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Calcium (Ca) is an essential plant nutrient, required for signaling, cell wall fortification and growth and development. Calcium deficiency (Ca-deficiency) in maize causes leaf tip rot and a so-called “bull-whipping” or “buggy-whipping” phenotype. Seedlings of the maize line B73 displayed these Ca-deficiency-like symptoms when grown in the greenhouse with excess fertilizer during the winter months, while seedlings of the Mo17 maize line did not display these symptoms under the same conditions. These differential phenotypes could be recapitulated in ‘mini-hydroponic’ systems in the laboratory in which high ammonium, but not nitrate, levels induced the symptoms in B73 but not Mo17 seedlings. Consistent with this phenotype being caused by Ca-deficiency, addition of Ca2+ completely relieved the symptoms. These data suggest that ammonium reduces the seedling’s ability to absorb calcium, which causes the Ca-deficiency phenotype, and that this trait varies among genotypes. A recombinant inbred line (RIL) population derived from a B73 x Mo17 cross was used to map quantitative trait loci (QTL) associated with the Ca-deficiency phenotype. QTL associated with variation in susceptibility to Ca-deficiency were detected on chromosomes 1, 2, 3, 6 which explained between 3.30–9.94% of the observed variation. Several genes predicted to bind or be activated by calcium map to these QTL on chromosome 1, 2, 6. These results describe for the first time the genetics of Ca-deficiency symptoms in maize and in plants in general.

As bermudagrass (Cynodon dactylon (L.) Pers.) transitions from winter dormancy to active growth in spring, nitrogen is essential for new tissue growth. We examined the relative contributions of internally stored nitrogen and that taken up by preexisting and newly produced roots. Field-collected dormant bermudagrass was transferred to a nutrient solution culture system in a growth chamber. Cultures were provided either a non-nitrogen-containing solution or one amended with nitrate labeled with the 15N isotope of nitrogen, which allowed tracking of endogenous and exogenous N pools in all tissues as growth began. Nitrogen in stolon internodes was the largest N source for early growth. Though mass increased at the same rate in both N treatments over 3 weeks of growth, the unfertilized treatment showed early signs of nitrogen deficiency: low tissue N, slowed leaf elongation, and fewer but longer roots. Preexisting roots were active in absorption almost immediately; new roots were produced quickly and h...

Limitations in water availability for irrigation due to drought and water-use regulations necessitate accurate approaches to estimate water use. An energy balance approach is commonly used that is inherently empirical and requires an ill-defined coefficient. An alternative is to use a relationship based on vapor pressure deficit (VPD) and plant growth to predict plant transpiration rate. This study was undertaken to evaluate these approaches for tall fescue (Festuca arundinacea Schreb.). Experiments examined differences in water loss of tall fescue plants when grown in three temperatures with varying vapor pressure deficit (VPD), and with treatments of low nutrition and of growth regulator trinexapac-ethyl, which depressed growth. Within a temperature, the low-nutrition and growth-regulator treatments greatly affected clipping mass, however water loss remained similar. In hydroponic experiments, treatments altering clipping mass did not necessarily change total plant growth. Hence, a challenge to using whole-plant growth for estimating transpiration of this grass is to accurately determine growth only from clipping data. Transpiration was positively correlated with VPD, especially within each temperature, but there were indications that the higher temperature treatments caused decreased plant control over transpiration. The instability of physiological control over transpiration highlights the potential limitations of both equations in estimating transpiration rates.

Excessive organic matter (OM) accumulation in creeping bentgrass (Agrostis palustris Huds.) putting greens, and its restriction of permeability, is one of the most difficult problems in turfgrass management. In this transition zone study, we characterized temporal and spatial aspects of OM accumulation, in an attempt to assess the effectiveness of management and to begin to uncover the processes controlling C sequestration. Root zone samples were collected from sand-based putting greens at 49 golf courses of various ages, generating 212 individual observations. Organic matter accumulated hyperbolically over time in the top 2.5 cm; apparent critical levels of 40 g kg -1 were exceeded within 5 yr. At a depth of 2.5 to 7.6 cm, accumulation was much slower and linear over time, and critical levels were not reached even after 20 yr. Oxygen levels were never depressed more than 15%, indicating that intensive management of the upper soil profile was successfully allowing gas exchange into the root zone. Carbon accumulated in the soil profile hyperbolically, reflecting changes in the large OM pool near the soil surface. The sequestration rate of 59 g m -2 yr -1 over 25 yr was less than that observed by others examining soil under bentgrass greens in different environments. The evidence indicates that OM and C accumulation are strongly influenced by increasing microbial degradation rates as turfgrass systems age.

The noxious weed Benghal dayflower has become a severely troublesome agricultural weed in Georgia in the southeastern Unite States, and there are indications that it is moving northward. Benghal dayflower is glyphosate tolerant and possesses a high degree of reproductive elasticity, making it a formidable threat in many crop systems. The purpose of these experiments was to develop the first temperature response profiles for Benghal dayflower, and use them to evaluate whether temperature might limit its northward invasion into North Carolina and adjacent states on the U.S. east coast. Experiments focused on vegetative and early reproductive growth, stages considered crucial for establishment and competitiveness. Exposure to a range of aerial temperatures revealed that Benghal dayflower growth and production of aerial and subterranean reproductive structures were maximized at 30 C, with sharp declines occurring at cooler temperatures. When exposed to differing root temperatures in hydroponics, with a constant aerial temperature, Benghal dayflower growth did not show the same cool temperature sensitivity, but reproductive performance declined when temperatures decreased below about 29 C. The root temperature responses of several other weed species known to thrive in the climate of this geographic area also were determined. Growth of sicklepod, hemp sesbania, and jimsonweed was more sensitive than Benghal dayflower to cool temperatures, whereas the growth response of velvetleaf was similar. Based on the comparison of the Benghal dayflower temperature responses in controlled environments to (1) seasonal air and soil temperatures in the field, and (2) the temperature responses of agronomic weeds known to thrive in the region, it is concluded that cool temperatures will not restrain the northward spread of Benghal dayflower into North Carolina.