Research Scope Studi Genetik Toleransi Genangan Pada Padi

7 plants cannot easily elongate out of the water due to the elongation-suppressive effect of SUB1 Fukao et al. 2006, Xu et al. 2006, Fukao and Bailey-Serres 2008b. However, in cultivars that are taller 100 cm a sufficient part of the canopy remains above the water level to allow the plants to grow well. Partial elongation ability is an important attribute of stagnant flooding tolerance so that rice plants can grow ahead of rising water. However, if elongation is too much, plants will be lodge after the water recedes, therefore this trait needs to be combined with lodging resistance. IRRI119 was considered to be stagnant flooding tolerant in rice breeding program at IRRI Collard et al. 2013, Kato et al. 2014, and Vergara et al. 2014. The plant height under stagnant flooding stress is 135-140 cm and with days to flowering is ± 94 days. IRRI119 is semidwarf types under well-drained conditions Collard et al. 2013. IRRI119 was developed using conventional breeding and was not specifically bred for stagnant flooding trait. Elucidating the genetic basis, that are heritability, genetic control, mapping QTL of stagnant flooding tolerance is major objective of the IRRI breeding and research programs. Classical QTL mapping efforts are currently underway Collard et al. 2013. A bulk-pedigree method was used to develop IRRI119. Submergence screening is done at F2 and F3 generations using bulk selection at F2 generation. At F3 generation, screening of submergence is repeated to ensure there are few escapes. At F4 to F6 generations, selection are done based on plant type, yield, grain quality, and insect and disease resistance. Screening of stagnant flooding stress was done at F7-F8 generations. IRRI119 was considered to be stagnant flooding tolerant in the rice breeding program at IRRI Collard et al. 2013. IR 42 is IRRI line which is derived from crossing of IR1561-228-1- 2IR1737CR94-13. IR42 is susceptible for submergence stress Das et al. 2009; Serres et al. 2010; Sarkar et al. 2011. IR42 is determined as stagnant flooding susceptible by Vergara et al. 2014 and Yullianida et al. 2015. Under stagnant flooding stress, the yield reduction of IR42 is 57 , stem elongation is 36.7 cm, stem elongation rate is 1 cm day -1 and the number of tillering are 3 Yullianida et al. 2015. Meanwhile the yield reduction higher 85 based on Vergara et al. 2014.

2.5 Selection Criterion

Under stagnant flooding stress, yield is primary selection criterion based on visual selection. There are sufficient genetic variation for yield in IRRI material, although heritability of the trait is low to medium. For improving of phenotyping method, that is easy to measure physiological traits, it is need to look for traits which are highly correlated with yield or relatively yield under stagnant flooding stress. The traits are preferably non-destructive and pre-flowering phase. Collard et al. 2013 suggest that number of tillers, elongation ability at vegetative stage, leaf area development, and lodging resistance can be used to estimate tolerance. All traits, except lodging resistance can be measured at one month after transplanting. Singh et al. 2011 and Kato et al. 2014 also recommended that reduction in tiller number directly affected rice yield under stagnant flooding. Therefore, anatomical, biochemical and molecular studies on this temporal tiller suppression 8 should be consider in future studies. Faster shoot elongation contributed to establishing a larger aerial leaf area and higher light interception, biomass production, and plant survival under stagnant flooding. Conversely, stem non- structural carbohydrate NSC concentration correlated negatively with shoot elongation rate, suggesting that fast-elongating genotypes actively consume NSCs to avoid complete submergence.