A two-year factorial arranged field experiment in randomized complete block design with three replications was carried out in 2014 and 2015 at Michael Okpara University of Agriculture Teaching and Research Farm, Umudike (latitude 05° 29′N; longitude 07° 33′E; altitude 122 m above sea level), Nigeria. The
objective
s were to assess growth and yield response of twenty newly released cowpea genotypes to different planting dates (July, August and September). Plant height, number of leaves/plant, number of branches/plant, shoot biomass, total dry matter, number of nodules/plant, weight of pod, number of seeds/pod, seed weight/pod and grain yield varied amongst the genotypes and across the different planting dates in both years. The association between grain yield and other variables analysed across both years was significant and positive except 100-seed weight and the phenological characters of the plant. Path coefficients analysis across two years indicated that seed weight/pod followed by number of branches/plant and number of seeds/pod had positive direct effect on grain yield of cowpea in contrast to characters that exhibited negative but direct effect on yield. The other traits had relatively negligible to low indirect effects that were positive through other component traits. The grain yield sequence of interaction between genotype and date of planting was in this order: IT06K-141 planted in July > IT11K-61-82 planted in September > IT99K-573-1-1 planted in August. IT06K-141 genotype was considered to be better endowed genetically while the mean across both years indicated August as appropriate planting date to ensure high and sustainable grain yield.
The present study was conducted to evaluate the biological responses of soybean irradiated by gamma-rays. Four elite Korean soybean cultivars, Kwangankong, Shinpaldal-2, Shinhwakong, and Ilmikong, were irradiated with 100–400 Gy of gamma-rays. All cultivars showed significant reductions in morphological parameters. Seedling emergence rates of Kwangankong, Shinpaldal-2, Shinhwakong, and Ilmikong decreased by 46%, 31%, 44%, and 43% at 400 Gy, respectively. Plant height and fresh weight decreased with increasing dose. The median reduction dose (RD50) for plant height ranged from 184 to 278 Gy with an average of 212 Gy. The optimal dose of gamma irradiation for inducing mutation in the four elite soybean cultivars was in the range 200–300 Gy. Contents of malonaldehyde (MDA) in the gamma-ray irradiated plants were higher than those in the controls. With the exception of Kwangankong, activities of ascorbate peroxidase (APX) in other cultivars decreased at 100 Gy and started to increase significantly at 200 Gy and Shinhwakong cultivar had highest APX value observed at 300 Gy. No significant changes in peroxidase (POD) activity were observed in the Kwangankong, Shinpaldal-2, and Shinhwakong, while, POD activity increased with increasing dose in Ilmikong. In addition, gamma-ray treatments elicited a marked reduction in chlorophyll
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Pathogen attack and abiotic stress affect grain yields in rice fields worldwide. Rice leaf blast is caused by the fungal pathogen
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In this study, two near-isogenic lines (NILs) were selected from a series of chromosome segment substitution lines developed from an interspecific cross between
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Seedling vigor in drought stress conditions is an important characteristic of the dry direct-seeded rice system. The drought stress in the seedling stage disrupts seed germination and delays the establishment of seedlings. However, little is known about the genetic mechanism of seedling vigor in drought conditions. The identification of quantitative trait loci (QTL) was conducted using 162 recombinant inbred lines (RILs) derived from a cross between two rice varieties—a Tongil-type Milyang23 and a temperate japonica Tong88-7. The seedling vigor of these RILs was characterized by measuring 10 morphological traits of the seedlings grown under drought conditions. The Tong88-7 seedlings showed significantly higher values than the Milyang23 seedlings for all traits. The genotyping-by-sequencing method was used to construct a map of 6140 single nucleotide polymorphisms. Six main-effect QTLs (M-QTLs) associated with seedling vigor traits under drought stress were identified on chromosomes 9 and 11. In particular, five out of these six QTLs were located on chromosome 11, explaining the phenotypic variances of 4.3% through 10.1%. In addition, 21 epistatic QTLs (E-QTLs) were detected, and the 27 loci involved in this interaction were distributed on 11 chromosomes. Both M-QTLs and E-QTLs detected in this study would be useful in breeding programs to develop elite rice varieties especially adapted to dry direct-seeded rice system.
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We evaluated genetic diversity and population structure in 32 Canadian maize inbred lines and performed association analysis for five agronomical traits and 50 simple sequence repeat (SSR) markers. Genetic diversity analysis revealed a total of 381 alleles at the 50 SSR loci. The average number of alleles per locus was 7.6. The average genetic diversity and polymorphic information content values were 0.709 and 0.676, respectively. The average major allele frequency was 0.414. Population structure analysis indicated that these maize inbred lines were comprised of four major groups and one admixed group based on a membership probability threshold of 0.80. A general linear model showed 20 marker-trait associations involving 12 SSR markers associated with the four agronomic traits except for leaf length. For these marker-trait associations, phi056, mmc0022, bnlg1621, bnlg1695, phi116, and bnlg1028 were associated with only one trait. The other nc005, bnlg1012, phi065, and umc1982 were associated with two traits. Two SSR markers, mmc0111 and umc1038, were associated with three traits. These results will help in optimizing the choice of parents for crossing combinations, as well as in selecting markers for marker-assisted selection for maize improvement.
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