Identification of Superior Segregants for Drought Tolerance and Productivity Traits in Backcross Inbred Lines (BILs) Derived from NERICA Introgression under Rainfed Ecosystem  

E. A  Sangodele 1 , R. R.  Hanchinal 1 , N. G Hanamaratti 1 , V. V Shenoy 2 , H. L Nadaf 1
1. Department of Genetics and Plant Breeding, University of Agricultural Sciences, Dharwad, Karnataka State, India;
2. Barwale Foundation, Hyderabad, AP, India
Author    Correspondence author
Rice Genomics and Genetics, 2013, Vol. 4, No. 3   doi: 10.5376/rgg.2013.04.0003
Received: 05 Feb., 2013    Accepted: 15 Mar., 2013    Published: 08 May, 2013
© 2013 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:
Sangodele et al., 2013, Identification of Superior Segregants for Drought Tolerance and Productivity Traits in Backcross Inbred Lines (BILs) Derived from NERICA Introgression under Rainfed Ecosystem, Rice Genomics and Genetics, Vol.04, No.2 9-13 (doi: 10.5376/rgg.2013.04.0003)

The aim of this study was to identify promising genotypes for upland rice ecosystem especially in drought prone areas. Backcross inbred line (BC1F6) developed from inter varietal cross of Swarna X NERICA were evaluated under water stressed environment for physiological and productivity related traits in the pot experiment. The result showed a clear expression of donor (NERICA) genome on the background of the recurrent parent (Swarna) in the BILs evaluated. Performance of BILs is generally lower under water stressed treatment when compared with non-stressed treatment for all the traits studied except leaf temperature which was higher under water stressed condition. Except for traits like leaf area and plant height, percentage reduction in performance of BILs for physiological and productivity component traits under water stress treatment are generally lower than the recurrent parent Swarna indicating their superiority over recurrent parent for drought tolerance.

Rice; Backcross inbred line; Drought tolerance; Poductivity; Rainfed ecosystem

1 Introduction
There is an extensive genetic variation for drought tolerance in rice germplasm (Serraj et al., 2011) but not much is achieved in breeding for drought tolerance in rice because of complexity and nature of drought. A good knowledge of complexity and the nature of drought is necessary in breeding for drought tolerance. Variability of drought within and between seasons is location specific. Therefore breeding for drought tolerance requires adequate study of environmental factors which interact with water deficit to create complexity called “drought”. Several breeding programme aim at developing high yielding drought tolerant cultivar has not been able to overcome yield barrier.  According to Serraj et al., (2011) most of the varieties grown in rainfed ecosystems were originally developed for irrigated ecosystems; such varieties were basically screened for yield without screening for drought tolerance; such varieties often fail in the season where there is severe drought. It is imperative to develop high yielding drought tolerant rice varieties for rainfed upland rice especially sub-Saharan Africa where most rice areas are in upland ecosystem.
Management practice such as delay transplanting has been employed by farmers in respond to delay rainfall and water stress; this however results in yield loss (Verulkar et al., 2010). Serraj et al., (2011) reported an experiments conducted at IRRI in 2005, where rice seedlings  transplanted at 65-day-old as opposed to 22-day-old resulted in a yield reduction of more than 50%, averaged across 125 cultivars (Atlin et al., 2006). It is important to mention at this point that risk of crop failure due to drought stress can be reduced by selection for high yielding and drought tolerant genotypes adapted to target drought prone areas in any crop improvement programme. Although there is a lot of variability in rice germplasm for drought tolerance, variability to delay transplanting has not been fully studied transplanting (Verulkar et al., 2010).  
Resource poor farmers in drought prone areas need variety adaptable to rainfed upland with high yielding potential coupled with good quality attributes. Such variety must be superior to traditional land race under farmer management skill (Verulkar et al., 2010). Evidently, there is enough variability in the cultivated rice gene pool and it wild relative (Lafitte et al., 2006; Jongdee et al., 2006; Liu et al., 2004) to work with in any breeding programme. Plant breeder has a duty of selection for drought tolerant breeding materials for crop improvement programme. The focus of this study was to identify superior and promising drought tolerant rice genotypes for rice farmers in rainfed ecosystem that can be easily spread through farmer-to-farmer seed exchange.
2 Material and Methods
The investigation was carried out at Agricultural Research Station of University of Agricultural Sciences Dharwad. The Research Station is located at Mugad latitude of 15°15'North and longitude of 70°40' East and altitude of 695 meters above Mean Sea Level (MSL) belonging to Agro-climatic zone No.8 of Karnataka. The average rainfall of the Research Station is 101 6.20 mm in 75 rainy days distributed mainly during kharif (June to October) season. 
Breeding material for this study was a backcross population (BC1F6) developed in India by Barwale Foundation in Hyderabad using WAB-450, an inter-specific derivative as donor and Swarna, a mega rice variety in India, as recurrent parent. 188 BILs along with 10 checks transplanted in 12' pots were screened inside rain out shelter (poly house) for physiological traits during summer 2011 while evaluation for productivity related traits was carried out during kharif 2012 in the field. Three weeks old seedlings were transplanted one seedling per pot in randomized block design in two replications each for two treatments (non-stress and water-stress). In the water-stressed experiment (water-stressed treatment), moisture stress was imposed by withholding irrigation until severe leaf rolling was observed from the onset of the reproductive growth phase till grain filling stage; in control (non-stressed treatment) experiment was daily irrigation until crop maturity. 
Recommended agronomic practices were duly followed for raising a good and healthy crop using Package of practices for Paddy developed by UAS Dharwad. Data was taken and analysed using simple ANOVA to determine the mean performance of the BILs and parents for physiological and productivity traits.
3 Results and Discussion 
The ANOVA in respect of all the characters studied in BILs showed highly significant MSS for genotypes indicating wide genetic differences for all physiological and productivity traits (Table 1). Heritability of most of the traits studied range from moderate to high in the stressed and non-stressed treatment. Heritability of traits like leaf temperature and number of tiller showed a clear difference between water-stress and non-stress treatment (Table 2); this may be due to effect of environment on the BILs.  

