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Xiuli Shen and Myeong-Je Cho

Sugar pine ( Pinus lambertiana Dougl.), a gymnosperm belonging to the family of Pinaceae prized for its economic and ecological value, is one of the most valuable softwood forest plant species in the western United States. Native to the region from

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María Victoria González, Manuel Rey, Raffaela Tavazza, Stefano La Malfa, Luigi Cuozzo, and Giorgio Ancora

Plant regeneration was obtained from adventitious buds induced in isolated cotyledons of Italian stone pine (Pinus pinea L.). The best results for bud induction were obtained by using half-strength LePoivre medium with 4.5 μM 6-benzyladenine for 30 days. Shoot elongation was achieved in the same medium without growth regulators but with the addition of 0.5% activated charcoal. The induction medium was the best also for shoot multiplication, but it was necessary to include subcultures on elongation medium. The slow elongation rate of adventitious shoots remains the greatest obstacle to multiplication. Root formation (15%) after 5 months was observed when shoots were cultured on elongation medium for long periods.

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Bohun B. Kinloch Jr.

After a century since introduction to North America from Europe, white pine blister rust, caused by Cronartium ribicola J.C. Fisch., is recognized as one of the catastrophic plant disease epidemics in history. It has not yet stabilized and continues to spread and intensify. Its nine native white pine hosts comprise major timber producers, important watershed protectors, keystone ecological species, and the oldest trees on earth. All are highly susceptible and some have been damaged severely in parts of their native range, as well as where they have been planted as exotics. Resistance, the most promising approach to control, requires understanding of genetic interactions between hosts and pathogen, a quest that has been ongoing for half a century. Unlike other hosts of spectacular exotic diseases, such as chestnut blight [caused by Cryphonectria parasitica (Murrill) M.E. Barr] and dutch elm disease [caused by Ophiostoma ulmi (Buisman) Nannf.], white pines (Pinus L.) exhibit a surprising number of resistance mechanisms to blister rust, if at only low frequencies. There are three main kinds:

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Sven E. Svenson and F. T. Davies Jr.

Pinus taeda L. seedlings inoculated with the ectomycorrhizal fungus, Pisolithus tinctorius, were grown in a glasshouse for eight months, and then subjected to rapidly developing cyclic water deficits, or to a single slowly developing water deficit. Water deficits developed at a rate of -0.16 MPa per day (predawn total water potential) for five cyclic water deficits, and at -0.04 MPa per day for the slow water deficit. In unstressed seedlings, carbon exchange rates (CER) did not differ between noninoculated and inoculated seedlings. During slow water deficit development, CER steadily declined. During rapid water deficit development, CER remained unchanged, then declined rapidly when water potentials fell below -1.3 MPa. Inoculated seedlings had higher CER when water potential was lower than -1.5 MPa.

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Sven E. Svenson and F. T. Davies Jr.

Pinus taeda L. seedlings inoculated with the ectomycorrhizal fungus, Pisolithus tinctorius, were grown in a glasshouse for eight months, and then subjected to rapidly developing cyclic water deficits, or to a single slowly developing water deficit. Water deficits developed at a rate of -0.16 MPa per day (predawn total water potential) for five cyclic water deficits, and at -0.04 MPa per day for the slow water deficit. In unstressed seedlings, carbon exchange rates (CER) did not differ between noninoculated and inoculated seedlings. During slow water deficit development, CER steadily declined. During rapid water deficit development, CER remained unchanged, then declined rapidly when water potentials fell below -1.3 MPa. Inoculated seedlings had higher CER when water potential was lower than -1.5 MPa.

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Henry E. DeVries II, Joseph P. Lardner, and Kenneth W. Mudge

To test the hypothesis that phytohormone production is related to mycorrhizae formation 29 isolates of ectomycorrhizal fungi have been evaluated for production of ethylene and auxin in pure culture and for their ability to form ectomycorrhizae with Pinus mugo. The fungi tested included a series of monokaryotic isolates of Laccaria bicolor and dikaryotic isolates of Amanita muscaria, Hebeloma crustuliniforme, L. laccata, L. proxima, Pisolithus tinctorius, Rhizopogon ellenae, and R. vinicolor. Inoculated root systems were rated for mycorrhizae formation, root/shoot ratio and root morphology. P. tinctorius isolates which formed abundant mycorrhizae produce no ethylene in vitro, but did produce the auxin IAA. L. bicolor isolates produced ethylene as well as auxins putatively identified as IAA, and IBA. Correlations between phytohormone production and mycorrhizogenicity will be presented.

