Successful commercial pecan [Carya illinoinensis (Wangenh.) K. Koch] production relies on mitigation of alternate bearing, which is a function of pistillate flower production. Mechanisms of floral initiation in pecan are not well understood. Our objective was to assess the impact of select plant growth regulators (PGRs) on return bloom for commercial application in pecan trees grown in the Southwestern United States. A 2-year study evaluated effects of ethephon, aminoethoxyvinylglycine (AVG), and gibberellin GA3 (GA3) on subsequent season return bloom in fruiting and nonfruiting pecan shoots. Cultivars used were mature Western and immature Western and Pawnee. Effects of PGRs on return bloom of nonfruiting shoots were different from fruiting shoots. As compared with untreated control, a GA3 treatment on fruiting shoots of mature ‘Western’ trees increased the number of flowers per new shoot by 125%. For nonfruiting shoots on the mature ‘Western’ trees, the number of flowers per new shoot decreased significantly by all PGR treatments and as much as 93% for AVG. In previously nonfruiting shoots on the immature ‘Western’ trees, a GA3 treatment reduced the number of flowers per new shoot in the next season by 88.2%. Results from immature ‘Pawnee’ shoots did not show statistically significant differences. The effects of these PGRs on subsequent season flowering in pecan are complex. This study suggests that PGRs can be used to increase or decrease cropload through effects on return bloom and therefore have potential uses for mitigating alternate bearing.
Marisa Y. Thompson, Jennifer Randall, Richard J. Heerema, and Dawn VanLeeuwen
Malik G. Al-Ajlouni, Dawn M. VanLeeuwen, and Rolston St. Hilaire
Linking an urban residential landscapes type to a specific landscape water budget is important to water resource management in a desert environment. Yet, no research that we are aware of has effectively associated a specific water budget with a quantitatively determined urban landscape type. The objective of this research was to determine whether a landscape water budget and residential urban landscape type could be related. We previously quantitatively classified urban residential landscapes in the desert environment of Las Cruces, NM, into hard-surface shade-structure, mulch, hard-surface, hard-surface-mulch, mulch tree, turf mulch, turf, tree mulch turf, and turf tree landscape types. In this study, we determined water budget, landscape coefficient, and the portion of the coverage of irrigated and nonirrigated elements for each landscape type. Landscape types in Las Cruces grouped into four distinct water budget groups: no-water, low-, moderate-, and high-water budget. Because of the heterogeneity of the coefficients for grass, plants, and water surfaces that constituted it, the landscape coefficient correlated weakly (r 2 = 0.3) with the water budget. Coverage of the irrigated elements correlated highly (r 2 = 0.95) with the water budget. Our results suggest that the coverage of irrigated elements in a desert urban landscape is a major driver of landscape water budgets.
Clare A. Bowen-O'Connor*, Rolston St. Hilaire, John Hubsten-berger, and Dawn VanLeeuwen
Bigtooth maple (Acer grandidentatum Nutt.) is indigenous to the southwestern United States. This species is not widely used in managed landscapes but the plant holds promise as a useful ornamental tree. Micropropagation might provide additional sources of selected genotypes for the nursery industry, but tissue culture has not been used successfully to propagate this species. We cultured double-node explants from greenhouse-grown, 2-year old seedlings of bigtooth maples that originated from Utah, Texas and New Mexico. Seedling height ranged from 15-90 cm. The shoot region was divided into three equal zones designated as terminal, intermediate and basal. Explants were selected from each of those zones. Explants were established on Murashige-Skoog (MS), Linsmaier-Skoog (LS), Woody Plant Medium (WPM) and Driver-Kuniyuki (DKW) tissue culture media. Shoot proliferation, area of the plate covered by callus and foliar pigment development (hue as determined by Royal Horticultural Society Color charts) were monitored for 17 weeks. Media affected shoot proliferation (P = 0.0042) but the zone of origin (P = 0.6664) of the explant did not. Callus area showed no significant difference among the four media and three zones (P = 0.2091) and averaged 3.60 centimeters2. After four subcultures, each lasting 30 days, explants on DKW media produced 10 shoots per explant. This media might hold promise for the micropropagation of bigtooth maple. Twenty-nine percent of all explants expressed foliar pigmentation, which ranged from red-purple to orange-red. Whether foliar pigment development in tissue culture correlates with expressed pigmentation in nature warrants further investigation.
