Inheritance of pericarp and hull colour pigments on crossing between white rice and red rice (Oryza sativa L.)

Introduction

Rice (Oryza sativa L.) is one of the major staple food crop being grown worldwide. It provides 20 per cent of the calories and 15 per cent of protein consumed by world's population. Besides being the chief source of carbohydrate and protein, it also provides minerals and fibre. This crop is the backbone of livelihood for millions of rural households and plays vital role in the country's food security, so the term "rice is life" is most appropriate in Indian context. Most of the rice consumed is the white coloured, although many rice cultivars have a variety of seed pericarp colours owing to black (dark purple), brown, red and green pigments deposition. Red rice constitute a small but special group of rice which are considered the best in quality in view of nutritive purpose. In India, rice is often considered the main culprit in aggravating the diabetic condition. For all those people, relief is now available in the form of brown rice and red rice. Red rice is a special variety of rice that gets its red colour due to anthocyanins. This rice is generally unhulled or partially hulled rice which has a red pericarp colour. As it contains anthocyanins, it helps in reducing inflammation, allergy, preventing risks of cancer and helping in weight management. Manganese in red rice helps in strengthening metabolism, Magnesium helps in migraine, lowers blood pressure as well as reduces the risk of heart attacks. Selenium in red rice protects the body against infections. The experimental material for present investigation consisted of 36 entries including 6 females, 4 males, their 24 crosses and two checks. All the females were semi-dwarf, high yielding, white pericarp, fine grain type rice varieties which are used as lines, while all males were red pericarp land races used as testers in this experiment. The crosses were developed by line x Tester fashion given by Kempthorne in 1957 [4] . Evaluation of pericarp pigment of the rice is done on each individual rice plants. Rice pericarp pigment of each population morphology observed with partial peeling grains. The spikelets of the F 1 plant were dehulled and the caryopses were scored for colour. The F 1 seeds were planted to raise F 2 progeny. The pericarps were scored for colour segregantion to determine caryopsis colour ratio and subsequently validate the inheritance pattern by the ratio. Rice pigment observation based scoring colors as shown in Table 1. Kristamtini et al. (2019) [5] . The χ 2 test is a valuable tool that aids investigator in determining the goodness of fit of genetic ratios Fisher, (1936) [1] . The expected values corresponding to the observed values for each characters were calculated based on the presumed ratio. The deviations were put to χ 2 test. If the deviation of expected frequencies from the observed ones were small χ 2 would approach to zero and it would be less than 3.841 at 5 per cent level of significance and one degree of freedom. So the deviations were taken as nonsignificant and the ratio presumed was taken as fit. But if the deviations were large the χ 2 would be more than 3.841 at 5 per cent level of significance and one degree of freedom and the goodness of fit would be poor.

Materials and Methods

Results and Discussion

Pericarp colour

The F 1 plants of all the crosses were found to have red pericarp colour. This indicated that red pericarp colour was dominant over white pericarp colour. These F 1 progenies were observed in F 2 generation for pericarp colour. The proportion of plants with red and white pericarp in F 2 population closely fitted in the ratio of 3:1 (red to white Pericarp) for all 24 crosses, this indicated that red colour of pericarp in all testers Bela, Munga, Valai and Kudai was governed by single dominant gene. Qualitative traits differ markedly in their expression among the individuals of a species. Such characters are under the control of major genes. The occurrence as well as distribution of anthocyanin pigmentation in different part of the rice plant are more variable and are a striking feature of the crop. This feature has been the subject of interest for several earlier studies. Such morphological variants with distinct phenotypic expression and simple inheritance pattern can be used to establish linkages and for indirect selection if found associated with useful traits (Reddy et al., 1995) [6] . Gealy et al. (2006) [2] observed that F 1 plants from white rice x red rice combinations produced red seeds, confirming that red seed colour is a dominant trait. F 2 populations derived from LA 3 or TX 4 red rice segregated in ratios of approximately 3:1 (red:white) seed colouration, consistent with single dominant gene control of this trait. In the present investigation, the mode of inheritance of red pericarp was studied in 24 crosses. Red pericarp commonly known as red rice. All F 1 plants from white rice x red rice crosses produced red pericarp colour, confirmed that red pericarp colour was a dominant trait. Proportion of plants with red and white pericarp in F 2 population closely fitted in the ratio of 3:1 (red:white) seed colouration (Table 2). It showed that the red pericarp colour is dominant over white pericarp colour. It indicated that red colour of pericarp in the varieties Bela, Munga, Valai and Kudai was governed by a single dominant gene. This is in consonance with the findings of Hemprabha et al. (2007) [3] , Sahu et al. (2010) [7] and Waghmode et al. (2017) [8] .

