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Fred T. Davies Jr., Constantino M. Calderón, and Zosimo Huaman

The influence of arbuscular mycorrhizal fungi (AMF) [two Peruvian mixed isolates, a pure isolate of Glomus intraradices] and the flavonoid, formononetin, were tested on growth, yield, and leaf elemental concentration of the Peruvian potato (Solanum tuberosum L.) `Yungay'. Plants started from tissue culture-produced prenuclear minitubers of `Yungay' were subjected to seven treatments, which included noncolonized (non-AMF) plants fertilized with Long Ashton nutrient solution modified to supply P at 11 and 44 μg·mL-1. All AMF plants received low P (11 μg·mL-1) and were inoculated with either a sierra-maize mixed isolate, sierra-papa mixed isolate, pure isolate of G. intraradices, sierra-maize mixed isolate + formononetin, or a sierra-papa mixed isolate + formononetin. Plants were grown in 3-L containers under shade house conditions in Lima, Peru. Non-AMF plants at low P had the poorest growth, while high P plants had the greatest overall growth. All AMF plants had greater growth, including a higher root to shoot ratio, higher phosphorus use efficiency [(g tuber)/(g P/kg tissue)], and a lower leaf to tuber ratio (indicating greater leaf efficiency in producing tuber dry matter), compared to non-AMF plants at low P. The mycorrhizal inoculation effect (MIE) ranged from +44% to +57%, indicating that `Yungay' was moderately to highly mycorrhizal dependent. Plants colonized with the sierra-papa isolate + formononetin had the same tuber development and leaf to tuber ratio, compared to high P, non-AMF plants. Formononetin increased extraradical hyphae formation. Mycorrhizal enhancement was in part due to greater P, Fe, and Mg uptake, a higher phosphorus-use efficiency and greater extraradical hyphae formation.

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Andrès A. Estrada-Luna and Fred T. Davies Jr.

Micropropagated cactus pear plantlets (Opuntia amyclaea Tenore) cv. Reyna were colonized with a Mexican endomycorrhiza isolate, ZAC-19 (containing Glomus etunicatum and two unknown Glomus spp.) and fertilized with two phosphorous levels (0 and 11 μg P/ml) to study their effect on plant growth and nutrient uptake. After 7 months of greenhouse culture, there was 100% survival of the micropropagated cactus pear plants. Evidence of mycorrhizal colonization was observed 5 days after inoculation, with the development of internal hyphae in root cortices. At the end of the study, high colonization occurred (48% to 54%) with no differences in P treatments. Plantlets transferred to soil began to actively grow with no lag phase. However, plant growth rate was significantly affected by treatments. Absence of P supply and lack of colonization resulted in lower dry mass and surface area of prickly pear cactus plants. In contrast, the combination of supplementary P and mycorrhizal colonization significantly increased plant growth.

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Larry J. Shoemake, Michael A. Arnold, and Fred T. Davies Jr.

A series of six experiments was conducted over eight years to investigate impacts of provenance on transplant establishment in landscapes and the role of adventitious root regeneration in differential genotypic responses during establishment of Platanus occidentalis L. Fall, spring, and summer transplants of container-grown half-sib families (HSF = seedlings derived from a single mother tree with unknown male parentage), including two selections native to Brazos County, Texas (Brazos-C, Brazos-D), one native to Cookeville, Tenn. (Cookeville), two Kentucky/Tennessee HSF from the Westvaco Corp. (WV-10, WV-14), and two Texas HSF from the Texas Forest Service tree improvement program (TFS-09, TFS-24), were established to determine field/landscape growth responses. Subsequent studies were conducted to investigate differential leaf gas exchange responses of TFS-09 and Cookeville during moderate water deficits and to determine root regeneration potential (RRP) responses of TFS-09, Brazos-C, WV-14, and Cookeville HSF following fall, spring, and summer transplant. To investigate consistency of within-family genotypic responses and to determine relationships among adventitious root initiation from shoot cuttings, RRP, and landscape establishment, five seedlings of TFS-09 and five from Cookeville HSF were clonally propagated and ramets tested under field and RRP conditions similar to those with seedling-derived plants. Regionally native HSF consistently grew taller, had larger trunk diameters, and often had greater survival during the first 3 years in the landscape than HSF not native to the region in which the studies were conducted. Rapidity of root regeneration among HFS at the time of transplant was the best root growth related predictor of successful landscape establishment. Some growth advantages were found using genetically improved HSF, but not as consistent an improvement as with the use of seedlings from regional provenances. Within-family variation in landscape performance was greater with nonregional Cookeville clones than with regional TFS-09 clones, however there was overlap among the more vigorous Cookeville clones and the least vigorous TFS-09 clones. Increased rapidity of root regeneration and drought adaptations related to leaf morphology and gas exchange characteristics may be involved in enhanced growth responses of Texas regional genotypes. No consistent relationships were found among adventitious rooting responses from shoot cuttings and subsequent RRP of the same genotypes from root tissues or their growth during the first 3 years in landscapes.

