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Arthur Villordon and Christopher Clark

‘Beauregard’ sweetpotato plants infected with a complex of viruses ( Villordon and Clark, 2014 ). Such findings provide evidence about the potential influence of biotic factors on RSA development in sweetpotato. The primary objective of this work was to

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F.A. Buffone, D.R. LaBonte, and C.A. Clark

Chlorotic leaf distortion is a common disease of sweetpotato caused by Fusarium lateritium. This fungus is unique among Fusarium species in that it grows epiphytically on leaves and shoot tips of sweetpotato. Fusarium lateritium mycelia appear as white masses on leaves, and this fungus can cause chlorosis under periods of bright sunlight. When environmental conditions are not favorable for growth, this organism is not readily observed on sweetpotato. The objective of this research was to see if DNA of F. lateritium is amplified using PCR techniques during amplification of sweetpotato DNA. Our results show cTAB extracts of sweetpotato inoculated with F. lateritium have additional bands not present in a control free of F. lateritium. Furthermore, these bands correspond to banding patterns obtained from the F. lateritium isolate DNA when amplified alone. Researchers who use sweetpotato tissue in PCR-based research, e.g., phylogenetic research, should be aware of these amplified products. This situation is further compounded because numerous F. lateritium biotypes are present in the environment.

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Estuardo Marroquin, Frank B. Matta, Clinton H. Graves Jr., and Barbara Smith

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Robert R. Tripepi and Mary W. George

Mung bean (Vigna radiata (L.) R. Wilcz.) cuttings are used in rooting bioassays, and nonexperimental variability must be rigorously controlled to obtain meaningful results. This study was conducted to document bacterial disease problems of mung bean and identify the causal organisms. `Berken' seeds were surfaced sterilized and aerated 24 hr before sowing. Nine-day-old seedlings were used in rooting bioassays. Up to 10% of the seedlings and 17% of the cuttings had collapsed stems or wilted leaves. A white and two yellow (Y1 and Y2) bacteria were isolated from diseased cuttings and used in subsequent pathogenicity tests. The Y2 isolate was nonpathogenic. Stems of healthy mung beans inoculated with the white isolate turned brown and collapsed 2 days after inoculation, whereas leaves of plants inoculated with the yellow isolate wilted after 7 days. Standard biochemical and physiological tests revealed that the white isolate was Pseudomonas syringue pv. syringae van Hall and the yellow isolate was Curtobacterium flaccumfaciens subsp. flaccumfaciens (Hedges) Collins and Jones. This research is the first report of a disease in mung bean caused by P.s. pv. syringae. These results demonstrate the need or disease-free seeds being used in bioassays since both pathogens were seed-borne.

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Jordi Canals, Jorge Pinochet, and Antonio Felipe

The influence of temperature and age of the plant was determined on nematode reproduction on a susceptible almond (Prunus amygdalus Batsch.) and on a resistant peach-almond hybrid (P. persica Stok. × P. amygdalus Batsch.) rootstock inoculated with Meloidogyne javanica (Treub) Chitwood. Experiments were conducted under greenhouse conditions in heated and unheated sand beds. `Garrigues' almond inoculated with 3000 nematodes per plant showed extensive galling, high final nematode population levels, and high counts of nematodes per gram of root at 27 and 32C. The hybrid G × N No. 1 showed minimal galling and reproduction at 27C but higher levels of galling and final population and nematode counts per gram of root at 32C, suggesting a partial loss of resistance with temperature increase. One-month-old and 1-year-old plants of `Garrigues' were susceptible following inoculation with 2000 nematodes per plant, although plantlets (l-month) were significantly more affected. Plantlets of hybrid G × N No. 1 were also susceptible, but 1-year-old plants were resistant. Resistant genotypes (G × N selections) seem to require root tissue maturation before expressing full resistance.

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Jorge Pinochet, Carolina Fernández, María de Carmen Jaizme, and Pedro Tenoury

The effects of the interaction between the vesicular-arbuscular mycorrhizal fungus Glomus intraradices Schenk and Smith and the root-knot nematode Meloidogyne javanica (Treub) Chitwood on growth and nutrition of micropropagated `Grand Naine' banana (Musa AAA) were studied under greenhouse conditions. Inoculation with G. intraradices significantly increased growth of plants in relation to nonmycorrhizal plants and was more effective than P fertilization in promoting plant development. Mycorrhizal colonization did not affect nematode buildup in the roots, although plants with the nematode and mycorrhiza were more galled. Meloidogyne javanica had no effect on the percentage of root colonization in mycorrhiza-inoculated plants. No element deficiency was detected by foliar analysis. All elements were within sufficiency levels for banana with exception of N, which was low. Potassium levels were lower in mycorrhizal plants, while Ca and Mg levels were higher with mycorrhiza than without, with or without the nematode. Early inoculation with G. intraradices appears to favor growth of banana plants by enhancing plant nutrition.