Richard J. Heerema, Dawn VanLeeuwen, Rolston St. Hilaire, Vince P. Gutschick, and Bethany Cook
Photosynthetic function in nut trees is closely related to nitrogen (N) nutrition because much of tree N is held within the leaf photosynthetic apparatus, but growing fruit and seeds also represent strong N sinks. When soil N availability is low, nut trees remobilize and translocate N from leaves to help satisfy N demand of developing fruit. Our objective was to describe shoot-level impacts of pecan [Carya illinoinensis (Wangenh.) K. Koch.] fruiting on leaf N and photosynthesis (Pn) during kernel fill under a range of tree N statuses. Our study was conducted in a mature ‘Western’ pecan orchard near Las Cruces, NM. In 2009, 15 trees showing a range of N deficiency symptom severity were grouped according to leaf SPAD into low, medium, and high N status categories. Differential N fertilizer rates were applied to the soil around high and medium N trees to accentuate differences in N status among the three categories. Light-saturated leaf Pn was measured on fruiting and non-fruiting shoots during kernel fill in 2009 and 2010. After measurement of Pn, the leaflet and its leaflet pair partner were collected, dried, and analyzed for tissue N. Leaf N concentration was significantly lower on fruiting shoots than non-fruiting shoots on all three sampling dates. The tree N status main effect was also significant, whereas the two-way interaction of shoot fruiting status and tree N status was not. Photosynthesis of leaves on fruiting shoots was significantly lower than that of non-fruiting shoots on all sampling dates. These data suggest that N demand by the growing kernel reduced N in leaves on the same shoot. Consequently, Pn of those leaves was reduced. The effect of tree N status and shoot fruiting status was best summarized with an additive model where there is a larger relative reduction in leaf N and Pn for fruiting shoots on trees with low N status.
Marisa T. Potter, Richard J. Heerema, Jill Schroeder, Jamshid Ashigh, Dawn VanLeeuwen, and Cheryl Fiore
Pecan [Carya illinoinensis (Wangenh.) K. Koch] growers are advised to control orchard floor vegetation when establishing new orchards, but there is not a set recommendation for vegetation control in mature orchards. The objective of this study was to measure the effect of orchard floor vegetation on water and nitrogen (N) status of flood-irrigated mature pecan trees. Four treatments studied were: completely vegetated orchard floor, vegetation-free inner area directly under the tree canopy with vegetation in the outer area, completely vegetation-free, and vegetated inner area under the canopy with a vegetation-free outer area. Treatments were organized as a 2 × 2 factorial structure with inner and outer treatment factors, both with levels vegetated and vegetation-free. Soil moisture and tree midday stem water potential (MSWP) were measured during irrigation cycles to evaluate the development of water stress in the pecan trees. Soil moisture data showed a significant outer main effect when the soil in the entire orchard was the driest, that is, just before irrigation events. Areas with vegetation cover that were exposed to full sun were significantly drier than shaded vegetated areas and vegetation-free areas in the orchard floor. However, this was not correlated with differences in tree water status as indicated by MSWP. Leaf tissue and soil analyses showed no significant differences in N concentrations among treatments in either year. Treatments with orchard floor vegetation in the outer area had significantly higher yield efficiency and marginally significant improvements in percent kernel fill and number of nuts per kilogram. Our findings suggest that there may be more benefits to maintaining orchard floor vegetation in mature orchards than were previously acknowledged.
