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A.Q. Villordon, J.W. Franklin, and W. McLemore

This report summarizes the results of irrigation studies conducted from 2000 to 2005 at the Sweet Potato Research Station, Chase, La. These studies investigated the role of various scheduling methods, soil moisture measurement devices, and irrigation delivery methods in sweetpotato production. The studies indicate that 15 to 20 inches of total rainfall and supplemental irrigation is required to produce 400 to 525 bu/acre of US#1 storage roots in Beauregard. Supplemental irrigation can be scheduled based on this benchmark, potentially reducing over-irrigation during dry periods. We have also found that during dry periods, irrigating every furrow can bring about 50% difference in US#1 yield vs. supplying irrigation to alternate furrows. During growing seasons characterized by optimum rainfall patterns, we did not detect any response in US#1 yield to various irrigation treatments. We evaluated several moisture measurement devices including granular matrix sensors, evaporation pan, time domain reflectometry (TDR)-based instrument, and tensiometers. We found the TDR-based device easy to use and convenient in terms of its portability. Based on studies conducted in 2001 and 2002, this device demonstrated potential as a management tool in sweetpotato production. For instance, a management allowable deficit (MAD) of 25% available moisture as measured using the TDR-based device can potentially result in the same yield as weekly irrigation and a MAD of 50% available moisture. When used properly, irrigation scheduling can reduce over-irrigation and contribute to overall efficiency in the use of production inputs.

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A.Q. Villordon, C.A. Clark, R.A. Valverde, R.L. Jarret, and D.R. LaBonte

Previous work by our group has detected the presence of a heterogeneous population of Ty1-copia-like reverse transcriptase retrotransposon sequences in the sweetpotato genome. Recently, we detected the presence of putatively active Ty1-copia-like reverse transcriptase sequences from a virus-infected `Beauregard' sweetpotato clone. In the current study, we report the differential detection of putatively stress-activated sequences in clones from seedling 91-189. The clones were infected with different combinations of virus isolates followed by extraction of leaf RNA samples at three sampling dates (weeks 2, 4, and 6) after inoculation. After repeated DNAse treatments to eliminate contaminating DNA, the RNA samples were subjected to first strand cDNA synthesis using random decamer primers followed by PCR analysis utilizing Ty1-copia reverse transcriptase-specific primers. Through this approach, we detected amplified fragments within the expected size range (280-300 bp) from clones infected with isolates of sweetpotato leaf curl (SPLC) and feathery mottle viruses (FMV) (week 2 and 6) and FMV (week 4). We were unable to detect PCR products from the noninfected clones or the other infected samples. The data suggests that specific viruses may be involved in the expression of these Ty1-copia-related reverse transcriptase sequences. It also appears that sampling at various dates is necessary to detect putative activity over time. This preliminary information is essential before proceeding to the construction and screening of cDNA libraries to isolate and fully characterize the putatively active sweetpotato Ty1-copia-like retrotransposon sequences. Through the partial or complete characterization of sweetpotato Ty1-copia elements, sequences that correspond to cis-regulatory element(s) can be identified and further studied for their roles in responding to specific stress factors.

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Don R. La Bonte, Arthur Q. Villordon, Christopher A. Clark, Paul W. Wilson, and C. Scott Stoddard

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Don R. La Bonte, Paul W. Wilson, Arthur Q. Villordon, and Christopher A. Clark

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Christopher A. Clark, Tara P. Smith, Donald M. Ferrin, and Arthur Q. Villordon

Because sweetpotato (Ipomoea batatas) is vegetatively propagated, viruses and mutations can accumulate readily, which can lead to cultivar decline. Sweetpotato foundation seed programs in the United States maintain the integrity of commercial seed stock by providing virus-tested (VT) foundation seed to commercial producers. A survey was conducted in Louisiana from 2007 to 2009 to examine the performance and quality of the foundation seed after it had been integrated into commercial sweetpotato operations. G1 seed [grown 1 year after virus therapy in the foundation seed production field at the Sweet Potato Research Station, Louisiana State University Agricultural Center (LSU AgCenter), at Chase, LA] was used as a reference to compare the yield and virus incidence of growers' generation 2 (G2) and generation 3 (G3) seed roots (grown in the growers' seed production fields 1 or 2 years following the year of foundation seed production). Although yields of plants grown from G2 and G3 seed were 86.3% and 86.1% for U.S. No. 1 and 83.3% and 86.0% for total marketable, respectively, compared with the yields from G1 seed, they were not significantly different. Yield and virus incidence data suggest that seed quality may vary from year to year and from location to location. Results from this study suggest that producers are realizing yield benefits by incorporating VT foundation seed into their production schemes, but further benefits could be attained if ways to reduce re-infection with viruses can be found.

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A.Q. Villordon, J.W. Franklin, T.P. Talbot, J.M. Cannon, and W. McLemore

Transplant survivability is important in achieving consistent economic yields in sweetpotatoes. We are conducting a series of studies that investigate the role of transplant quality in sweetpotato yield. In 2004, in addition to investigating the role of transplant diameter, we also investigated the influence of transplant water (about 6 oz per hill) on stand and yield. Even though rainfall events were regular and mean rainfall during the growing season was above average for the year, there was a significant increase in US#1 yield (23.57%) among plots derived from thick transplants (≥0.25 inches, no transplant water) versus thin transplants (no transplant water). There was a 44.16% increase in US #1 yield among plots planted with thick transplants vs. plots with thin transplants (with transplant water). In 2005, there was also a significant difference (14%) in US #1 yield between plots planted to thick and thin transplants, respectively. This indicates the possible role of transplant thickness on stand and yield. We also investigated the relationship between root spacing during bedding on cutting diameter as well as a farmer's practice of planting two transplants per hill. In both preliminary tests, no differences among the treatments were observed. Additional studies are planned to investigate the possible use of chemical-based treatments to enhance transplant thickness and survivability.

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Don R. La Bonte, Christopher A. Clark, Tara P. Smith, and Arthur Q. Villordon

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Don R. La Bonte, Christopher A. Clark, Tara P. Smith, Arthur Q. Villordon, and C. Scott Stoddard

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Don R. La Bonte, Christopher A. Clark, Tara P. Smith, and Arthur Q. Villordon

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D.R. La Bonte, A.Q. Villordon, J.R. Schultheis, and D.W. Monks

The influence of a black polyethylene tunnel cover (BTC) was evaluated for its effect on quantity and quality of sweetpotato [Ipomoea batatas (L.) Lam.] transplants in plant beds in Louisiana and North Carolina. Use of BTC increased production of `Beauregard' transplants from 63% to 553% in comparison with the bare ground control. `Jewel' was less responsive; BTC treatments increased transplant production by at least 48% in Louisiana over the bare ground control, but no increase was observed in North Carolina. Individual transplant weight was at least 34% less in BTC treatments than in the control. The first harvest of cuttings in BTC beds was at least 14 days prior to that in control beds. Transplant quality was assessed as yield of storage roots in repeated trials that extended throughout the normal growing season. Yield of storage roots was not affected by BTC in early season plantings, but was frequently lower for BTC treatment transplants in middle and late season plantings. We therefore do not recommend this method as a means of increasing sweetpotato plant production from bedded roots.