Christine T. Stephens

Factors influencing shoot regeneration from cotyledonary explants ofCucumis melo

Cotyledonary explants of 4-day-oldCucumis melo cv. ‘Hales Best Jumbo’ in vitro seedlings showed maximum initiation of shoot buds when cultured onto a revised Murashige & Skoog medium supplemented with 5 μM indole-3-acetic acid and 5 μM benzylaminopurine and cultured at 25–29°C under low light intensity (5–30 μmol m-2 s-1). Subculture of the shoot buds onto the same medium without auxin and supplemented with 3 μM benzylaminopurine caused the development of shoots from 30% of the buds. The presence of abscisic acid significantly increased the number of explants producing shoot buds. Bud initiation was affected by genotype, seedling age, light intensity, and temperature. Addition of gibberellic acid, thidiazuron or silver nitrate to regeneration medium did not improve either bud initiation or shoot regeneration.

Effects of ferulic acid onGlomus fasciculatum and associated effects on phosphorus uptake and growth of asparagus (Asparagus officinalis L.)

The effect of ferulic acid, an allelochemical produced by asparagus, on hyphal elongation and colonization of asparagus byG. fasciculatum was studied. Spore germination in vitro was not affected, but hyphal elongation decreased significantly with increasing ferulic acid concentration. In the greenhouse, mycorrhizal colonization of roots and growth of mycorrhizal asparagus decreased significantly with increasing ferulic acid concentration, while growth of nonmycorrhizal plants was not affected by ferulic acid. Although plant tissue phosphorus levels were not affected by ferulic acid or mycorrhizal status, ferulic acid inhibition of hyphal elongation in vitro and fungal root colonization in vivo suggests that production of ferulic acid by asparagus reduces the symbiotic effectiveness of the fungus and subsequently reduces plant growth.

Effects of allelopathic substances produced by asparagus on incidence and severity of asparagus decline due toFusarium crown rot

The effects of toxic components isolated from asparagus tissue onFusarium spp. and other soil microorganisms and their effects on the susceptibility of asparagus toFusarium crown rot was investigated to determine what role allelopathic substances may play in the asparagus ecosystem and in asparagus crown rot decline. Dried sterilized asparagus crown and root tissues were incorporated into pots of 3-month-old asparagus seedlings with and withoutFusarium inoculum. Root tissue alone and treatments in which crown and root tissues were combined with theFusarium inoculum showed significant reduction of plant growth over nontreated controls. Root and crown tissues were partitioned with polar and nonpolar solvents and bioassayed on pregerminated asparagus and cress seeds. Inhibition of radicle growth was confined to the polar fractions. Further separation with paper chromatography gave several fractions that were inhibitory to radish, cress, tomato seed germination as well as inhibitory to growth of pregerminated asparagus seeds. Crude extracts from roots and crown residues were bioassayed on many different fungal isolates on Petri plates and were found to inhibit the growth of oomycetous fungi. Extracts from the roots were found to be more active than extracts from other portions of the asparagus plants.

Shoot regeneration of hybrid seed geranium (Pelargonium x hortorum) and regal geranium (Pelargonium x domesticum) from primary callus cultures

Procedures have been developed that increase the rate of shoot regeneration of hybrid seed geranium from month-old primary callus cultures. Hybrid geranium callus tissue covered with green nodular structures was initiated by placing shoot tip explants on solidified Murashige & Skoog medium (MS) supplemented with 2.0 mgl-1 zeatin and 1.9 mgl-1 indoleacetic acid. Hybrids Red Orbit, White Orbit and Scarlet Orbit were shown to produce 5–50 shoot primordia per explant when callus was initiated on this medium. Regal geranium callus was initiated by placing leaf explants on MS medium supplemented with 2.0 mgl-1 6-benzylaminopurine and 2.0 mgl-1 naphthaleneacetic acid. Regal geranium cultivars Tiny Tot and Lavender Grand Slam were shown to produce between 2–50 shoot primordia per explant when initiated on the same medium.

