Interest in the health benefits of vegetables prompted an investigation of the levels of carotenoids in commercial varieties and UA breeding lines of spinach. Plant carotenoids perform a critical function as antioxidants, providing protection against a variety of reactive oxygen species generated primarily during photosynthesis. When ingested by humans, these compounds maintain their antioxidant activities and are receiving considerable attention in relation to multiple health benefits, including cancer prevention. While the best-known and most-studied carotenoid is beta-carotene, other carotenoids are now receiving attention due to their higher antioxidant activity compared to beta-carotene. Most dark-green leafy vegetables, such as spinach and kale, are relatively high in carotenoids, especially lutein. In this study, significant differences in average content of both lutein and beta-carotene were found between genetic lines of spinach. Some lines exhibited considerable variation between plants, while others were highly uniform. There was a very high correlation (r 2 = 0.96) between lutein content and betacarotene content. The significant difference between spinach lines suggests that improvement of general carotenoid antioxidants and lutein could be obtained through a breeding program.
J.A. Kirkpatrick, J.B. Murphy, and T.E. Morelock
T.E. Morelock, J.C. Correll, and L.P. Brandenberger
Downy mildew (Blue mold) is probably the most common spinach disease in most parts of the world, and it can be a problem in the mid-South. Frequently, other diseases such as white rust and fusarium cause major crop loss. The Arkansas breeding program was initiated 25 years ago to address white rust and fusarium, as well as other diseases that destroy spinach crops. Since single gene resistance is not available for most spinach diseases, it was necessary to utilize polygenic resistance to develop varieties that are resistant to most of the common spinach diseases that occur in the Arkansas River Valley of Arkansas and Oklahoma. Highly resistant genotypes have been developed by using disease nurseries and field screening, so frequent selections are made based on the reaction to 3-4 diseases.
Justin Butcher, T.E. Morelock, and D.R. Williams
Fresh-shelled southernpeas [Vignaunguiculata(L.) Walp.] is a popular vegetable. Postharvest storage of fresh-shelled peas is a crucial step in the production process. Farmers strive to produce a product that is high in quality and freshness with appropriate texture and appealing color. Improper storage and handling of southernpeas will result in deterioration. In an effort to prevent potential losses of southernpeas, this study was conducted to determine the best method to ship and store shelled peas. Five southernpea varieties: `Early Acre', `Early Scarlet', `Excel Select', `Coronet', and `Arkansas Blackeye #1' were planted in a randomized block design at the University of Arkansas. Twelve mature green pods of each variety were subjected to a sweated and unsweated treatment and then shelled. After shelling, seed were subjected to four different environmental conditions, and each treatment was evaluated for changes in physical appearance. Objectives of the study were to determine the best variety and environmental condition to maintain a quality marketable product. The study showed that a refrigerated environment at or near 3 to 5 °C allowed the crop to be stored for up to 2 weeks. It also appeared that sweating assisted with the shelling process and maintained appearance of each variety longer.
L.A. Wasilwa, T.E. Morelock, and J.C. Correll
Anthracnose of cucurbits, caused by Colletotrichum orbiculare, is composed of three races (race 1, 2, and 2B). The inheritance of race 1 in cucumber is reported to be controlled by a single recessive gene. Although the mode of inheritance to race 2 in cucumber has not been determined, it has been suggested that is quantitatively inherited. Four cucumber cultivars, H19 from two sources [the commercial seed (P1) and the breeders seed (P2)], Pixie (P3), and Marketer (P4), that were considered highly resistant, moderately resistant and highly susceptible, respectively, to race 2 were used as the parents in this study. Crosses between resistant × susceptible and resistant × moderately resistant were made. Some reciprocal crosses also were made. The F1 progeny were then evaluated for resistance to race 2 in a cotyledon assay. Disease severity was assessed 8 days after inoculation using a disease rating scale of 0–7, whereby 0 = healthy plant and 7 = 100% chlorosis or necrosis. All progeny from P1 × P1 were highly resistant (disease severity 19 < 2.5); P2 × P2 and P3 × P3 were highly moderately resistant (disease severity 2.6–4.9); and all P4 × P4 progeny were highly susceptible (disease severity > 5.0) to race 2. All F1 progeny showed a continuum of disease ratings from highly resistant to moderately resistant to race 2. The disease ratings of the F1 progeny would indicate that resistance to race 2 is controlled by multiple genes.
T.E. Morelock, D.R. Motes, and A.R. Gonzalez
Southernpea (Vigna unguiculata) is an important crop in the southern United States. The Arkansas Agricultural Experiment Station announces the release of three varieties. `Excel' produces a compact bush plant, from 45–60 cm tall with no basal runners. Pods are deep purple, 20–25 cm long and shell easily at the green mature stage. Flowering and fruiting are concentrated, with the pods produced at the top of the plant on medium-length peduncles. Seed has a bright pinkeye and is similar in size to pinkeye purple hull BVR but matures 3–4 days earlier. `Early Scarlet' produces a medium sized plant, from 60–75 cm tall with no basal runners. Pods are light red, 20–25 cm long and shell easily at the green mature stage. Flowering and fruiting are concentrated at the top of the plant with pods produced on medium-length peduncles. Seed has a light pinkeye and is similar in size to `Pinkeye Purple Hull BVR' but matures 2–3 days earlier. `Arkansas Blackeye #1' produces a bush plant, from 50–65 cm tall with no basal runners. The pods are silver, 20–25 cm long and shell easily. Flowering and fruiting are concentrated with the pods produced in the top of the plant on medium-length peduncles. Seed has a distinct medium-sized blackeye and the seed are very similar in size, type and eye pattern to `California #5 Blackeye'. Maturity is normally 2–3 days earlier than `Pinkeye Purple Hull BVR'.
