Introgression of Gene for Non-Pollen Type Thermo-Sensitive Genic Male Sterility to Thai Rice Cultivars

For the two-line hybrid rice system, pol en sterility is regulated by recessive gene that responds to temperature. The recessive gene controlling thermo-sensitive genetic male sterility （TGMS） is expressed when the plants are grown in conditions with higher or lower critical temperatures. To transfer tgms gene（s） control ing TGMS to Thai rice cultivars by backcross breeding method, a male sterile line was used as a donor parent while Thai rice cultivars ChaiNat 1, PathumThani 1, and SuphanBuri 1 were used as recurrent parents. The BC2F2 lines were developed from backcrossing and selfing. Moreover, the simple sequence repeat （SSR） markers were developed for identifying tgms gene and the linked marker was used for assisting selection in backcrossing. The identification lines were confirmed by pol en observation. The results showed the success of introgression of the tgms gene into Thai rice cultivars. These lines will be tested for combining ability and used as female parent in hybrid rice production in Thailand.     

Cryptic improvement for fertility by continuous selfing of diploid potatoes using Sli gene

While a diploid potato was continuously selfed by a function of Sli gene, the level of heterozygosity reduced, and the fertility also reduced (inbreeding depression), which might be improved because continuous selfing could eliminate undesirable recessive alleles. To explore what was occurring as advancing self-generations in terms of fertility, 51 plants of an S₃ diploid potato family were evaluated for fertility-related traits and analyzed by RFLP markers. The level of heterozygosity was positively correlated with any of fertility-related traits (r = 0.108−0.333). At least six loci on six chromosome sections were associated with fertility-related quantitative trait loci (QTLs), of which three performed better in the heterozygotes and three in the homozygotes. By further continued selfing, QTLs performing better in heterozygotes were likely fixed to homozygotes with secondly better performance, and those performing better in homozygotes were fixed to the best genotypes. Thus, the selfed progenies were cryptically being improved for fertility by genetic fixation to the best or better genotypes in fertility-related QTLs.     

SSR-based and grain yield-based diversity of hybrid maize in Thailand

Commercial hybrid maize varieties are often used to extract new inbred lines in hybrid breeding programs. Seven commercial hybrid maize varieties were crossed in a diallel design, and the resulting hybrids and selfed progeny were evaluated for yield and adaptability grown in six locations in Thailand. The parental varieties were analyzed with a set of 64 Simple Sequence Repeat (SSR) loci, spanning all 10 chromosomes. The average number of alleles per SSR locus was 4.98 with a range of 2–11. The polymorphic information content (PIC) varied from 0.24 to 0.89, with an average of 0.69. Using SSR-based genetic distance (GD), an UPGMA dendrogram showed seven field corn varieties classified into three distinct groups. Troyer's genetic distance (TGD) calculated from yield data, which is a function of inbreeding depression, varied from 0.493 to 1.015 between different parental combinations. A significant positive correlation was found between the GD and TGD across the six locations (0.66^**). The GD correlated positively with specific combining ability (SCA) as well across all locations (r = 0.76^**) heterosis was significant for grain yield and SCA, accounting for 47% of the sum of the square among entries. Therefore, we suggest that broad base populations derived from each of the distinct groups can be formed using combined criteria of SSR-based GD, TGD, grain yield, GCA and SCA.     

Detection and integration of gene mapping of downy mildew resistance in maize inbred lines though linkage and association

Association mapping relies on the variation and extent of linkage disequilibrium within a species to identify genes of interest; this is an alternative to linkage mapping in traditional biparental population, which exploits only the variation in the two parents of the mapping population. This study was designed to identify association between 48 SSR markers and downy mildew (DM) resistance using a set of 60 public and private maize inbred lines in Thailand. Genetic diversity and population structure in the set were calculated. A total of 489 alleles with an average gene diversity of 0.70 revealed two subpopulations among the 60 maize inbred lines. Analysis of variance resulted in significant effects of phenotypic values of tested entries, with significant effects of inbred lines, locations, and their interaction. In addition, the analysis of variance for broad sense heritability also indicated high heritability (0.97), and association analysis revealed three significant SSR-trait associations (P < 0.05). These three significant SSR loci have not been reported in previous linkage mapping studies. Our results suggest that new allelic variants associated with DM resistance in these germplasm collections should be useful to help identify new lines carrying alleles for DM resistance in breeding marker-assisted selection programs.     

