Eleven species of Pythium were isolated from leaf blight symptoms on creeping bentgrass (Agrostis palustirs Huds.), Kentucky bluegrass (Poa pratenisis L.) and zoysiagrasses (Zoysia japonica Steud., and Z. matrella (L.) Merr.) planted on golf courses in Korea. Mycelial growth on potato carrot agar medium under various temperature conditions indicated that Pythium species obtained in this study could be divided into four groups based on their responses to temperature conditions. P. vanterpoolii was found to favor low temperature conditions with the optimum temperature of $25^{\circ}$, whereas P. aphanidermatum and P. myriotylum favored relatively high temperature conditions with the optimum temperature of $35^{\circ}$. Other species including P. arrhenomanes, P. catenulatum, P. graminicola, P. oligandrum, P. rostratum, P. torulosum, and P. ultimum were the intermediate group with the optimum temperature of 25~$35^{\circ}$. P. periplocum was similar to the intermediate group but the minimum temperature for its mycelial growth was $15^{\circ}$, which was approximately $5^{\circ}$ above that for the intermediate Pythium spp.group. In the pathogenicity tests conducted in the lab using potted plants, P. aphanidermatum, P.a arrhenomanes, P. catenulatum, P. graminicola, P. myriotylum, P. periplocum, P. rostratum, P. torulosum, P. ultimum, and P. vanterpoolii were found to be pathogenic to creeping bentgrass and Kentucky bluegrass. P. aphanidermatum, P. catenulatum, and P. graminicola were frequently isolated from leaf blight symptoms of creeping bentgrass and Kentucky bluegrass in golf courses during the warm and humid periods in July-August. On the other hand, P. vanterpoolii and P. torulosum were frequently isolated during the cool and humid periods in March-May, suggesting both species might be the major causes of leaf blight occurring in the spring time. Zoysiagrass was susceptible to P. arrhenomanes and the heterothallic Pythium sp. (Ht-F), showing stem and crown rot of turf-grasses at poorly drained areas under coool and humid or rainy conditions. P. oligandrum and the heterothallic Pythium sp. (Ht-L) isolated from creeping bentgrass were avirulent to all species of turfgrasses tested in this study.

Chrysanthemums showing leaf mottling were collected from three southern locations in Korea in 1998. Two kinds of viruses were isolated from the leaves and were identified as tomato aspermy virus ch-TAV) and chrysanthemum virus B (ch-CVB), according to their host range, morphology, intracellular location, agar gel double diffusion test, and double-stranded RNA (dsRNA) analysis. The purified ch-TAV was spherical particles of approximately 29 nm in diameter and ch-CVB was filamentous particles of 685 nm long. Inclusion bodies were not observed in ch-TAV and/or ch-CVB infected chrysanthemum. ch-TAV showed positive serological reaction with TAV antiserum (ATCC-127) but not with CMV-pepper antiserum. In dsRNA analysis, four kinds of viral dsRNA were observed on ch-TAV and one viral dsRNA was shown on ch-CVB. Rate of co-infection with TAV and CVB in commercial chrysanthemums was 20.9%. On the other hand, infection with CVB alone was 97.2%. However, chrysanthemums naturally infected with TAV alone were not found.

A fungus associated with the leaf spot of German iris (Iris germanica) was identified as Cladosporium iridis based on the morphological characteristics of the condiophores and conidia. A conidial suspension of the fungus was artificially inoculated onto a healthy unwounded plant, proving its pathogenicity. This is the first record of this disease from Korea.

Cytological changes of cowpea root at the early stage of root nodule formation (within 5 days after inoculation) were viewed by light and electron microscopy. The root region affected by the rhizobial infection, which was composed of a redial array of cortical cells, had prominent cell divisions, mostly anticlinal in the inner cortical cells and in addition oblique and periclinal in the outer cells. An infected root hair cell (or root hair-producing epidermal cell) had numerous infection threads and degenerated cytoplasm. Module meristem was formed adjacent to the infected root hair cell, and characterized by dense cytoplasm, prominent nucleus, numerous small vacuoles, and increased plastids, containing infection threads as well. Bacterial cells were dividing inside the infection thread, the wall materials of which appeared to be dissolved ad accumulated in small vacuoles. inner cortical cells contiguous to the nodule meristem appeared to be actively dividing and dedifferentiating; however, they were not infected by the rhizobia. These structural characteristics are similar to those in the Bradyrhizobium-soybean association previously reported, and may reflect the similar cytological process in cowpea in the early nodule formation.