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Robert F. Bevacqua and Dawn M. VanLeeuwen

Chile pepper (Capsicum annuum L.) yields are highly variable and are strongly influenced by disease and weather. The goal of two field experiments was to evaluate crop management factors, especially planting date, that could contribute to improved and more consistent crop production. Current practice in New Mexico is to direct seed the crop from 13 to 27 Mar. In the first experiment, chile pepper was direct seeded on three planting dates, 13, 20, and 27 Mar. 2000, without or with a fungicide treatment of pentachloronitrobenzene and mefenoxam for the control of damping off. The results indicate planting date had no effect on stand establishment or yield. Fungicide treatment, significantly reduced stand, but had no effect on yield. In the second experiment, chile pepper was direct seeded on six planting dates, 13, 20, 27 Mar. and 3, 10, 17, Apr. 2001, with or without an application of phosphorus fertilizer, P at 29.4 kg·ha-1, banded beneath the seed row. During the growing season, this experimental planting suffered, as did commercial plantings in New Mexico, from high mortality and stunting due to beet curly top virus, a disease transmitted by the beet leafhopper. The results indicate planting date had a significant effect on crop performance. The best stand establishment and highest yield were associated with the earliest planting date, 13 Mar. This date also resulted in the least viral disease damage. Phosphorus fertilizer had no effect on stand establishment or yield. Chemical names used: pentachloronitrobenzene (PCNB); (R)-2-[(2,6-dimethylphenyl)-methoxyacetylamino]-propionic acid methyl ester (mefenoxam).

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Cathleen Feser, Rolston St. Hilaire, and Dawn VanLeeuwen

Mexican elder (Sambucus mexicana Presl.) is used in arid landscapes of the Southwest, but the plant is known for its unpredictable performance in those landscapes. We studied drought responses of mexican elder plants grown in an arid environment using an in-ground nursery production system. Plants were maintained as well-irrigated controls or exposed to cyclic drought and irrigated based on evapotranspiration. Drought treatment lasted 165 days. Plants exposed to drought had more negative predawn and midday water potentials than well-watered plants. The ratio of variable to maximal fluorescence (Fv/Fm) for the drought group (0.76), was near the optimum value of 0.8, suggesting that chloroplasts of drought-stressed plants maintained high levels of activity. Drought cycle, but not drought treatment affected stomatal conductance. Drought-stressed plants had lower transpiration rates than controls except at drought cycle five when transpiration rates were similar between irrigation treatments. Relative water content was higher in controls (76%) than plants exposed to drought (66%). Leaf area of well-irrigated plants was over four times higher than that of plants exposed to drought. Leaf area to root dry weight ratio of drought-stressed plants was 79% lower than control plants. Severely reduced leaf area of drought-stressed plants might be one reason why landscape personnel conclude that mexican elder plants perform poorly in arid landscapes.

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Yahia Othman, Dawn VanLeeuwen, Richard Heerema, and Rolston St. Hilaire

Demand for New Mexico’s limited water resources coupled with periodic drought has increased the necessity for tree water status monitoring to guide irrigation scheduling of pecan (Carya illinoinensis) orchards. The objectives of this study were to assess the impact of water status developed during the flood irrigation dry-down cycles on photosynthesis (P n), and gas exchange [stomatal conductance (g S) to H2O (g H2O), transpiration (E), and intercellular CO2 (c i)] and to establish values of midday stem water potential (Ψsmd) that are needed to maintain P n and gas exchange of pecan. We conducted the study simultaneously on two southern New Mexico mature pecan orchards from 2011 through 2013. Flood irrigation as determined by grower practice was used on both orchards and P n, g H2O, E, and c i were assessed at Ψsmd of –0.4 to –2.0 MPa. Photosynthesis and gas exchange were higher in pecan trees shortly after irrigation than trees exhibiting water deficit near the end of a flood irrigation dry-down cycle. The decline in P n was markedly noticeable when Ψsmd dropped below –0.9 MPa. We attributed the reduction in P n mostly to stomatal limitation. The decline in P n and g H2O exceeded 50% when Ψsmd ranged from –1.5 to –2.0 MPa. For those reasons, we recommended that pecan orchards be maintained at Ψsmd higher than –0.90 MPa to prevent significant reductions in carbon assimilation and gas exchange.