Hallie G. Dodson, J.B. Murphy, and T.E. Morelock
Anthocyanins are naturally occurring plant pigments that are classified as flavonoids. Anthocyanins have important antioxidant properties which may help in prevention of cancer, arthritis, and cardiovascular disease. Finding common sources and possibly increasing levels of anthocyanins in food could be important to human health. This research project determined amount and type of anthocyanins in 16 cultivars and breeding lines of cowpeas (Vigna unguiculata). The information obtained from this research project will be used to improve anthocyanin content of cowpeas by breeding. Of the 16 cultivars and breeding lines, only a black cowpea breeding line, 95-356, contained measurable levels of 3 types of anthocyanins: delphinidin, peonidin, and an unknown anthocyanin. Total anthocyanin content was 0.00242 mg·g–1, which is equal to 0.21 mg per ½-cup serving. In another study with 95-356 Rabi A. Musah, found a total anthocyanin content of 121.26 mg per serving and also found three other types of anthocyanins. The difference in the studies could be explained by the storage time of two weeks after the anthocyanins were extracted, but before they were eluded in this study. Additional studies are needed to determine if cowpeas can provide anthocyanin levels comparable to other fruits and vegetables.
L.P. Brandenberger, T.E. Morelock, and J.C. Correll
Spinach germplasm (707 accessions) from collections from six countries were screened for resistance to race 4 of the downy mildew pathogen Peronospora farinosa f. sp. spinaciae; these collections contained germplasm that originated from 41 countries. The predominant species examined was Spinacia oleracea L., however, eight accessions of S. turkestanica Iljin and two accessions of S. tetrandra Stev. were also tested. About 40 seedlings of each accession were inoculated. The cultivar St. Helens was included as a susceptible control in each test. The majority of accessions tested (>98%) were susceptible to race 4. Nine accessions exhibited some resistance to race 4 (9% to 38% of the seedlings within an accession were resistant), and two accessions, CGNO 9546 and SPI 82/87, exhibited a high level of resistance (60% and 80% resistant, respectively). Resistance identified in several of the accessions in this study may be useful for breeding for race 4 resistance.
J.M. Al-Khayri, F.H. Huang, T.E. Morelock, and H.T. Zhang
The objective of this study was to determine the efficacy of Agrobacterium tumefaciens in transforming spinach (Spinacia oleracea L.) callus. Callus was induced from leaf disks of `Baker' on Murashige and Skoog (MS) medium supplemented with 2 mg L-1 kinetin and 0.5 mg L-1 2,4-D. Callus was cut into 2-mm pieces, and 0.5 g of callus was placed in each 250-ml flask which contained 20 ml of MS liquid medium. The suspension cultures were inoculated with 100 μl of an overnight culture of A. tumefaciens harboring pMON 9749 (provided by S. Rogers, Monsanto Co., St. Louis), a plasmid cointegrated with kanamycin resistance and β -glucuronidase (GUS) genes. After coculturing for 2 days at 22C with shaking at 100 rpm, the medium was replaced with selection medium containing (in μg/ml) 75 kanamycin, 100 cefotaxime, and 200 carbenicillin and maintained for 3 weeks. Transient expression of GUS gene in transformed cells was detected with X-glu assay. This method resulted in a high level of transformation and provides the first report of transformation in spinach. This study was funded by a grant (92-B-32) from the Arkansas Science & Technology Authority.
J.M. Al-Khayri, F.H. Huang, T.E. Morelock, and T.A. Busharar
S.M. Hum-Musser, T.E. Morelock, J.B. Murphy, and R.L. Henry
Seed germination of spinach (Spinacia oleracea L.) is partially inhibited by a high germination temperature (35 °C). Tolerance of high germination temperatures varies widely depending on the variety used. We ascertained that seed germination of these spinach varieties was thermoinhibited at 35 °C and secondary dormancy was not induced as seeds germinated when transferred to optimum germination conditions (20 °C). Treatment with 99% oxygen and 10 ppm kinetin significantly increased germination of thermoinhibited varieties at 35 °C. During heat stress, all organisms produce heat shock proteins (HSPs), which may function as molecular chaperons, are possibly required for the development of thermotolerance, and may be crucial for cell survival during heat stress. Western blotting of SDS-PAGE gels using antibodies to various heat shock proteins indicated that spinach varieties with the highest degree of thermotolerance have higher levels of HSP expression than varieties with the lowest degree of thermotolerance during germination. These results suggest that thermotolerance could be further improved, either through a breeding program or possibly by genetic engineering.