BOX-like DNA sequences are widely distributed in phytopathogenic Xanthomonas and Pseudomonas strains. REP-, ERIC-, and BOX-PCR (collectively known as rep-PCR) were used to generate genomic fingerprints of a variety ofXanthomonas and Pseudomonas isolates and to identify pathovars and strains that were previously not distinguishable by other classification methods. Analogous rep-PCR-derived genomic fingerprints were generated from purified genomic DNA, colonies on agar plates, liquid cultures, and directly from lesions on infected plants. REP-, ERIC-, and BOX-PCR-generated fingerprints of specific Xanthomonas and Pseudomonas strains were found to yield similar conclusions with regard to the identity of and relationship between these strains. This suggests that the distribution of REP-, ERIC-, and BOX-like sequences in these strains is a reflection of their genomic structure. Thus, the rep-PCR technique appears to be a rapid, simple, and reproducible method to identify and classify Xanthomonas and Pseudomonas strains, and it may be a useful diagnostic tool for these important plant pathogens.

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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.

Cotyledonary explants of 4-day-old Cucumis melo cv. 'Hale's Best Jumbo' in vitro seedlings showed maximum initiation of shoot buds when cultured onto a revised Murashige & Skoog medium supplemented with 5/~M indole-3-acetic acid and 5/~M benzylaminopurine and cultured at 25-29°C under low light intensity (5-30#molm-2s-~). Subculture of the shoot buds onto the same medium without auxin and supplemented with 3 #M 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.

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