A simple and fast method for measuring low boiling point (LBP) volatile terpenoids in carrots (Daucus carota L.) was developed by using a direct headspace sampling technique. Seven LBP terpenoid compounds were separated with high sensitivity and consistency via gas chromatography. High boiling point terpenoids above terpinolene were not well characterizable. Standard compounds showed highly linear responses up to 10 μg.g-1, with a detection limit of 0.01 μg.g-1. We confirmed that high α- and β-pinene and/or total terpenoids contributed to harsh or oily flavors. Up to 40 samples can be analyzed in an 8-h day using this method, compared to 10 samples using previous methods.
Kil Sun Yoo, Leonard M. Pike, and Brian K. Hamilton
Kil Sun Yoo, Leonard M. Pike, and Brian K. Hamilton
Josefina Alcalá, Leonard M. Pike, and James J. Giovannoni
The relatively low evolution rate of the chloroplast DNA has made it an ideal tool to study evolutionary processes in plants above the species levels. However, recent studies have demonstrated that intraspecific variation in the chloroplast DNA is also common. This variation has provided useful insights into population level evolutionary processes. The polymerase chain reaction and sequencing of a noncoding chloroplast region used to classify onion lines for cytoplasmic type facilitated the identification of one sterile and two normal plastome variants in onion (Allium cepa L.). Sequence comparison revealed that differences between plastome variants included the presence of single-nucleotide polymorphisms associated with cytoplasmic type and variable numbers of tandem repeats, possibly resulting from slipped-strand mispairing. Our observations support the use of chloroplast-specific markers to assist in the selection of specific cytoplasmic types, suggest the potential to facilitate genotype determination, and demonstrate the presence of additional variation within cytoplasm type which gives insight into plastome evolution and may facilitate more accurate genotyping and selection.
Bhimanagouda S. Patil, Leonard M. Pike, and Kil Sun Yoo
The aglycone, or free quercetin, and total quercetin content of 75 cultivars and selections was analyzed by reverse-phase high-performance liquid chromatography. Quercetin glycosides were hydrolyzed into aglycones. Total quercetin content in yellow, pink, and red onions varied from 54 to 286 mg·kg-1 fresh weight in different onion entries grown during 1992. White onions contained trace amounts of total quercetin. Free quercetin content in all the onions was low (< 0.4 mg·kg-1) except in `20272-G' (12.5 mg·kg-1 fresh weight). Bulbs stored at 5, 24, and 30C and controlled atmosphere (CA) for 0,1,2,3,4, and 5 months showed a most marked change in total quercetin content at 24C compared to other treatments, with a rise in mid-storage followed by a drop. Storage at 5 and 30C also demonstrated a similar change. However, total quercetin content did not vary significantly in bulbs stored at CA for 5 months. We conclude that genetic and storage factors affect quercetin content on onions.
Soon O. Park*, Kevin M. Crosby, Jonathan W. Sinclair, Kilsun Yoo, and Leonard M. Pike
Sucrose, fructose, total sugars and soluble solids are major factors in determining mature melon fruit sweetness. Bulked segregant analysis was utilized to detect RAPD markers associated with QTL for sucrose, total sugars and soluble solids in an F2 population from the ananas melon cross of Deltex (high sugars) × TGR1551 (low sugars). Sucrose, glucose, fructose and total sugar data were obtained from 108 F2 plants by means of HPLC. Clear separations for sucrose, total sugars and soluble solids between Deltex and TGR1551 were observed, whereas slight differences for glucose and fructose were found. Continuous distributions for sucrose, total sugars and soluble solids were observed in the F2 population indicating quantitative inheritance for the sweetness traits. A significant negative correlation was observed between sucrose and glucose (r = -25) or fructose (r = -0.31). A significant positive correlation was noted between sucrose and total sugars (r = 0.80) or soluble solids (r = 0.64). Three low and high DNA bulk pairs for sucrose, total sugars and soluble solids were developed. A total of 360 primers were used to simultaneously screen between the low and high bulks, and between Deltex and TGR1551. Sixty-eight RAPD markers were polymorphic for the low and high bulks. Of the 68 markers, 24 were found to be significantly associated with sucrose, total sugars or soluble solids on the basis of single-factor ANOVA. Marker OM15.550 was consistently associated with QTL affecting sucrose, glucose, fructose, total sugars and soluble solids, and accounted for 7% to 25% of the phenotypic variation for the traits. These markers associated with the sugar synthesis QTL could be useful to transfer these genes into a low sugar cultivar to enhance the fruit sweetness.
Shibu M. Poulose*, Jennifer S. Brodbelt, Leonard M. Pike, and Bhimanagouda S. Patil
Limonoids, chemically related triterpinoids predominantly found in citrus and neem relatives, are known to play a pivotal role in the prevention of different types of cancer and cardiovascular diseases. Since the concentrations of these compounds are low in the plant tissues, the isolation of pure compounds is the limiting factor for the individual activity studies in animal models. In this study, combinations of chromatographic techniques were used to isolate limonoid aglycones and limonoid glucosides from citrus byproducts such as seeds and molasses. The compounds were initially extracted with different polar solvents and the concentrated extracts were passed through a series of adsorbent resin (SP-70) and ion-exchange resins (WA-30, Dowex-50, Q-sepharose) to remove further impurities. The use of increasing ionic strength of NaCl from 0 to 800 mm to release the exchanged compounds from the ion exchange columns further separated the limonoids from flavonoids, which was confirmed through TLC, UV, and analytical HPLC methods. Individual compounds were further purified using flash chromatography and preparative HPLC methods and identified by using LC-MS analysis. Direct crystallization of limonin resulted in a 17% increase in the yield as compared to the previously reported methods. The results suggest that application of these purification methods are useful for the bulk purification of compounds in order to further investigate their biological activity.