Genetic diversity of physic nut (<Emphasis Type="Italic">Jatropha curcas</Emphasis> L.) revealed by SSR markers

Ten microsatellite markers were used to investigate genetic diversity and genetic structure among 32 accessions of Jatropha curcas. Low levels of average genetic diversity were observed (H _E = 0.160). A dendrogram produced by the Unweighted Pair Group Method with Arithmetic Mean (UPGMA) based on Nei’s genetic distances revealed 3 groups among 32 accessions. The genetic differentiation (F _ST ) among two groups was significant (P < 0.01). The model-based Bayesian clustering method indicated that a population structure (ΔK) was separated into two groups. The analysis of molecular variance (AMOVA) showed higher variability (63.753%) among groups than within groups (36.247%). These findings could assist in defining the best method of genetic conservation and studies in breeding programs for genetic improvement of J. curcas.     

Detection of candidate R genes and single nucleotide polymorphisms for downy mildew resistance in maize inbred lines by association analysis

Downy mildew (DM) is a plant disease that strongly limits maize production. The resistance (R) genes for this disease have been identified and characterized and serve as important tools for plant disease evaluation. In this study, partial genes for PIC15, PO145579, and zmcf5 were identified and analyzed in a panel of 60 public and private maize inbred lines using bioinformatics and statistics tools. These candidate R genes exhibited an average nucleotide diversity value of 0.015. The negative Tajima’s D values for these genes suggested that purifying selection has played a role in the evolution of maize DM resistance genes. In addition, linkage disequilibrium among these genes occurred across an extent of ~ 200 bp. Using association analysis methods, a general linear model, and a mixed linear model, five polymorphisms within the partial PIC15 and PO145579 genes were detected and associated with DM disease. These are new polymorphisms that have not previously been reported in association with DM disease traits. Therefore, correlations between these new polymorphisms and DM disease in these germplasm collections could advance the development of a functional marker for marker-assisted selection of DM disease resistance in maize breeding programs.     

Expression of S-locus inhibitor gene (Sli) in various diploid potatoes

Summary S-locus inhibitor gene (Sli), which can inhibit gametophytic self-incompatibility in diploid potatoes and alter self-incompatible to self-compatible plants, was introduced by crossing into 32 diploid genotypes as females and its expression in the F₁ and S₁ progenies was investigated. We found that the expression of self-compatibility in the F₁ hybrid progeny depended largely upon the female genotypes and partly upon the male genotypes (=Sli gene donor clones). Successful females produced hybrid plants, in which 67.1% of self-pollinated plants set S₁ seeds. By second selfing upon the S₁ plants, an average of 44.2% of self-pollinated plants were self-compatible. Unsuccessful females produced hybrids, most of which were self-incompatible or male-sterile. Restriction fragment patterns of chloroplast DNA (ctDNA) were able to distinguish successful females (S- or A-type ctDNA) from unsuccessful females (W- or T-type ctDNA). A ctDNA high-resolution marker analysis using seven microsatellites and H3 marker supported a higher degree of differentiation between the two groups of ctDNA types and implied a possible interaction between the cytoplasm and Sli gene function. However, it has been known that the cytoplasm having T-type ctDNA and that derived from Solanum demissum (haplotype 26 of W-type ctDNA) cause male sterility, and the present case with unsuccessful females were likely caused by male sterility rather than the failure of Sli gene function.