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R.R. Tripepi and M.W. George

Seeds of `Berken' mung bean [Vigna radiata (L.) R. Wilcz.] were surface-sterilized with NaOCl and then either aerated 24 hours before sowing (routine procedure), planted immediately after the NaOCl treatment, or treated with hot cupric acetate and antibiotics before planting. Nine- or 10-day-old seedlings were used in rooting bioassays. Up to 10% of the seedlings and 17% of the cuttings had collapsed upper stems or wilted leaves. None of the seed treatments completely eliminated the pathogen, but the combination of hot cupric acetate plus antibiotics reduced the quantity of diseased cuttings to 3.3%. A white and two yellow-pigmented (Y1 and Y2) bacteria were isolated from diseased cuttings and used in subsequent pathogenicity tests. The Y2 strain was nonpathogenic. Stems of plants inoculated with the white strain turned brown and collapsed 2 days after inoculation, whereas leaves of plants inoculated with the Y1 strain wilted after 7 days. Electron microscopy, fatty acid analysis, and standard biochemical and physiological tests were used to identify the white strain as Pseudomonas syringae pv. syringae van Hall and the Y1 strain as Curtobacterium flaccumfaciens ssp. flaccumfaciens (Hedges) Collins and Jones. These results emphasize that seeds of mung bean should be checked for seedborne pathogens to avoid experimental artifacts.

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L.S. Chang, A.F. Iezzoni, G.C. Adams, and F.W. Ewers

Eight open-pollinated peach families [Prunus persica (L.) Batsch] were selected from a germplasm collection that was screened for tolerance to Leucostoma persoonii (Nits.) Höhn. [imperfect state, .Leucocytospora leucostoma (Pers.) Höhn] following field inoculation. The eight peach families were either susceptible or tolerant to L. persoonii infection based on canker length measurements. Three open-pollinated seedlings per family were chosen for evaluation. Following artificial inoculation, measurements of hydraulic conductance per pressure gradient (Kh) were made on 2-year-old branch segments from the 24 seedlings, and safranin dye was used to mark the conductive xylem pathways. For the peach families tolerant to L. persoonii, the specific Kh of the canker branch segments was greater than that for the most susceptible peach families. The inoculated branch segments from the tolerant peach families maintained ≈15% to 30% of the water transport of control segments. Safranin dye movement indicated that the sapwood in inoculated branch segments of seedlings from the susceptible peach families was almost completely blocked. Isolation experiments indicated deeper penetration of the fungus into the xylem of seedlings of susceptible than tolerant families. Xylem dysfunction appears to be correlated with a reduction in Kh, and the seedlings in the tolerant peach families are better able to maintain water transport through the stem segment invaded by the fungus.

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Wendy J. Wagoner, Jill A. Kellogg, Richard K. Bestwick, and James A Stamp

Broccoli and cauliflower are among the most regeneratively intractable genotypes found in the brassicaceae. To develop a method for transfer of the gene encoding S-adenosylmethionine hydrolase (SAMase) into inbred broccoli and cauliflower germplasm, we investigated the morphogenic competence and Agrobacterium susceptibility of a wide range of tissues of varied source. Appropriately controlled expression of the SAMase gene should, theoretically, reduce the plant's capacity for ethylene biosynthesis and extend the post harvest shelf life of the flower head.

Through examination of the in vitro response of a wide range of tissues we identified procedures which support caulogenesis from 100% of explants, each producing more than 30 shoots which readily convert to plantlets. Studies with several wild type and disarmed Agrobacterium strains, and utilization of the binary vector system and appropriate marker and reporter genes, led to the identification of methods for high frequency T-DNA transfer to explant tissues and the flow frequency of transgenic plants containing SAMase gene.

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Tamar Y. Harnik, Monica Mejia-Chang, James Lewis, and Matteo Garbelotto

Phytophthora ramorum (Oomycota) (Werres et al., 2001) is the plant pathogen responsible for the lethal disease of several oak species in California known as sudden oak death. The pathogen also causes a foliar disease on Umbellularia californica (bay laurel or simply bay). Bay leaves have been identified as the major source of natural inoculum in California coastal woodlands. Because of the epidemiological relevance of bay leaves, their movement needs to be regulated. Our study shows that P. ramorum is highly heat tolerant and can be reisolated from artificially inoculated bay laurel leaves placed at 55 °C for up to 1 week. The pathogen cannot be recovered after 2 weeks at 55 °C. Prolonged heat treatments, however, are impractical for bay leaves intended to be sold commercially as a spice, since they negatively impact the quality of the leaves. Here we describe a treatment involving a progressive and gradual heating process combined with the application of moderate vacuum. This method can be completed in 22 hours and is shown here to eliminate the recovery of P. ramorum without having a negative impact on the quality of the bay leaves.