conditions severely affect crop survival and yield, and also increase the cost of production, and since the Mid-South, especially the Southeast Arkansas and North Mississippi regions are prone to drought in the summer months that severely affects crop survival and yield, and increase production costs, we hypothesize that drought tolerant sweet potato varieties will increase profitability to farmers in the regions by reducing irrigation and associated production overhead costs. Consequently, we aim to amass sweet potato germplasm from research and breeding centers, screen and select water stress tolerant parental sweet potato lines to establish the bases for a breeding program focused on developing drought tolerant varieties. Thus our research is guided by the following objectives: 1. Collect sweet potato lines and varieties from several research and breeding centers. 2. Screen the sweet potato pool and select reliable drought tolerant varieties and lines through plant-water relation studies. 3. Associate developmental and metabolic characteristics with water stress and stress tolerance traits. The goal of this project is to provide sweet potato farmers in the Mid-South with planting materials that are high yielding and drought tolerant. This goal will be achieved through cultivar selection and future establishment of a breeding program.
Project Methods
Sweet potato cultivars and lines will be collected from several sources to supplement the germplasm maintained at MSU and UAPB. The varieties and lines will be multiplied in the greenhouse and screened for survival and drought tolerance under controlled conditions. Evaluation of the varieties for drought tolerance will be conducted in the fields and greenhouses at UAPB and MSU-Pontotoc Station. Plants will be grown in 1 gallon pots in the greenhouse with day (16 hr) and night (8 hr) temperatures set at 32oC (90oF) and 18oC (65oF) respectively, 70% RH. The pots will be filled with a one: one mixture of topsoil and sand which will average about 7.5% clay, 84% sand, 8.5% silt, and 0.8% organic matter. Each variety or genotype will be replicated four times and arranged in randomized complete blocks design. The same quantity of water will be supplied daily using a watering can until slips establish and young leaves start appearing up to the three fully expanded leaf stage, after which water stress treatments will follow. The plants in the greenhouse will be evaluated for water loss and for wilting following water stress. Based on the days taken to wilt and percentage recovery, the varieties will be rated as drought tolerant or susceptible. Long root system will be treated as a drought tolerance characteristic and number of roots will be taken as indicator of yield. Field experiments will be conducted between June and August at Arkansas. The experimental plot will consist of rows 20ft long, planted on 10-inches high beds with 40 inches between rows. Water will be supplied through irrigation two times a week until slips establish. Subsequent treatments will follow as described in the greenhouse experiments. Soil-plant-water relations will be investigated at MSU. Selected lines with the highest drought tolerance capacity will be compared to commercial varieties under optimal and drought conditions to associate plant water status with soil moisture levels and yield. Plants will be grown under rain shelters to avoid rainfall. Trials will follow appropriate experimental design with three repetitions. Treatments will begin when plants are established and will consist of irrigation schedules based on soil moisture levels of 20 and 60 kPa at 12 in. depth and a non-irrigated control. Standard production practices will be followed, with exception of irrigation that will be determined by the treatment. Soil moisture will be monitored with watermark soil moisture sensors. Leaf water potential and water content will be monitored weekly to correlate them with soil moisture. Canopy temperature will be monitored also to correlate heat tolerance with drought tolerance. Photosynthesis and chlorophyll fluorescence will be monitored to determine the loss in assimilates resulting from water stress in sweet potato and the effect on storage root growth and productivity. Other parameters such as growth characteristics of roots and vines and root yield/quality will be evaluated. All experiments will be replicated 4x, and repeated 3x. Data will be subjected to analysis of variance (ANOVA) to determine differences among lines.