Sara Andrea Moran-Duran, Robert Paul Flynn, Richard Heerema, and Dawn VanLeeuwen
In recent years, nickel (Ni) deficiency symptoms has been observed in commercial pecan [Carya illinoinensis (Wangenh.) K. Koch.] orchards in New Mexico. Nickel deficiency can cause a reduction in lignin formation, which could affect the risk for breakage on pecan tree shoots. Ni deficiency might furthermore disrupt ureide catabolism in pecan and, therefore, could negatively affect nitrogen (N) nutrition in the plant. The objective of this study was to identify the effects of Ni and N fertilizer applications, at two rates, on net photosynthesis (Pn), leaf greenness (SPAD), and branch lignin concentration in New Mexico’s nonbearing pecan trees. Sixty trees for year 2012 (Pawnee and Western cultivars) and 40 trees for year 2013 (Pawnee cultivar) were used at two New Mexico locations (Artesia and Las Cruces) to evaluate the effects of Ni and N on tree measures. Treatments were as follows: (1) High N plus Ni (+Ni); (2) Low N no Ni (−Ni); (3) High N −Ni; and (4) Low N +Ni. In 2012 and 2013, there was an increase in leaf greenness for each location and cultivar (tree group) through time (June to September). Photosynthesis measures in 2012 differed between tree group, time in the season, and N and Ni treatments. In 2013, Pn was influenced by tree group and time (P < 0.0001), but N and Ni interaction did not present a significant effect related to Ni benefits. Photosynthesis varied over time in 2012 and 2013, with an inconsistent pattern. In this study, Ni application at the high N rate had a negative effect on ‘Pawnee’ Pn early in the season at the Artesia site, but this application had a positive effect for ‘Western’ from Artesia at the low N level, also early in the season. Lignin content varied between tree groups only. The application of N and Ni did not affect lignin in pecan shoots. The results show an inconsistent pattern regarding the benefits of Ni on nonbearing pecan orchards for leaf greenness, Pn, and lignin content during the 2-year study. Future studies on Ni should focus on pecan trees exhibiting leaf Ni deficiency symptoms or on soils with less than 0.14 mg·kg−1 of DTPA extractable Ni, as well as the long-term effect of Ni on pecan growth and development to optimize the addition of Ni into an efficient fertilization program.
Junxin Huang, Robert Heyduck, Richard D. Richins, Dawn VanLeeuwen, Mary A. O’Connell, and Shengrui Yao
Vitamin C profiles of 46 jujube cultivars were assessed from 2012 to 2015, and fruit nutrient dynamics of 10 cultivars during maturation were examined from 25 Aug. to 7 Oct. 2014 at 2-week intervals at New Mexico State University’s Alcalde Sustainable Agriculture Science Center and Los Lunas Agricultural Science Center. This is the first report in the United States profiling Vitamin C in jujube cultivars. The vitamin C content of mature fruit of 45 (of 46) cultivars ranged from 225 to 530 mg/100 g fresh weight (FW) plus ‘Youzao’ having the highest content of 820 mg/100 g FW at early mature stage. In general, drying cultivars had higher vitamin C content than fresh-eating cultivars whereas ‘Jinsi’ series (multipurpose) had relatively higher vitamin C content than others (>400 mg/100 g FW). Fruit vitamin C and moisture content decreased significantly during the maturation process. The average vitamin C contents of nine cultivars at Alcalde decreased more than 40% based on FW from 25 Aug. to 7 Oct. To maximize the vitamin C benefit, the ideal stage to consume fresh-eating cultivars is the creamy stage. Titratable acidity and soluble solids increased significantly during maturation. In mature jujubes, the titratable acidity and soluble solids ranged between 0.27% to 0.46% and 27.2% to 33.7%, respectively. Glucose, fructose, and sucrose content also rose significantly during ripening. Mature fruits contained 31–82 mg/g FW glucose, 32–101 mg/g FW fructose, and 53–159 mg/g FW sucrose among the cultivars tested. Based on sucrose contents, cultivars can be divided into two groups, “high-sucrose” (more sucrose than glucose or fructose) and “low-sucrose” (less sucrose than glucose or fructose). ‘Dagua’, ‘Honeyjar’, ‘Lang’, ‘Li’, ‘Maya’, ‘Sugarcane’, and ‘Sherwood’ belong to the “high-sucrose” group. Total phenolic content and 2,2-diphenyl-1-picrylhydrazyl (DPPH)-reducing capacity in fruit decreased during maturation, and the total phenolic content of mature jujube was 12–16 mg gallic acid equivalent (GAE)/g dry weight (DW). For mature fruit, ‘Li’ and ‘Li-2’ had the highest DPPH-scavenging efficiency whereas ‘Sugarcane’, ‘So’, and ‘Lang’ had the lowest at Alcalde, NM.
