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A total of 108 pectolytic, soft-rotting Erwinia strains were collected from 11 types of cacti growing in Arizona, Texas, northern Mexico, and Australia between 1958 and. Four strains were collected from soils beneath or close to naturally rotting saguaro cacti. Collectively, these strains caused soft rots of saguaro, organ pipe, and senita cacti, Opuntia (cactus) fruits and pads, tomato fruits, and potato slices, but only occasionally caused soft rots of slices of carrot roots. A numerical cluster analysis showed that 98 of the 112 strains formed a uniform group (cluster 1A) that was distinguished from other pectolytic erwinias by an API 20E code of 1205131, by negative reactions in API 5OCHE tests for L-arabinose, myo-inositol, D-cellobiose, melibiose, and D-raffinose, and, in supplemental tests, by positive reactions for malonate and growth at 43°C. The average levels of DNA relatedness of 22 cluster 1A strains to the proposed type strain (strain 1-12) as determined by the hydroxyapatite method were 88% in 60°C reactions (with 1% divergence within related sequences) and 87% in 75°C reactions. The levels of relatedness to the type strains of other Erwinia spp. were 138% in 75°C reactions. Cluster 1A strains also had a characteristic cellular fatty acid profile containing cyclo-( 11,12)-nonadecanoic acid (C19:o cycle cll-lz) and missing tridecanoic acid (CI3J, heptadecanoic acid (C1,:o), and cis-9-heptadecenoic acid (Cl,:l g ) , which separated them from other pectolytic erwinias. Collectively, these data indicate that the members of cluster 1A are members of a new species, which we name Erwinia cacticida. Three cactus strains in cluster 1B appear to represent a second new species that is closely related to E. cacticida; these strains are designated E . cacticida-like pending the availability of additional strains for testing. The remaining cactus strains (in cluster 4) have the physiological, DNA, and fatty acid profiles of Erwinia carotovora.To our knowledge, Johnston and Hitchcock (22) were the first workers to describe a bacterial soft-rot disease of cacti in the United States. The cultures of these authors were isolated from prickly pear cacti (Opuntia tomentella Berger and OpuntiaJicus-indica (L.) Mill.) that were originally from Guatemala and Columbia but were growing in the U.S. Department of Agriculture plant introduction garden in Florida. The bacterium was briefly characterized as "an actively motile, gram-negative, aerobic, and facultative anaerobic bacillus" which produced an acid reaction when it was grown in broth containing "glucose, saccharose, mannite, and salicin but none in maltose, lactose, dulcite, and arabinose" (22). Subsequently, another new bacterial species, Erwinia carnegieana Standring 1942 (23), was described (3, 6, 23, 28) as being the causal agent of bacterial necrosis (a soft-rot disease) of saguaro cacti (Carnegiea gigantea Britt. & Rose). Among the soft-rot erwinias, this species was unique in that it was gram positive, a characteristic also noted by Boyle (6), and had a host ...

No abstract

Only 26 of an original 800 5—cm—tall saguaros (Carnegiea gigantea) survived for 3 months when accessible to the rodents and rabbits at Saguaro National Monument, Arizona; after 1 year all of these small plants were gone. Although losses among a group of larger (15—cm—tall) seedlings were less abrupt, only one plant of an original 120 remained by the end of a year. When protected from these herbivores by cages, 12% of the smaller plants remained at the end of 1 year but only 2% after 5 years. Although browsing by rodents and lagomorphs quickly destroyed most uncaged small plants, the planting design probably accentuated the losses from the herbivores; in any event, many of these seedlings would soon have died from other causes.

In a large cage, free-flying western white-winged doves, nectar-feeding Leptonycteris bats, and honey bees were each effective as cross-pollinators of self-sterile saguaro flowers. Seed production and seed viability were not significantly different in fruit from flowers pollinated by these agents. Pollination is not a limiting factor in saguaro repopulation.