Progress 09/01/08 to 08/31/11
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.
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.
- 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: 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.
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.
- No publications reported this period