ABSTRACT Drought and salinity are important abiotic stress factors negatively affecting productivity of the world-renowned jasmine rice (Oryza sativa L. subsp. indica Kato) ‘KDML105’ in the northeast Thailand. Two chromosome segment substitution lines (CSSLs) of ‘KDML105’ which were introgressed with drought tolerance quantitative trait loci (DT-QTLs), designated CSSL94 and CSSL103, and two improved ‘KDML105’ lines, designated RGD1 and RGD4, carrying the salt tolerant gene (SKC1) were used for evaluation of growth, physiological and biochemical traits in response to drought and salt stress conditions in comparison with ‘KDML105’ (sensitive parental cultivar) and DH103 (DT-QTL donor). Seedlings were grown for 21 d in hydroponic solutions and then subjected to drought stress (20% polyethylene glycol 6000) or salt stress (150 mM NaCl) for 10 d. Under both stresses, all four improved rice lines showed lower percent reduction in growth compared with ‘KDML105’. Under drought stress, CSSL94 and CSSL103 had significantly higher relative water content (88% and 89%) compared with that of ‘KDML105’ (82%). These lines accumulated 42% and 45% lower hydrogen peroxide, resulting in 25% and 32% lower malondialdehyde, and less membrane damage (24% lower electrolyte leakage). On the other hand, better growth of RGD1 and RGD4 under salt stress, compared with ‘KDML105’, was associated with an efficient maintenance of ion homeostasis (57% and 69% lower Na+/K+), 34% and 43% lower hydrogen peroxide, and 54% lower electrolyte leakage. The introgression of DT-QTL conferred not only drought but also salt tolerance to the recipient genotype. Likewise, introgression of SKC1 conferred both salt and drought tolerance.

ABSTRACT Drought is a major cause of potential plant stress in areas of rain fed lowland rice (Oryza sativa L.) cultivation. The characteristics of the root system are important for rice plant adaptation and acquiring water under drought conditions. This study aims to evaluate the root responses contributing the plant adaptation to drought stress of 'KDML105' chromosome segment substitution lines (CSSLs). The rice genotypes were grown in PVC tubes. At 30 d after planting (DAP), the plants were subjected to two water regimes, well-watered and early drought stress. The two experiments were different in water status shown as relative water content and soil moisture content and classified as two stress condition in particular years i.e. mild and severe stress in 2013 and 2014 respectively. Shoot dry weight (SDW) and leaf area (LA) increased by mild stress while root dry weight (RDW) and total root length were increased by severe stress. The comparison between WW and DS in the percentage of SDW, RDW and LA showed that the CSSL#6 was the great maintenance genotype in both 2013 and 2014 as well as the donor parent (DH212) while 'KDML105' showed a decreasing RDW in DS than WW. Root length density of all CSSLs was higher than 'KDML105' in the shallow soil layer (37%), but CSSL#12 was greatest in root length density at the deeper soil layers (76.7%) under mild stress. Interestingly, CSSL#1, #4, #5, #6, #12, #14 and #15 tended to produce a higher root depth (59.6%, 52.0%, 53.6%, 58.6%, 52.7%, 49.7% and 53.3%, respectively) at 30 to 90 cm of soil depth compared to 'KDML105' under severe stress. It is possible that several chromosome segments associated with root depth were introgressed from the donors (DH103 and DH212) through the breeding procedure, which can be used as a promising breeding material in Thailand.

Verificou-se o uso do marcador LW7 para identificação de linhas mantenedoras B e restauradoras R em sorgo granífero e doce e para identificação de linhas mantenedoras B nas gerações F2, RC1F2 e RC2F2. Vinte e cinco acessos de sorgo foram avaliados e o marcador LW7 identificou corretamente aqueles que possuem o gene de macho-esterilidade (rf4) como Suphan Buril e 03B, os quais não mostraram a banda de 779 pb. O cruzamento entre Suphan Buri1 e uma linha macho-estéril (A) 03A resultou macho-estéril, confirmando a utilidade do marcador em programas de melhoramento. Linhas B em gerações F2, RC1F2 e RC2F2 foram identificadas pelo marcador LW7 e a taxa de segregação de 3:1 para fertilidade e macho-esterilidade nas progênies das três gerações apoiaram o modelo de segregação Mendeliana de um gene. O uso da seleção assistida por marcador foi bem sucedido para o desenvolvimento de linhas de sorgo sacarino com macho-estéreis.

The objectives of this study were to verify the use of LW7 marker in identifying maintainer lines (B-lines) and restorer lines (R-lines) in grain sorghum and sweet sorghum, and to identify B-lines in the F2, BC1F2 and BC2F2 generations. Twenty five accessions of sorghum were evaluated, and LW7 marker correctly identified accessions which presented male sterility gene (rf4) in Suphan Buri1 and 03B cultivars; moreover, these genotypes did not show 779 bp band. The cross between Suphan Buri1 and a male-sterile line (A-line) 03A resulted in a sterilized male, confirming the usefulness of the marker in breeding programs. B-lines in the F2, BC1F2 and BC2F2 generations were identified by LW7 marker. The segregation ratio of 3:1 for male fertility and male sterility in the progenies of the three generations supported the one-gene model of Mendelian segregation. The use of marker assisted selection was successful for line development of sweet sorghum with male sterility.

Thirty rice cultivars were evaluated for salinity tolerance during the seedling stage and were divided into five tolerance groups including tolerant (T), moderately tolerant (MT), moderately susceptible (MS), susceptible (S) and highly susceptible (HS) which comprised 5, 10, 9, 4 and 2 cultivars respectively. Genetic diversity of all rice cultivars was evaluated using random amplified polymorphic DNA (RAPD) and simple sequence repeats (SSR) markers. The cultivars were evaluated for polymorphisms after amplification with 20 random decamer primers and 20 SSR primer pairs. A total of 161 RAPD markers and 190 SSR alleles were produced which revealed 68.94% and 89.47% polymorphism respectively. Mean genetic similarity coefficient was 0.82 for RAPD and 0.70 for SSR. Cluster analysis based on RAPD markers was effective in grouping cultivars based on their salt tolerance ability. Group IA1, IB and IV contained three T, three S and two HS rice cultivars respectively. The MT and MS cultivars which showed similar physiological responses to salinity were resolved into two groups: Group IA2 and Group II comprising ten and eight MT/MS cultivars respectively. Cluster analysis based on SSR markers separated rice cultivars into groups based on genetic relatedness which did not correspond to salinity tolerance level. The results from this study provided some useful implications for salt tolerance breeding programs. The evaluation of genetic similarity and cluster analysis together with salt tolerance ability provides some useful guides for assisting plant breeders in selecting suitable genetically diverse parents for the crossing program.