Influence of Nitrogen Rate and Sampling Date on Soil Analysis Values of Highbush Blueberries

Three studies were conducted on nitrogen (N) fertilization effects on soil of highbush blueberries in Arkansas. Objectives included: 1) determination of varying N rate effects on the standard soil analysis variables, 2) determination of date of soil sampling effects on soil analyses, 3) evaluation of the interactions of N rate and time of sampling, and 4) determination of changes in soil content over years. This research was done in two of the more important highbush blueberry production areas in Arkansas: the Arkansas River Valley where blueberries are grown on sandy loam soils, and northwest Arkansas where production is more common on silt loam soils. This information provides greater insight into the soil dynamics of highbush blueberry plantings in Arkansas and can be used to increase precision of fertility and other soil property recommendations provided to growers

Effect of Media Constituents on In Vitro Culturing of Cowpea (Vigna unguiculata) Shoot Tip and Leaf Disk Explants

Cowpea is an important legume food crop that is commonly grown in Arkansas and numerous other southern states. The application of biotechnological approaches for the improvement of U.S. cowpea genotypes is currently not possible due to the lack of a regeneration and transformation system. Therefore, the first priority of our research efforts is the development of a plant regeneration system that will facilitate plant transformation studies. In an effort to optimize the media requirements for tissue culturing cowpea, we evaluated the in vitro response of shoot tip and leaf disk explants to various levels of Murashige and Skoog (MS) macro and micro nutrients, vitamins, and iron. One commercial cultivar, Early Scarlet (formerly 91-135), and one advanced Arkansas breeding line, 91-245, were used as tissue sources. Shoot tips were cultured on media augmented with 5 mg/L kinetin and 0.01 mg/L naphthaleneacetic acid (NAA). Multiple shoots were produced from shoot tips, and these grew well when cultured on full strength MS. However, increasing MS levels to 1.5 times the standard concentration induced taller shoots from both genotypes. Leaf disks were cultured on MS media supplemented with 0.5 mg/L benzylaminopurine (BAP) and 1mg/L 2,4 dichlorophenoxyacetic acid (2,4-D). Callus proliferation was greatest on media containing full strength MS supplemented with 0.5 mg/L BAP and 1 mg/L 2,4-D. The effects of the media constituents were genotype dependent, with Early Scarlet generally producing larger shoots and greater amounts of calli. The results obtained from this study demonstrate that the plant genotype and growth hormones have the greatest influence on cowpea growth in vitro. Therefore, in developing a cowpea regeneration system, it will be necessary to test numerous genotypes in combination with various growth regulators. To improve regeneration frequencies the media components can be optimized for the genotypes of interest