Mycorrhizal-induced growth depression of plants in high-P soil has been reported in many species. The carbon costs of factors contributing to this growth depression were analyzed in Volkamer lemon (Cifrus volkameriana Tan. & Pasq.) colonized by the mycorrhizal (M) fungus Clomus infraradices Schenck and Smith. M and nonmycorrhizal (NM) plants were each grown at two P-supply rates. Carbon budgets of M and NM plants were determined by measuring whole-plant carbon assimilation and respiration rates using gas-exchange techniques. Biomass, M colonization, tissue-P concentration, and total fatty acid concentration in the fibrous roots were determined. Construction costs of the fibrous roots were estimated from heat of combustion, N, and ash content. Rootgrowth respiration was derived from daily root growth and rootconstruction cost. M and NM plants grown in high-P soil were similar in P concentration, daily shoot carbon assimilation, and daily shoot dark respiration. At 52 d after transplanting (DAT), however, combined daily root plus soil respiration was 37% higher for M than for NM plants, resulting in a 20% higher daily specific carbon gain (mmol COz [mmol carbonl-' d-') in NM than M plants. Estimates of specific carbon gain from specific growth rates indicated about a 10% difference between M and NM plants. Absolute values of specific carbon gain estimated by whole-plant gas exchange and by growth analysis were in general agreement. At 52 DAT, M and NM plants at high P had nearly identical whole-plant growth rates, but M plants had 19% higher root dry weight with 10% higher daily rates of root growth. These allocation differences at high P accounted for about 51% of the differences in root/soil respiration between M and NM plants. Significantly higher fatty acid concentrations in M than NM fibrous roots were correlated with differences in construction costs of the fibrous roots. Of the 37% difference in daily total root/soil respiration observed between high-P M and NM plants at 52 DAT, estimated daily growth respiration accounted for only about 16%, two-thirds of which was associated with construction of lipid-rich roots, and the remaining one-third with greater M root growth rates. Thus, of the 37% more root/soil respiration associated with M colonization of high-P plants, 10% was directly attributable to building lipid-rich roots, Florida Agricultural Experiment Station Joumal Senes No. R-02500.

Arbuscule-forming fungi in the order Glomales form obligate endomycorrhizal associations with plants that make them difficult to quantify, and taxonomy of the group is only beginning to be objectively understood. Fatty acid methyl ester (FAME) profiles were analyzed to assess the diversity and quantity of fatty acids in 53 isolates of 24 glomalean species. Spores and endomycorrhizal roots of sudan grass (Sorghum sudanense) and the citrus rootstock Carrizo citrange (Poncirus trifoliata ؋ Citrus sinensis) were examined. Spores yielded reproducible FAME profiles from replicate spore collections extracted from soil pot cultures despite being grown in association with a host plant and with contaminating microorganisms present. Unweighted pair group analysis revealed relatively tight clusters of groups at the intraspecific, specific, and generic levels; however, lipid profiles at the family level were convergent. Thus, FAME profile comparisons provided a robust measure of similarity below the family level. FAME profiles in sudan grass roots containing vesicles and/or spores of Glomus intraradices were more similar to spore profiles than to profiles from nonmycorrhizal roots. The FAME profiles for Gigaspora species, which do not form vesicles or spores in roots, were less distinct from nonmycorrhizal roots. G. intraradices and G. rosea produced fatty acids in roots that were distinguishable from each other as well as from the host root. Production in citrus roots of the fatty acid 16:1 5 cis by two Glomus species was correlated with the development of mycorrhizal colonization as measured by clearing and staining procedures and by estimates of total incidence and vesicle intensity. FAME analysis of roots not only provided a measure of colonization development but also served as an index of carbon allocated to intraradical fungal growth and lipid storage.

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Two genetically diverse groups of strains were identified among cultures of Xunthomonas campestris pv. vesicatoria isolated from plants with bacterial spot of pepper and tomato. Group A strains do not pit pectate gels or hydrolyze starch, whereas group B strains are strongly positive for these reactions. Group A strains cause a hypersensitive reaction in plants of tomato breeding line Hawaii 7998, but group B strains do not. Other differences between the two groups of strains were discovered in tests for utilization of carbon compounds, serology, fatty acid profiles, silver-stained protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels, and DNA restriction enzyme digestion profiles. The levels of DNA homology between strains belonging to the same group were more than 74%, but the levels of DNA homology between strains belonging to different groups were less than 46%. The two groups of strains have different genetic backgrounds, but cause essentially the same disease of tomato and pepper.The bacterial spot disease of tomato and pepper is caused by the bacterium Xanthomonas campestris pv. vesicatoria. Necrotic spots on leaves, stems, peduncles, and fruits are distinctive symptoms of the disease (5, 17). Lesions may enlarge or coalesce and cause leaves to become chlorotic and eventually die. When prevalent, lesions on fruits result in loss of marketability. Bacterial spot occurs in all regions of the world where tomatoes and peppers are grown (17).A large collection of strains of the bacterial spot pathogen of tomato and pepper was accumulated for study (4), and two characteristics, pitting of pectate gels and hydrolysis of starch, were determined for each strain as aids for identifying possible opportunistic xanthomonads in the collection (14). Strains that were pectolytic and amylolytic, characteristics expected for opportunistic xanthomonads, were discovered, but these strains were pathogenic for tomato and/or pepper. One of the pectolytic and amylolytic strains was from Brazil and was designated a new race of X. campestris pv. vesicatoria on the basis of its ability to cause disease in the resistant tomato breeding line Hawaii 7998 (29). Of 522 strains tested (4), 104 were pectolytic and amylolytic. Most of these 104 strains were from Argentina, but similar strains were received from Australia, Brazil, New Zealand, and Spain. Only 1 of 331 strains from the United States was pectolytic and amylolytic, and no such strain was among the 28 strains from Taiwan tested. The pectolytic and amylolytic strains were not evenly distributed in all regions of the world where bacterial spot of tomato and pepper occurs, but seemed to be most prevalent in countries in the southern hemisphere.The two groups of strains, which are placed in X. campestris pv. vesicatoria because of their host specificity, were further characterized to determine the extent of genotypic

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