Progress 10/01/02 to 09/30/07

Outputs
OUTPUTS: Most plant disease resistance genes identified to date belong to the nucleotide binding site (NBS) leucine rich repeat (LRR) family. In studies with sweetpotatoes, three hundred forty two disease resistance gene homologs (RGHs) were identified from sweet potato genomes using degenerate primer approaches. These RGH sequences were deposited in GenBank (accession number DQ903322-DQ903664, GenBank, National Center for Biotechnology Information. http://www.ncbi.nlm.nih.gov). These RGH sequences identified from sweetpotato genome provide tools for practical application to sweetpotato breeding. For example, the isolation of full-length sequences and gene expression analyses will help to identify resistance gene alleles and paralogs that underlie important resistance phenotypes. Such knowledge will feed directly into the sweetpotato disease resistance molecular breeding program using approaches such as marker assisted selection once DNA markers tightly linked to resistance phenotype wire identified. In other studies, four sweetpotato cultivars, D-3, J6/66, NCC-58 and Whatley-Loretan were used to establish a relationship between canopy (as opposed to single leaf) photosynthesis rates and yield of sweetpotato storage roots. Elevated CO2 significantly increased total shoot fresh and dry weights for all sweetpotato cultivars except J6-66. Fibrous root fresh and dry weights, storage root numbers and harvest index also increased with elevated CO2. Net photosynthetic rates increased with increasing CO2 and there appears to be a linear relationship between canopy gas exchange and yield. As net photosynthetic rates increased, radiation absorption increased for cultivars J6-66 and D-3. TARGET AUDIENCES: Target audiences include scientific community particularly plant breeders and physiologists.

Impacts
Identification of disease resistant genes will provide breeders with a faster method of evaluating and selecting sweetpotato germplasm for disease resistance. It will also assist disease resistance gene isolation and transformation in sweetpotato. Understanding the physiological response of sweetpotato cultivars will assist breeders in identifying cultivars with high yields under CO2 stressed conditions.

Publications

• Mortley, D.G., C.S. Williams, C.F. Davis, J.W. Williams, C.K. Bonsi, W.A. Hill, C.E. Morris, L.H. Levine, B.V. Petersen, and R.M. Wheeler. 2007. Influence of microgravity on root growth, soluble sugars and starch concentration of sweetpotato stem cuttings. J. Amer. Soc. Hort. Sci. (In Press).
• Egnin, M., H. Gao, D. Mortley, J. Scoffield, S. Jack, and B. Bay. 2007. Gene expression profiling and the physiological role of t-Zeatin Riboside (ZR) in sweetpotato storage root initiation and enlargement. HortScience 42:976.
• McDonald,S. P., P.N. Gichuhi, D. Mortley and A.C. Bovell-Benjamin. 2007 β-Carotene Content of Dehydrated Hydroponic Sweetpotatoes Grown under Different Lighting Conditions., Technical Paper 2007-01-3051, SAE, Warrendale, PA
• Mortley, D.G., J.H. Hill, D. Hileman, D. Barta, C.K. Bonsi, W.A. Hill and C.E. Morris. 2008. Sweetpotato and Human Exploration of Space: Some Observations from NASA-Sponsored Controlled Environment Studies. In: Recent Advances In Agriculture. (In Press).

Progress 10/01/05 to 09/30/06

Outputs
Studies were conducted to determine the relationship between endogenous cytokinins and the possible genes controlling storage root initiation and development. t-Zeatin riboside (ZR) extraction and quantification in developing storage roots of four different sweetpotato cultivars (Whatley-Loretan, NCC-58, J6/66 and D-3) with bulked RNA treated samples revealed an up and down regulated of the hormone in developing roots. cDNA from developing storage roots of five harvests (2-6 weeks after planting- WAP) of the four cultivars' RNA were profiled to understand the developmental pattern of gene expression. Four different expression patterns, including up-regulated expression (8), decreased expression (9), transient expression (16) and constitutive expression (43) were detected in all cultivars. During sweetpotato storage root development, gene expression level is rigidly regulated, and results also confirmed different developmental stages. TDFs are currently being eluted, cloned and sequenced for BLAST search and function assignment. The expression profile work has afforded us the opportunity to understand key physiological and biochemical processes of storage root development with the discovery of genes that are related to storage root development. In related studies germplasm conservation and in-vitro protocols, expression profiling techniques and transformation model systems critical for germplasm maintenance and developmental studies, gene discover and genetic engineering were successfully developed for several sweetpotato cultivars and other root and tuber crops including yam and Frafra potato. In other studies, the four sweetpotato cultivars were enriched with carbon dioxide to assess the impact on canopy photosynthesis and to determine the correlation with sweetpotato storage root yield.Results biomass produced indicated that the number of storage roots appeared to be cultivar related. Whereas the number of storage roots were enhanced by CO2 in two of the cultivars, the effect on the other two were negligible. A new sweetpotato cultivar, Whatley-Loretan was released for hydroponic production.

Impacts
Understanding the role of genes and endogenous hormones as well as the physiological response of the storage root in initiation and development will assist the breeders in breeding sweetpotato cultivars for higher productivity.