Progress 09/01/08 to 08/31/11

Outputs
OUTPUTS: The main objective of this research was to assemble and screen sweetpotato lines and varieties, and select varieties/lines with promising drought tolerant characteristics. This was to be accomplished through plant-water relation studies. Research was conducted in Mississippi (Pontotoc) and Arkansas (Pine Bluff). Research results were shared with sweetpotato farmers, especially those in the Southeast Arkansas during the annual rural life conference. Information relating to cultivar susceptibility or tolerance to drought was also disseminated and shared with farmers and other stakeholders through phone-calls and e-mails. Results were also presented at the meeting of project directors, sponsored by AFRI/USDA, San Diego, CA, January 14 - 15, 2011. Additionally, information generated in this study was presented to the sweetpotato scientific community at the National Sweetpotato Collaborators Group meeting in February 6-7, Orlando, Fl. Information was also presented to stakeholders in the Research and Demonstration tour held on August 17, 2010 at the Pontotoc Research Station in MS. Manuscripts dealing on selection methods for drought tolerance among sweetpotatoes are being prepared for publication in peer reviewed journals. PARTICIPANTS: Dr. Joseph Onyilagha, Dr. Shahidul Islam, Dr. Obadiah Njue, and Dr. James Garner Jr.worked on the project at Pine Bluff, AR, while Dr. Ramon Arancibia collaborated and worked on the project at Pontotoc, Mississippi. The following undergraduate students have been trained under this project. Each student received training on leaf surface temperature measurement, assessment of water strees, estimation of anthocyanin flashes, and data entry and management. 1. Devon Cunningham 2. Edina Okwemba 3. Clyde Williams 4. Usman Abdullahi 5. Tofuli Baedo 6. Abdur Chowdhury 7. Lynette Moss 8. Chinyelu Amaka Devon Cunningham and Clyde Williams collected and planted the different varieties and recorded leaf surface temperatures. Edina and Tofuli conducted leaf dehydration experiements and recorded changes in leaf weight. Usman and Abdur worked over the summer on plant regeneration after water stress. They also conducted further experiments on water stress. Lynette and Chinyelu conducted greenhouse experiments in 2011 test period. TARGET AUDIENCES: The project target audiences are primarily sweetpotato farmers (limited-resource farmers) and growers in the Southeast Arkansas and North Mississippi regions. Others include students, scientists, and the general public. Sweetpotato is treated as an alternative crop or a minor crop in Arkansas. Farming in alternative crops is the major business of the limited-resource farmers (LRF). The LRF, most of whom are ethnic minorities, own and farm small acreages (less than 50 acres) and do not have enough capital to successfully compete in the major crops (rice, soybean, corn, and cotton) agribusiness. However, several medium level farmers, especially in the Southeast Arkansas are beginning to show significant interest in sweetpotato cultivation. Our findings will help sweetpotato farmers, especially those residing in the lower delta region in reducing overhead costs associated with constant irrigation during the hot-humid summer months. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
At UAPB, Pine Bluff research center, we determined through Whole-Plant-Water-Stress experiment that sweetpotato cultivars could be grouped into three: a) drought susceptible, b) drought semi-tolerant, and c) drought tolerant. Group (a) plants died within 45 days following water stress; group (b) plants died between 45 and 60 days; while group (c) plants were alive up to 90 or more days. The study on leaf surface temperature suggests that this parameter has no statistical relationship with drought tolerance among sweetpotato cultivars. Therefore, high or low leaf surface temperature may not be a reliable indicator of drought tolerance or susceptibility in sweetpotato. We observed that some sweetpotato cultivars tend to accumulate higher concentration of anthocyanins as water stress persists. We are investigating whether sweetpotatoes' abilities to accumulate anthocyanin may be related to drought tolerance. In the leaf water loss study, we determined that weight of leaf does not provide a clear indication of drought tolerance or susceptibility among the sweetpotato cultivars tested. Contrary to earlier studies, there was no clear significant difference between weights of excised leaves over time, as well as rate of water loss among cultivars. We observe that many of the cultivars in our studies were advanced cultivars with very close characteristics, and this may have masked the usefulness of this screening method. At Pontotoc, Mississippi, varieties were further evaluated in the greenhouse to associate morphological and physiological characteristics to drought tolerance and in the field under rain shelter to evaluate storage root initiation under water stress. Photosynthesis, stomatal conductance, transpiration, leaf water content, and leaf temperature were measured and associated with volumetric soil moisture and plant water status. Varieties were planted and drip-irrigated for three days until established, then subjected to water stress at two growing periods: 4 to 33 days after planting (DAP) and 34 to 63 DAP. Water potential at 6 in and 18 in was also monitored with Watermark sensors throughout the study. Samples from each cultivar were evaluated for storage root initiation and growth. Data indicate that as soil moisture is depleted, plant water status (water potential) decreases until stomatal conductance is halted (9-13 Bars depending on the variety) resulting in minimal transpiration and photosynthesis shut down. Differences among varieties subjected to water stress suggest that the Stomata Index (plant water status at stomatal closure and photosynthesis shut down) can be used to identify drought tolerant varieties. Similarly, differences among varieties suggest that the Wilting Index (water status at wilting point which is different from the stomata index) can also be used to identify drought tolerant varieties. Data from storage roots initiation in potted plants as well as in the field showed that the potential for adventitious roots to become storage roots (initiation) appears to be intrinsic of the variety. Adventitious roots with five or more protoxylem elements are thought to have the potential to develop into storage roots.

