Fred T. Davies

Arbuscular mycorrhizal fungi influence water relations, gas exchange, abscisic acid and growth of micropropagated chile ancho pepper (Capsicum annuum) plantlets during acclimatization and post- acclimatization

Little is known about the role of arbuscular mycorrhiza fungi (AMF) on physiological changes of micropropagated plantlets during acclimatization and post-acclimatization. Using chile ancho pepper (Capsicum annuum L. cv. San Luis), measurements were made of water relations, gas exchange, abscisic acid (ABA), plantlet growth and AMF development. Plantlets had low photosynthetic rates (A) and poor initial growth during acclimatization. Relative water content (RWC) decreased during the first days after transfer from tissue culture containers to ex vitro conditions. Consequently, transpiration rates (E) and stomatal conductance (gs) declined, confirming that in vitro formed stomata were functional and able to respond ex vitro to partial desiccation--thus avoiding excessive leaf dehydration and plant death. Colonization by AMF occurred within 3 days after inoculation. Colonized plantlets had lower leaf ABA and higher RWC than noncolonized (NonAMF) plantlets during peak plant dehydration (6 days after plant transfer)--and a higher A and gs as early as days 5 and 7. During post-acclimatization [after day 8, when RWC increased and stabilized], A increased in all plantlets; however, more dramatic changes occurred with AMF plantlets. Within 48 days, 45% of the roots sampled of inoculated plantlets were colonized and had extensive arbuscule development. At this time, AMF plantlets also had greater E, A, leaf chlorophyll, leaf elemental N, P and K, leaf dry biomass and leaf area, fruit production and differences in carbon partitioning [lower root/shoot ratio and higher leaf area ratio] compared with NonAMF plantlets. Rapid AMF colonization enhanced physiological adjustments, which helped plantlets recover rapidly during acclimatization and obtain greater growth during post-acclimatization.

Arbuscular Mycorrhiza and Petroleum-Degrading Microorganisms Enhance Phytoremediation of Petroleum-Contaminated Soil

While plants can phytoremediate soils that are contaminated with petroleum hydrocarbons, adding microbes to remediate contaminated sites with petroleum-degrading microorganisms and arbuscular mycorrhizal fungi (AMF) is not well understood. The phytoremediation of Arabian medium crude oil (ACO) was done with a Lolium multiflorum system inoculated with an AMF (Glomus intraradices) and a mixture of petroleum-degrading microorganisms—the bacterium, Sphingomonas paucimobilis (Sp) and the filamentous fungus, Cunninghamella echinulata (Ce, SpCe)—or with a combination of microorganisms (AMF + SpCe). Based on an earlier study on screening plants for phytoremediation of ACO, L. multiflorum (Italian ryegrass) was selected for its tolerance and rapid growth response (Alarcón, 2006). The plants were exposed to ACO-contaminated soil (6000 mg kg−1) for 80 d under greenhouse conditions. A modified Long Ashton Nutrient Solution (LANS) was supplied to all treatments at 30 μg P mL−1, except for a second, higher P, control treatment at 44 μg P mL−1. Inoculation with AMF, SpCe, or AMF + SpCe resulted in significantly increased leaf area as well as leaf and pseudostem dry mass as compared to controls at 30 μg P mL−1. Populations of bacteria grown on a nitrogen-free medium and filamentous fungi increased with AMF + SpCe and SpCe treatments. The average total colonization and arbuscule formation of AMF-inoculated plants in ACO-contaminated soil were 25% and 8%, respectively. No adverse effects were caused by SpCe on AMFcolonization. Most importantly, ACOdegradation was significantly enhanced by the addition of petroleum-degrading microorganisms and higher fertility controls, as compared to plants at 30 μg P mL−1. The highest ACOdegradation (59%) was observed with AMF + SpCe. The phytoremediation of ACO was also enhanced by single inoculation of AMF or SpCe. The effect of AMF and petroleum-degrading microorganisms on plant growth and ACOdegradation was not attributable to differences in proline, total phenolics, nitrate reductase levels, or variation in plant–gas exchange.

Effect of hypobaric conditions on ethylene evolution and growth of lettuce and wheat.