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Leonardo Lombardini, Mauro Falusi, Roberto Calamassi, and James A. Flore

Aleppo Pine (Pinus halepensis Mill.) is known to be the most drought-resistant Mediterranean Pine. This species is widely distributed throughout the Mediterranean region and displays a high intraspecific variability, with respect to its physiological and morphological response to environmental conditions. In this experiment we evaluated the response of Pinus halepensis seedlings to drought. Sixty germinated seeds (accession A6, Shaharia, Israel) were grown in soil for 8 weeks and then transferred to black plexiglass tanks containing half-strength air-sparged Hoagland solution. After 6 weeks of acclimation to hydroponics, the osmotic potential of the solution was lowered by adding polyethylene-glycol (PEG) 8000. Water potential was lowered in 0.2 MPa increments every 4 days, until a final value of –0.8 was reached. The seedlings were then maintained at –0.8 MPa for a further 8 days. Ultrasonic acoustic emissions, pressure–volume (P–V) curves, shoot and root growth, leaf area, xylem diameter, root apex mitotic index and cell length were measured on control and stressed seedlings. Seedlings were then transferred to normal Hoagland solution for 24 hours to simulate rewatering, and P–V curves and ultrasonic emissions measurements were repeated. Results showed that the final root growth is maintained in the stressed seedlings at the same rate as controls, whereas shoot growth was significantly reduced. The leaf area was reduced by stress to 36%, but the xylem diameter only to 10%, leading to a lower leaf area:xylem section ratio in the stressed plants. Ultrasonic emissions in the stressed plants were 365% of the control, and 182%, after rewatering. Specific details of the growth and physiology data are presented.

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D.R. Bergdahl and H.B. Teillon

White pine blister rust (WPBR) (Cronartium ribicola J. C. Fischer) has been present in Vermont and other northeastern states since the early 1900s. The fungus is commonly observed on currants and gooseberries (Ribes L.) every year, but incidence varies on eastern white pine (Pinus strobus L.). Our general impression has been that Vermont has had a relatively low level of infection on eastern white pines; however, we recently found rust incidence in Christmas tree plantings in northern Vermont to range from 10 to 42% (average 20%) based on 721 trees surveyed. Also, in pole-sized stands in southern Vermont, incidence ranged from 12 to 46% (average 32%) and 76% of these trees had main stem infections. In the southern survey, 98% of wild ribes plants had varied amounts of both urediniospores and teliospores. These preliminary survey data suggest that incidence of WPBR may be more significant than previously thought and therefore, additional survey work is needed. We screened cultivars of Ribes for susceptibility to WPBR. Eighteen cultivars were inoculated in the field with a mass collection of aeciospores of C. ribicola. The percentages of leaf area infected ranged from 0 to 49 for the urediniospore stage and from 0 to 55 for teliospores. The gooseberry (Ribes uva-crispa L.) `Welcome' had the highest percentage of leaf area with urediniospores, while black currants (R. nigrum L.) `Coronet,' `Consort,' and `Crusader' had no visible infection. Presently, Vermont has no WPBR regulations. However, previous federal laws did restrict black currant cultivation. Little is known about the genetic diversity of WPBR or its potential for change. Caution must be used when considering any cultivation of Ribes for the purpose of producing fruit because our valued white pine resources could be negatively impacted.

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Todd P. West, Gregory Morgenson, Larry Chaput, and Dale E. Herman

Herman is a new cultivar of Pinus cembra L. (common names include Swiss Stone pine, Arolla pine, Swiss pine, Stone pine, or Austrian Stone pine). Its lateral branches curve markedly upward and slightly inward, resulting in a narrowly erect

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Panayiotis A. Nektarios, Garyfalia Economou, and Christos Avgoulas

Fresh, senesced, and decaying pine needles from Pinus halepensis were evaluated for their allelopathic potential on Festuca arundinacea, Cynodon dactylon and the biosensor plants Avena sativa and Lemna minor through in vivo and in vitro studies. The in vivo study was performed in growth chambers, using 6, 12, and 18 g of pine needle tissue mixed with screened perlite as a substrate. The effects of the different pine needle types were evaluated by determining the total root length, total root surface, root dry weight, total shoot length, total shoot surface, and shoot dry weight. The in vitro study was performed in Petri dishes where seeds from each species were subjected to an increasing concentration of pine needle extract. The extracts were obtained from pine needle ground tissue that was diluted with water and either shacked at room temperature or placed in water bath at 40 °C for 24 h. The evaluation of the allelopathic potential was performed with the determination of radicle length. The allelopathic potential of the pine needle tissues was confirmed with bioassays using oat (A. sativa) and duckweed (L. minor). The results strongly suggested the allelopathic potential of the pine needle tissue, being more pronounced in the fresh, moderate in the senesced, and low in the decaying pine needles. The allelopathic substances were species-specific, and the inhibition resistance of the species tested followed the order F. arundinacea > C. dactylon > A. sativa. The inhibition of the L. minor suggested that the water soluble phytotoxic compounds were inhibitors of Photosystem II.