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Sven E. Svenson, Fred T. Davies Jr., and Sharon A. Duray

Gas exchange, water relations, and dry weight partitioning of shoot tip cuttings of `Eckespoint Lilo Red' (`Lilo') and `Gutbier V-10 Amy Red' (`Amy') poinsettia (Euphorbia pulcherrima Wind. ex Klotzsch) were studied during the initiation and development of adventitious roots. Net photosynthesis (A) and stomatal conductance (g) of cuttings were initially low and remained low until root primordia formation. Foliar relative water content (RWC) and osmotic potential (ψπ) increased upon formation of root primordia. Following formation of root primordia (2 days before visible root emergence) and concurrent with increasing RWC and ψπ, g increased. As roots initially emerged, A and g increased rapidly and continued to increase with further root primordia development and subsequent emergence of adventitious roots. Cutting stem and leaf dry mass and leaf area increased during the first few days after sticking cuttings. During primordium development and initial root emergence, the highest percent increase in dry weight was accounted for by basal stem sections. AU cuttings of both cultivars rooted and had similar root numbers after 23 days, but `Lilo' cuttings had 15% better rooting and 44% more roots than `Amy' after 15 days. This research supports the hypothesis that formation and elongation of root primordia coincides with increased gas exchange in poinsettia cuttings, and that gas exchange can be used as a nondestructive indicator of adventitious root development.

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Carlos A. Lazcano, Fred T. Davies Jr., Sharon A. Duray, Andres Estrada-Luna, and Victor Olalde-Portugal

Mature cladodes of prickly-pear cactus (Opuntia amyclaea Tenore. cv. Reina) were treated with five wounding methods and four concentrations of potassium salt indolebutyric acid (K-IBA) to stimulate adventitious root formation. K-IBA from 4144 to 41,442 μm (1000 to 10,000 mg·L-1) increased root number and root dry weight; however, root length was decreased at 41,442 μm (10,000 mg·L-1). Root number and root dry weight were higher with wounding methods that had larger wounded surface areas. K-IBA altered rooting polarity and stimulated adventitious root formation along the wounded cladode surfaces. Treatments without suberization had a higher percentage of rotted cladodes. This research validates the commercial practice in Mexico of suberizing cladodes early in the propagation cycle. Auxin application could be of commercial benefit for enhanced rooting in the clonal regeneration of new selections for prickly-pear cactus orchards. The wounding methods and auxin treatments utilized make an excellent classroom demonstration for manipulating rooting polarity.

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Fred T. Davies Jr., Sharon A. Duray, Sein Hla Bo, and Lop Phavaphutanon

The Neem tree is of ornamental, revegetation, biomass and medicinal value. The compound azadirachtin, which is derived from Neem seeds, is commercially used for insecticidal properties. In a 2×2 factorial experiment, Neem seedlings were either colonized with the mycorrhizal fungi Glomus intraradices or noninoculated and fertilized with full strength Long Ashton Mineral Solution at 11 or 22 ppm P. Mycorrhizal and P main effects were highly significant (p-value<0.001) with all growth parameters except R:S ratio. Mycorrhizal plants had greater leaf number, leaf area, leaf dry weight, shoot and root dry weight than noncolonized seedlings. The higher P (22 ppm) level plants had superior growth compared with low P plants. Leaf area and leaf dry weight were similar in mycorrhizal/low P plants and nonmycorrhizal/high P plants. These results suggest that mycorrhizal growth enhancement has important implications for Neem trees which are found in agriculturally poor soils in hot and arid regions.

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Andres A. Estrada-Luna, Fred T. Davies Jr., and Jonathan N. Egilla

Micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plants were transferred to ex vitro conditions to study plantlet performance and selected physiological changes that occur during acclimatization and post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry mass. Measurements were taken at 0, 1, 2, 3, 6, 12, and 24 days after transplanting. After initial transplanting ex vitro to liner pots with soilless media, plantlet wilting was observed that correlated with reduced leaf relative water content (RWC). Water stress was partially alleviated by a reduction in stomatal conductance (gs), confirming that the in vitro formed stomata were functional and able to regulate transpiration (E) to minimize desiccation losses. Because of this stomatal control, plantlets had minimal transplant shock, recovered, and survived. Prior to transplanting, micropropagated plantlets showed heterotrophic/mixotrophic characteristics as indicated by low photosynthesis [(A) 4.74 μmol·m2·s-1]. During acclimatization, RWC, gs, E, and A were significantly lower 2 days after transplanting. However, within 6 days after transplanting, plantlets recovered and became autotrophic, attaining high A (16.3 μmol·m-2·s-1), gs, and E. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with dramatic increases in plantlet growth.