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Rolston St. Hilaire, Dawn M. VanLeeuwen, and Patrick Torres

We surveyed homeowners with residential landscapes in Santa Fe, NM, to determine their attitudes toward high desert plants and to assess their preferences for urban landscapes and water conservation strategies in a high desert urban environment. While there was low acceptance for the traditional turf lawn, 64% of residents agreed that high desert plants provided the variety they needed in their residential landscapes and 92% of residents would use high desert plants to landscape their front yard. Homeowners had a strong preference for retaining their current desert landscapes and converting traditional landscapes to high desert-adapted landscapes. Logistic regression revealed a negative relationship between length of residency in the southwestern United States and the willingness to use high desert plants. When homeowners who irrigated their landscape were asked whether water shortages, environmental concerns, information on water, city regulations, high water bills, or water rate increases would cause them to use less water on their landscapes, the highest level of agreement (94%) was for water shortages. Eighty-eight percent of respondents agreed that they liked any type of landscape that contains interesting features and is well planned. We conclude that homeowners have a preference for desert-adapted landscapes and agree that high desert plants provide an adequate palette of plants for urban landscapes. Additionally, the length of residency in the southwestern U.S. and the possibility of water shortages have the potential to impact water conservation strategies in high desert urban landscapes.

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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.

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Yahia Othman, Caiti Steele, Dawn VanLeeuwen, and Rolston St. Hilaire

For large fields, remote sensing might permit plant low moisture status to be detected early, and this may improve drought detection and monitoring. The objective of this study was to determine whether canopy and soil surface reflectance data derived from a handheld spectroradiometer can detect moisture status assessed using midday stem water potential (ψsmd) in pecan (Carya illinoinensis) during cyclic flood irrigations. We conducted the study simultaneously on two mature pecan orchards, one in a sandy loam (La Mancha) and the other in a clay loam (Leyendecker) soil. We were particularly interested in detecting moisture status in the −0.90 to −1.5 MPa ψsmd range because our previous studies indicated this was the critical range for irrigating pecan. Midday stem water potential, photosynthesis (A) and canopy and soil surface reflectance measurements were taken over the course of irrigation dry-down cycles at ψsmd levels of −0.40 to −0.85 MPa (well watered) and −0.9 to −1.5 MPa (water deficit). The decline in A averaged 34% in La Mancha and 25% in Leyendecker orchard when ψsmd ranged from −0.9 to −1.5 MPa. Average canopy surface reflectance of well-watered trees (ψsmd −0.4 to −0.85 MPa) was significantly higher than the same trees experiencing water deficits (ψsmd −0.9 to −1.5 MPa) within the 350- to 2500-nm bands range. Conversely, soil surface reflectance of well-watered trees was lower than water deficit trees over all bands. At both orchards, coefficient of determinations between ψsmd and all soil and canopy bands and surface reflectance indices were less than 0.62. But discriminant analysis models derived from combining soil and canopy reflectance data of well-watered and water-deficit trees had high classification accuracy (overall and cross-validation classification accuracy >80%). A discriminant model that included triangular vegetation index (TVI), photochemical reflectance index (PRI), and normalized soil moisture index (NSMI) had 85% overall accuracy and 82% cross-validation accuracy at La Mancha orchard. At Leyendecker, either a discriminant model weighted with two soil bands (690 and 2430 nm) or a discriminant model that used PRI and soil band 2430 nm had an overall classification and cross-validation accuracy of 99%. In summary, the results presented here suggest that canopy and soil hyperspectral data derived from a handheld spectroradiometer hold promise for discerning the ψsmd of pecan orchards subjected to flood irrigation.

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Emad Bsoul, Rolston St. Hilaire, and Dawn M. VanLeeuwen

