PhD

The research work entitled “Genetic analysis of drought tolerance in rice (Oryza sativa L. )” was carried out in the Department of Plant Breeding and Genetics College of Agriculture,Vellayani, Thiruvananthapuram during the period 2014 – 2016. The study aimed at estimating the nature and magnitude of gene effects in the inheritance of drought tolerance in rice under upland conditions. Screening of the selected parents and superior progenies for the presence of molecular markers associated with drought tolerance was envisaged.
Twenty diverse genotypes including varieties recommended for uplands and popular high yielding varieties widely cultivated in the state were screened for drought tolerance under rainfed upland condition during May to October, 2014. Morphological observations were taken at appropriate plant growth stages following the Standard Evaluation System for Rice [IRRI, 1996]. The screening of genotypes was done as per the protocols of DRR (2012). The rice genotypes were further screened for drought tolerance imposing reproductive stage moisture stress under protected condition.
The data from rainfed and protected condition screening were utilized for the development of a selection index based on which the genotypes were ranked. The six top ranking genotypes with high yield and drought tolerance viz., Vaishak, Thottacheera, Kalladiaryan, Vyttila 6, Harsha and Swarnaprabha were hybridized in half diallel pattern. The 15 F1 hybrids were evaluated along with their parents under rainfed situation to select the top five heterotic hybrids which were carried forward to F2.
In all populations studied, qualitative traits related to drought such as nature of panicle exsertion (DRR, 2004) and scoring for leaf rolling (IRRI, 1991) were analysed. Degree of panicle exsertion has a direct bearing on spikelet sterility. Leaf rolling is a tricky character where the breeder has to strike a balance between the onset, intensity and duration of rolling as well as the recovery from rolling when moisture is provided. This is because leaf rolling reduces transpiration loss at the expense of photosynthate production. Mild incidence of insect pests viz., gandhi bug and leaf folder and diseases viz., brown spot, blast and bacterial leaf blight was observed in the field experiments. The variety Swarnaprabha had good cooking quality. Kanchana had excellent milling recovery and good cooking quality with high volume expansion on cooking and comparatively high protein content. Prathyasha had high nutrient content and good cooking quality. Aathira possessed excellent milling recovery and cooking quality. Parambuvattan had appreciable quality and is preferred for certain special preparations. The traditional upland varieties viz., Katta Modan, Karutha Modan and Chuvana Modan had superior milling recovery.
High PCV and GCV values were observed for yield related characters such as filled grains panicle-1, grain yield plant-1, harvest index etc. Based on the studies on correlation and path coefficient analysis, biological yield plant-1, harvest index and panicle length exhibited maximum positive direct effect on grain yield.
Vaishak was the best combiner for panicle length, number of spikelets panicle-1, spikelet fertility, total chlorophyll content, leaf temperature and good combiner for number of filled grains panicle-1, proline content, cell membrane stability index, chlorophyll a, chlorophyll b, total chlorophyll content, leaf temperature, transpiration rate, leaf soluble protein content and number of days for reaching critical stress level. Thottacheera was a good general combiner for days to 50 % flowering, total chlorophyll content and leaf temperature. Kalladiaryan showed good general combining ability for number of productive tillers plant-1, straw yield plant-1, proline content, chlorophyll b content and total chlorophyll content. Vyttila 6 was the best combiner for plant height at maturity and also for physiological and biochemical traits such as water use efficiency, relative leaf water content, proline content, cell membrane stability index, chlorophyll a content, carotenoides content, leaf temperature, transpiration rate, stomatal conductance, leaf soluble protein content and good combiner for total chlorophyll content and number of days taken for reaching critical stress level. Harsha was a good general combiner for short stature at maturity, 1000 grain weight and grain weight panicle-1 while parent Swarnaprabha showed good general combining ability for number of days taken for reaching critical stress level. Considering the preponderance of non additive gene action for most of the characters and gca and sca variances it can be concluded that heterosis breeding would yield better results. The hybrids Vyttila 6 x Harsha, Vyttila 6 x Swarnaprabha and Vaishak x Thottacheera exhibited highest heterosis for grain yield under upland condition.
Six parents and their best hybrids were subjected to molecular analysis using three SSR markers linked to quantitative traits. The allele linked to the respective trait was present in all the hybrids, as in the parent with resistance to drought.
Transgressive segregants for yield and yield attributing traits were observed in the F2. The F2 segregants Vaishak x Swarnaprabha, Vaishak x Thottacheera and Vaishak x Kalladiaryan were early maturing, playing an important role in the mechanism for drought escape. Drought tolerance mechanism can also be attributed to these segregants. These types will be valuable for the development of early maturing drought tolerant upland varieties. . The hybrids Vyttila 6 x Harsha and Vyttila 6 x Swarnaprabha ranked best for grain yield plant-1. Drought resistance was conferred to these hybrids via. , root length and osmotic adjustment traits and the hybrids had various yield attributing traits also , which was further confirmed by trait specific SSR markers.
Desirable F2 segregants from the combinations Vaishak x Swarnaprabha, Vaishak x Thottacheera and Vaishak x Kalladiaryan may be carried forward further for the development of drought escaping early maturing upland varieties with high grain yield. The combinations Vyttila 6 x Harsha and Vyttila 6 x Swarnaprabha can be carried forward further for the development of drought tolerant upland varieties with high grain yield.