Elevated levels of ethylene occur in enclosed crop production systems and in spaceflight environments, leading to adverse plant growth and sterility. There are engineering advantages in growing plants at hypobaric (reduced atmospheric pressure) conditions in biomass production for extraterrestrial base or spaceflight environments. Objectives of this research were to characterize the influence of hypobaria on growth and ethylene evolution of lettuce (Lactuca sativa) and wheat (Triticum aestivum). Plants were grown under variable total gas pressures [from 30 to 101 kPa (ambient)]. In one study, lettuce and wheat were direct seeded, germinated and grown in the same chambers for 28 d at 50 or 101 kPa. Hypobaria increased plant growth and did not alter germination rate. During a 10-day study, 28-day-old lettuce and 40-day-old wheat seedlings were transplanted together in the same low and ambient pressure chambers; ethylene accumulated in the chambers, but the rate of production by both lettuce and wheat was reduced more than 65% under 30 kPa compared with ambient pressure (101 kPa). Low O2 concentrations [partial pressure of O2 (pO2) = 6.2 kPa] inhibited ethylene production by lettuce under both low (30 kPa) and ambient pressure, whereas ethylene production by wheat was inhibited at low pressure but not low O2 concentration. There was a negative linear correlation between increasing ethylene concentration and decreasing chlorophyll content of lettuce and wheat. Lettuce had higher production of ethylene and showed greater sensitivity to ethylene than wheat. The hypobaric effect on reduced ethylene production was greater than that of just hypoxia (low oxygen).

Landscape rose response to low moisture levels and a hydrophilic gel

Abstract Containerized plants of five low-maintenance rose (Rosa hybrida L.) cultivars were irrigated at intervals which limited moisture availability for plant growth and development. The cultivars were grown both in a medium amended with a hydrophilic gel and in a control medium. Of the five cultivars, ‘Pink Meidiland’ had the highest leaf water potential (ψL) and lowest transpiration (E), while ‘Ferdy’ maintained the highest E. The smaller leaf surface area of ‘Pink Meidiland’ and larger root to shoot ( R S ) ratio and lower leaf area ratio (LAR) of ‘Ferdy’ contributed to a more favorable water status despite limited moisture availability. When hydrophilic gel was utilized as a medium amendment, ψL was generally higher. Gel had little effect on plant biomass and tended to decrease tissue nutrient content.

Mycorrhizae, survival and growth of selected woody plant species in lignite overburden in Texas.

Abstract Seedlings of live oak ( Quercus virginiana (Mill.)), Chinese tallow tree ( Sapium sebiferum (L.) Roxb.), and Texas mountain laurel ( Sophora secundiflora (Ort.) Lag.) were inoculated with either ectomycorrhizal fungi ( Pisolithus tinctorius (Mich. ex Pers.) Ckr. and Couch) or vesicular-arbuscular mycorrhizal (VAM/endomycorrhizal) fungi ( Glomus fasciculatum (Thaxter) Gerd. & Trappe, Gigaspora margarita (Becker & Hall), and Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe) in a containerized system and transplanted into lignite overburden at two separate mine sites in the Post Oak Savannah region of Texas. Ectomycorrhizal Q. virginiana and endomycorrhizal S. sebiferum exhibited greater growth, and endomycorrhizal S. secundiflora showed greater survival and growth than noninoculated controls. Overburden at one site was low in P, while the second site was moderately high in P; however, root colonization levels of inoculated plants were high at both sites, while non inoculated plants had low levels of colonization. Both ecto- and endomycorrhizal fungi enhanced growth of the three woody species in these nitrogen-deficient overburden sites, independent of overburden P.

Response of Hibiscus rosa-sinensis L. to varying levels of potassium fertilization: growth, gas exchange and mineral element concentration

Abstract Little is known about the effect of varying levels of potassium (K) on the mineral element concentration, growth, and gas exchange, characteristics of woody ornamental plants. The commercially important woody ornamental species Hibiscus rosa‐sinensis L. cv. Leprechaun was evaluated for K response in a series of three experiments with full strength Hoaglands nutrient solution, which supplied 0 to 10 mM K. Plants grown with 4 mM K in nutrient solution (2.4% leaf tissue K) had the greatest shoot growth and root extension. Gas exchange rates (net photosynthesis, transpiration, and stomatal conductance) were also highest at 4 mM K compared to the control (0 mM K /0.6% leaf tissue K), 0.2, 2.0 and 10 mM K treatments. The application of 4 mM K increased net photosynthesis and tranpiration by 2.1 fold and stomatal conductance by 4.5 fold over 0 mM K controls. Increasing K in nutrient solution correlated positively with tissue K, manganese (Mn), and zinc (Zn), but negatively with nitrogen (N), phosphorus...