Ecological traits such as an extensive range of natural distribution and tolerance to varying soil conditions, suggest that bigtooth maples (Acer grandidentatum Nutt.) could be popular landscape trees. But information on the tolerance of bigtooth maples to environmental stresses, such as drought, is virtually nonexistent. We studied physiological, growth and developmental traits of bigtooth maple plants from 15 trees native to Arizona, New Mexico, Texas, and Utah. Plants were grown in pots in a greenhouse and maintained as well-irrigated controls or exposed to drought and irrigated in cycles based on evapotranspiration. The ratio of variable to maximal fluorescence (Fv/Fm) was not different between drought-stressed and control plants, but the low Fv/Fm in plants designated as LM2 from the Lost Maples State Natural Area in Vanderpool, Tex., suggests these plants were relatively inefficient in capturing energy at PSII. Plants from another tree (LM5) originating from Lost Maples State Natural Area maintained similar predawn water potentials between drought-stressed and control plants after five cycles of drought. Plants from Dripping Springs State Park in Las Cruces, N.M., and those from LM2 had a strong, significant linear relationship between transpiration and stomatal conductance. Drought-stressed plants from Dripping Springs State Park, two plant sources from the Guadalupe Mountains in Salt Flat, Tex., designated as GM3 and GM4, and plants from trees designated as LM1 and LM2, had high relative growth rates and net assimilation rates. Drought-stressed plants from three of the four Guadalupe Mountain sources (GM1, GM3, GM4) had among the longest and thickest stems. Drought reduced shoot and root dry weight (DW). Although bigtooth maples showed several provenance differences in drought adaptation mechanisms, the lack of an irrigation effect on biomass allocation parameters such as root to shoot DW ratio and leaf area ratio implies that altered biomass allocation patterns may not be a common drought adaptation mechanism in bigtooth maples. Plants from selected provenances from the Guadalupe Mountains and Lost Maples State Natural Area in Texas, and to a lesser extent, provenances from Dripping Springs State Park in New Mexico might hold promise for selecting bigtooth maples for arid environments.

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Dawn M. VanLeeuwen, Rolston St. Hilaire, and Emad Y. Bsoul

Statistical analysis of data from repeated measures experiments with missing factor combinations encounters multiple complications. Data from asynchronous cyclic drought experiments incorporate unequal numbers of drought cycles for different sources and provide an example of data both with repeated measures and missing factor combinations. Repeated measures data are problematic because typical analyses with PROC GLM do not allow the researcher to compare candidate covariance structures. In contrast, PROC MIXED allows comparison of covariance structures and several options for modeling serial correlation and variance heterogeneity. When there are missing factor combinations, the cross-classified model traditionally used for synchronized trials is inappropriate. For asynchronous data, some least squares means estimates for treatment and source main effects, and treatment by source interaction effects are inestimable. The objectives of this paper were to use an asynchronous drought cycle data set to 1) model an appropriate covariance structure using mixed models, and 2) compare the cross-classified fixed effects model to drought cycle nested within source models. We used a data set of midday water potential measurements taken during a cyclic drought study of 15 half-siblings of bigtooth maples (Acer grandidentatum Nutt.) indigenous to Arizona, New Mexico, Texas, and Utah. Data were analyzed using SAS PROC MIXED software. Information criteria lead to the selection of a model incorporating separate compound symmetric covariance structures for the two irrigation treatment groups. When using nested models in the fixed portion of the model, there are no missing factors because drought cycle is not treated as a crossed experimental factor. Nested models provided meaningful F tests and estimated all the least squares means, but the cross-classified model did not. Furthermore, the nested models adequately compared the treatment effect of sources subjected to asynchronous drought events. We conclude that researchers wishing to analyze data from asynchronous drought trials must consider using mixed models with nested fixed effects.

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Marisa Y. Thompson, Jennifer Randall, Richard J. Heerema, and Dawn VanLeeuwen

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.

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Jane E. Spinti, Rolston St. Hilaire, and Dawn VanLeeuwen

We surveyed homeowners with residential landscapes in Las Cruces, N.M., to determine design features participants valued in their landscapes, their attitudes toward the landscape use of desert plants and opinions on factors that would encourage respondents to reduce landscape water use. We also determined whether the willingness to use desert plants in their landscapes related to the length of residency in the southwestern United States. At least 98% of respondents landscaped to enhance the appearance of their home and increase their property value. About half (50.6%) of the participants strongly agreed or agreed that the main reason to landscape was to display their landscape preferences. Many participants indicated they would use desert plants to landscape their front yard (80.3%) and back yard (56.3%), but relatively lower percentages of participants actually had desert landscapes in their front yard and back yard. Regardless of their property value, respondents were more likely to use desert plants in their backyard the shorter their stay in the desert. Data revealed that participants rank water shortages as the factor that would most likely cause them to reduce the amount of water they applied to their landscapes. We conclude that homeowners report willingness to use desert plants but desert-type landscapes are not a widespread feature of managed residential landscapes. Furthermore, water shortages and the length of time respondents spent in a desert environment would most likely influence water use in their landscapes.