A Recessive Lesion Mimic Mutant of Rice with Elevated Resistance to Fungal Pathogens

A gamma-ray-induced rice mutant, M1009, which spontaneously forms brown specks on leaves was isolated. In appearance, these lesions very much resemble those that are produced during the hypersensitive resistance response of rice to pathogens. A similar phenotype has been associated with a number of mutants in maize or Arabidopsis, which have been briefly categorized as disease lesion mimics. Brown speck formation was suppressed at temperatures of 25°C and above, and was severe at 20°C. Light irradiation is also required to initiate brown specks. In addition, the mutant exhibits heightened resistance to two major fungal pathogens of rice, Magnaporthe grisea and Cochliobolus miyabeanus. Genetic characterization of the mutant has indicated that its les-bs (lesion-brown speck) phenotype segregates as a monogenic recessive mutation. Received 13 September 1999/ Accepted in revised form 15 December 1999     

Interannual variability in stock abundance of the neon flying squid, Ommastrephes bartramii, in the North Pacific Ocean during 1979–1998: impact of driftnet fishing and oceanographic conditions

Variability in catch-per-unit-effort (CPUE) was examined for the autumn cohort of Ommastrephes bartramii collected with research driftnets during 1979–1998 along five longitudinal transects passing through the Subarctic, Transitional and Subtropical Domains in the North Pacific. CPUE was generally low during the period of intensive commercial driftnet fishing (1980–1992) and increased following the 1992 moratorium on the use of large-scale driftnets. However, CPUE levels were low for the cohorts hatched in 1992 and 1996 (captured in subsequent years owing to a one-year life of O. bartramii ) that experienced low sea surface temperatures from hatching to recruitment. Among similar-aged squid collected from 180° and 179°30'W in June, mantle lengths were significantly greater in 1997 than during 1995–96. These findings suggest that the driftnet fishery and sea surface temperatures from hatching to recruitment strongly affected stock abundance and possibly growth.     

Relationship between resistance to vole browsing and content of ether extract in the bark of larch species and hybrids

We determined the survival rate of tree families produced by the intra- and interspecific crossing of larch species damaged by browsing of vole (Clethrionomys rufocanus bedfordiae Thomas) and the contents of ether extracts (EE) in their bark. The average survival ofLarix gmelini var.japonica Pilg. (L. gmelini)×L. gmelini (G×G) was highest, followed by the hybridL. gmelini×L. leptolepis Gordon (G×L). The families of the hybrid G×L, which is considered suitable for silviculture in Hokkaido, Japan, showed significant differences in survival rates, suggesting that it is possible to produce improved varieties of the hybrid which are more resistant to vole browsing. The EE contents of the bark were under strong hereditary control, and the rank of the EE content among the various families hardly fluctuated between the location of the test fields. The correlation coefficient between the survival rates and the EE contents was highly significant (r=0.89,n=24,p<0.01), indicating that the EE content in the bark may be used as a possible index of resistance or susceptibility to vole browsing in larch plantations. A part of this report was presented at the 106th Annual Meeting of the Japanese Forestry Society, at Sapporo, April, 1995.     

Growth comparison of Asian Nile and red tilapia strains in controlled and uncontrolled farm conditions

Growth of several genetically improved Nile tilapia (GIFT or Genetically Improved Farmed Tilapia, FaST or Freshwater Aquaculture Center Selected Tilapia, SEAFDEC-selected) and domesticated red tilapia (BFS or Binangonan Freshwater Station, NIFI-red or National Inland Fisheries Institute red, HL or Hacienda Luisita) stocks were compared in controlled (tank) and uncontrolled farm conditions (lake-based cages) with unselected NIFI or Chitralada Nile tilapia as control. Specific growth rate differed significantly (P = 0.009) in tank-reared Nile tilapia stocks where GIFT grew best at 1.358%/day followed by FaST (1.307%/day), control stock NIFI (1.257%/day) and SEAFDEC-selected (1.202%/day). Genetic effect explained 84.4% of the variance in growth of Nile tilapia in tanks. Although Nile tilapia growth in cages followed the same trend where GIFT grew best at 1.570%/day, no significant stock differences (P = 0.479) were noted. Meanwhile, red tilapia reared in either tanks or cages showed no significant stock differences in terms of growth. However, survival of the red tilapia stocks in cages differed significantly with HL having the highest percentage survival at 93.3%. The different growth responses of the Nile tilapia stocks especially under controlled (tank) farm conditions were largely due to genetic factors (stock differences).Under uncontrolled farm conditions, environmental factors were generally observed to have also affected the survival and to some extent, the growth of Asian Nile and red tilapia stocks.     

Relationship between zooplankton abundance and the early marine life history of juvenile chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> in eastern Hokkaido,Japan

Interannual variations in abundance, timing of outmigration from rivers, growth rate and condition of juvenile chum salmon (Oncorhynchus keta) were studied in the Nemuro Strait (eastern Hokkaido, Japan) during 1999–2002 to establish a possible relationship to zooplankton abundance. The otolith microstructure of juveniles was examined each year in late June to determine their time and size at sea entry (i.e., outmigration), and to estimate the early marine growth rates. Salmon outmigration peaked in mid- or late May, which coincided, in three of the four study years, with the peak release of juveniles into rivers within the study area. Abundance, growth rate and condition of fish were higher in 2001, when—compared to other years—smaller fish experienced higher growth rates, coinciding with greater zooplankton abundance for that year. Our results suggest that high zooplankton abundance positively influenced juvenile chum salmon growth and the condition of the fish during their early marine life despite their small size at sea entry.     

Estimation of the mode of inheritance of thermal tolerance in the guppy <Emphasis Type="Italic">Poecilia reticulata</Emphasis>

High water temperature influences the survival, growth, and maturation of fish. Genetically characterizing thermal tolerance is one of the most important subjects in fish culture. To identify the genetic characterization of thermal tolerance, this characteristic was compared among strains, and among parents and their offspring, in the guppy Poecilia reticulata. In the strain comparison, significant differences in survival rate were observed among the five strains examined, and between females and males. Females exhibited greater tolerance than males in four of five strains examined. In the comparison between parents and their offspring, stronger influence of female parent than of male parent was observed. Offspring obtained from surviving females exhibited greater tolerance than those from dead females. This tendency was typically observed in male offspring. The survival rate in male offspring obtained from dead female parents was lower than that of those from surviving females. The high-temperature tolerance of male parents did not influence this characteristic in offspring as strongly as that of female parents. These results suggest that the major gene or genes, which has a dominant resistant allele and a recessive sensitive allele, are probably passed on by sex-linked inheritance, located on the X chromosome.