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  • Author or Editor: F.A. Hammerschlag x
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Abstract

Callus was induced from anthers of peach [Prunus persica (L.) Batsch] at several stages of pollen development. Cold pretreatments of isolated anthers did not enhance callus formation. Maximum callusing of ‘Sunhigh’ and ‘Compact Redhaven’ anthers was 71% and 87%, respectively, which occurred when anthers containing uninucleate microspores (35 μm) were floated on shallow layers of liquid medium and transferred to fresh medium after 7, 10, and 14 days. Cytofluorometric measurements (UV excitation) of 4, 6-diamidino-2-phenylindole (DAPI)-stained nuclei suggested that the majority of cells were haploid.

Open Access

Abstract

Explants from haploid, diploid, and tetraploid geraniums (Pelargoniumhortorum Bailey) were grown under 1, 5, and 10 klx of continuous cool white fluorescent lamps. Maximum callus production, measured by fresh weight increase occurred at 5 klx for ‘Kleine Liebling (haploid) and at 1 klx for ‘Sprinter’ (diploid) and ‘Sincerity’ (tetraploid). All cultivars grew poorly at 10 klx. Increase in fresh weight of ‘Sprinter’ tissue was 3 times greater than that of ‘Kleine Liebling’ and ‘Sincereity’ at 1 klx and 2 times greater at 5 klx. Differences among light treatments and among cultivars were more apparent with explants taken in winter versus explants taken in the summer.

Open Access

Immature `Redhaven' peach (Prunus persica L. Batsch) embryos were infected with Agrobacterium tumefaciens strain tms328::Tn5 carrying the functional cytokinin gene. Shoots were regenerated from callus grown on MS medium without added phytohormones and subsequently rooted on half-strength MS medium with 2.8 -naphthaleneacetic acid. These plants exhibited an increased frequency of branching in vitro. Low levels of cytokinin gene transcripts were detected in these cells by Northern analysis, and using an ELISA assay, the cytokinins zeatin and zeatinriboside were determined to be on the average 30-fold higher. From these results, the expression of the cytokinin gene appears to promote growth of cells in the absence of phytohormones thus serving as a marker for transformation and a promoter of morphogenesis without a 2,4-dichlorophenoxyacetic acid inductive step.

Free access

A detached-leaf bioassay was used to evaluate peach [Prunus persica (L.) Batsch] regenerants derived from zygotic embryo callus cultures of cultivars Sunhigh (susceptible to leaf spot) and Redhaven (moderately resistant to leaf spot) for resistance to Xanthomonas campestris pv. pruni [(E.F. Sm.) Dews], the causal agent of bacterial leaf spot. Regenerants obtained from calli produced on two `Sunhigh' embryos, #61 and #156, and on three `Redhaven' embryos were evaluated. Sixty-four percent of the regenerants derived from `Sunhigh' embryo #156 and 13% of the regenerants derived from `Sunhigh' embryo #61 demonstrated significantly greater spot resistance than `Sunhigh'. Regenerants with resistance greater than `Redhaven' were also obtained from both `Sunhigh' embryos. The frequency of variation in the `Sunhigh' seedling population, with respect to the response to bacterial leaf spot, was not so great as that exhibited by the regenerants derived from `Sunhigh' embryo #156. None of the `Redhaven' seedlings or any of the regenerants derived from `Redhaven' embryos were more resistant than `Redhaven'. These studies suggest that the frequency of somaclonal variation is genetically determined and that screening for somaclonal variation may be a feasible approach to obtaining leaf spot-resistant peach plants.

Free access

Abstract

A wick bioassay was developed to screen peach [Prunus persica (L.) Batsch] shoot cultures for resistance to bacterial spot [Xanthomonas campestris pv. pruni (E. F. Sm.) Dows)]. Three weeks after inoculation, the number of colony forming units (CFU) from 1-cm stem sections excised from highly susceptible cultivars was significantly greater than CFU from several resistant cultivars. Neither growth regulators nor the length of time that shoots were maintained in vitro prior to inoculation significantly influenced the response of these cultivars to bacterial leaf spot. This technique should be useful in screening for somaclonal variants obtained from peach cell cultures.

Open Access

A detached-leaf bioassay was used to evaluate peach [Prunus persica (L.) Batsch] somaclone 122-1 (derived from callus produced on an immature embryo of peach cultivar Redhaven) for resistance to several virulent strains of Xanthomonas campestris pv. pruni [E.F. Sm.) Dows], causal agent of bacterial leaf spot, and to a virulent isolate of Pseudomonas syringae van Hall pv. syringae, causal agent of bacterial canker. The detached-leaf bioassay was also used to evaluate progeny of 122-1 for resistance to X. campestris pv. pruni virulent strain XP1. Somaclone 122-1 was significantly more resistant to most strains of X. campestris pv. pruni than was `Redhaven', and all of its progeny exhibited high levels of resistance to X. campestris pv. pruni strain XP1. Somaclone 122-1 exhibited significantly higher levels of resistance to Pseudomonas syringae pv. syringae than did `Redhaven' and this resistance was retained over time in the greenhouse and following a 2-year cycle of tissue culture propagation.