Studies of protoplast culture types and plant regeneration from callusderived protoplasts of Asparagus officinalis L. cv. Lucullus 234

Plating efficiency and colony formation of callus-derived protoplasts of Asparagus officinalis L. cv. Lucullus 234 differed significantly with different protoplast culture media and types of culture. Osmotic conditions and hormone concentrations of liquid media produced the greatest influence on plating efficiency and colony formation in bead culture. Protoplasts grew best in bead culture with a solid modified Kao & Michayluk protoplast culture medium (KM) supplemented with 0.5 mg l−1 α-naphthaleneacetic acid (NAA), 0.5 mg l−1 2,4-dichlorophenoxyacetic acid (2,4-D), 0.5 mg l−1 kinetin, and 0.6% agarose (KM6) and a liquid modified KM medium differing from KM6 medium in sugar content, having 0.18 M sucrose and 0.18 M mannitol (A8). An average plating efficiency of 19.1% and colony formation of 15.5% was obtained one week after isolation in bead culture with the KM6 and A8 media. The highest average shoot regeneration of 92.3% was obtained with a Murashige & Skoog medium (MS) containing 0.125 mg l−1 NAA, 0.125 mg l−1 2,4-D, 0.25 mg l−1 6-benzylaminopurine (6-BAP) and 3% sucrose. Plants have been regenerated and transferred to the greenhouse.

Impact of reduced fungicide and tillage on foliar blight, fruit rot, and yield of processing tomatoes

The effect of reduced tillage, soil-surface crop residue maintenance, and reduced fungicide input on processing tomato yield and disease incidence was studied in 1990 to 1992. Fall-seeded rye was desiccated in strips in early spring; the remainder, after 1.2 m of growth. Strips were zone tilled (ZT) 35 cm deep with no soil inversion. The ZT system permitted desiccated interrow rye residue to persist throughout the summer, providing approximately 90% cover of the soil surface. Tomatoes were transplanted into the prepared strips. The ZT system did not affect marketable yield or percent fruit with mold (1991 to 1992); but it decreased (1990), increased (1991), and did not affect (1992) defoliation caused by early blight (EB) compared to a conventional tillage production system using a moldboard plow, disk, or both. The fungicide, Bravo 720 (chlorothalonil), was applied as follows: none, weekly, or a full or reduced rate at intervals according to the disease forecasting model, TOM-CAST. Fungicide treatment did not enhance marketable yield compared to that of the unsprayed treatment. TOM-CAST-based treatments did not consistently provide control of defoliation compared to that in plots sprayed weekly. However, compared to weekly sprays, select forecast-generated spray schedules required 45 to 80% fewer applications to limit fruit mold incidence caused by Alternaria solani (EB), Colletotrichum coccodes (anthracnose), and Rhizoctonia solani (soil rot). Conservation tillage practices, soil-surface residue maintenance, and reduced fungicide input were integrated without compromising yield and management of disease, affording advantages of sustained farmland productivity.

The effect of asparagus virus infection on asparagus tissue culture

The impact of asparagus virus I (AV-I), a potyvirus, and asparagus virus II (AV-II), an ilarvirus, on micropropagation of field-grown asparagus was studied. Apical shoot tips excised from singly or doubly-infected plants were slow to develop roots and had a 15 to 75% reduction in survival in culture, respectively, compared to those excised from virus-free plants. The four virus infection groups were ranked: virus-free >AV-II>AV-I>AV-I & II for capacity of explants to both root and survivein vitro. Micropropagated plants infected with AV-II exhibited slight reductions in fresh and dry weights, with greater reductions associated with infection with AV-I and double infection, compared to the virus-free controls. Eighty-one virus-infected apical shoot tips yielded 7 (8.6%) virus-free clones, as determined by rub inoculation on indicator plants.