Data base establishment of rice breeding program in Laos

One of the national research priorities is to improve the efficiency of the current breeding and variety testing program in order to accelerate the introduction of better varieties for farmer’s adoption. The database for the rice breeding is the key to achieve the breeding program and would provide valuable scientific information to improve the efficiency of the breeding program for target environments. The objectives of this database were to collect, document and utilize the available data from the national rice breeding program in Laos. Rice breeding program was established at Rice and Cash Crop Research Center in 1991, in collabolation with IRRI, and supported of funding by the government of Switzerland. From 1991 to Philippines and from Thai-IRRI program. Out of 1.627 lines of F2 population, 4 lines were released as TDK and PNG varieties. Out of 64 imported promising lines, 13 lines were released as TDK, TSN, PNG and NTN varieties for different agro climatic zones in Lao PDR. Hybridization at RCCRC was started in 1994, since than, about 272 crosses were made by the Lao breeders. Out of 272 crosses made, so far 8 clones were released as TDK and TSN vareieties and 34 lines were identified as promising lines. Among all parents used in the crossing program at RCCRC, TDK 1 was the dominant parent for evolving promising lines for Lao PDR

Contribution of potential yield, drought tolerance and escape to adaptation of 15 rice varieties in rainfed lowlands in Cambodia

In Cambodia, grain yield in rainfed lowland rice is often affected by drought during late vegetative or reproductive stage. Several experiments were conducted to quantify the contribution of potential yield, drought tolerance and drought escape mechanisms to yield under water stress conditions. In total nine pairs of well irrigated and simulated drought (by draining water) experiments were conducted. Potential yield was obtained under irrigation. Grain yields and flowering dates were recorded in 15 varieties. Drought tolerance was quantified by using drought response index (DRI), which is grain yield under drought adjusted for potential yield and flowering date of the variety. Drought escape is expressed as days to flower under drought conditions. Mean yield reduction due to drought of nine experiments was 27 % (range 12-44). The relative contribution of yield potential, flowering date and DRI to observe yield under drought were evaluated by multiple regression for each experiment. Potential yield accounted for 54% (with a range of 10-80) of the variation in actual yield under drought. This was followed by DRI and flowering date with 34 (with a range of 0-60) and 12 (with a range of 0-30) of the contribution, respectively. It is concluded that selecting for drought tolerance as well as for high yield potential would be important in developing cultivars for rainfed lowlands in Cambodia. Although flowering dates are important for drought escape, it had a small contribution probably because drought developed slowly in these experiments in Cambodia

High-throughput phenotyping of indirect traits for early-stage selection in sugarcane breeding

One of the major limitations for sugarcane genetic improvement is the low heritability of yield in the early stages of breeding, mainly due to confounding inter-plot competition effects. In this study, we investigate an indirect selection index (Si), developed based on traits correlated to yield (indirect traits) that were measured using an unmanned aerial vehicle (UAV), to improve clonal assessment in early stages of sugarcane breeding. A single-row early-stage clonal assessment trial, involving 2134 progenies derived from 245 crosses, and a multi-row experiment representative of pure-stand conditions, with an unrelated population of 40 genotypes, were used in this study. Both experiments were screened at several stages using visual, multispectral, and thermal sensors mounted on a UAV for indirect traits, including canopy cover, canopy height, canopy temperature, and normalised difference vegetation index (NDVI). To construct the indirect selection index, phenotypic and genotypic variance-covariances were estimated in the single-row and multi-row experiment, respectively. Clonal selection from the indirect selection index was compared to single-row yield-based selection. Ground observations of stalk number and plant height at six months after planting made from a subset of 75 clones within the single-row experiment were highly correlated to canopy cover (rg = 0.72) and canopy height (rg = 0.69), respectively. The indirect traits had high heritability and strong genetic correlation with cane yield in both the single-row and multi-row experiments. Only 45% of the clones were common between the indirect selection index and single-row yield based selection, and the expected efficiency of correlated response to selection for pure-stand yield based on indirect traits (44%–73%) was higher than that based on single-row yield (45%). These results highlight the potential of high-throughput phenotyping of indirect traits combined in an indirect selection index for improving early-stage clonal selections in sugarcane breeding