Micropropagation of Cryptanthus with leaf explants with attached intercalary meristems excised from greenhouse stock plants

Abstract By using the leaves with attached intercalary meristems from greenhouse grown stock plants, five cultivars of Cryptanthus were cultured on modified MS media with 4.5 μ M NAA and IBA and 3 μ M BA to induce adventitious shoot formation from callus tissue. Contamination was 17–21% for explants taken from stock plants which were sprayed weekly with Agribrom and 27–75% for those taken from stock plants which were not treated. More than 99% true to type plantlets were obtained from non-chimeric plants. Green and albino plantlets were obtained from chimeric plants. The chimeric C . ‘Costers Favorite’ DeCoster also produced a few chimeric plantlets with intermarginal pink stripes in addition to the green and albino plantlets. Most of the non-chimeric plants took a shorter time to produce plantlets of transplantable size (8–12 mm) than the chimeric ones. Except for albino plantlets, survival rate of plantlets exceeded 95%. A minimum average of 500 rooted plantlets can be obtained in a year from a single well-callused leaf explant. The protocol in this report should speed up the mass production and introduction of desirable new cultivars and hybrids of non-chimeric Cryptanthus .

Ethylene reduces plant gas exchange and growth of lettuce grown from seed to harvest under hypobaric and ambient total pressure

Naturally occurring high levels of ethylene can be a problem in spaceflight and controlled environment agriculture (CEA) leading to sterility and irregular plant growth. There are engineering and safety advantages of growing plants under hypobaria (low pressure) for space habitation. The goals of this research were to successfully grow lettuce (Lactuca sativa cv. Buttercrunch) in a long-term study from seed to harvest under hypobaric conditions, and to investigate how endogenously produced ethylene affects gas exchange and plant growth from seed germination to harvest under hypobaric and ambient total pressure conditions. Lettuce was grown under two levels of total gas pressure [hypobaric or ambient (25 or 101 kPa)] in a long-term, 32-day study. Significant levels of endogenous ethylene occurred by day-15 causing reductions in photosynthesis, dark-period respiration, and a subsequent decrease in plant growth. Hypobaria did not mitigate the adverse ethylene effects on plant growth. Seed germination was not adversely affected by hypobaria, but was reduced by hypoxia (6 kPa pO(2)). Under hypoxia, seed germination was higher under hypobaria than ambient total pressure. This research shows that lettuce can be grown from seed to harvest under hypobaria (≅25% of normal earth ambient total pressure).

GROWTH, ROOT ALTERATION, AND NUTRIENT UPTAKE OF NEEM TREE (Azadirachta indica A. Juss) SEEDLINGS IN RESPONSE TO VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI AND PHOSPHORUS NUTRITION

SUMMARY Growth and nutrient uptake of neem tree (Azadirachta indica A. Juss) seedlings were studied in response to vesicular-arbuscular mycorrhizal (VAM) fungi Glomus intraradices Schenck and Smith, and 2 levels of phosphorus (P). Extensive VAM colonization in neem roots occurred at both P levels: 0.65 and 1.30 mM P. Growth of VAM plants at both P levels was similar, while growth of noncolonized (Non-VAM) plants increased with increasing P supply. At the low P level, VAM plants had greater leaf area, shoot, root and leaf dry weight, and a greater root: shoot ratio than Non-VAM plants. Low P, VAM plants had a greater leaf area and root dry weight and a comparable leaf and shoot dry weight and root: shoot ratio, when compared with high P, Non-VAM plants. VAM inoculation also altered dry mass partitioning to root systems resulting in greater root length and dry weight of suberized roots in VAM plants. The length of nonsuberized roots increased with increasing P supply regardless of VAM inoculation. VAM inocu...

Water use, water-use efficiency and growth analysis of selected woody ornamental species under a non-limiting water regime

Abstract Selected woody ornamental species were grown in a glasshouse under a non-limiting irrigation regime. Relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), whole plant transpiration (T), evapotranspiration (ET) and water-use efficiency (WUE) were determined during a 73 day period. Covering the container medium with polyethylene reduced evaporative losses from 13% to 88%, depending on plant species, without affecting growth. The greatest reduction in evaporation occurred in plants with open canopies and low T rates. The shrub/tree species Lagerstroemia indica had the highest NAR and RGR, while the prostrate (plagiotropic) ground covers Trachelospermum asiaticum and Jasminum floridum and the orthotropic shrub/tree species Ligustrum japonicum had the lowest NAR and RGR. Leaf area ratio was greatest in Ligustrum and Pittosporum tobira . Water consumption, leaf area and root:shoot ratio were greatest in Lagerstroemia. Sophora secundiflora , which is adapted to more xeric conditions, had the highest T and lowest WUE. The highest WUE was found in Lagerstroemia, Raphiolepis and Pittosporum .