Malik G. Al-Ajlouni, Dawn M. VanLeeuwen, Michael N. DeMers, and Rolston St. Hilaire
The apparent heterogeneity of human-generated materials in residential urban landscapes sustains concerns that the quantitative classification of urban residential landscapes is impossible. The objective of this research was to develop a method to quantitatively classify urban residential landscapes in a desert environment. Using a purposive sampling procedure, we studied the landscapable area around each of 54 residential homes in Las Cruces, NM. All materials in the landscape were identified, measured, and categorized. Using 30% as the cutoff to indicate that a material was dominant in the landscape, we classified 93% of all landscapes into nine common landscape types. Mulch-dominant landscapes were the most common, and landscape types differed between front- and backyards. Shrubs did not feature prominently in any of the common landscape types. Our classification method clearly identifies multiple landscape types, and for the first time, provides quantitative evidence that landscape types are distributed differently in front- and backyard landscapes in the desert environment of Las Cruces. Information on common landscape types will be valuable to landscape horticulturists wanting to craft water conservation plans that are landscape specific if the common landscape type can be linked to a landscape water budget.
Walter F. Ray, Geno A. Picchioni, Dawn M. VanLeeuwen, and Ryan M. Goss
Tall fescue (Festuca arundinacea) has desirable attributes as a cool-season turfgrass for the semiarid southwestern United States and the transition zone, but effects of cultural practices on newer cultivars within a desert climate are not adequately known. A field study was conducted between Sept. 1996 and Nov. 1997 to evaluate establishment of 15 turf-type tall fescue cultivars under two mowing heights (2 or 3 inches) and two different annual nitrogen (N), phosphorus (P), and potassium (K) application rates (N at 13.2 or 26.4 g·m−2, P at 0.9 or 1.8 g·m−2, and K at 11.0 or 22.0 g·m−2). The cultivars included ‘Amigo’, ‘Apache’, ‘Aztec’, ‘Bonanza’, ‘Chieftain’, ‘Cochise’, ‘Confederate’, ‘Coronado’, ‘Crossfire II’, ‘Falcon’, ‘Guardian’, ‘Kentucky 31’, ‘Leprechaun’, ‘Shortstop’, and ‘Virtue’. The fertilizer rate had no effect on turfgrass quality ratings throughout the establishment period, although overall quality was higher in Fall 1997 than during Spring and Summer 1997. The mowing height of 2 inches increased summer quality ratings of 11 of the 15 cultivars as compared with ratings under the 3-inch mowing height. The 2-inch mowing height improved fall quality ratings of seven of the 15 cultivars. No cultivars responded positively to the 3-inch mowing height. Consistently high summer through fall quality ratings were observed when ‘Apache’, ‘Aztec’, and ‘Crossfire II’ were mowed at the 2-inch height as compared with the other cultivar × mowing height treatment combinations. For turf-type tall fescue establishment in semiarid climates, findings support use of a 2-inch mowing height combined with the selective planting of ‘Apache’, ‘Aztec’, and ‘Crossfire II’ over other cultivar × mowing height combinations tested in the study.
Mark E. Uchanski, Kulbhushan Grover, Dawn VanLeeuwen, and Ryan Goss
Experiential learning can be used as part of the undergraduate curriculum to provide real-world experience in the classroom. A hands-on hoop house construction project was integrated into an undergraduate general education plant science course at New Mexico State University in Las Cruces. The objectives were to provide students with hands-on experience in hoop house construction and data collection and interpretation, evaluate students’ perception about the educational value of the hoop house construction activity and delivery methods, and evaluate individual student’s perceptions about their participation in the group activity and group dynamics. Eighty-four students were enrolled in Spring 2013 semester. Students were surveyed in a follow-up laboratory 10 weeks after the hoop house construction activity for data collection and reflection. The survey tool assessed the impacts of class materials, laboratory materials, and the laboratory teaching assistants (TAs) on the students’ learning experience: perceptions of group work, their role within their groups, and their participation. Ninety percent and 95% of the students agreed or strongly agreed knowledge of basic techniques and practical application of hoop house construction, respectively, were obtained in the exercise. Eighty-five percent of student respondents indicated a gain in their appreciation for scientific data collection and interpretation through this exercise. Also, a majority (65%) of the students agreed this hands-on task improved their appreciation for group activities indicating experiential learning group work during scheduled class time could be a useful tool for team building and other learning experiences. Finally, more than 90% of the students found this activity overall beneficial. We conclude that integrating hoop house construction and data collection into an undergraduate general education plant science course can be an effective way to enhance student learning.