Publications

  • R.A. Arancibia and J. Onyilagha (2010). Differential Responses to Water Stress among Sweetpotato Varieties. Paper presented at the National Sweetpotato Collaborators Group meeting in conjunction with the Southern Region-ASHS meeting in Orlando, FL on February 6-9, 2010.
  • R.A. Arancibia and J. Onyilagha (2010). Growth and Storage Root Initiation among Sweetpotato Varieties Subjected to Water Stress. Paper presented at the National Sweetpotato Collaborators Group meeting in conjunction with the Southern Region-ASHS meeting in Orlando, FL on February 6-9, 2010.
  • Onyilagha, J., Arancibia, R., Shahidul, I, Njue, O. and Garner, J. (2011). Selection Of Drought Tolerant Sweet Potato Varieties for the Hot-Humid Mid South. In Abstracts, AFRI/USDA, Plant genome, genetics, and breeding, San Diego, January 14, 2011.
  • Onyilagha, J., Arancibia, R., Shahidul, I, Njue, O. and Garner, J. (2011). Assessing the parameters for measuring drought tolerance in sweetpotato varieties. Arkansas J. of Agriculture and consumer sci. In preparation.


Progress 09/01/08 to 08/31/09

Outputs
OUTPUTS: Objective1 Thirty sweetpotato varieties have been assembled. This number includes six wild types, twenty-three advanced cultivars, and one old variety. We intend to identify and collect more varieties, especially the wild types. Objective2 We have subjected the 30 varieties to water stress experiments. These include whole plant water stress study, rate of leaf dehydration, leaf surface temperature, length of roots, and leaf/stem anthocyanin flashes. Water stress experiments were conducted in the greenhouse. All varieties were planted two slips in a pot. They were replicated 4x and arranged in a randomized block design of four blocks. The greenhouse automatic sprinkler system was set to water the pots every other day until slips are well established. The pots were then moved and subjected to water stress in a second greenhouse chamber with no water sprinkler system, and with day/night temperatures maintained at 80/60F. The rate of wilting was monitored in all varieties. Objective3 Soil-plant-water relationships are being investigated at MSU-Pontotoc Ridge-Flatwoods Branch Experiment Station on twenty sweet potato varieties to determine tolerance to drought conditions. Twenty varieties are being evaluated in the greenhouse to associate morphological and physiological characteristics with water stress. Potted plants, 4-week old, were subjected to water stress until wilting. Photosynthesis, stomatal conductance, transpiration, and leaf temperature were measured and associated with volumetric soil moisture and plant water status. Leaf moisture content was determined also. This study was repeated with potted plants grown outside the greenhouse. In a field study under a rain shelter (high tunnel), seven varieties (Beauregard B-14 and B63, Covington, Evangeline, Hatteras, Centennial, and Jewel) are being evaluated for their performance under water stress. Varieties were planted and drip-irrigated until established, then subjected to water stress at two growing periods: 4 to 30 days after planting (DAP) and 30 to 60 DAP. Volumetric soil moisture in the first 6 in was monitored in the first 30 DAP. Water potential at 10 in and 18 in was also monitored with Watermark sensors throughout the study. Samples from each cultivar at the end of each period were evaluated for storage root initiation and growth. We will repeat these studies in the coming months. Preliminary data indicate that although the varieties 99573-111 and 634471-104 could tolerate drought over four weeks, but mattie -115, 634474 -105, jap-110, 634468-103, and lo 232-108 are better. At a mean day/night temperature of 80/60F, the varieties could survive without water for over 12 weeks. Drought tolerance among varieties is inversely proportional to increase in temperature. We have not obtained a consistent pattern in leaf surface temperature and leaf water loss. Anthocyanin accumulation may provide