415 AJCS 6(3):415-420 (2012) ISSN:1835-2707 Genetic behaviour for plant capacity to produce chlorophyll in wheat (Triticum aestivum) under drought stress Mohammad Reza Naroui Rad *1,2 , Mihdzar Abdul Kadir 1 , Mohd Rafii Yusop 3 1 Department of Agriculture Technology, Faculty of Agriculture, University Putra Malaysia (UPM), 43400 UPM Serdang, Malaysia 2 Agriculture and Natural Resources Research Center of Sistan, Iran 3 Institue of Tropical Agriculture, University Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia *Corresponding author: narouirad@gmail.com Abstract The study was conducted with the objective of identifying parents to be used in a breeding program to develop high chlorophyll varieties. Combining ability, heterosis and inheritance of chlorophyll content, including chlorophyll a, chlorophyll b and total chlorophyll (a+b), were investigated in bread wheat obtained from half-diallel crossings among eight parental lines. Cultivars with names of Irena/Babax//Pastor, S-78-11, Tajan, Chamran, Moghan3, Hamoon, Veery/Nacozari and Hirmand have different capacities to produce chlorophyll. Eight parental genotypes and their resulting 28 F 1 s were grown in three replications of randomised complete block design. Drought stress was performed with irrigation at 75% soil moisture depletion, the data collected were subjected to analysis of variance and combining abilities were carried out according to Griffing’s method 2, model 1. The study was conducted with the objective of identifying parents to be used in a breeding program to develop high chlorophyll varieties. General combining ability and specific combining ability effects were significant for traits’ chlorophyll content, chlorophyll a, chlorophyll b and total chlorophyll; however, non-additive gene effects were predominant over additive effects. The line Irena/Babax//Pastor transmitted high chlorophyll content based on general combining ability to progenies that were made with it. Broad-sense heritabilities were high and strict-sense heritabilities were low for the traits, confirming the importance of non-additive gene effects. This could bring definition of reduced selection efficiency for these mentioned traits. Keywords: Chlorophyll; Combining ability; Dominance; Gene action; Heritability. Abbreviations: GCA-General combining ability; SCA-Specific combining ability; Chl-Chlorophyll; D-additive genetic variance; H1, H2- Dominance genetic variance and corrected dominance genetic variance respectively; E-Environment variance; RCBD - Randomised complete block design; h 2 (bs)- heritability for diallel in a broad sense; h 2 (ns)- heritability for diallel in a narrow sense. Introduction Plant breeders collaborate with plant physiologists in order to develop germplasm tolerant to abiotic stress. However, germplasm evaluation is hindered by the difficulty of creating screening methods which are simultaneously accurate and rapid. Drought stress also inhibits the photosynthesis of plants by causing changes in chlorophyll content, affecting chlorophyll components and also damaging the photosynthetic apparatus (Iturbe-Ormaetxe et al., 1998). The decrease in chlorophyll under drought stress is mainly the result of damage to chloroplasts caused by active oxygen species (Smirnoff, 1995). Drought stress also is one of the important factors in limiting plant photosynthesis, causes a large decline in the chlorophyll a content, chlorophyll b content, and eventually the total chlorophyll content in crops (Manivannan et al., 2007). Chlorophyll is an essential factor in the process of photosynthesis. Chlorophyll a and b are the two main forms of chlorophyll which contribute to the green- coloured matter in plants. Chlorophyll a is yellowish-green whereas chlorophyll b is bluish-green. Chlorophyll a donates energy directly to the photosynthetic reaction and all other pigments transfer their absorbed energy to it. Chlorophyll b and the carotenoids play a key role in protecting the plant cells against the photochemical reaction induced by the illumination of chlorophyll (Davies et al., 1964). However, a high correlation between the chlorophyll content and photosynthesis rate was not obtained (Marini, 1986). Photosynthetic pigments, and consequently their relationships, are an important indicator of senescence (Brown et al., 1991). Chlorophyll loss is associated with environmental stress and the variation in total chlorophyll/carotenoids ratio may be a good indicator of stress in plants (Hendry and Price, 1993). In addition, measuring gas exchange and chlorophyll content repeatedly on the same leaves in a field may provide useful information on the relationship between these parameters (Schaper and Chacko, 1991). Measurements of chlorophyll fluorescence from photosystem II (PSII) have become a useful method for the determination of mechanisms of photosynthesis and to study the effects of various environmental conditions on photosynthetic reactions (Bolhar-Nordenkampf et al., 1989; Krause, 1991; Demmig-Adams and Adams, 1992). It has been widely considered in research on photosynthesis, stress physiology and crop productivity evaluation (Lichtenthaler, 1988). The specific objective of this study was to estimate the