Evaluation of Agronomic Traits in Chromosome Segment Substitution Lines of KDML105 Containing Drought Tolerance QTL under Drought Stress

Drought is a major abiotic constraint to rice production in rainfed lowland and insufficiently irrigated areas. The improvement of drought tolerant varieties is one of the strategies to reduce the negative effects of drought. Quantitative trait loci （QTLs） for primary and secondary traits related to drought tolerance （DT） on chromosomes 1, 3, 4, 8 and 9 that determined from double haploid lines derived from a cross between CT9993 and IR62266 were introgressed and dissected into small pieces in the genetic background of Khao Dawk Mall 105 （KDML105） to develop chromosome segment substitution line （CSSL） population. The CSSLs were evaluated at the reproductive stage for their agronomic performance and yield components under drought stress, and results were compared with irrigated condition. The flowering of CSSL lines was 6 to 7 d earlier than KDML105. The mean values of grain yields in the CSSLs were higher than KDML105 under drought and irrigated conditions. At irrigated condition, the grain yields of introgression lines carrying DT-QTLs from chromosomes 4 and 8 were higher than that of KDML105, whereas other traits showed little difference with KDML105. Analysis indicated that grain yield has positive correlation with plant height, tiller and panicle number per plant, and total grain weight per plant under drought stress while negatively correlated with days to flowering. As mentioned above, CSSLs showing good adaptation under drought stress can be used as genetic materials to improve drought tolerance in Thai rainfed lowland rice breeding program, and as materials to dissect genes underlying drought tolerance.

Morphological and Anatomical Assessment of KDML 105 (Oryza sativa L.spp.indica) and Its Mutants Induced by Low-Energy Ion Beam

Thai jasmine rice KDML 105 is consumed around the world. BKOS, PKOS and TKOS are new cultivars produced from low-energy ion beam induction in KDML 105. The purpose of this study is to compare the morphology and anatomy between KDML 105 and the three new cultivars. Seeds of the four cultivars were germinated and grown in pots until flowering phase. The plants＇ organs were observed and the lengths of culms, ligules, leaves and panicles were measured. Leaf surface area was calculated and numbers of roots, spikelets and tillers were counted. BKOS and PKOS had significantly shorter culms than KDML 105 and TKOS. The largest leaf area was found in KDML 105 followed by TKOS, BKOS and PKOS, respectively. Numbers of roots and tillers in BKOS and TKOS were significantly fewer than those in KDML 105 and PKOS. The number of spikelets per plant in BKOS was the lowest among all cultivars. For anatomical comparison, cross sections of culms and roots were observed. All plants had a similar arrangement of tissues, but the number and size of cells were different. Furthermore, longitudinal sections of culms showed that the lengths of epidermal and parenchyma cells were directly related with the length of the culm. To compare the leaves, both stomata and epidermal cells were counted and the lengths of the guard cells were measured. The lengths of guard cells of BKOS and PKOS were shorter, but the stomatal density and the stomatal index were significantly greater than those of KDML 105. For TKOS, though the length of guard cells was shorter than that in KDML 105, the difference was not significant. However, the stomatal density and stomatal index were significantly higher than those in KDML 105.