additional information on the physiological condition of varieties during water stress. Some varieties naturally have anthocyanin pigments on leaf veins and stems, however, pigmentation increased three fold when plants were under water stress. PARTICIPANTS: The following undergraduate students have been trained under this project. Each student received training on leaf surface temperature measurement, estimation of anthocyanin flashes, and data entry and management. Devon Cunningham,Edina Okwemba,Clyde Williams,Usman Abdullahi,Tofuli Baedo, Abdur Chowdhury. Devon Cunningham and Clyde Williams collected and planted the different varieties and recorded leaf surface temperatures. Edina and Tofuli conducted leaf dehydration experiements and recorded changes in leaf weight. Usman and Abdur worked over the summer on plant regeneration after water stress. They also conducted further experiments on water stress. Edina Okwemba and Clyde Williams are still on the project to date. Collaborations: Dr. Victor Njiti, Alcorn State University, Mississippi Mr. Jeffrey Short, Hot Springs, Arkansas. Dr. Don Labonte, LSU Agricultural Center Dr. Ken Pecota, North Carolina State University. TARGET AUDIENCES: Target audience are sweetpotato farmers and the public. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
This study is investigating the response of selected sweet potato varieties to water stress at two levels: the effect on stomatal conductance that influences leaf transpiration and photosynthesis; and the plant capacity to initiate and sustain storage root growth, the determinant of yield. Preliminary data indicate that as soil moisture is depleted, plant water status (water potential) decreases. As plant water status reaches 9-12 Bars, depending on the variety, stomatal conductance is halted resulting in minimal transpiration and photosynthesis shut down. Soil moisture of 4% to 8% v/v, depending of the variety, were recorded when photosynthesis was shut down. In addition, the decrease in plant water status was well correlated to soil moisture. Similarly, preliminary data from the high tunnel study showed that varieties respond differently to water stress. Vegetative growth was reduced in all varieties, but the effect on storage root initiation and bulking differed among them and quality was affected significantly. Storage roots initiation in watered plants and under water stress were the same for B-63, although bulking was reduced. In contrast, storage root initiation and bulking were reduced in Centennial. Plants that were watered in the second period, after been stressed in the first period, had less storage roots but bulking increased in comparison to plants stressed in both periods. Soil moisture in the first 6 in of water stressed plots was 4% to 7% suggesting complete photosynthesis shut down, but soil moisture at 18 in was -20 kPa to -30 kPa. This deep soil moisture may have sustained limited plant growth and storage root initiation/bulking. It is still unclear whether stomatal closure at higher or lower plant water status would be more effective to tolerate drought. Sweet potato can withstand some weeks without water by shedding the leaves and then recover as soon as water is supplied. In contrast, the ability to initiate and sustain storage roots under water stress appears to differ among varieties and may be another determinant of drought tolerance. Although photosynthesis may influence storage root initiation and bulking indirectly, there appears to be other factors involved that are not fully understood. Plants under stress in the field can still open the stomata early in the morning and when conditions are favorable for photosynthesis to occur. However, can the plant initiate and sustain storage roots of commercial quality We are addressing this question by monitoring field conditions and testing varieties under different soil moisture conditions during storage root initiation and bulking.

Publications

  • No publications reported this period