Effects of seven different companion plants on cucumber productivity, soil chemical characteristics and Pseudomonas community

Companion cropping can influence cucumber productivity by altering soil chemical characteristics and microbial communities. However, how these alterations affect the growth of cucumber is still unknown. In this study, seven different plant species were selected as companion plants for testing their effects on cucumber productivity. The effects of different companion plants on changes in soil chemical properties such as electrical conductivity （EC） and contents of essential nutrients as well as the structure and abundance of the soil Pseudomonas community were evaluated. The results showed a higher cucumber yield in the wheat/cucumber companion system than that in the cucumber monocultured and other companion cropping systems. The lowest phosphorus （P） and potassium （K） contents in the soil were found in the cucumber monocultured system, and the highest NO3＋-N and NH4＊-N contents were observed in the rye/cucumber companion system. PCR-denaturing gradient gel electrophoresis （DGGE） and real-time PCR analysis showed that the trifolium/cucumber companion system increased the diversity of the soil Pseudomonas community, while the chrysanthemum/cucumber companion system increased its abundance. Interestingly, plant-soil feedback trials revealed that inoculating the soil of the wheat/cucumber companion system increased the growth of cucumber seedlings. In conclusion, the effects of different companion plants on cucumber productivity, soil chemical characteristics and the soil Pseudomonas community were different, and wheat was a more suitable companion plant for increasing cucumber productivity. In addition, the altered microbial community caused by companion cropping with wheat contributed to increased cucumber productivity.

Arthropods associated with medicinal plants in coastal South Carolina

Arthropods were sampled from feverfew [Tanacetum parthenium （L.） Schultz- Bip], Echinacea purpurea （L.） Moench, Echinacea pallida （Nutt.） Nutt., Valeriana officinalis L., and St. John＇s wort （Hypericum perforatum L.） during 1998-2001. In addition, arthropods were sampled on tansy （Tanacetum vulgare L.） from 2001-2004. In general, 50-60 arthropod species where collected and identified among all of the medicinal plant species. Among the predators, Orius insidiosus （Say） （Hemiptera： Anthocoridae）, Geocoris punctipes （Say） （Hemiptera： Lygaeidae） and spiders were most abundant from 1998-2004. The three-cornered alfalfa hopper, Spissistilus festinus （Say）, was the most abundant herbivore found from 1998 to 2001. Orius insidiosus and G. punctipes were 3-4 times more abundant on T. parthenium than on any other medicinal plant species. Based on the numbers of predatory arthropods found on T. parthenium, this crop could be suitable as a companion or ＂banker＂ plant to attract and maintain populations of predators, especially O. insidiosus and G. punctipes. Whitefly nymphs attacked by predators with piercing/sucking mouthparts are easily identified using a microscope because of the general appearance of the carcass left by the predators. Thus, populations of predators on T. parthenium suppressed Bemisia tabaci populations on E. purpurea when these crops were planted as companion crops.