Rice and weed interference in the paddy field caused by resource competition and allelopathy. Evaluation method of active weed suppressive behavior of rice to weed was developed by eliminating light competition at soil condition. Twenty eight days old rice seedlings (6-7 leaf stage) which was grown at saturated, no drainage pot were clipped above 3~~4cm from the soil surface. Weeds seeded around clipped rice stem, named ratoon seeding screening method, showed varietal suppressive difference to Echinochloa crus-galli, Echinochloa crusgalli var. praticola and Monochoria vaginalis. Potential allelopathic rice varieties, Sathi, AC1423 and PI312777 showed better suppressive activity to weed seedling growth than Nonganbyeo and Keumobyeo. Weed suppression of one plant of rice cultivars could be evaluated by the cell size of 2.5~times2.5cm at rice clipping of seedling 29 days after rice seeding.

Field studies were conducted in the southeastern Korea (36~circ N) on a commerce silt loam soil at paddy field. Seed were manually planted on 16 July 2003. Plants were planted with plant densities of 70~times 10 cm (row width x plant spacing), 50 x 10 cm, and 30 ~times 10 cm. Two seedlings per hill were taken prior to V3 stage. Fertilizer was applied prior to plant at a rate of 30-30-34 kg (N-~textrmP2~textrmO5 -~textrmK2~textrmO ) per ha. Experimental design was a randomized complete block in a split plot arrangement with three replications. Yield from different planting densities responded similarly in three soybean cultivars and increased when planting density increased. Somyeongkong showed the highest increasing rate of yield about 26% by 338 g ~textrmm-2 at 30 x l0 cm compared to yield of conventional planting density (70 x 10 cm). Also, the planting density significantly affected pod and seed number and seed weight, but not seed per pod. The tallest plant appeared at 30~times 10 cm. The change of leaf area according to days after emergence showed differently in soybean cultivars. The highest and lowest total dry matter production per square meter appeared at 30 x 10 cm and at 70 x 10 cm, respectively. Crop growth rate (CGR) showed greater at R3∼R4 stages compared with V7∼R2 or R2∼R3 growth stages and showed the greatest at 30 x 10 cm in three soybean cultivars. As late planted soybean, there was a significant relation between seed yield and CGR, and leaf area index (LAI) according to planting densities at before and after the flowering stage. Relationship between seed yield and CGR in three planting densities showed a highly significant positive relation (~textrmR2 =0.757) at R3 to R4 stages, and significant relations (~textrmR2 =0.505, 0.617) at V7 to R2 and V2 to V3. Also, there was a highly significant positive difference between seed yield and LAI during R3 to R4 and R2 to R3 stages.

This study was conducted to determine the effects of two plant populations (28 and 14 plants per m2 ) and two toppings in conventional plant population (28 plants per m2 ) on soybean (Glycine max L. cv. Pungsannamulkong) cultivated in the paddy field. The two topping time were taken at 6th to 7th and 8th to 9th trifoliolate leaf stages in the conventional plant population. Experimental design for growth data was a randomized complete block with three replications, and samples were taken at R1 (July 31), R3 (August 19), R5 (September 2) and R7 (September 23) growth stages. The branch number of soybean was relatively higher in the low plant population (14 plants per m2 ) and with the topping at the 6th to 7th leaf stage, in the conventional plant population (28 plants per m2 ), and with topping at the 8th to 9th trifoliolate leaf stage in descending order. The highest average branch length of soybean was observed in the low population and the longest branch length was observed from the soybean with topping at the 6th to 7th leaf stage. The leaf number per plant was decreased in order of in the low population, with the topping at 6th to 7th trifoliolate leaf stage, with the topping at 8th to 9th trifoliolate leaf stage, and in the conventional population. The leaf area was high in the low population and with topping at 6th to 7th trifoliolate leaf stage and was relatively low in the conventional population and with the topping at 8th to 9th trifoliolate leaf stage in soybean. The dry weight of leaves and branches was high in the low population and with the topping at 6th to 7th trifoliolate leaf stage and was relatively low in the conventional population and with topping at 8th to 9th trifoliolate leaf stage. The leaf number per plant was high in the low population and with topping at 6th to 7th trifoliolate leaf stage and was relatively low in the conventional population and with topping at 8th to 9th trifoliolate leaf stage. The grain yield per 10a was high with the topping at 6th to 7th trifoliolate leaf stage.

If a quantitative trait loci (QTL) marker identified in a population is applicable to different populations (marker universality), this will not only reduce the labor and cost in marker assisted selection (MAS), but accelerate the application of molecular markers to real breeding programs. Present study aims to evaluate the defined QTL related markers from a population to a different breeding population for the MAS. Four rice breeding populations were subjected to seventy-five simple sequence repeat (SSR) markers which were already identified for their polymorphism information content (PIC) in the parents of the crossings. Among them, eight markers were evaluated for their correlation between presence of marker alleles and phenotypic expression in breeding populations. A reasonable level of polymorphism for the mapped markers originated from any sources of rice accessions was observed between crosses of any sources (marker repeatability). However, correlation between presence of markers and expression of the traits in rice breeding populations was not significant except for minor portion of traits and markers examined (failure of marker universality). In the present study, various strategies were discussed to develop new markers with universality of breeding application.