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Andres A. Estrada-Luna, Fred T. Davies Jr., and Jonathan N. Egilla

The role of mycorrhiza fungi during acclimatization and post-acclimatization of micropropagated chile ancho plantlets was characterized through physiological and plantlet development changes. Regardless of mycorrhizal colonization, the pepper plantlets had initially low photosynthetic rates and poor growth following transplanting ex vitro. During the first days of acclimatization, water deficits occurred as evidenced by drastic reductions in relative water content. Consequently, transpiration rates and stomatal conductance (gs) declined, confirming that in vitro formed stomata were functional, thus avoiding excessive leaf dehydration and plant death. Mycorrhiza had a positive effect on gas exchange as early as day 7 and 8, as indicated by increasing photosynthesis (A) and gs. Mycorrhizal plantlets had reduced levels of abscisic acid (ABA) during peak stress (6 days after transplanting ex vitro), which corresponded with subsequent increases in gs and A. During acclimatization, A increased in both non-colonized and colonized plantlets, with greater rates observed in mycorrhizal plantlets. During post-acclimatization, mycorrhiza colonized 45% of the roots of pepper plantlets and enhanced plant growth by increasing leaf area, leaf dry mass, and fruit number. Mycorrhiza also enhanced total leaf chlorophyll content, A, and nutrient uptake of pepper plantlets, particularly N, P, and K. Early mycorrhizal colonization produced important benefits, which helped ex vitro transplanted plantlets recover during acclimatization and enhance physiological performance and growth during post-acclimatization.

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Fred T. Davies Jr., Sharon A. Duray, Lop Phavaphutanon, and Randy Stahl

The influence of P nutrition on gas exchange, plant development, and nutrient uptake of Capsicum annuum chile ancho `San Luis' and bell pepper `Jupiter' plants was studied. Plants were fertilized weekly using 250 ml of a modified Long-Ashton solution, containing 0, 11, 22, 44, 66 or 88 μg P/ml. Phosphorus stress was evident with both pepper cultivars at 0 and 11 μg P/ml, with reduced plant growth and development: leaf number and area and fruit, leaf, stem, root, shoot, and total plant dry weight. The root: shoot ratio was greatest at 0 μg P/ml, reflecting greater dry matter partitioning to the root system. Greater P stress occurred at 0 μg·ml–1 in `San Luis' compared to `Jupiter' (88% vs. 58% reduction in total plant dry weight compared to optimum P response). `San Luis' was also more sensitive to P stress at 11 μg P/ml than `Jupiter', as indicated by the greater reduction in growth responses. With increasing P nutrition, leaf tissue P increased in both cultivars with maximum leaf tissue P at 88 μg P/ml. In `San Luis', there were no differences in tissue P between plants treated with 0 and 11 μg P/ml, whereas the `Jupiter' plants treated with 0 μg P/ml had the lowest tissue P. Low P plants generally had the highest tissue N and lowest S, Fe, Mn, Zn, B, Mo, and Al. With both cultivars, gas exchange was lowest at 0 μg P/ml, as indicated by low transpiration (E), stomatal conductance (gs), and net photosynthesis (A). Internal CO2 (Cj) and vapor pressure deficit were generally highest at 0 μg P/ml, indicating that Cj was accumulating with lower gs, E, and A in these P-stressed plants. Generally, no P treatments exceeded the gas exchange levels obtained by 44 μg P/ml (full strength LANS) plants.

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Fred T. Davies Jr., Sharon A. Duray, Lop Phavaphutanon, and Randy Stahl

In two separate experiments, the influence of phosphorus nutrition on gas exchange, plant development, and nutrient uptake of Capsicum annuum chile ancho `San Luis' and bell pepper `Jupiter' plants were studied. Plants were fertilized weekly using 250 ml of a modified Long–Ashton solution (LANS) containing 0, 11, 22, 44, 66, or 88 μg P/ml. Phosphorus stress was evident with both pepper cultivars at 0 and 11 μg P/ml, with reduced plant growth and development: leaf number and area, fruit, leaf, stem, root, shoot, and total plant dry weight. The root: shoot ratio was greatest at 0 μg P/ml, reflecting greater dry matter partitioning to the root system. Greater phosphorus stress occurred at 0 μg P/ml in `San Luis' compared to `Jupiter' (88% vs. 58% reduction in total plant dry weight compared to optimum P response). `San Luis' was also more sensitive to phosphorus stress at 11 μg P/ml than `Jupiter' as indicated by the greater reduction in growth responses. With increasing P nutrition, leaf tissue P increased in both cultivars with maximum leaf tissue P at 88 μg P/ml. In `San Luis', there were no differences in tissue P between 0 and 11 μg P/ml plants, whereas 0 μg P/ml `Jupiter' plants had the lowest tissue P. Low P plants generally had the highest tissue N and lowest S, Fe, Mn, Zn B, Mo, and Al. With both cultivars, gas exchange was lowest at 0 μg P/ml, as indicated by low transpiration (E), stomatal conductance (gs), and net photosynthesis (A). Internal CO2 (Ci) and vapor pressure deficit were generally highest at 0 μg P/ml, indicating that Ci was accumulating with lower gs, E, and A in these phosphorus-stressed plants. Generally, no P treatments exceeded the gas exchange levels obtained by 44 μg P/ml (full strength LANS) plants.