Masao Yokoo

Photosynthesis and Dry-Matter Production during Ripening Stage in a Female-Sterile Line of Rice

Abstract The relation between the source capacity of leaves and the sink capacity of panicles affects dry-matter production and determines grain yield in rice. The source-sink relation has so far been studied on rice plants from which panicles were artificially removed. We examined the source-sink relation using a female-sterile line FS1 with intact panicles each havinga few fertile grains instead of panicle removal. The leaf photosynthetic rate during the ripening stage in FS1 was measured, in comparison with a normal counterpart Fujisaka 5, and the effect of losing sink function on dry-matter production in the rice plant was characterized. The photosynthetic rate in flag leaves was maintained at a slightly higher rate in FS1 than in Fujisaka 5 in the late ripening stage, though panicles did not function as a sink organ in FS1, and dry-matter production in this line was not lower than that in Fujisaka 5. In the early ripening stage of FS1, culms and leaf sheaths fulfilled the sink function instead of panicles, and the tillers that appeared in the late ripening stage became a new sink organ. Roots also functioned as a possible sink of photosynthates. Owing to the unique character of dry-matter production after heading, FS1 may be useful as a forage crop.

Identification of blast resistance genes in elite Indica-type varieties of rice (Oryza sativa L.).

Eight blast resistance genes --Pia, Pib, Pik-s, Pik-h, Pita, Piz-t, Pi20, and one of three (Pii, Pi3, or Pi5(t)) were identified in 42 IRRI-bred varieties following a differential system using Philippine blast isolates. Among these genes, two genes Pib and one of Pik alleles (Pik-s or Pik-h), were found in almost all IRRI varieties. The number of resistance genes in each variety varied from two to five, and the kinds of gene combination were also limited. This limitation might be due to the gene sources such that IR8, IR24, IR36, or their hybrid progenies were often included in the breeding of these varieties. Using the genefor-gene theory, this study was carried out in three steps: 1) estimation of genes following the reaction patterns of monogenic lines to blast isolates, 2) genetic analysis using BC1F2 populations with a susceptible variety as recurrent parent, and 3) allelism test with Japanese differential varieties. Through genetic analysis, each investigation’s ability to identify resistance genes was demonstrated.

Analysis of Glucose Phosphate Isomerase in Near-Isogenic Lines,and Cultivars of Rice(Oryza sativa L.)

Using the near-isogenic lines, the possible location of glucose phosphate isomeras-2 (phosphoglucose isomerase-2) locus (Pgi-2) in relation to photoperiod sensitivity locus (Se-1) and blast resistance locus (Pi-z) was investigated. The recombination frequency data indicate thatPgi-2 locus locates betweenSe-1 andPi-z loci. Furthermore, 15 Indica cultivars possessed two types of glucose phosphate isomerase-2 (GPI-2) isozyme, whereas only one type of GPI-2 isozyme was found in 30 Japonica cultivars.

Dry-Matter Partitioning and Accumulation of Carbon and Nitrogen during Ripening in a Female-Sterile Line of Rice

Abstract To evaluate the effect of sink restriction on dry-matter partitioning to rice plant organs during ripening, we observed the dry-weight partitioning and accumulation of carbon and nitrogen in a female-sterile line, FS1, which has intact panicles with only a few fertile grains, in comparison with those in a normal counterpart, Fujisaka 5. In spite of the loss of sink function in the panicles, FS1 produced a larger amount of dry-matter than Fujisaka 5. Without a change of panicle dry weight throughout the ripening period, FS1 increased dry weights of culms and leaf sheaths at the early stage and of late tillers at the late stage. The amounts of dry-matter partitioned to panicles, culms plus leaf sheaths and late tillers in FS1 were comparable to those amounts in Fujisaka 5 at maturity, indicating that the latter two organs function as a sink of dry matter to substitute for panicles. Carbon partitioning to plant organs was basically similar to the dry-matter partitioning. Since the amount of nitrogen in a plant hardly increased during the ripening period in FS1 and Fujisaka 5, nitrogen partitioning to plant organs was different from the partitioning of dry matter and that of carbon. Culms, leaf sheaths and late tillers function as a sink of nitrogen partly to substitute for panicles, but the sum of nitrogen partitioned to these organs and panicles in FS1 was markedly smaller than in Fujisaka 5 at maturity, suggesting that other organs do not substitute for panicles in the sink function for nitrogen partitioning. FS1 developed late tillers rapidly at the late stage and had a carbon-nitrogen ratio in the stems different from that in Fujisaka 5.