Agricultural plants and soil as a reservoir for Pseudomonas aeruginosa.
Pseudomonas aeruginosa was detected in 24% of the soil samples but in only 0.13% of the vegetable samples from various agricultural areas of California. The distribution of pyocin types of soil and vegetable isolates was similar to that of clinical strains, and three of the soil isolates were resistant to carbenicillin. Pseudomonas aeruginosa multiplied in lettuce and bean under conditions of high temperature and high relative humidity (27 C and 80-95% relative humidity) but declined when the temperature and humidity were lowered (16 C, 55-75% relative humidity). The results suggest that soil is a reservior for P. aeruginosa and that the bacterium has the capacity to colonize plants during favorable conditions of temperature and moisture.
A Pseudomonas aeruginosa‐secreted protease modulates host intrinsic immune responses, but how?
Recently, we found that the Pseudomonas aeruginosa type II secreted protease IV functions as a unique Arabidopsis innate immunity elicitor. The protease IV‐activated pathway involves G protein signaling and raises the question of how protease elicitation leads to the activation of G protein‐mediated signaling, because plants do not appear to have metazoan‐like G protein‐coupled receptors. Importantly, our data suggest that Arabidopsis has evolved a mechanism to detect the proteolytic activity of a pathogen‐encoded protease, supporting the host‐pathogen arms race model. In the case of opportunistic multi‐host pathogens like P. aeruginosa, however, it is not plausible that P. aeruginosa is simultaneously co‐evolving in a gene‐for‐gene manner with all of its potential hosts, which include plants, nematodes, insects, and mammals. This prompts us to ask what is the driving force for co‐evolution of defense response in Arabidopsis and pathogenesis of P. aeruginosa, which might not have been subject to iterative cycles of evolutionary selections.
Effect of Soybean Cyst Nematode (Heterodera glycines) on Yield of Resistant and Susceptible Soybean Cultivars Grown in Ohio.
Soybean (Glycine max) producers in Ohio rarely use soybean cyst nematode (Heterodera glycines, SCN)-resistant cultivars because of concerns over limited yield potential and lack of resistance to Phytophthora sojae. A two-year study was initiated to determine grain yield and nematode population increase on soybean cyst nematode-resistant cultivars in maturity groups II and III in production fields. Sites differed in soil texture, nematode densities, and P. sojae infestation at a number of locations in Ohio. Soil was assayed for nematode densities before planting and at harvest. Yields of resistant cultivars averaged 0% to 18% higher than those of susceptible cultivars in fine-textured soils with average preplant populations ranging from 463 to 14,330 SCN eggs/100 cm(3) soil. In coarse-textured soils, yields of susceptible cultivars were 21% to 56% less than the resistant cultivars with average preplant densities ranging from 1,661 to 15,558 SCN eggs/100 cm(3) soil. The reproductive index ranged from 0.1 to 5.5 for resistant cultivars and 0.4 to 112 for susceptible cultivars. In 1993, yield of P. sojae-susceptible, nematode-resistant 'Asgrow A 3431' was as high as yield of the P. sojae-resistant, nematode-susceptible cultivar 'Resnik' in a Phytophthora-infested field. The nematode-resistant cultivars Madison Experimental 131527 and Asgrow A3431 had higher yields than AgVenture AV1341 and susceptible cultivars Resnik and Kenwood when compared over five nematode-infested sites. Nematode-resistant cultivars were found to be excellent alternatives to currently grown susceptible cultivars for managing SCN where group III cultivars are used. However, better cultivar alternatives may be needed for sites with combined Phytophthora root rot and cyst nematode problems.