Table 1 ANOVA for physiological and productivity related traits under stressed and unstressed condition in pot experiment


Table 2 Genetic parameters for physiological and productivity related traits under stressed and unstressed condition in pot experiment

Performance of BILs was generally lower under water stressed treatment than non-stressed treatment for all the traits studied except leaf temperature which was higher under water stressed condition. Reaction of plant to water stress is complex, it involves physiological, morphological and biochemical changes within the plant tissue. The initial  responses to drought stress occur at the leaf level in response to stimuli generated in the leaf itself or elsewhere in the plant and they have a negative influence on carbon assimilation and growth (Chaves et al., 2002). The combine effect of various reactions within the plant tissues culminate in the actual behaviour of plant to drought stress (Pereira and Chaves, 1993).
Physiological and productivity performance of donor parent (WAB-450) under water stress are better than that of recurrent parent (Swarna) as indicated by the percentage reduction (Table 3). Except for traits like leaf area and plant height, percentage reduction in performance of BILs for physiological and productivity component traits when subjected to water stress treatment were generally lower than the recurrent parent Swarna. This can be interpreted to imply that drought tolerant traits from WAB-450 have been introgressed into Swarna background. WAB-450 is known to be superior in earliness, weed competetiveness, drought tolerance, pest or disease resistance and other grain quality attributes with yield advantage over O. glaberrima and O. sativa its parents (Africa Rice, 2011). The introgression of WAB-450 genome in mega variety like Swarna background could impart earliness, stress tolerance and productivity related traits. 

Table 3 Percentage reduction in performance of Parents and BILS population under water-stress for physiological and productivity related traits in pot experiment

Top 20 superior BILs (Table 4) that showed lowest percentage reduction in important component traits like relative water content, chlorophyll content, leaf temperature and leaf area under water stress will be suitable as breeding material for drought tolerance. It has been reported that under conditions of water stress, plants are often subjected to a high temperature, which increases their vulnerability to light stress and consequently the photo inhibition (Shahenshah et al., 2010). When carbon dioxide fixation is limited, the rate of active oxygen formation increases in chloroplasts as excess excitation energy, which would either become manifest as oxidative damages to the plant or would result in activation of defence and repair mechanisms which could prevent such damage from occurring (Shahenshah, 2010). The decrease in chlorophyll content under drought stress has been considered a typical symptom of oxidative stress and may be the result of pigment photo-oxidation and chlorophyll degradation. A decrease in the relative water content (RWC) in response to drought stress has been noted in wide variety of plants as reported by Shakeel et al., (2011). RWC related to water uptake by the roots as well as water loss by transpireation (Shakeel et al., 2011). Identification of superior drought tolerant rice genotypes is achievable through genetic manipulation for these physiological traits.

Table 4 Top 20 BILs with least percentage reduction in performance for physiological and morphological traits under water-stress in pot experiment

4 Conclusions
Drought stress is a serious threat to rice production in rainfed upland; it affects every stage of growth and development. Timing, duration, severity and speed of development undoubtedly have pivotal roles in determining how a plant responds to water deficit and this makes breeding for drought tolerance a herculean task. A model for upland rice breeding programme capable of identifying superior genotypes for drought prone upland ecosystem can be developed by screening genotypes under drought stress and select for least percentage reduction in physiological and productivity traits when breeding materials are subjected to stringent water stress.
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