Juan Pablo Arce-Ochoa, Frank Dainello, Leonard M. Pike, and David Drews
`Pavo', a commercially grown, virus-susceptible squash (Cucurbita pepo L.) hybrid, and two experimental virus-resistant transgenic squash hybrids, XPH-1719 and XPH-1739, were tested for field performance. The two transgenic squash hybrids possess the desired fruit and plant characteristics of their parental line, `Pavo', plus resistance to zucchini yellow mosaic virus and watermelon mosaic virus 2 (XPH-1719), and resistance to zucchini yellow mosaic virus, watermelon mosaic virus 2, and cucumber mosaic virus (XPH-1739). Percent emergence and days to flowering were similar among the three hybrids. XPH-1719 and XPH-1739 were equally effective in producing a high percentage of quality marketable fruit and yields with 90% and 13,800 kg·ha–1 and 87% and 16,500 kg·ha–1, respectively. XPH-1719 and XPH-1739 demonstrated their outstanding virus resistance over `Pavo' by producing only 3% and 14% symptomatic plants, respectively, compared to 53% for `Pavo'. They also produced the lowest percentage of infected fruit, 0% and 7%, respectively, with `Pavo' at 26%.
Juan Pablo Arce-Ochoa, Frank Dainello, Leonard M. Pike, Hector Quemada, and David Drews
Two of Asgrow's experimental virus resistant transgenic lines, XPH-1719 and XPH-1739, and their parental line, Pavo, a commercially grown virus susceptible hybrid, were tested for field performance at the Texas A&M University Experimental Farm in the summer of 1993. The two transgenic squash lines possessed the desired fruit and plant characteristics of Pavo plus resistance to ZYMV and WMV2 (XPH-1719), and resistance to ZYMV, WMV2 and CMV (XPH-1739). Under the conditions of this test it was determined that the two transgenic hybrids, were equally effective in producing high quality marketable fruits/ha with 89.64 % and 86.84 % respectively and marketable yields with 13,762 kg/ha and 16,525 kg/ha respectively. XPH-1719 and XPH-1739 also demonstrated their outstanding virus resistance by producing only 3.44% and 14.35% symptomatic plants/ha, and 0.00% and 7.17% infected fruits/ha respectively compared to 53.55% symptomatic Pavo plants/ha, and 25.73% infected Pavo fruits/ha.
Brian K. Hamilton, Leonard M. Pike, Alton N. Sparks, David A. Bender, and Richard W. Jones
Thrips are the major insect pest of onions grown in South Texas. Four cultivars, `IPA-3', `TG1015Y', `1664' (glossy control), and `1900B' (waxy control), were grown in a split-plot design with insecticide sprayed or nonsprayed treatments as the main plots and cultivar as the subplots. The experiment was conducted at the Texas Agricultural Experiment Station, Weslaco, Texas, in the 1995-96 season. The objectives of the study were to compare `IPA-3' and `TG1015Y' for thrips resistance and evaluate possible resistance mechanisms that may be present in `IPA-3'. The average number of thrips per plant and leaf damage rating were significantly higher for `TG1015Y', indicating that some resistance is present in `IPA-3'. However, there were no significant differences in yield between the two cultivars. A comparison of leaf wax characteristics indicated no significant difference between `TG1015Y' and `IPA-3' using gravimetric or gas chromatography techniques. However, scanning electron micrographs of `TG1015Y' leaves appeared more similar to `1900B' and `IPA-3' appeared more similar to `1664'. The insecticide spray treatment had significantly fewer thrips, less damage, and higher yield than the nonsprayed treatment.
Ryan L. Walker, Sunggil Kim, Javier F. Betran, Kilsun Yoo, and Leonard M. Pike
Onions suffer from severe inbreeding depression, which has inhibited the development of homozygous inbred lines in breeding programs. The creation of doubled haploid (DH) lines in onion provides a unique opportunity to evaluate the utility of such lines as parents in a breeding program. For this purpose, two diallele cross experiments were conducted. The first consisted of a six-parent diallele cross using six DH lines developed at Texas A&M University. The second, a four-parent diallele cross performed with two DH lines and two inbred lines from the breeding program. Bulbs from the various crosses were evaluated for diameter, height, centers/bulb, ring thickness, number of rings/bulb, bulb weight, soluble solids content, and pungency. For some traits, general combining ability (GCA) effects explained most of the variation. However, for other traits, specific combining ability (SCA) effects predominated. For all traits, GCA and SCA were always larger than the reciprocal effects (divided into maternal and nonmaternal components). The GCA and SCA effects show an inverse correlation between the number of centers/bulb and ring thickness.