Free access

As part of a program to develop transgenic highbush blueberry (Vaccinium corymbosum L.) and strawberry (Fragaria ×ananassa Duchesne) cultivars with increased levels of disease resistance, we have investigated the feasibility of introducing genes for the antimicrobial peptides cecropin B and MB39, α-thionin DB4 (DB4) and γ-thionin RsAFP1 (RsAFP1) by testing the effects of these peptides on several important pathogens of these two crop species. A thin-layer plate bioassay was conducted with these peptides and the pathogens Botrytis cinerea (Pers.ex. Fr.), Botryosphaeria dothidea (Mouq.ex. Fr.) Ces & de Not., Colletotrichum acutatum Simmonds, C. gloeosporioides (Penz.) Penz.et Sacc., C. fragariae Brooks, Monilinia vaccinii-corymbosi Reade (Honey), Phytophthora fragariae Hickman and Xanthomonas fragariae Kennedy and King. The minimum lethal concentration (μm) for cecropin ranged from 0.02 for X. fragariae strains 10 and 128 to 72.8 for C. gloeosporioides isolate Akp1. For DB4, the minimum inhibitory concentration (μm) ranged from 0.03 for X. fragariae strain 6 to 87.2 for B. cinerea isolate cc. For RsAFP1, the minimum inhibitory concentration (μm) ranged from 0.13 for X. fragariae strain 6 to 61.4 for M. vaccinii-corymbosi isolate 9423-x-45. These results indicate that introducing genes for either cecropin, DB4 or RsAFP1 into strawberry may be useful for controlling bacterial angular leaf spot disease caused by X. fragariae.

Free access

Transgenic plants containing introduced phytohorm one genes have been shown to display altered growth and morphogenetic potential. Peach plants transformed with the ipt gene from Agrobacterium tumefaciens strain tms 328::T n5 and containing elevated levels of cytokinins were screened in vitro for compact growth habit on four different levels of 6-benzyladenine (BA). After nine weeks in vitro, the average number of axillary shoots per plant foe two of the transformants, 99-1 and 40-1, ranged from 1.5 to 6.6 times that for the controls on 0-30 uM of BA, whereas average fresh weight ranged from 1.1 to 3.6 times that for the controls. One of the transformants, 94-1, produced a greater number of axillary shoots only on 30 μM BA. Rooted plants derived through micropropagation from the original transformants were monitored for 30 months under greenhouse conditions. The average height of transformants 94-1 and 99-1 after six months in the greenhouee was 88 and 77% of controls, respectively and after 30 months was 90 and 75% of controls, respectively. In comparison to controls, transformants exhibited a greater number of branches per meter per plant after six weeks, but a lesser number after 30 months. These results suggest that the introduction of a cytokinin gene may be a useful approach to obtaining peach trees with a compact growth habit.

Free access

Peach [Prunus persica (L.) Batsch] plants #94-1, #99-1, and #40-1, carrying a cytokinin biosynthesis (ipt) gene following transformation with the shooty mutant strain of Agrobacterium tumefaciens, were evaluated for altered growth habit and axillary shoot formation, both in vitro and in the greenhouse. After 9 weeks of in vitro propagation on four different levels of 6-benzyladenine (BA), only transformant #99-1 exhibited significantly greater axillary shoot formation (on 10 μm BA), and significantly greater fresh mass (on 3,10, and 30 μm BA) than the control #RG-3. Tolerance to a supra-optimal (30 μm) concentration of BA was indicated by fresh mass increases for #99-1 shoot cultures. Delayed senescence on 0 μm BA was exhibited by 87% of the transformants, but by only 12% of the control plants. Greenhouse-grown #99-1 and #40-1 were significantly shorter than #RG-3 plants at 6 weeks and at 1 year, but only #40-1 exhibited significantly greater branching than the controls. Chemical names used: 6-benzyladenine (BA); isopentenyl transferase (ipt).

Free access

Five in vitro propagated peach scion cultivars (Suncrest, Rio Oso Gem, Compact Redhaven, Redhaven, Jerseyqueen) and two rootstock (Nemaguard and Lovell) were screened in vitro and in microplots for their susceptibility to the root-knot nematode, Meloidogyne incognita. Evaluations in tissue culture for galling were conducted at 5 wk. Trees in microplots were evaluated for 3 years for nematode populations, trunk diameter, and yield. Comparative results indicated that the number and size of galls observed at 5 wk in vitro is indicative of the response of peaches to nematodes under field conditions after three years. Cultivar Compact Redhaven was significantly more tolerant to root-knot than `Lovell' the most widely used peach rootstock. These results suggest that Compact Redhaven might be potentially useful as a rootstock in the Southeast where Nemaguard is used sparingly because of its lack of cold tolerance. In addition, these results indicate that in vitro screening holds promise as a rapid technique for evaluating root-knot nematode resistance.

Free access