title: Drought yield index to select high yielding rice lines under different drought stress severities.
abstract: BACKGROUND
  Drought is the most severe abiotic stress reducing rice yield in rainfed drought prone ecosystems. Variation in intensity and severity of drought from season to season and place to place requires cultivation of rice varieties with different level of drought tolerance in different areas. Multi environment evaluation of breeding lines helps breeder to identify appropriate genotypes for areas prone to similar level of drought stress. From a set of 129 advanced rice (Oryza sativa L.) breeding lines evaluated under rainfed drought-prone situations at three locations in eastern India from 2005 to 2007, a subset of 39 genotypes that were tested for two or more years was selected to develop a drought yield index (DYI) and mean yield index (MYI) based on yield under irrigated, moderate and severe reproductive-stage drought stress to help breeders select appropriate genotypes for different environments.
  
  
  RESULTS
  ARB 8 and IR55419-04 recorded the highest drought yield index (DYI) and are identified as the best drought-tolerant lines. The proposed DYI provides a more effective assessment as it is calculated after accounting for a significant genotype x stress-level interaction across environments. For rainfed areas with variable frequency of drought occurrence, Mean yield index (MYI) along with deviation in performance of genotypes from currently cultivated popular varieties in all situations helps to select genotypes with a superior performance across irrigated, moderate and severe reproductive-stage drought situations. IR74371-70-1-1 and DGI 75 are the two genotypes identified to have shown a superior performance over IR64 and MTU1010 under all situations.
  
  
  CONCLUSIONS
  For highly drought-prone areas, a combination of DYI with deviation in performance of genotypes under irrigated situations can enable breeders to select genotypes with no reduction in yield under favorable environments compared with currently cultivated varieties. For rainfed areas with variable frequency of drought stress, use of MYI together with deviation in performance of genotypes under different situations as compared to presently cultivated varieties will help breeders to select genotypes with superior performance under all situations.
authors.affiliation: International Rice Research Institute (IRRI), DAPO Box 7777, Metro Manila, Philippines.
authors.forename: Anitha
authors.initials: A
authors.lastname: Raman
authors.affiliation: Indira Gandhi Krishi Vishwavidyalaya (IGKV), Raipur, India.
authors.forename: Satish
authors.initials: S
authors.lastname: Verulkar
authors.affiliation: Central Rainfed Upland Rice Research Station (CRURRS), Hazaribag, India.
authors.forename: Nimai
authors.initials: N
authors.lastname: Mandal
authors.affiliation: Central Rainfed Upland Rice Research Station (CRURRS), Hazaribag, India.
authors.forename: Mukund
authors.initials: M
authors.lastname: Variar
authors.affiliation: Central Rainfed Upland Rice Research Station (CRURRS), Hazaribag, India.
authors.forename: V
authors.initials: V
authors.lastname: Shukla
authors.affiliation: Narendra Dev University of Agriculture and Technology (NDUAT), Faizabad, India.
authors.forename: J
authors.initials: J
authors.lastname: Dwivedi
authors.affiliation: Birsa Agricultural University (BAU), Ranchi, India.
authors.forename: B
authors.initials: B
authors.lastname: Singh
authors.affiliation: Central Rice Research Institute (CRRI), Cuttack, India.
authors.forename: O
authors.initials: O
authors.lastname: Singh
authors.affiliation: Central Rice Research Institute (CRRI), Cuttack, India.
authors.forename: Padmini
authors.initials: P
authors.lastname: Swain
authors.affiliation: International Rice Research Institute (IRRI), DAPO Box 7777, Metro Manila, Philippines.
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Mall
authors.affiliation: Tamil Nadu Agricultural University (TNAU), Coimbatore, India.
authors.forename: S
authors.initials: S
authors.lastname: Robin
authors.affiliation: Tamil Nadu Agricultural University (TNAU), Coimbatore, India.
authors.forename: R
authors.initials: R
authors.lastname: Chandrababu
authors.affiliation: Barwale Foundation (BF), Hyderabad, India.
authors.forename: Abhinav
authors.initials: A
authors.lastname: Jain
authors.affiliation: Directorate of Rice Research, Hyderabad, India.
authors.forename: Tilatoo
authors.initials: T
authors.lastname: Ram
authors.affiliation: University of Agricultural Sciences, Bangalore, India.
authors.forename: Shailaja
authors.initials: S
authors.lastname: Hittalmani
authors.affiliation: International Rice Research Institute (IRRI), DAPO Box 7777, Metro Manila, Philippines.
authors.forename: Stephan
authors.initials: S
authors.lastname: Haefele
authors.affiliation: Bioinformatics Unit, Universitaet Hohenheim, 70593, Stuttgart, Germany.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Piepho
authors.affiliation: International Rice Research Institute (IRRI), DAPO Box 7777, Metro Manila, Philippines. a.kumar@cgiar.org.
authors.forename: Arvind
authors.initials: A
authors.lastname: Kumar
keywords: Drought; Drought yield index; Genotype x environment interaction; Mixed model; Rice