Hull colour

Genetics of hull colour was studied in 24 crosses. The In five crosses which females (Karjat 4, Palghar 1, Ratnagiri 5, Ratanagiri 6 and Trombay Karjat Kolam) having straw hull colour and blackish brown hull colour male (Kudai) showed all blackish brown hull coloured F 1 plants. This indicated that blackish brown hull colour was dominant over straw hull colour. These F 1 progenies were observed in F 2 generation for hull colour. The proportion of plants with blackish brown hull colour in F 2 population closely fitted in the ratio of 9:7 indicating the action of two major genes either of them complementing with other dominant gene responsible for expression of hull colour. The cross between golden hull colour female (Karjat 9) and brown hull colour males (Bela and Munga) recorded brown hull colour and cross Karjat 9 x Valai having golden hull colour (female) and straw hull colour (male) parents was observed golden hull colour, while cross Karjat 9 x Kudai having golden hull colour (female) and black hull colour (male) parents was observed black hull colour indicating dominant nature of trait. The proportion of plants with golden to brown and golden to straw and golden to black hull colour in F 2 population closely fitted in the ratio of 13:3 genetic ratio for the hull colour indicating the digenetic inheritance with inhibitory gene interaction.

The observations on hull colour (straw or purple/straw or red) and pericarp colour (white or red) recorded at appropriate stage of crop. The observations on the parents and F 1 's were recorded on row basis, while F 2 population on individual plant basis. The data were analysed independently for each trait to determine the fitness with diverse segregation ratios to determine mode of inheritance by χ 2 (Chi-square) test as suggested by Fisher (1936) [1] .

Sahu et al. (2010) [7] reported that, the proportion of purple hull and straw hull plants in the F 2 population of the cross Mahamaya x Mainagali closely fitted to the ratio of 13 purple: 3 straw hull. This result revealed that anthocyanin pigmentation on lemma palea in the variety Mainagali was due to two independent genes, one dominant and other one recessive (Pr-1, pr-2). In case of genetics of hull colour trait in the present study, the crosses between straw hull x brown hull, golden hull x brown hull, straw hull x black hull and golden hull x black hull colour, it was observed that brown hull was dominant over straw hull and golden hull, golden hull was dominant over straw hull and black hull was dominant over golden hull colour, indicating dominant nature of these hull colours in F 1 generation. The F 2 population of these crosses segregated into ratio of 13:3. This result revealed that anthocyanin pigmentation on hull colour was due to two independent genes, one dominant and other one recessive. The result was in agreement with Hemprabha et al. (2007) [3] and Waghmode et al. (2017) [8] . Whereas, Sahu et al. (2010) [7] also reported these dominant and recessive gene as Pr-1, pr-2.

The remaining five crosses between black hull colour x straw hull colour found to have all black hull colour F 1 progeny. It indicated the dominant effect of black hull colour over straw hull colour. The F 2 population of all five crosses segregated into ratio of 9:7 black hull to straw hull, indicating two independent recessive genes responsible for expression of hull colour in the varieties. The results were in accordance with Hemprabha et al. (2007) [3] , Sahu et al.

(2010) [7] and Waghmode et al. (2017) [8] , Sahu et al. (2010) [7] also reported these recessive genes as hr1 and hr2.

Conclusion

The study on rice pericarp and hull color genetics demonstrated that red pericarp color is controlled by a single dominant gene, with F2 segregation fitting the 3:1 ratio. Similarly, hull color exhibited more complex inheritance patterns. Brown hull color was dominant over straw and golden hull colors, and black hull color was dominant over straw, with F2 segregation fitting 13:3 and 9:7 ratios, respectively. These findings confirm that both pericarp and hull colors in rice are influenced by major genes with simple and digenetic inheritance patterns. The study aligns with previous research and provides insight into genetic control of rice pigmentation traits.

References

1. Fisher RA. On the interpretation of χ² from contingency tables and the calculation of P. J Royal Stat Soc. 1936;85(1):87-94.
2. Gealy DR, Yan W, Rutger JN. Red rice (Oryza sativa L.) plant types affect growth, coloration, and flowering characteristics of first-and second-generation crosses with rice. Weed Technol. 2006;20:839-852.
3. Hemprabha E, Thiruvengadam V, Maheswaran M, Shanmugasundaram P. Inheritance of anthocyanin pigmentation in rice (Oryza sativa L.). Plant Arch. 2007;7(2):549-552.
4. Reddy VS, Dash S, Reddy AR. Anthocyanin pathway in rice (Oryza sativa L.): identification of a mutant showing dominant inhibition of anthocyanins in leaf and accumulation of proanthocyanidins in pericarp. Theor Appl Genet. 1995;91:301-312.
5. Sahu GR, Sarawgi AK, Sharma B, Parikh M. Inheritance of anthocyanin pigmentation in rice. J Rice Res. 2010;3(1):20-27.