Publications

• Mortley, D.G., M. Egnin, C.K. Bonsi, W.A. Hill and C.E. Morris. 2006. Impact of t-zeatin riboside on early storage root development of four sweetpotato cultivars. Proc. Intl. Soc. Trop. Root Crops pp 220-221
• Scoffield, Jessica, M. Egnin, B, Bey, M. Quain, C.S. Prakash and D. Mortley. (2006). Development of an Efficient Agrobacterium-Mediated Gene Transfer System for Multiple Sweetpotato Cultivars. In Vitro Cell and Dev. Journal, 42 (4):36A.

Progress 10/01/04 to 09/30/05

Outputs
During the 2004 2005 growing season, 15 advanced breeding lines and more than 2000 new accessions representing 10 families were evaluated in an advanced yield trial and seedling trial respectively. The advance lines were tested for yield, disease resistance, storage abilityand nutritional quality and the new accessions in the seedling trial were evaluated for several different desiarable traits. This report presents the result of these trials. The result of the elite selections over a 4 year period showed that the best of the four years was 2003 followed by 2002 and 2005. The elite selections will be indexed for multi-location trials. Several desirable traits, which are of interest for molecular genetic studies were identified in the seedling trial. Non-storage root forming types will be of particular interest for the study of up or down-regulated genes that could be associated with storage root formation. Advance lines, consisting of orange-flesh and white-flesh accessions, were evaluated during the 2004 and 2005 growing seasons at George Washington Carver Agricultural Experiment Station. The check lines were B94 14G2 obtained from North Carolina State University breeding program. All the highest yielders were those derived from clean seed production. Graduate, and high school summer students participated in the evaluation of the different varieties and trials for various characteristics of interest. The total marketable yield result and distribution by class, Us No.1, Canners and Jumbo, as percent of total yield, was used for evaluation. The additional features for which the seedling lines were evaluated were shape, flesh color, skin color, disease resistance, number of storage roots. Based on this criteria, several hundred lines were selected for the coming season preliminary trial. Three of the best selections which have been virus indexed will enter into large-scale multiplication. Six newly introduced indexed, disease free lines from Guyana and Guam have been released from quarantine and are being maintained in tissue culture at the biotechnology laboratory at Tuskegee University for preservation and for multiplication. These will be increased and evaluated in the coming season.

Impacts
Sweetpotato variety released for breeders and researchers. Improved technique is used for nutritional content evaluation of the breeding lines. Release of nutritionally improved types consisting of high quality antioxidants will result in increased diversity of affordable source of nutriments for consumers.

Publications

• No publications reported this period

Progress 10/01/03 to 09/30/04

Outputs
During the 2003 and 2004 growing season, breeding lines were evaluated for yield, disease resistance and storage ability. This report presents the result of the advance yield trial. The result of the elite selections over a 3 year period showed that the best of the three years was 2003 and 2004 was the worst. This could be attributed to hurricane Ivan, which brought heavy rains and wind. There was also a heavy infestation of leaf hoppers. The best selections from here will be included in the poly-cross nursery for the recombination of desirable genes for priority traits. Advance lines, consisting of orange-flesh and white-flesh accessions, were evaluated during the 2003 and 2004 growing seasons at George Washington Carver Agricultural Experiment Station. The check lines were Beauregard from our previous production, and B94-14, which is a G2 cycle clone obtained from North Carolina. The total marketable yield result and distribution by class (US#1, Canners and Jumbo), as percent of total yield, was used for evaluation. The additional features for which the lines were evaluated are shape, dry matter content, storage ability, nutritional content and disease resistance. Three of the best selections have been indexed for virus. Two indexed, disease free lines (NC-C58 and J6-66) were received and are being maintained in tissue culture at the biotechnology lab for preservation and for multiplication. Some of these are growing in isolation for experiments in controlled environment. One introduced line from Guyana, selected for flavor and rapid establishment was released from quarantine. In the coming season, this line will enter the preliminary yield trial to be grown on a small scale for characterization. In addition, selected lines from our elite lines will be evaluated for nutritional content and natural food colorant characteristics using advanced rapid techniques in the nutrition lab. The best new selections will be indexed for multi-location testing.

Impacts
Increase the diversity of sweetpotato types available to different ethnic groups with varied preference. This will result in better market opportunities and higher income for sweetpotato farmers in Alabama.

Publications

• No publications reported this period

Progress 10/01/02 to 09/30/03

Outputs
Using Agrobacterium gene transfer system, adapted sweetpotato varieties were transformed with dnp-2 gene, an aritifical storage protein gene rich in essential amino acids. Resulting transgenic plants were confirmed for the presence of the transgene and expression of the transgenic protein. Further studies are in progress in the greenhouse to determine protein content and quality and nutritional parameters. The transgenic plants will be grown in the field later this summer to determine field performance. In another study twenty elite sweetpotato breeding lines were evaluated for yield, disease resistance and storageability. Five high yielding and disease resistance lines were selected for further testing and inclusion in the ploy-cross nursery for recombination of desirable genes and traits.

Impacts
Development of nutritionally enhanced high yielding and disease resistant adaptable sweetpotato cultivars will result in high income for sweetpotato farmers in the country.

Publications

• No publications reported this period