Naotaka Matsuzoe

Behavior and mutation of Ralstonia solanacearum in Solanum toxicarium grown in aseptic culture

To study the behavior and mutation of Ralstonia solanacearum in Solanum toxicarium, which is resistant to bacterial wilt, S. toxicarium was grown in aseptic culture and inoculated with R. solanacearum. Although 60%–80% of the inoculated plants were wilting after 2 to 3 days, most wilted plants had recovered by 20 days after inoculation. The pathogen was reisolated from over 98% of inoculated plant stems, but the percentage of recovery decreased the closer the isolation sites were toward the upper stem sections. Three colony types, characterized as fluidal white, nonfluidal red, and a mixture of fluidal white and nonfluidal red, were reisolated from the stems. Nonfluidal red colonies were less virulent on tomato plants than fluidal white colonies.

PHENOTYPIC CONVERSION OF RALSTONIA SOLANACEARUM IN WATER EXTRACT OF SOLANUM TOXICARIUM

Ralstonia solanacearum is a soil-borne pathogen that causes bacterial wilt in numerous plant species worldwide. In soil and culture media, the pathogen can undergo spontaneous phenotypic conversion (PC) from a pathogenic to a non-pathogenic form. This PC occurs also in Solanum plants and their homogenates. Little is known about the PC mechanism so that, to elucidate it, the culture conditions that influence bacterial PC were investigated using water extract of Solanum toxicarium. The pathogen was incubated in static culture in the water extract at various initial bacterial concentrations and incubation temperatures. PC did not occur during the exponential phase, but the pathogen underwent PC at the 4-5th day after reaching the level of 108 CFU ml-1. However, PC occurred infrequently when the bacterium was grown under conditions that did not allow a high concentration. Thus, R. solanacearum undergoes PC when the bacteria are present in the water extract for a certain period (4-5 days) at a high concentration (108 CFU ml-1). It is thought that the bacteria consume the nutrients in the water extract at the initial stage of culture, and that a starvation state will be reached if the pathogen is present for a certain period at a high concentration. Thus, it is supposed that the pathogen undergoes PC in order to express a phenotype advantageous to growth under nutrient starvation stress. Bacterial PC was not influenced by low temperature stress in the water extract, though it was induced at high temperature.

Varietal differences in the chlorogenic acid, anthocyanin, soluble sugar, organic acid, and amino acid concentrations of eggplant fruit

Summary Eggplant (Solanum melongena L.) is an important crop in Japan, with a long history of cultivation. Although many eggplant cultivars and lines have been developed, their nutrient concentrations, including phenolic compounds, have not been investigated in detail. In the present study, we investigated varietal differences in the concentrations of taste (e.g., soluble sugars, organic acids, and amino acids) and functional (e.g., chlorogenic acid, anthocyanins, and amino acids) compounds in eggplant fruit using 34 cultivars and lines with diverse growth habits, fruit shapes, sizes, and colours. The concentrations of taste and functional compounds differed among cultivars and lines. Variations in chlorogenic acid [0.1 – 2.5 mg g–1 fresh weight (FW)] and anthocyanin (0.0 – 0.4 A532 units g–1 FW) concentrations were greater than those of soluble sugars (e.g., sucrose, 0.5 – 1.7 mg g–1 FW; glucose, 7.6 – 13.7 mg g–1 FW; fructose, 6.2 – 15.0 mg g–1 FW) and organic acids (e.g., citric acid, 0.07 – 0.21 mg g–1 FW; malic acid, 0.9 – 1.9 mg g–1 FW). We also found that the coefficient of variation in amino acid concentrations varied with amino acid. Glutamine (27.4 – 135.8 mg 100 g–1 FW) and arginine (4.5 – 23.1 mg 100 g–1 FW) had the largest variation between varieties. These results indicate the importance of cultivar selection to optimise the concentrations of ingredients and will contribute to improvements in the functionality of eggplant through breeding.