Genetic diversity in mutated and non-mutated rice varieties.

We studied the genetic variability due to mutation induced by γ-rays (10, 15, and 20 Kr) on various traits of twelve rice genotypes. Mutated and non-mutated seeds were sown in the field between July 2013 and 2014 using a split plot design. Yield and yield-related trait data was recorded, which showed significant (P < 0.05) genotypic and irradiation effects. Gamma radiation exerted non-significant effects on the panicle length of all plants, indicating the uniformity of performance of this character at different radiation levels. The plant height, grains per main panicle, panicle length, 1000-grain weight, grain weight per main panicle, and fertility percentage was minimum in Basmati-198, Basmati-Pak, Shaheen-2000, Super Basmati, Basmati-385, and Super Basmati, respectively, when exposed to radiation at 20 Kr. However, Basmati-370 attained maximum flag leaf area at this level of radiation. Broad sense heritability ranged from 72.0 to 97.7%, indicating the possibility of selection during earlier generations. Phenotypic correlation was positive and significant between grain weight per main panicle with panicle length and flag leaf area. Number of grains per main panicle and genotypic correlation were positive among grain weight per main panicle, panicle length, fertility percentage, 1000-grain weight, and plant height, indicating the effectiveness of these traits in the selection for yield. Phylogenetic analyses revealed a pair-wise similarity ranging from 0.51-0.76 before mutation and 0.39-0.89 after mutation. This study proved that γ-rays at 20 Kr would be most effective in creating genetic variability in the existing germplasm.

Drought-tolerant rice germplasm developed from an Oryza officinalis transformation-competent artificial chromosome clone.

Oryza officinalis has proven to be a natural gene reservoir for the improvement of domesticated rice as it carries many desirable traits; however, the transfer of elite genes to cultivated rice by conventional hybridization has been a challenge for rice breeders. In this study, the conserved sequence of plant stress-related NAC transcription factors was selected as a probe to screen the O. officinalis genomic transformation-competent artificial chromosome library by Southern blot; 11 positive transformation-competent artificial chromosome clones were subsequently detected. By Agrobacterium-mediated transformation, an indica rice variety, Huajingxian 74 (HJX74), was transformed with a TAC clone harboring a NAC gene-positive genomic fragment from O. officinalis. Molecular analysis revealed that the O. officinalis genomic fragment was integrated into the genome of HJX74. The transgenic lines exhibited high tolerance to drought stress. Our results demonstrate that the introduction of stress-related transformation-competent artificial chromosome clones, coupled with a transgenic validation approach, is an effective method of transferring agronomically important genes from O. officinalis to cultivated rice.

Identification of neutral genes at pollen sterility loci Sd and Se of cultivated rice (Oryza sativa) with wild rice (O. rufipogon) origin.

Pollen sterility is one of the main hindrances against the utilization of strong intersubspecific (indica-japonica) heterosis in rice. We looked for neutral alleles at known pollen sterility loci Sd and Se that could overcome this pollen sterility characteristic. Taichung 65, a typical japonica cultivar, and its near isogenic lines E7 and E8 for pollen sterility loci Sd and Se were employed as tester lines for crossing with 13 accessions of wild rice (O. rufipogon). Pollen fertility and genotypic segregations of the molecular markers tightly linked with Sd and Se loci were analyzed in the paired F(1)s and F(2) populations. One accession of wild rice (GZW054) had high pollen fertility in the paired F(1)s between Taichung 65 and E7 or E8. Genotypic segregations of the molecular markers tightly linked with Sd and Se loci fit the expected Mendelian ratio (1:2:1), and non-significances were shown among the mean pollen fertilities with the maternal, parental, and heterozygous genotypes of each molecular markers tightly linked with Sd and Se loci. Evidentially, it indicated that the alleles of Sd and Se loci for GZW054 did not interact with those of Taichung 65 and its near isogenic lines, and, thus were identified as neutral alleles Sd(n) and Se(n). These neutral genes could become important germplasm resources for overcoming pollen sterility in indica-japonica hybrids, making utilization of strong heterosis in such hybrids viable.

Genetic analysis of NaCl tolerance in tomato.

We attempted to find the suitable parents for the development of tomato hybrids for high salt soils by exploiting combining ability, gene action and heterosis. Six salt-tolerant and three salt-intolerant genotypes, along with their 18 F1 crosses, were evaluated at seedling stage under 10 and 15 dS/m (NaCl) salinity stress, compared to the control level of salinity. The experiment was laid out based on a two-way complete randomized design factorial arrangement with two replications; data on root and shoot length, fresh and dry weights, leaf area, plant length, Na(+), K(+) and K(+)/Na(+) concentrations were recorded. There was significant variation within genotypes, lines, testers, crosses, and line × tester interaction for all plant characters studied under normal and two salinity levels. Estimates of combining ability indicated that under low (10 dS/m) and high (15 dS/m) salinities, line BL1176 and tester LO2875 showed significant GCA effects for most of the traits studied. The cross-combinations 6233 × LO2875, CLN2498A x LO2875 and BL1176 × 17902 showed highest SCA values for most of the characters under 10 and 15 dS/m, respectively. Potence ratio showed that under low and high salinities, all the traits showed over dominant type of gene action except leaf area and K(+) concentration (in 10 dS/m) and shoot length, and leaf area (in 15 dS/m). The highest heterosis for most of the parameters was observed in cross-combinations BL1176 × LO2875 and CLN2498A x LO2875.