Canopy temperature: a predictor of sugarcane yield for irrigated and rainfed conditions

Our recent work with a large genetically diverse sugarcane germplasm (131 clones) grown at different commercial production regions over multiple years with varying water supply (a total of 27 crop cycles) has shown that canopy conductance (gc), and a related easy-to-measure trait, canopy temperature (Tc), when integrated with canopy development, have a strong genetic correlation with crop yield irrespective of the growing condition. In order to exploit this result for variety improvement in the Sugar Research Australia breeding program, three different Tc measurement systems were assessed for their accuracy, genetic correlation of measured Tc with cane yield (tonnes cane per hectare, TCH) and trait (Tc) and heritability. The methods include manual ground-level Tc measurements taken at 3-6 month crop age, aerial screening using UAV-assisted infra-red and optical imagery and continuous real-time absolute Tc measurements using ArduCrop infra-red radiometers. Significant genetic variation for Tc among genotypes was detected with all three methods, with aerial screening and ArduCrop being more accurate and useful than manual groundlevel measurements. Both UAV-aided and ArduCrop-based Tc measurements showed high heritability and high negative genetic correlation under variable moisture conditions. Results of field experiments suggest that aerial Tc measurements taken under the appropriate conditions will be an effective, rapid screening method for selecting superior, water-efficient and high-yielding clones from large breeding trials

Estimating Percolation and Lateral Water Flow on Sloping Land in Rainfed Lowland Rice Ecosystem

Quantifying water losses in paddy fields assists estimation of water availability in rainfed lowland rice ecosystem. Little information is available on water balance in different toposequence positions of sloped rainfed lowland. Therefore, the aim of this work was to quantify percolation and the lateral water flow with special reference to the toposequential variation. Data used for the analysis was collected in Laos and northeast Thailand. Percolation and water tables were measured on a daily basis using a steel cylindrical tube with a lid and perforated PVC tubes, respectively. Percolation rate was determined using linear regression analysis of cumulative percolation. Assuming that the total amount of evaporation and transpiration was equivalent to potential evapotranspiration, the lateral water flow was estimated using the water balance equation. Separate perched water and groundwater tables were observed in paddy fields on coarse-textured soils. The percolation rate varied between 0 and 3 mm/day across locations, and the maximum water loss by lateral movement was more than 20 mm/day. Our results are in agreement with the previously reported findings, and the methodology of estimating water balance components appears reasonably acceptable. With regard to the toposequential variation, the higher the position in the topoesquence, the greater potential for water loss because of higher percolation and lateral flow rates

Measurement and management of genotype-environment interaction (GxE) for the improvement of rainfed lowland rice yield in Cambodia

The magnitude and nature of genotype-by-environment interactions (G×E) for grain yield (GY) and days to flower (DTF) in Cambodia were examined using a random population of 34 genotypes taken from the Cambodian rice improvement program. These genotypes were evaluated in multi-environment trials (MET) conducted across three years (2000 to 2002) and eight locations in the rainfed lowlands. The G×E interaction was partitioned into components attributed to genotype-by-location (G×L), genotype-by-year (G×Y) and genotype-by-location-by-year (G×L×Y) interactions. The G×L×Y interaction was the largest component of variance for GY. The G×L interaction was also significant and comparable in size to the genotypic component (G). The G×Y interaction was small and non significant. A major factor contributing to the large G×L×Y interactions for GY was the genotypic variation for DTF in combination with environmental variation for the timing and intensity of drought. Some of the interactions for GY associated with timing of plant development and exposure to drought were repeatable across the environments enabling the identification of three-target populations of environments (TPE) for consideration in the breeding program. Four genotypes were selected for wide adaptation in the rainfed lowlands in Cambodia