Assessing genetic divergence among rice germplasm based on qualitative traits

Rice is cultivated worldwide under wide range of ecological conditions and is a daily staple food crop for more than half of world’s population. The morphological characterization is usually performed to select better genotypes. This type of characterization identifies elite genotypes based on qualitative as well as quantitative traits. In present study 45 diverse rice germplasm were screened for important qualitative traits. The experiment was designed as augmented and important qualitative traits including leaf related traits, lodging, panicle shape, seed coat color and awn related traits were studied. Significant variations were observed for all the examined traits. Majority of genotypes showed resistance to lodging, and only few showed slight lodging. The brown seed coat color was found dominant among genotypes. All the studied traits included in the study were found useful for the identification of improved genotypes and these traits have direct relation with yield or yield related traits. However, to elucidate the particular responsible genes for these traits, further molecular based studies are recommended.


Introduction
The rice belongs to important plant family Poaceae. The 22 species of rice has been identified, two species (Oryza sativa and Oryza glaberrima) are widely cultivated than rest ones [1]. It is the one of the major energy source for the world population and key contributor to world agriculture sector [2]. Oryza sativa cultivated worldwide, including Asia, North and South America, throughout Europe, Middle Eastern and African countries. Oryza glaberrima is grown in many parts of Africa due to higher yields [3]. Its cultivars are divided into three main types including Indica, Javanica and Japonica. The japonica grains are shorter and broaden as compared to Indica grain and become soft and sticky when cooked [4]. Abiotic stresses affect both the morphobiochemical, physiological and molecular processes of crop species [5,6]. The rice crop has been affected by both the biotic and abiotic environmental extremes. The low temperature stress decreases its yield many times. The japonica type shows resistance to low temperature (15 to 20 0 C) as compared to other two types. However, low temperatures (below 18 0 C) at night time produce sterile pollens [7]. The bacterial blight disease is one of the key diseases that significantly affect both qualitative and quantitative traits including yield [8].
Agro-morphological diversity studies play key role in the identification of improved genotypes for both qualitative and quantitative traits and to differentiate both local and exotic germplasm [9][10][11][12][13]. It also helps us to screen best genotypes among large population that can be further characterized in different location for both preliminary and advanced yield trails [14][15][16][17]. The rice genotypes can be characterized through various qualitative and quantitative traits like growth parameters, culms color, leaf blades types, grain color, height, diseases resistance and many more [18] (Table 1 & 2) were sown in field by using augmented design. The row length was 4.5 meters, row to row distance 30 cm and plant to plant distance was 15 cm. Proper water treatment was applied and recommended cultural practices were followed from germination to till maturity. The following qualitative traits were measured at different growth stages.

Flag leaf angle
Four different types of flag leaves were studied like descending, horizontal, erect and semi-erect.

Leaf shape
The three different shapes of leaf (droopy, erect and semi-erect) were observed for 45 rice genotypes 3. Leaf appearance Three different types of leaf (narrow, broaden and intermediate types) were checked for all tested genotypes.

Lodging
Three standard lodging categories (slight, heavy or no lodging) were used to note the different lodging ability among genotypes 5. Panicle type The diversity in panicle types i.e. open type, compact and intermediate types were recorded.

Panicle exertion
The 5 different panicle exertion types (well, partly, just, moderate and enclosed) of rice were noted.

Awn type
The rice genotypes were divided for different awn related codes (awned, awnless and awnlated).

Awn color
Awn color (white, light and dark brown or red-black).

Seed coat color
The seed coat color is one the important qualitative traits. The rice genotypes were screened for different types of seed coat colors (white, brown, light/ dark/ red/ speckled/ blackish brown).

Results and discussion Morphological characterization of rice genotypes through qualitative traits
In present study 45 diverse rice germplasm were evaluated for nine important qualitative traits. The genotypes which belong to tropical, subtropical and temperate zones were analyzed under similar environmental condition at Plant Genetic Resources Institute (PGRI), National Agricultural Research Centre (NARC), Islamabad, Pakistan. All the studied genotypes showed considerable variability under similar environmental conditions. The data of following nine qualitative traits were recorded from five random selected samples. In present study maximum diversity was observed among genotypes for flag leaf angle. Maximum genotypes (26) showed erect angle, 17 were semi-erect and 2 had horizontal type. Similar type of variability was observed for leaf shape trait. The leaf shape trait play key role in photosynthesis and the erect and semi-erect are considered more important. In our study, majority of genotypes showed erect and semierect leaf shape. In addition the different types of leaf appearance were observed in all 45 tested genotypes. Maximum genotypes (34) showed intermediate appearance, and 7 genotypes had broad leaves. The remaining genotypes were found narrow types (Table 1). Lodging trait is one of the key traits that have direct impact on final yield. In present study the lodging was observed visually and majority of genotypes (37) showed resistance to lodging, 2 genotypes showed maximum lodging. While 6 genotypes showed slight lodging ( Awn is one of the key qualitative traits that help in the identification of genotype and also protect grain from bird or other pest attack. In this study 26 genotypes were found awnless and 19 were awned. For awned panicle the brown color were predominantly observed ( Table 2). In current study maximum divergence was observed among genotypes for seed coat color. Majority of genotypes (23) showed light brown color. 20 genotypes had brown seed coat color, while other 2 genotypes had dark brown color ( Table 2). Rice is one of the key cash crops of Pakistan and cultivated as one of the major crop. Therefore, Pakistan needs to further expand its export and improve its local consumption by improving grain quality as per the consumer demand around the globe and in the country. Agro-morphological based diversity helps in the identification of elite genotypes. In present study various qualitative traits of 45 rice genotypes were evaluated. High level of variability was recorded for all nine qualitative traits (